Merge tag 'ktest-v5.13' of git://git.kernel.org/pub/scm/linux/kernel/git/rostedt...
[linux-2.6-microblaze.git] / kernel / trace / ring_buffer.c
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Generic ring buffer
4  *
5  * Copyright (C) 2008 Steven Rostedt <srostedt@redhat.com>
6  */
7 #include <linux/trace_recursion.h>
8 #include <linux/trace_events.h>
9 #include <linux/ring_buffer.h>
10 #include <linux/trace_clock.h>
11 #include <linux/sched/clock.h>
12 #include <linux/trace_seq.h>
13 #include <linux/spinlock.h>
14 #include <linux/irq_work.h>
15 #include <linux/security.h>
16 #include <linux/uaccess.h>
17 #include <linux/hardirq.h>
18 #include <linux/kthread.h>      /* for self test */
19 #include <linux/module.h>
20 #include <linux/percpu.h>
21 #include <linux/mutex.h>
22 #include <linux/delay.h>
23 #include <linux/slab.h>
24 #include <linux/init.h>
25 #include <linux/hash.h>
26 #include <linux/list.h>
27 #include <linux/cpu.h>
28 #include <linux/oom.h>
29
30 #include <asm/local.h>
31
32 static void update_pages_handler(struct work_struct *work);
33
34 /*
35  * The ring buffer header is special. We must manually up keep it.
36  */
37 int ring_buffer_print_entry_header(struct trace_seq *s)
38 {
39         trace_seq_puts(s, "# compressed entry header\n");
40         trace_seq_puts(s, "\ttype_len    :    5 bits\n");
41         trace_seq_puts(s, "\ttime_delta  :   27 bits\n");
42         trace_seq_puts(s, "\tarray       :   32 bits\n");
43         trace_seq_putc(s, '\n');
44         trace_seq_printf(s, "\tpadding     : type == %d\n",
45                          RINGBUF_TYPE_PADDING);
46         trace_seq_printf(s, "\ttime_extend : type == %d\n",
47                          RINGBUF_TYPE_TIME_EXTEND);
48         trace_seq_printf(s, "\ttime_stamp : type == %d\n",
49                          RINGBUF_TYPE_TIME_STAMP);
50         trace_seq_printf(s, "\tdata max type_len  == %d\n",
51                          RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
52
53         return !trace_seq_has_overflowed(s);
54 }
55
56 /*
57  * The ring buffer is made up of a list of pages. A separate list of pages is
58  * allocated for each CPU. A writer may only write to a buffer that is
59  * associated with the CPU it is currently executing on.  A reader may read
60  * from any per cpu buffer.
61  *
62  * The reader is special. For each per cpu buffer, the reader has its own
63  * reader page. When a reader has read the entire reader page, this reader
64  * page is swapped with another page in the ring buffer.
65  *
66  * Now, as long as the writer is off the reader page, the reader can do what
67  * ever it wants with that page. The writer will never write to that page
68  * again (as long as it is out of the ring buffer).
69  *
70  * Here's some silly ASCII art.
71  *
72  *   +------+
73  *   |reader|          RING BUFFER
74  *   |page  |
75  *   +------+        +---+   +---+   +---+
76  *                   |   |-->|   |-->|   |
77  *                   +---+   +---+   +---+
78  *                     ^               |
79  *                     |               |
80  *                     +---------------+
81  *
82  *
83  *   +------+
84  *   |reader|          RING BUFFER
85  *   |page  |------------------v
86  *   +------+        +---+   +---+   +---+
87  *                   |   |-->|   |-->|   |
88  *                   +---+   +---+   +---+
89  *                     ^               |
90  *                     |               |
91  *                     +---------------+
92  *
93  *
94  *   +------+
95  *   |reader|          RING BUFFER
96  *   |page  |------------------v
97  *   +------+        +---+   +---+   +---+
98  *      ^            |   |-->|   |-->|   |
99  *      |            +---+   +---+   +---+
100  *      |                              |
101  *      |                              |
102  *      +------------------------------+
103  *
104  *
105  *   +------+
106  *   |buffer|          RING BUFFER
107  *   |page  |------------------v
108  *   +------+        +---+   +---+   +---+
109  *      ^            |   |   |   |-->|   |
110  *      |   New      +---+   +---+   +---+
111  *      |  Reader------^               |
112  *      |   page                       |
113  *      +------------------------------+
114  *
115  *
116  * After we make this swap, the reader can hand this page off to the splice
117  * code and be done with it. It can even allocate a new page if it needs to
118  * and swap that into the ring buffer.
119  *
120  * We will be using cmpxchg soon to make all this lockless.
121  *
122  */
123
124 /* Used for individual buffers (after the counter) */
125 #define RB_BUFFER_OFF           (1 << 20)
126
127 #define BUF_PAGE_HDR_SIZE offsetof(struct buffer_data_page, data)
128
129 #define RB_EVNT_HDR_SIZE (offsetof(struct ring_buffer_event, array))
130 #define RB_ALIGNMENT            4U
131 #define RB_MAX_SMALL_DATA       (RB_ALIGNMENT * RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
132 #define RB_EVNT_MIN_SIZE        8U      /* two 32bit words */
133
134 #ifndef CONFIG_HAVE_64BIT_ALIGNED_ACCESS
135 # define RB_FORCE_8BYTE_ALIGNMENT       0
136 # define RB_ARCH_ALIGNMENT              RB_ALIGNMENT
137 #else
138 # define RB_FORCE_8BYTE_ALIGNMENT       1
139 # define RB_ARCH_ALIGNMENT              8U
140 #endif
141
142 #define RB_ALIGN_DATA           __aligned(RB_ARCH_ALIGNMENT)
143
144 /* define RINGBUF_TYPE_DATA for 'case RINGBUF_TYPE_DATA:' */
145 #define RINGBUF_TYPE_DATA 0 ... RINGBUF_TYPE_DATA_TYPE_LEN_MAX
146
147 enum {
148         RB_LEN_TIME_EXTEND = 8,
149         RB_LEN_TIME_STAMP =  8,
150 };
151
152 #define skip_time_extend(event) \
153         ((struct ring_buffer_event *)((char *)event + RB_LEN_TIME_EXTEND))
154
155 #define extended_time(event) \
156         (event->type_len >= RINGBUF_TYPE_TIME_EXTEND)
157
158 static inline int rb_null_event(struct ring_buffer_event *event)
159 {
160         return event->type_len == RINGBUF_TYPE_PADDING && !event->time_delta;
161 }
162
163 static void rb_event_set_padding(struct ring_buffer_event *event)
164 {
165         /* padding has a NULL time_delta */
166         event->type_len = RINGBUF_TYPE_PADDING;
167         event->time_delta = 0;
168 }
169
170 static unsigned
171 rb_event_data_length(struct ring_buffer_event *event)
172 {
173         unsigned length;
174
175         if (event->type_len)
176                 length = event->type_len * RB_ALIGNMENT;
177         else
178                 length = event->array[0];
179         return length + RB_EVNT_HDR_SIZE;
180 }
181
182 /*
183  * Return the length of the given event. Will return
184  * the length of the time extend if the event is a
185  * time extend.
186  */
187 static inline unsigned
188 rb_event_length(struct ring_buffer_event *event)
189 {
190         switch (event->type_len) {
191         case RINGBUF_TYPE_PADDING:
192                 if (rb_null_event(event))
193                         /* undefined */
194                         return -1;
195                 return  event->array[0] + RB_EVNT_HDR_SIZE;
196
197         case RINGBUF_TYPE_TIME_EXTEND:
198                 return RB_LEN_TIME_EXTEND;
199
200         case RINGBUF_TYPE_TIME_STAMP:
201                 return RB_LEN_TIME_STAMP;
202
203         case RINGBUF_TYPE_DATA:
204                 return rb_event_data_length(event);
205         default:
206                 WARN_ON_ONCE(1);
207         }
208         /* not hit */
209         return 0;
210 }
211
212 /*
213  * Return total length of time extend and data,
214  *   or just the event length for all other events.
215  */
216 static inline unsigned
217 rb_event_ts_length(struct ring_buffer_event *event)
218 {
219         unsigned len = 0;
220
221         if (extended_time(event)) {
222                 /* time extends include the data event after it */
223                 len = RB_LEN_TIME_EXTEND;
224                 event = skip_time_extend(event);
225         }
226         return len + rb_event_length(event);
227 }
228
229 /**
230  * ring_buffer_event_length - return the length of the event
231  * @event: the event to get the length of
232  *
233  * Returns the size of the data load of a data event.
234  * If the event is something other than a data event, it
235  * returns the size of the event itself. With the exception
236  * of a TIME EXTEND, where it still returns the size of the
237  * data load of the data event after it.
238  */
239 unsigned ring_buffer_event_length(struct ring_buffer_event *event)
240 {
241         unsigned length;
242
243         if (extended_time(event))
244                 event = skip_time_extend(event);
245
246         length = rb_event_length(event);
247         if (event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
248                 return length;
249         length -= RB_EVNT_HDR_SIZE;
250         if (length > RB_MAX_SMALL_DATA + sizeof(event->array[0]))
251                 length -= sizeof(event->array[0]);
252         return length;
253 }
254 EXPORT_SYMBOL_GPL(ring_buffer_event_length);
255
256 /* inline for ring buffer fast paths */
257 static __always_inline void *
258 rb_event_data(struct ring_buffer_event *event)
259 {
260         if (extended_time(event))
261                 event = skip_time_extend(event);
262         WARN_ON_ONCE(event->type_len > RINGBUF_TYPE_DATA_TYPE_LEN_MAX);
263         /* If length is in len field, then array[0] has the data */
264         if (event->type_len)
265                 return (void *)&event->array[0];
266         /* Otherwise length is in array[0] and array[1] has the data */
267         return (void *)&event->array[1];
268 }
269
270 /**
271  * ring_buffer_event_data - return the data of the event
272  * @event: the event to get the data from
273  */
274 void *ring_buffer_event_data(struct ring_buffer_event *event)
275 {
276         return rb_event_data(event);
277 }
278 EXPORT_SYMBOL_GPL(ring_buffer_event_data);
279
280 #define for_each_buffer_cpu(buffer, cpu)                \
281         for_each_cpu(cpu, buffer->cpumask)
282
283 #define for_each_online_buffer_cpu(buffer, cpu)         \
284         for_each_cpu_and(cpu, buffer->cpumask, cpu_online_mask)
285
286 #define TS_SHIFT        27
287 #define TS_MASK         ((1ULL << TS_SHIFT) - 1)
288 #define TS_DELTA_TEST   (~TS_MASK)
289
290 static u64 rb_event_time_stamp(struct ring_buffer_event *event)
291 {
292         u64 ts;
293
294         ts = event->array[0];
295         ts <<= TS_SHIFT;
296         ts += event->time_delta;
297
298         return ts;
299 }
300
301 /* Flag when events were overwritten */
302 #define RB_MISSED_EVENTS        (1 << 31)
303 /* Missed count stored at end */
304 #define RB_MISSED_STORED        (1 << 30)
305
306 struct buffer_data_page {
307         u64              time_stamp;    /* page time stamp */
308         local_t          commit;        /* write committed index */
309         unsigned char    data[] RB_ALIGN_DATA;  /* data of buffer page */
310 };
311
312 /*
313  * Note, the buffer_page list must be first. The buffer pages
314  * are allocated in cache lines, which means that each buffer
315  * page will be at the beginning of a cache line, and thus
316  * the least significant bits will be zero. We use this to
317  * add flags in the list struct pointers, to make the ring buffer
318  * lockless.
319  */
320 struct buffer_page {
321         struct list_head list;          /* list of buffer pages */
322         local_t          write;         /* index for next write */
323         unsigned         read;          /* index for next read */
324         local_t          entries;       /* entries on this page */
325         unsigned long    real_end;      /* real end of data */
326         struct buffer_data_page *page;  /* Actual data page */
327 };
328
329 /*
330  * The buffer page counters, write and entries, must be reset
331  * atomically when crossing page boundaries. To synchronize this
332  * update, two counters are inserted into the number. One is
333  * the actual counter for the write position or count on the page.
334  *
335  * The other is a counter of updaters. Before an update happens
336  * the update partition of the counter is incremented. This will
337  * allow the updater to update the counter atomically.
338  *
339  * The counter is 20 bits, and the state data is 12.
340  */
341 #define RB_WRITE_MASK           0xfffff
342 #define RB_WRITE_INTCNT         (1 << 20)
343
344 static void rb_init_page(struct buffer_data_page *bpage)
345 {
346         local_set(&bpage->commit, 0);
347 }
348
349 /*
350  * Also stolen from mm/slob.c. Thanks to Mathieu Desnoyers for pointing
351  * this issue out.
352  */
353 static void free_buffer_page(struct buffer_page *bpage)
354 {
355         free_page((unsigned long)bpage->page);
356         kfree(bpage);
357 }
358
359 /*
360  * We need to fit the time_stamp delta into 27 bits.
361  */
362 static inline int test_time_stamp(u64 delta)
363 {
364         if (delta & TS_DELTA_TEST)
365                 return 1;
366         return 0;
367 }
368
369 #define BUF_PAGE_SIZE (PAGE_SIZE - BUF_PAGE_HDR_SIZE)
370
371 /* Max payload is BUF_PAGE_SIZE - header (8bytes) */
372 #define BUF_MAX_DATA_SIZE (BUF_PAGE_SIZE - (sizeof(u32) * 2))
373
374 int ring_buffer_print_page_header(struct trace_seq *s)
375 {
376         struct buffer_data_page field;
377
378         trace_seq_printf(s, "\tfield: u64 timestamp;\t"
379                          "offset:0;\tsize:%u;\tsigned:%u;\n",
380                          (unsigned int)sizeof(field.time_stamp),
381                          (unsigned int)is_signed_type(u64));
382
383         trace_seq_printf(s, "\tfield: local_t commit;\t"
384                          "offset:%u;\tsize:%u;\tsigned:%u;\n",
385                          (unsigned int)offsetof(typeof(field), commit),
386                          (unsigned int)sizeof(field.commit),
387                          (unsigned int)is_signed_type(long));
388
389         trace_seq_printf(s, "\tfield: int overwrite;\t"
390                          "offset:%u;\tsize:%u;\tsigned:%u;\n",
391                          (unsigned int)offsetof(typeof(field), commit),
392                          1,
393                          (unsigned int)is_signed_type(long));
394
395         trace_seq_printf(s, "\tfield: char data;\t"
396                          "offset:%u;\tsize:%u;\tsigned:%u;\n",
397                          (unsigned int)offsetof(typeof(field), data),
398                          (unsigned int)BUF_PAGE_SIZE,
399                          (unsigned int)is_signed_type(char));
400
401         return !trace_seq_has_overflowed(s);
402 }
403
404 struct rb_irq_work {
405         struct irq_work                 work;
406         wait_queue_head_t               waiters;
407         wait_queue_head_t               full_waiters;
408         bool                            waiters_pending;
409         bool                            full_waiters_pending;
410         bool                            wakeup_full;
411 };
412
413 /*
414  * Structure to hold event state and handle nested events.
415  */
416 struct rb_event_info {
417         u64                     ts;
418         u64                     delta;
419         u64                     before;
420         u64                     after;
421         unsigned long           length;
422         struct buffer_page      *tail_page;
423         int                     add_timestamp;
424 };
425
426 /*
427  * Used for the add_timestamp
428  *  NONE
429  *  EXTEND - wants a time extend
430  *  ABSOLUTE - the buffer requests all events to have absolute time stamps
431  *  FORCE - force a full time stamp.
432  */
433 enum {
434         RB_ADD_STAMP_NONE               = 0,
435         RB_ADD_STAMP_EXTEND             = BIT(1),
436         RB_ADD_STAMP_ABSOLUTE           = BIT(2),
437         RB_ADD_STAMP_FORCE              = BIT(3)
438 };
439 /*
440  * Used for which event context the event is in.
441  *  TRANSITION = 0
442  *  NMI     = 1
443  *  IRQ     = 2
444  *  SOFTIRQ = 3
445  *  NORMAL  = 4
446  *
447  * See trace_recursive_lock() comment below for more details.
448  */
449 enum {
450         RB_CTX_TRANSITION,
451         RB_CTX_NMI,
452         RB_CTX_IRQ,
453         RB_CTX_SOFTIRQ,
454         RB_CTX_NORMAL,
455         RB_CTX_MAX
456 };
457
458 #if BITS_PER_LONG == 32
459 #define RB_TIME_32
460 #endif
461
462 /* To test on 64 bit machines */
463 //#define RB_TIME_32
464
465 #ifdef RB_TIME_32
466
467 struct rb_time_struct {
468         local_t         cnt;
469         local_t         top;
470         local_t         bottom;
471 };
472 #else
473 #include <asm/local64.h>
474 struct rb_time_struct {
475         local64_t       time;
476 };
477 #endif
478 typedef struct rb_time_struct rb_time_t;
479
480 #define MAX_NEST        5
481
482 /*
483  * head_page == tail_page && head == tail then buffer is empty.
484  */
485 struct ring_buffer_per_cpu {
486         int                             cpu;
487         atomic_t                        record_disabled;
488         atomic_t                        resize_disabled;
489         struct trace_buffer     *buffer;
490         raw_spinlock_t                  reader_lock;    /* serialize readers */
491         arch_spinlock_t                 lock;
492         struct lock_class_key           lock_key;
493         struct buffer_data_page         *free_page;
494         unsigned long                   nr_pages;
495         unsigned int                    current_context;
496         struct list_head                *pages;
497         struct buffer_page              *head_page;     /* read from head */
498         struct buffer_page              *tail_page;     /* write to tail */
499         struct buffer_page              *commit_page;   /* committed pages */
500         struct buffer_page              *reader_page;
501         unsigned long                   lost_events;
502         unsigned long                   last_overrun;
503         unsigned long                   nest;
504         local_t                         entries_bytes;
505         local_t                         entries;
506         local_t                         overrun;
507         local_t                         commit_overrun;
508         local_t                         dropped_events;
509         local_t                         committing;
510         local_t                         commits;
511         local_t                         pages_touched;
512         local_t                         pages_read;
513         long                            last_pages_touch;
514         size_t                          shortest_full;
515         unsigned long                   read;
516         unsigned long                   read_bytes;
517         rb_time_t                       write_stamp;
518         rb_time_t                       before_stamp;
519         u64                             event_stamp[MAX_NEST];
520         u64                             read_stamp;
521         /* ring buffer pages to update, > 0 to add, < 0 to remove */
522         long                            nr_pages_to_update;
523         struct list_head                new_pages; /* new pages to add */
524         struct work_struct              update_pages_work;
525         struct completion               update_done;
526
527         struct rb_irq_work              irq_work;
528 };
529
530 struct trace_buffer {
531         unsigned                        flags;
532         int                             cpus;
533         atomic_t                        record_disabled;
534         cpumask_var_t                   cpumask;
535
536         struct lock_class_key           *reader_lock_key;
537
538         struct mutex                    mutex;
539
540         struct ring_buffer_per_cpu      **buffers;
541
542         struct hlist_node               node;
543         u64                             (*clock)(void);
544
545         struct rb_irq_work              irq_work;
546         bool                            time_stamp_abs;
547 };
548
549 struct ring_buffer_iter {
550         struct ring_buffer_per_cpu      *cpu_buffer;
551         unsigned long                   head;
552         unsigned long                   next_event;
553         struct buffer_page              *head_page;
554         struct buffer_page              *cache_reader_page;
555         unsigned long                   cache_read;
556         u64                             read_stamp;
557         u64                             page_stamp;
558         struct ring_buffer_event        *event;
559         int                             missed_events;
560 };
561
562 #ifdef RB_TIME_32
563
564 /*
565  * On 32 bit machines, local64_t is very expensive. As the ring
566  * buffer doesn't need all the features of a true 64 bit atomic,
567  * on 32 bit, it uses these functions (64 still uses local64_t).
568  *
569  * For the ring buffer, 64 bit required operations for the time is
570  * the following:
571  *
572  *  - Only need 59 bits (uses 60 to make it even).
573  *  - Reads may fail if it interrupted a modification of the time stamp.
574  *      It will succeed if it did not interrupt another write even if
575  *      the read itself is interrupted by a write.
576  *      It returns whether it was successful or not.
577  *
578  *  - Writes always succeed and will overwrite other writes and writes
579  *      that were done by events interrupting the current write.
580  *
581  *  - A write followed by a read of the same time stamp will always succeed,
582  *      but may not contain the same value.
583  *
584  *  - A cmpxchg will fail if it interrupted another write or cmpxchg.
585  *      Other than that, it acts like a normal cmpxchg.
586  *
587  * The 60 bit time stamp is broken up by 30 bits in a top and bottom half
588  *  (bottom being the least significant 30 bits of the 60 bit time stamp).
589  *
590  * The two most significant bits of each half holds a 2 bit counter (0-3).
591  * Each update will increment this counter by one.
592  * When reading the top and bottom, if the two counter bits match then the
593  *  top and bottom together make a valid 60 bit number.
594  */
595 #define RB_TIME_SHIFT   30
596 #define RB_TIME_VAL_MASK ((1 << RB_TIME_SHIFT) - 1)
597
598 static inline int rb_time_cnt(unsigned long val)
599 {
600         return (val >> RB_TIME_SHIFT) & 3;
601 }
602
603 static inline u64 rb_time_val(unsigned long top, unsigned long bottom)
604 {
605         u64 val;
606
607         val = top & RB_TIME_VAL_MASK;
608         val <<= RB_TIME_SHIFT;
609         val |= bottom & RB_TIME_VAL_MASK;
610
611         return val;
612 }
613
614 static inline bool __rb_time_read(rb_time_t *t, u64 *ret, unsigned long *cnt)
615 {
616         unsigned long top, bottom;
617         unsigned long c;
618
619         /*
620          * If the read is interrupted by a write, then the cnt will
621          * be different. Loop until both top and bottom have been read
622          * without interruption.
623          */
624         do {
625                 c = local_read(&t->cnt);
626                 top = local_read(&t->top);
627                 bottom = local_read(&t->bottom);
628         } while (c != local_read(&t->cnt));
629
630         *cnt = rb_time_cnt(top);
631
632         /* If top and bottom counts don't match, this interrupted a write */
633         if (*cnt != rb_time_cnt(bottom))
634                 return false;
635
636         *ret = rb_time_val(top, bottom);
637         return true;
638 }
639
640 static bool rb_time_read(rb_time_t *t, u64 *ret)
641 {
642         unsigned long cnt;
643
644         return __rb_time_read(t, ret, &cnt);
645 }
646
647 static inline unsigned long rb_time_val_cnt(unsigned long val, unsigned long cnt)
648 {
649         return (val & RB_TIME_VAL_MASK) | ((cnt & 3) << RB_TIME_SHIFT);
650 }
651
652 static inline void rb_time_split(u64 val, unsigned long *top, unsigned long *bottom)
653 {
654         *top = (unsigned long)((val >> RB_TIME_SHIFT) & RB_TIME_VAL_MASK);
655         *bottom = (unsigned long)(val & RB_TIME_VAL_MASK);
656 }
657
658 static inline void rb_time_val_set(local_t *t, unsigned long val, unsigned long cnt)
659 {
660         val = rb_time_val_cnt(val, cnt);
661         local_set(t, val);
662 }
663
664 static void rb_time_set(rb_time_t *t, u64 val)
665 {
666         unsigned long cnt, top, bottom;
667
668         rb_time_split(val, &top, &bottom);
669
670         /* Writes always succeed with a valid number even if it gets interrupted. */
671         do {
672                 cnt = local_inc_return(&t->cnt);
673                 rb_time_val_set(&t->top, top, cnt);
674                 rb_time_val_set(&t->bottom, bottom, cnt);
675         } while (cnt != local_read(&t->cnt));
676 }
677
678 static inline bool
679 rb_time_read_cmpxchg(local_t *l, unsigned long expect, unsigned long set)
680 {
681         unsigned long ret;
682
683         ret = local_cmpxchg(l, expect, set);
684         return ret == expect;
685 }
686
687 static int rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
688 {
689         unsigned long cnt, top, bottom;
690         unsigned long cnt2, top2, bottom2;
691         u64 val;
692
693         /* The cmpxchg always fails if it interrupted an update */
694          if (!__rb_time_read(t, &val, &cnt2))
695                  return false;
696
697          if (val != expect)
698                  return false;
699
700          cnt = local_read(&t->cnt);
701          if ((cnt & 3) != cnt2)
702                  return false;
703
704          cnt2 = cnt + 1;
705
706          rb_time_split(val, &top, &bottom);
707          top = rb_time_val_cnt(top, cnt);
708          bottom = rb_time_val_cnt(bottom, cnt);
709
710          rb_time_split(set, &top2, &bottom2);
711          top2 = rb_time_val_cnt(top2, cnt2);
712          bottom2 = rb_time_val_cnt(bottom2, cnt2);
713
714         if (!rb_time_read_cmpxchg(&t->cnt, cnt, cnt2))
715                 return false;
716         if (!rb_time_read_cmpxchg(&t->top, top, top2))
717                 return false;
718         if (!rb_time_read_cmpxchg(&t->bottom, bottom, bottom2))
719                 return false;
720         return true;
721 }
722
723 #else /* 64 bits */
724
725 /* local64_t always succeeds */
726
727 static inline bool rb_time_read(rb_time_t *t, u64 *ret)
728 {
729         *ret = local64_read(&t->time);
730         return true;
731 }
732 static void rb_time_set(rb_time_t *t, u64 val)
733 {
734         local64_set(&t->time, val);
735 }
736
737 static bool rb_time_cmpxchg(rb_time_t *t, u64 expect, u64 set)
738 {
739         u64 val;
740         val = local64_cmpxchg(&t->time, expect, set);
741         return val == expect;
742 }
743 #endif
744
745 /*
746  * Enable this to make sure that the event passed to
747  * ring_buffer_event_time_stamp() is not committed and also
748  * is on the buffer that it passed in.
749  */
750 //#define RB_VERIFY_EVENT
751 #ifdef RB_VERIFY_EVENT
752 static struct list_head *rb_list_head(struct list_head *list);
753 static void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
754                          void *event)
755 {
756         struct buffer_page *page = cpu_buffer->commit_page;
757         struct buffer_page *tail_page = READ_ONCE(cpu_buffer->tail_page);
758         struct list_head *next;
759         long commit, write;
760         unsigned long addr = (unsigned long)event;
761         bool done = false;
762         int stop = 0;
763
764         /* Make sure the event exists and is not committed yet */
765         do {
766                 if (page == tail_page || WARN_ON_ONCE(stop++ > 100))
767                         done = true;
768                 commit = local_read(&page->page->commit);
769                 write = local_read(&page->write);
770                 if (addr >= (unsigned long)&page->page->data[commit] &&
771                     addr < (unsigned long)&page->page->data[write])
772                         return;
773
774                 next = rb_list_head(page->list.next);
775                 page = list_entry(next, struct buffer_page, list);
776         } while (!done);
777         WARN_ON_ONCE(1);
778 }
779 #else
780 static inline void verify_event(struct ring_buffer_per_cpu *cpu_buffer,
781                          void *event)
782 {
783 }
784 #endif
785
786
787 static inline u64 rb_time_stamp(struct trace_buffer *buffer);
788
789 /**
790  * ring_buffer_event_time_stamp - return the event's current time stamp
791  * @buffer: The buffer that the event is on
792  * @event: the event to get the time stamp of
793  *
794  * Note, this must be called after @event is reserved, and before it is
795  * committed to the ring buffer. And must be called from the same
796  * context where the event was reserved (normal, softirq, irq, etc).
797  *
798  * Returns the time stamp associated with the current event.
799  * If the event has an extended time stamp, then that is used as
800  * the time stamp to return.
801  * In the highly unlikely case that the event was nested more than
802  * the max nesting, then the write_stamp of the buffer is returned,
803  * otherwise  current time is returned, but that really neither of
804  * the last two cases should ever happen.
805  */
806 u64 ring_buffer_event_time_stamp(struct trace_buffer *buffer,
807                                  struct ring_buffer_event *event)
808 {
809         struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[smp_processor_id()];
810         unsigned int nest;
811         u64 ts;
812
813         /* If the event includes an absolute time, then just use that */
814         if (event->type_len == RINGBUF_TYPE_TIME_STAMP)
815                 return rb_event_time_stamp(event);
816
817         nest = local_read(&cpu_buffer->committing);
818         verify_event(cpu_buffer, event);
819         if (WARN_ON_ONCE(!nest))
820                 goto fail;
821
822         /* Read the current saved nesting level time stamp */
823         if (likely(--nest < MAX_NEST))
824                 return cpu_buffer->event_stamp[nest];
825
826         /* Shouldn't happen, warn if it does */
827         WARN_ONCE(1, "nest (%d) greater than max", nest);
828
829  fail:
830         /* Can only fail on 32 bit */
831         if (!rb_time_read(&cpu_buffer->write_stamp, &ts))
832                 /* Screw it, just read the current time */
833                 ts = rb_time_stamp(cpu_buffer->buffer);
834
835         return ts;
836 }
837
838 /**
839  * ring_buffer_nr_pages - get the number of buffer pages in the ring buffer
840  * @buffer: The ring_buffer to get the number of pages from
841  * @cpu: The cpu of the ring_buffer to get the number of pages from
842  *
843  * Returns the number of pages used by a per_cpu buffer of the ring buffer.
844  */
845 size_t ring_buffer_nr_pages(struct trace_buffer *buffer, int cpu)
846 {
847         return buffer->buffers[cpu]->nr_pages;
848 }
849
850 /**
851  * ring_buffer_nr_pages_dirty - get the number of used pages in the ring buffer
852  * @buffer: The ring_buffer to get the number of pages from
853  * @cpu: The cpu of the ring_buffer to get the number of pages from
854  *
855  * Returns the number of pages that have content in the ring buffer.
856  */
857 size_t ring_buffer_nr_dirty_pages(struct trace_buffer *buffer, int cpu)
858 {
859         size_t read;
860         size_t cnt;
861
862         read = local_read(&buffer->buffers[cpu]->pages_read);
863         cnt = local_read(&buffer->buffers[cpu]->pages_touched);
864         /* The reader can read an empty page, but not more than that */
865         if (cnt < read) {
866                 WARN_ON_ONCE(read > cnt + 1);
867                 return 0;
868         }
869
870         return cnt - read;
871 }
872
873 /*
874  * rb_wake_up_waiters - wake up tasks waiting for ring buffer input
875  *
876  * Schedules a delayed work to wake up any task that is blocked on the
877  * ring buffer waiters queue.
878  */
879 static void rb_wake_up_waiters(struct irq_work *work)
880 {
881         struct rb_irq_work *rbwork = container_of(work, struct rb_irq_work, work);
882
883         wake_up_all(&rbwork->waiters);
884         if (rbwork->wakeup_full) {
885                 rbwork->wakeup_full = false;
886                 wake_up_all(&rbwork->full_waiters);
887         }
888 }
889
890 /**
891  * ring_buffer_wait - wait for input to the ring buffer
892  * @buffer: buffer to wait on
893  * @cpu: the cpu buffer to wait on
894  * @full: wait until the percentage of pages are available, if @cpu != RING_BUFFER_ALL_CPUS
895  *
896  * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
897  * as data is added to any of the @buffer's cpu buffers. Otherwise
898  * it will wait for data to be added to a specific cpu buffer.
899  */
900 int ring_buffer_wait(struct trace_buffer *buffer, int cpu, int full)
901 {
902         struct ring_buffer_per_cpu *cpu_buffer;
903         DEFINE_WAIT(wait);
904         struct rb_irq_work *work;
905         int ret = 0;
906
907         /*
908          * Depending on what the caller is waiting for, either any
909          * data in any cpu buffer, or a specific buffer, put the
910          * caller on the appropriate wait queue.
911          */
912         if (cpu == RING_BUFFER_ALL_CPUS) {
913                 work = &buffer->irq_work;
914                 /* Full only makes sense on per cpu reads */
915                 full = 0;
916         } else {
917                 if (!cpumask_test_cpu(cpu, buffer->cpumask))
918                         return -ENODEV;
919                 cpu_buffer = buffer->buffers[cpu];
920                 work = &cpu_buffer->irq_work;
921         }
922
923
924         while (true) {
925                 if (full)
926                         prepare_to_wait(&work->full_waiters, &wait, TASK_INTERRUPTIBLE);
927                 else
928                         prepare_to_wait(&work->waiters, &wait, TASK_INTERRUPTIBLE);
929
930                 /*
931                  * The events can happen in critical sections where
932                  * checking a work queue can cause deadlocks.
933                  * After adding a task to the queue, this flag is set
934                  * only to notify events to try to wake up the queue
935                  * using irq_work.
936                  *
937                  * We don't clear it even if the buffer is no longer
938                  * empty. The flag only causes the next event to run
939                  * irq_work to do the work queue wake up. The worse
940                  * that can happen if we race with !trace_empty() is that
941                  * an event will cause an irq_work to try to wake up
942                  * an empty queue.
943                  *
944                  * There's no reason to protect this flag either, as
945                  * the work queue and irq_work logic will do the necessary
946                  * synchronization for the wake ups. The only thing
947                  * that is necessary is that the wake up happens after
948                  * a task has been queued. It's OK for spurious wake ups.
949                  */
950                 if (full)
951                         work->full_waiters_pending = true;
952                 else
953                         work->waiters_pending = true;
954
955                 if (signal_pending(current)) {
956                         ret = -EINTR;
957                         break;
958                 }
959
960                 if (cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer))
961                         break;
962
963                 if (cpu != RING_BUFFER_ALL_CPUS &&
964                     !ring_buffer_empty_cpu(buffer, cpu)) {
965                         unsigned long flags;
966                         bool pagebusy;
967                         size_t nr_pages;
968                         size_t dirty;
969
970                         if (!full)
971                                 break;
972
973                         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
974                         pagebusy = cpu_buffer->reader_page == cpu_buffer->commit_page;
975                         nr_pages = cpu_buffer->nr_pages;
976                         dirty = ring_buffer_nr_dirty_pages(buffer, cpu);
977                         if (!cpu_buffer->shortest_full ||
978                             cpu_buffer->shortest_full < full)
979                                 cpu_buffer->shortest_full = full;
980                         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
981                         if (!pagebusy &&
982                             (!nr_pages || (dirty * 100) > full * nr_pages))
983                                 break;
984                 }
985
986                 schedule();
987         }
988
989         if (full)
990                 finish_wait(&work->full_waiters, &wait);
991         else
992                 finish_wait(&work->waiters, &wait);
993
994         return ret;
995 }
996
997 /**
998  * ring_buffer_poll_wait - poll on buffer input
999  * @buffer: buffer to wait on
1000  * @cpu: the cpu buffer to wait on
1001  * @filp: the file descriptor
1002  * @poll_table: The poll descriptor
1003  *
1004  * If @cpu == RING_BUFFER_ALL_CPUS then the task will wake up as soon
1005  * as data is added to any of the @buffer's cpu buffers. Otherwise
1006  * it will wait for data to be added to a specific cpu buffer.
1007  *
1008  * Returns EPOLLIN | EPOLLRDNORM if data exists in the buffers,
1009  * zero otherwise.
1010  */
1011 __poll_t ring_buffer_poll_wait(struct trace_buffer *buffer, int cpu,
1012                           struct file *filp, poll_table *poll_table)
1013 {
1014         struct ring_buffer_per_cpu *cpu_buffer;
1015         struct rb_irq_work *work;
1016
1017         if (cpu == RING_BUFFER_ALL_CPUS)
1018                 work = &buffer->irq_work;
1019         else {
1020                 if (!cpumask_test_cpu(cpu, buffer->cpumask))
1021                         return -EINVAL;
1022
1023                 cpu_buffer = buffer->buffers[cpu];
1024                 work = &cpu_buffer->irq_work;
1025         }
1026
1027         poll_wait(filp, &work->waiters, poll_table);
1028         work->waiters_pending = true;
1029         /*
1030          * There's a tight race between setting the waiters_pending and
1031          * checking if the ring buffer is empty.  Once the waiters_pending bit
1032          * is set, the next event will wake the task up, but we can get stuck
1033          * if there's only a single event in.
1034          *
1035          * FIXME: Ideally, we need a memory barrier on the writer side as well,
1036          * but adding a memory barrier to all events will cause too much of a
1037          * performance hit in the fast path.  We only need a memory barrier when
1038          * the buffer goes from empty to having content.  But as this race is
1039          * extremely small, and it's not a problem if another event comes in, we
1040          * will fix it later.
1041          */
1042         smp_mb();
1043
1044         if ((cpu == RING_BUFFER_ALL_CPUS && !ring_buffer_empty(buffer)) ||
1045             (cpu != RING_BUFFER_ALL_CPUS && !ring_buffer_empty_cpu(buffer, cpu)))
1046                 return EPOLLIN | EPOLLRDNORM;
1047         return 0;
1048 }
1049
1050 /* buffer may be either ring_buffer or ring_buffer_per_cpu */
1051 #define RB_WARN_ON(b, cond)                                             \
1052         ({                                                              \
1053                 int _____ret = unlikely(cond);                          \
1054                 if (_____ret) {                                         \
1055                         if (__same_type(*(b), struct ring_buffer_per_cpu)) { \
1056                                 struct ring_buffer_per_cpu *__b =       \
1057                                         (void *)b;                      \
1058                                 atomic_inc(&__b->buffer->record_disabled); \
1059                         } else                                          \
1060                                 atomic_inc(&b->record_disabled);        \
1061                         WARN_ON(1);                                     \
1062                 }                                                       \
1063                 _____ret;                                               \
1064         })
1065
1066 /* Up this if you want to test the TIME_EXTENTS and normalization */
1067 #define DEBUG_SHIFT 0
1068
1069 static inline u64 rb_time_stamp(struct trace_buffer *buffer)
1070 {
1071         u64 ts;
1072
1073         /* Skip retpolines :-( */
1074         if (IS_ENABLED(CONFIG_RETPOLINE) && likely(buffer->clock == trace_clock_local))
1075                 ts = trace_clock_local();
1076         else
1077                 ts = buffer->clock();
1078
1079         /* shift to debug/test normalization and TIME_EXTENTS */
1080         return ts << DEBUG_SHIFT;
1081 }
1082
1083 u64 ring_buffer_time_stamp(struct trace_buffer *buffer)
1084 {
1085         u64 time;
1086
1087         preempt_disable_notrace();
1088         time = rb_time_stamp(buffer);
1089         preempt_enable_notrace();
1090
1091         return time;
1092 }
1093 EXPORT_SYMBOL_GPL(ring_buffer_time_stamp);
1094
1095 void ring_buffer_normalize_time_stamp(struct trace_buffer *buffer,
1096                                       int cpu, u64 *ts)
1097 {
1098         /* Just stupid testing the normalize function and deltas */
1099         *ts >>= DEBUG_SHIFT;
1100 }
1101 EXPORT_SYMBOL_GPL(ring_buffer_normalize_time_stamp);
1102
1103 /*
1104  * Making the ring buffer lockless makes things tricky.
1105  * Although writes only happen on the CPU that they are on,
1106  * and they only need to worry about interrupts. Reads can
1107  * happen on any CPU.
1108  *
1109  * The reader page is always off the ring buffer, but when the
1110  * reader finishes with a page, it needs to swap its page with
1111  * a new one from the buffer. The reader needs to take from
1112  * the head (writes go to the tail). But if a writer is in overwrite
1113  * mode and wraps, it must push the head page forward.
1114  *
1115  * Here lies the problem.
1116  *
1117  * The reader must be careful to replace only the head page, and
1118  * not another one. As described at the top of the file in the
1119  * ASCII art, the reader sets its old page to point to the next
1120  * page after head. It then sets the page after head to point to
1121  * the old reader page. But if the writer moves the head page
1122  * during this operation, the reader could end up with the tail.
1123  *
1124  * We use cmpxchg to help prevent this race. We also do something
1125  * special with the page before head. We set the LSB to 1.
1126  *
1127  * When the writer must push the page forward, it will clear the
1128  * bit that points to the head page, move the head, and then set
1129  * the bit that points to the new head page.
1130  *
1131  * We also don't want an interrupt coming in and moving the head
1132  * page on another writer. Thus we use the second LSB to catch
1133  * that too. Thus:
1134  *
1135  * head->list->prev->next        bit 1          bit 0
1136  *                              -------        -------
1137  * Normal page                     0              0
1138  * Points to head page             0              1
1139  * New head page                   1              0
1140  *
1141  * Note we can not trust the prev pointer of the head page, because:
1142  *
1143  * +----+       +-----+        +-----+
1144  * |    |------>|  T  |---X--->|  N  |
1145  * |    |<------|     |        |     |
1146  * +----+       +-----+        +-----+
1147  *   ^                           ^ |
1148  *   |          +-----+          | |
1149  *   +----------|  R  |----------+ |
1150  *              |     |<-----------+
1151  *              +-----+
1152  *
1153  * Key:  ---X-->  HEAD flag set in pointer
1154  *         T      Tail page
1155  *         R      Reader page
1156  *         N      Next page
1157  *
1158  * (see __rb_reserve_next() to see where this happens)
1159  *
1160  *  What the above shows is that the reader just swapped out
1161  *  the reader page with a page in the buffer, but before it
1162  *  could make the new header point back to the new page added
1163  *  it was preempted by a writer. The writer moved forward onto
1164  *  the new page added by the reader and is about to move forward
1165  *  again.
1166  *
1167  *  You can see, it is legitimate for the previous pointer of
1168  *  the head (or any page) not to point back to itself. But only
1169  *  temporarily.
1170  */
1171
1172 #define RB_PAGE_NORMAL          0UL
1173 #define RB_PAGE_HEAD            1UL
1174 #define RB_PAGE_UPDATE          2UL
1175
1176
1177 #define RB_FLAG_MASK            3UL
1178
1179 /* PAGE_MOVED is not part of the mask */
1180 #define RB_PAGE_MOVED           4UL
1181
1182 /*
1183  * rb_list_head - remove any bit
1184  */
1185 static struct list_head *rb_list_head(struct list_head *list)
1186 {
1187         unsigned long val = (unsigned long)list;
1188
1189         return (struct list_head *)(val & ~RB_FLAG_MASK);
1190 }
1191
1192 /*
1193  * rb_is_head_page - test if the given page is the head page
1194  *
1195  * Because the reader may move the head_page pointer, we can
1196  * not trust what the head page is (it may be pointing to
1197  * the reader page). But if the next page is a header page,
1198  * its flags will be non zero.
1199  */
1200 static inline int
1201 rb_is_head_page(struct buffer_page *page, struct list_head *list)
1202 {
1203         unsigned long val;
1204
1205         val = (unsigned long)list->next;
1206
1207         if ((val & ~RB_FLAG_MASK) != (unsigned long)&page->list)
1208                 return RB_PAGE_MOVED;
1209
1210         return val & RB_FLAG_MASK;
1211 }
1212
1213 /*
1214  * rb_is_reader_page
1215  *
1216  * The unique thing about the reader page, is that, if the
1217  * writer is ever on it, the previous pointer never points
1218  * back to the reader page.
1219  */
1220 static bool rb_is_reader_page(struct buffer_page *page)
1221 {
1222         struct list_head *list = page->list.prev;
1223
1224         return rb_list_head(list->next) != &page->list;
1225 }
1226
1227 /*
1228  * rb_set_list_to_head - set a list_head to be pointing to head.
1229  */
1230 static void rb_set_list_to_head(struct list_head *list)
1231 {
1232         unsigned long *ptr;
1233
1234         ptr = (unsigned long *)&list->next;
1235         *ptr |= RB_PAGE_HEAD;
1236         *ptr &= ~RB_PAGE_UPDATE;
1237 }
1238
1239 /*
1240  * rb_head_page_activate - sets up head page
1241  */
1242 static void rb_head_page_activate(struct ring_buffer_per_cpu *cpu_buffer)
1243 {
1244         struct buffer_page *head;
1245
1246         head = cpu_buffer->head_page;
1247         if (!head)
1248                 return;
1249
1250         /*
1251          * Set the previous list pointer to have the HEAD flag.
1252          */
1253         rb_set_list_to_head(head->list.prev);
1254 }
1255
1256 static void rb_list_head_clear(struct list_head *list)
1257 {
1258         unsigned long *ptr = (unsigned long *)&list->next;
1259
1260         *ptr &= ~RB_FLAG_MASK;
1261 }
1262
1263 /*
1264  * rb_head_page_deactivate - clears head page ptr (for free list)
1265  */
1266 static void
1267 rb_head_page_deactivate(struct ring_buffer_per_cpu *cpu_buffer)
1268 {
1269         struct list_head *hd;
1270
1271         /* Go through the whole list and clear any pointers found. */
1272         rb_list_head_clear(cpu_buffer->pages);
1273
1274         list_for_each(hd, cpu_buffer->pages)
1275                 rb_list_head_clear(hd);
1276 }
1277
1278 static int rb_head_page_set(struct ring_buffer_per_cpu *cpu_buffer,
1279                             struct buffer_page *head,
1280                             struct buffer_page *prev,
1281                             int old_flag, int new_flag)
1282 {
1283         struct list_head *list;
1284         unsigned long val = (unsigned long)&head->list;
1285         unsigned long ret;
1286
1287         list = &prev->list;
1288
1289         val &= ~RB_FLAG_MASK;
1290
1291         ret = cmpxchg((unsigned long *)&list->next,
1292                       val | old_flag, val | new_flag);
1293
1294         /* check if the reader took the page */
1295         if ((ret & ~RB_FLAG_MASK) != val)
1296                 return RB_PAGE_MOVED;
1297
1298         return ret & RB_FLAG_MASK;
1299 }
1300
1301 static int rb_head_page_set_update(struct ring_buffer_per_cpu *cpu_buffer,
1302                                    struct buffer_page *head,
1303                                    struct buffer_page *prev,
1304                                    int old_flag)
1305 {
1306         return rb_head_page_set(cpu_buffer, head, prev,
1307                                 old_flag, RB_PAGE_UPDATE);
1308 }
1309
1310 static int rb_head_page_set_head(struct ring_buffer_per_cpu *cpu_buffer,
1311                                  struct buffer_page *head,
1312                                  struct buffer_page *prev,
1313                                  int old_flag)
1314 {
1315         return rb_head_page_set(cpu_buffer, head, prev,
1316                                 old_flag, RB_PAGE_HEAD);
1317 }
1318
1319 static int rb_head_page_set_normal(struct ring_buffer_per_cpu *cpu_buffer,
1320                                    struct buffer_page *head,
1321                                    struct buffer_page *prev,
1322                                    int old_flag)
1323 {
1324         return rb_head_page_set(cpu_buffer, head, prev,
1325                                 old_flag, RB_PAGE_NORMAL);
1326 }
1327
1328 static inline void rb_inc_page(struct buffer_page **bpage)
1329 {
1330         struct list_head *p = rb_list_head((*bpage)->list.next);
1331
1332         *bpage = list_entry(p, struct buffer_page, list);
1333 }
1334
1335 static struct buffer_page *
1336 rb_set_head_page(struct ring_buffer_per_cpu *cpu_buffer)
1337 {
1338         struct buffer_page *head;
1339         struct buffer_page *page;
1340         struct list_head *list;
1341         int i;
1342
1343         if (RB_WARN_ON(cpu_buffer, !cpu_buffer->head_page))
1344                 return NULL;
1345
1346         /* sanity check */
1347         list = cpu_buffer->pages;
1348         if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev->next) != list))
1349                 return NULL;
1350
1351         page = head = cpu_buffer->head_page;
1352         /*
1353          * It is possible that the writer moves the header behind
1354          * where we started, and we miss in one loop.
1355          * A second loop should grab the header, but we'll do
1356          * three loops just because I'm paranoid.
1357          */
1358         for (i = 0; i < 3; i++) {
1359                 do {
1360                         if (rb_is_head_page(page, page->list.prev)) {
1361                                 cpu_buffer->head_page = page;
1362                                 return page;
1363                         }
1364                         rb_inc_page(&page);
1365                 } while (page != head);
1366         }
1367
1368         RB_WARN_ON(cpu_buffer, 1);
1369
1370         return NULL;
1371 }
1372
1373 static int rb_head_page_replace(struct buffer_page *old,
1374                                 struct buffer_page *new)
1375 {
1376         unsigned long *ptr = (unsigned long *)&old->list.prev->next;
1377         unsigned long val;
1378         unsigned long ret;
1379
1380         val = *ptr & ~RB_FLAG_MASK;
1381         val |= RB_PAGE_HEAD;
1382
1383         ret = cmpxchg(ptr, val, (unsigned long)&new->list);
1384
1385         return ret == val;
1386 }
1387
1388 /*
1389  * rb_tail_page_update - move the tail page forward
1390  */
1391 static void rb_tail_page_update(struct ring_buffer_per_cpu *cpu_buffer,
1392                                struct buffer_page *tail_page,
1393                                struct buffer_page *next_page)
1394 {
1395         unsigned long old_entries;
1396         unsigned long old_write;
1397
1398         /*
1399          * The tail page now needs to be moved forward.
1400          *
1401          * We need to reset the tail page, but without messing
1402          * with possible erasing of data brought in by interrupts
1403          * that have moved the tail page and are currently on it.
1404          *
1405          * We add a counter to the write field to denote this.
1406          */
1407         old_write = local_add_return(RB_WRITE_INTCNT, &next_page->write);
1408         old_entries = local_add_return(RB_WRITE_INTCNT, &next_page->entries);
1409
1410         local_inc(&cpu_buffer->pages_touched);
1411         /*
1412          * Just make sure we have seen our old_write and synchronize
1413          * with any interrupts that come in.
1414          */
1415         barrier();
1416
1417         /*
1418          * If the tail page is still the same as what we think
1419          * it is, then it is up to us to update the tail
1420          * pointer.
1421          */
1422         if (tail_page == READ_ONCE(cpu_buffer->tail_page)) {
1423                 /* Zero the write counter */
1424                 unsigned long val = old_write & ~RB_WRITE_MASK;
1425                 unsigned long eval = old_entries & ~RB_WRITE_MASK;
1426
1427                 /*
1428                  * This will only succeed if an interrupt did
1429                  * not come in and change it. In which case, we
1430                  * do not want to modify it.
1431                  *
1432                  * We add (void) to let the compiler know that we do not care
1433                  * about the return value of these functions. We use the
1434                  * cmpxchg to only update if an interrupt did not already
1435                  * do it for us. If the cmpxchg fails, we don't care.
1436                  */
1437                 (void)local_cmpxchg(&next_page->write, old_write, val);
1438                 (void)local_cmpxchg(&next_page->entries, old_entries, eval);
1439
1440                 /*
1441                  * No need to worry about races with clearing out the commit.
1442                  * it only can increment when a commit takes place. But that
1443                  * only happens in the outer most nested commit.
1444                  */
1445                 local_set(&next_page->page->commit, 0);
1446
1447                 /* Again, either we update tail_page or an interrupt does */
1448                 (void)cmpxchg(&cpu_buffer->tail_page, tail_page, next_page);
1449         }
1450 }
1451
1452 static int rb_check_bpage(struct ring_buffer_per_cpu *cpu_buffer,
1453                           struct buffer_page *bpage)
1454 {
1455         unsigned long val = (unsigned long)bpage;
1456
1457         if (RB_WARN_ON(cpu_buffer, val & RB_FLAG_MASK))
1458                 return 1;
1459
1460         return 0;
1461 }
1462
1463 /**
1464  * rb_check_list - make sure a pointer to a list has the last bits zero
1465  */
1466 static int rb_check_list(struct ring_buffer_per_cpu *cpu_buffer,
1467                          struct list_head *list)
1468 {
1469         if (RB_WARN_ON(cpu_buffer, rb_list_head(list->prev) != list->prev))
1470                 return 1;
1471         if (RB_WARN_ON(cpu_buffer, rb_list_head(list->next) != list->next))
1472                 return 1;
1473         return 0;
1474 }
1475
1476 /**
1477  * rb_check_pages - integrity check of buffer pages
1478  * @cpu_buffer: CPU buffer with pages to test
1479  *
1480  * As a safety measure we check to make sure the data pages have not
1481  * been corrupted.
1482  */
1483 static int rb_check_pages(struct ring_buffer_per_cpu *cpu_buffer)
1484 {
1485         struct list_head *head = cpu_buffer->pages;
1486         struct buffer_page *bpage, *tmp;
1487
1488         /* Reset the head page if it exists */
1489         if (cpu_buffer->head_page)
1490                 rb_set_head_page(cpu_buffer);
1491
1492         rb_head_page_deactivate(cpu_buffer);
1493
1494         if (RB_WARN_ON(cpu_buffer, head->next->prev != head))
1495                 return -1;
1496         if (RB_WARN_ON(cpu_buffer, head->prev->next != head))
1497                 return -1;
1498
1499         if (rb_check_list(cpu_buffer, head))
1500                 return -1;
1501
1502         list_for_each_entry_safe(bpage, tmp, head, list) {
1503                 if (RB_WARN_ON(cpu_buffer,
1504                                bpage->list.next->prev != &bpage->list))
1505                         return -1;
1506                 if (RB_WARN_ON(cpu_buffer,
1507                                bpage->list.prev->next != &bpage->list))
1508                         return -1;
1509                 if (rb_check_list(cpu_buffer, &bpage->list))
1510                         return -1;
1511         }
1512
1513         rb_head_page_activate(cpu_buffer);
1514
1515         return 0;
1516 }
1517
1518 static int __rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1519                 long nr_pages, struct list_head *pages)
1520 {
1521         struct buffer_page *bpage, *tmp;
1522         bool user_thread = current->mm != NULL;
1523         gfp_t mflags;
1524         long i;
1525
1526         /*
1527          * Check if the available memory is there first.
1528          * Note, si_mem_available() only gives us a rough estimate of available
1529          * memory. It may not be accurate. But we don't care, we just want
1530          * to prevent doing any allocation when it is obvious that it is
1531          * not going to succeed.
1532          */
1533         i = si_mem_available();
1534         if (i < nr_pages)
1535                 return -ENOMEM;
1536
1537         /*
1538          * __GFP_RETRY_MAYFAIL flag makes sure that the allocation fails
1539          * gracefully without invoking oom-killer and the system is not
1540          * destabilized.
1541          */
1542         mflags = GFP_KERNEL | __GFP_RETRY_MAYFAIL;
1543
1544         /*
1545          * If a user thread allocates too much, and si_mem_available()
1546          * reports there's enough memory, even though there is not.
1547          * Make sure the OOM killer kills this thread. This can happen
1548          * even with RETRY_MAYFAIL because another task may be doing
1549          * an allocation after this task has taken all memory.
1550          * This is the task the OOM killer needs to take out during this
1551          * loop, even if it was triggered by an allocation somewhere else.
1552          */
1553         if (user_thread)
1554                 set_current_oom_origin();
1555         for (i = 0; i < nr_pages; i++) {
1556                 struct page *page;
1557
1558                 bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1559                                     mflags, cpu_to_node(cpu_buffer->cpu));
1560                 if (!bpage)
1561                         goto free_pages;
1562
1563                 rb_check_bpage(cpu_buffer, bpage);
1564
1565                 list_add(&bpage->list, pages);
1566
1567                 page = alloc_pages_node(cpu_to_node(cpu_buffer->cpu), mflags, 0);
1568                 if (!page)
1569                         goto free_pages;
1570                 bpage->page = page_address(page);
1571                 rb_init_page(bpage->page);
1572
1573                 if (user_thread && fatal_signal_pending(current))
1574                         goto free_pages;
1575         }
1576         if (user_thread)
1577                 clear_current_oom_origin();
1578
1579         return 0;
1580
1581 free_pages:
1582         list_for_each_entry_safe(bpage, tmp, pages, list) {
1583                 list_del_init(&bpage->list);
1584                 free_buffer_page(bpage);
1585         }
1586         if (user_thread)
1587                 clear_current_oom_origin();
1588
1589         return -ENOMEM;
1590 }
1591
1592 static int rb_allocate_pages(struct ring_buffer_per_cpu *cpu_buffer,
1593                              unsigned long nr_pages)
1594 {
1595         LIST_HEAD(pages);
1596
1597         WARN_ON(!nr_pages);
1598
1599         if (__rb_allocate_pages(cpu_buffer, nr_pages, &pages))
1600                 return -ENOMEM;
1601
1602         /*
1603          * The ring buffer page list is a circular list that does not
1604          * start and end with a list head. All page list items point to
1605          * other pages.
1606          */
1607         cpu_buffer->pages = pages.next;
1608         list_del(&pages);
1609
1610         cpu_buffer->nr_pages = nr_pages;
1611
1612         rb_check_pages(cpu_buffer);
1613
1614         return 0;
1615 }
1616
1617 static struct ring_buffer_per_cpu *
1618 rb_allocate_cpu_buffer(struct trace_buffer *buffer, long nr_pages, int cpu)
1619 {
1620         struct ring_buffer_per_cpu *cpu_buffer;
1621         struct buffer_page *bpage;
1622         struct page *page;
1623         int ret;
1624
1625         cpu_buffer = kzalloc_node(ALIGN(sizeof(*cpu_buffer), cache_line_size()),
1626                                   GFP_KERNEL, cpu_to_node(cpu));
1627         if (!cpu_buffer)
1628                 return NULL;
1629
1630         cpu_buffer->cpu = cpu;
1631         cpu_buffer->buffer = buffer;
1632         raw_spin_lock_init(&cpu_buffer->reader_lock);
1633         lockdep_set_class(&cpu_buffer->reader_lock, buffer->reader_lock_key);
1634         cpu_buffer->lock = (arch_spinlock_t)__ARCH_SPIN_LOCK_UNLOCKED;
1635         INIT_WORK(&cpu_buffer->update_pages_work, update_pages_handler);
1636         init_completion(&cpu_buffer->update_done);
1637         init_irq_work(&cpu_buffer->irq_work.work, rb_wake_up_waiters);
1638         init_waitqueue_head(&cpu_buffer->irq_work.waiters);
1639         init_waitqueue_head(&cpu_buffer->irq_work.full_waiters);
1640
1641         bpage = kzalloc_node(ALIGN(sizeof(*bpage), cache_line_size()),
1642                             GFP_KERNEL, cpu_to_node(cpu));
1643         if (!bpage)
1644                 goto fail_free_buffer;
1645
1646         rb_check_bpage(cpu_buffer, bpage);
1647
1648         cpu_buffer->reader_page = bpage;
1649         page = alloc_pages_node(cpu_to_node(cpu), GFP_KERNEL, 0);
1650         if (!page)
1651                 goto fail_free_reader;
1652         bpage->page = page_address(page);
1653         rb_init_page(bpage->page);
1654
1655         INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
1656         INIT_LIST_HEAD(&cpu_buffer->new_pages);
1657
1658         ret = rb_allocate_pages(cpu_buffer, nr_pages);
1659         if (ret < 0)
1660                 goto fail_free_reader;
1661
1662         cpu_buffer->head_page
1663                 = list_entry(cpu_buffer->pages, struct buffer_page, list);
1664         cpu_buffer->tail_page = cpu_buffer->commit_page = cpu_buffer->head_page;
1665
1666         rb_head_page_activate(cpu_buffer);
1667
1668         return cpu_buffer;
1669
1670  fail_free_reader:
1671         free_buffer_page(cpu_buffer->reader_page);
1672
1673  fail_free_buffer:
1674         kfree(cpu_buffer);
1675         return NULL;
1676 }
1677
1678 static void rb_free_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
1679 {
1680         struct list_head *head = cpu_buffer->pages;
1681         struct buffer_page *bpage, *tmp;
1682
1683         free_buffer_page(cpu_buffer->reader_page);
1684
1685         rb_head_page_deactivate(cpu_buffer);
1686
1687         if (head) {
1688                 list_for_each_entry_safe(bpage, tmp, head, list) {
1689                         list_del_init(&bpage->list);
1690                         free_buffer_page(bpage);
1691                 }
1692                 bpage = list_entry(head, struct buffer_page, list);
1693                 free_buffer_page(bpage);
1694         }
1695
1696         kfree(cpu_buffer);
1697 }
1698
1699 /**
1700  * __ring_buffer_alloc - allocate a new ring_buffer
1701  * @size: the size in bytes per cpu that is needed.
1702  * @flags: attributes to set for the ring buffer.
1703  * @key: ring buffer reader_lock_key.
1704  *
1705  * Currently the only flag that is available is the RB_FL_OVERWRITE
1706  * flag. This flag means that the buffer will overwrite old data
1707  * when the buffer wraps. If this flag is not set, the buffer will
1708  * drop data when the tail hits the head.
1709  */
1710 struct trace_buffer *__ring_buffer_alloc(unsigned long size, unsigned flags,
1711                                         struct lock_class_key *key)
1712 {
1713         struct trace_buffer *buffer;
1714         long nr_pages;
1715         int bsize;
1716         int cpu;
1717         int ret;
1718
1719         /* keep it in its own cache line */
1720         buffer = kzalloc(ALIGN(sizeof(*buffer), cache_line_size()),
1721                          GFP_KERNEL);
1722         if (!buffer)
1723                 return NULL;
1724
1725         if (!zalloc_cpumask_var(&buffer->cpumask, GFP_KERNEL))
1726                 goto fail_free_buffer;
1727
1728         nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
1729         buffer->flags = flags;
1730         buffer->clock = trace_clock_local;
1731         buffer->reader_lock_key = key;
1732
1733         init_irq_work(&buffer->irq_work.work, rb_wake_up_waiters);
1734         init_waitqueue_head(&buffer->irq_work.waiters);
1735
1736         /* need at least two pages */
1737         if (nr_pages < 2)
1738                 nr_pages = 2;
1739
1740         buffer->cpus = nr_cpu_ids;
1741
1742         bsize = sizeof(void *) * nr_cpu_ids;
1743         buffer->buffers = kzalloc(ALIGN(bsize, cache_line_size()),
1744                                   GFP_KERNEL);
1745         if (!buffer->buffers)
1746                 goto fail_free_cpumask;
1747
1748         cpu = raw_smp_processor_id();
1749         cpumask_set_cpu(cpu, buffer->cpumask);
1750         buffer->buffers[cpu] = rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
1751         if (!buffer->buffers[cpu])
1752                 goto fail_free_buffers;
1753
1754         ret = cpuhp_state_add_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1755         if (ret < 0)
1756                 goto fail_free_buffers;
1757
1758         mutex_init(&buffer->mutex);
1759
1760         return buffer;
1761
1762  fail_free_buffers:
1763         for_each_buffer_cpu(buffer, cpu) {
1764                 if (buffer->buffers[cpu])
1765                         rb_free_cpu_buffer(buffer->buffers[cpu]);
1766         }
1767         kfree(buffer->buffers);
1768
1769  fail_free_cpumask:
1770         free_cpumask_var(buffer->cpumask);
1771
1772  fail_free_buffer:
1773         kfree(buffer);
1774         return NULL;
1775 }
1776 EXPORT_SYMBOL_GPL(__ring_buffer_alloc);
1777
1778 /**
1779  * ring_buffer_free - free a ring buffer.
1780  * @buffer: the buffer to free.
1781  */
1782 void
1783 ring_buffer_free(struct trace_buffer *buffer)
1784 {
1785         int cpu;
1786
1787         cpuhp_state_remove_instance(CPUHP_TRACE_RB_PREPARE, &buffer->node);
1788
1789         for_each_buffer_cpu(buffer, cpu)
1790                 rb_free_cpu_buffer(buffer->buffers[cpu]);
1791
1792         kfree(buffer->buffers);
1793         free_cpumask_var(buffer->cpumask);
1794
1795         kfree(buffer);
1796 }
1797 EXPORT_SYMBOL_GPL(ring_buffer_free);
1798
1799 void ring_buffer_set_clock(struct trace_buffer *buffer,
1800                            u64 (*clock)(void))
1801 {
1802         buffer->clock = clock;
1803 }
1804
1805 void ring_buffer_set_time_stamp_abs(struct trace_buffer *buffer, bool abs)
1806 {
1807         buffer->time_stamp_abs = abs;
1808 }
1809
1810 bool ring_buffer_time_stamp_abs(struct trace_buffer *buffer)
1811 {
1812         return buffer->time_stamp_abs;
1813 }
1814
1815 static void rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer);
1816
1817 static inline unsigned long rb_page_entries(struct buffer_page *bpage)
1818 {
1819         return local_read(&bpage->entries) & RB_WRITE_MASK;
1820 }
1821
1822 static inline unsigned long rb_page_write(struct buffer_page *bpage)
1823 {
1824         return local_read(&bpage->write) & RB_WRITE_MASK;
1825 }
1826
1827 static int
1828 rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned long nr_pages)
1829 {
1830         struct list_head *tail_page, *to_remove, *next_page;
1831         struct buffer_page *to_remove_page, *tmp_iter_page;
1832         struct buffer_page *last_page, *first_page;
1833         unsigned long nr_removed;
1834         unsigned long head_bit;
1835         int page_entries;
1836
1837         head_bit = 0;
1838
1839         raw_spin_lock_irq(&cpu_buffer->reader_lock);
1840         atomic_inc(&cpu_buffer->record_disabled);
1841         /*
1842          * We don't race with the readers since we have acquired the reader
1843          * lock. We also don't race with writers after disabling recording.
1844          * This makes it easy to figure out the first and the last page to be
1845          * removed from the list. We unlink all the pages in between including
1846          * the first and last pages. This is done in a busy loop so that we
1847          * lose the least number of traces.
1848          * The pages are freed after we restart recording and unlock readers.
1849          */
1850         tail_page = &cpu_buffer->tail_page->list;
1851
1852         /*
1853          * tail page might be on reader page, we remove the next page
1854          * from the ring buffer
1855          */
1856         if (cpu_buffer->tail_page == cpu_buffer->reader_page)
1857                 tail_page = rb_list_head(tail_page->next);
1858         to_remove = tail_page;
1859
1860         /* start of pages to remove */
1861         first_page = list_entry(rb_list_head(to_remove->next),
1862                                 struct buffer_page, list);
1863
1864         for (nr_removed = 0; nr_removed < nr_pages; nr_removed++) {
1865                 to_remove = rb_list_head(to_remove)->next;
1866                 head_bit |= (unsigned long)to_remove & RB_PAGE_HEAD;
1867         }
1868
1869         next_page = rb_list_head(to_remove)->next;
1870
1871         /*
1872          * Now we remove all pages between tail_page and next_page.
1873          * Make sure that we have head_bit value preserved for the
1874          * next page
1875          */
1876         tail_page->next = (struct list_head *)((unsigned long)next_page |
1877                                                 head_bit);
1878         next_page = rb_list_head(next_page);
1879         next_page->prev = tail_page;
1880
1881         /* make sure pages points to a valid page in the ring buffer */
1882         cpu_buffer->pages = next_page;
1883
1884         /* update head page */
1885         if (head_bit)
1886                 cpu_buffer->head_page = list_entry(next_page,
1887                                                 struct buffer_page, list);
1888
1889         /*
1890          * change read pointer to make sure any read iterators reset
1891          * themselves
1892          */
1893         cpu_buffer->read = 0;
1894
1895         /* pages are removed, resume tracing and then free the pages */
1896         atomic_dec(&cpu_buffer->record_disabled);
1897         raw_spin_unlock_irq(&cpu_buffer->reader_lock);
1898
1899         RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages));
1900
1901         /* last buffer page to remove */
1902         last_page = list_entry(rb_list_head(to_remove), struct buffer_page,
1903                                 list);
1904         tmp_iter_page = first_page;
1905
1906         do {
1907                 cond_resched();
1908
1909                 to_remove_page = tmp_iter_page;
1910                 rb_inc_page(&tmp_iter_page);
1911
1912                 /* update the counters */
1913                 page_entries = rb_page_entries(to_remove_page);
1914                 if (page_entries) {
1915                         /*
1916                          * If something was added to this page, it was full
1917                          * since it is not the tail page. So we deduct the
1918                          * bytes consumed in ring buffer from here.
1919                          * Increment overrun to account for the lost events.
1920                          */
1921                         local_add(page_entries, &cpu_buffer->overrun);
1922                         local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
1923                 }
1924
1925                 /*
1926                  * We have already removed references to this list item, just
1927                  * free up the buffer_page and its page
1928                  */
1929                 free_buffer_page(to_remove_page);
1930                 nr_removed--;
1931
1932         } while (to_remove_page != last_page);
1933
1934         RB_WARN_ON(cpu_buffer, nr_removed);
1935
1936         return nr_removed == 0;
1937 }
1938
1939 static int
1940 rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer)
1941 {
1942         struct list_head *pages = &cpu_buffer->new_pages;
1943         int retries, success;
1944
1945         raw_spin_lock_irq(&cpu_buffer->reader_lock);
1946         /*
1947          * We are holding the reader lock, so the reader page won't be swapped
1948          * in the ring buffer. Now we are racing with the writer trying to
1949          * move head page and the tail page.
1950          * We are going to adapt the reader page update process where:
1951          * 1. We first splice the start and end of list of new pages between
1952          *    the head page and its previous page.
1953          * 2. We cmpxchg the prev_page->next to point from head page to the
1954          *    start of new pages list.
1955          * 3. Finally, we update the head->prev to the end of new list.
1956          *
1957          * We will try this process 10 times, to make sure that we don't keep
1958          * spinning.
1959          */
1960         retries = 10;
1961         success = 0;
1962         while (retries--) {
1963                 struct list_head *head_page, *prev_page, *r;
1964                 struct list_head *last_page, *first_page;
1965                 struct list_head *head_page_with_bit;
1966
1967                 head_page = &rb_set_head_page(cpu_buffer)->list;
1968                 if (!head_page)
1969                         break;
1970                 prev_page = head_page->prev;
1971
1972                 first_page = pages->next;
1973                 last_page  = pages->prev;
1974
1975                 head_page_with_bit = (struct list_head *)
1976                                      ((unsigned long)head_page | RB_PAGE_HEAD);
1977
1978                 last_page->next = head_page_with_bit;
1979                 first_page->prev = prev_page;
1980
1981                 r = cmpxchg(&prev_page->next, head_page_with_bit, first_page);
1982
1983                 if (r == head_page_with_bit) {
1984                         /*
1985                          * yay, we replaced the page pointer to our new list,
1986                          * now, we just have to update to head page's prev
1987                          * pointer to point to end of list
1988                          */
1989                         head_page->prev = last_page;
1990                         success = 1;
1991                         break;
1992                 }
1993         }
1994
1995         if (success)
1996                 INIT_LIST_HEAD(pages);
1997         /*
1998          * If we weren't successful in adding in new pages, warn and stop
1999          * tracing
2000          */
2001         RB_WARN_ON(cpu_buffer, !success);
2002         raw_spin_unlock_irq(&cpu_buffer->reader_lock);
2003
2004         /* free pages if they weren't inserted */
2005         if (!success) {
2006                 struct buffer_page *bpage, *tmp;
2007                 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
2008                                          list) {
2009                         list_del_init(&bpage->list);
2010                         free_buffer_page(bpage);
2011                 }
2012         }
2013         return success;
2014 }
2015
2016 static void rb_update_pages(struct ring_buffer_per_cpu *cpu_buffer)
2017 {
2018         int success;
2019
2020         if (cpu_buffer->nr_pages_to_update > 0)
2021                 success = rb_insert_pages(cpu_buffer);
2022         else
2023                 success = rb_remove_pages(cpu_buffer,
2024                                         -cpu_buffer->nr_pages_to_update);
2025
2026         if (success)
2027                 cpu_buffer->nr_pages += cpu_buffer->nr_pages_to_update;
2028 }
2029
2030 static void update_pages_handler(struct work_struct *work)
2031 {
2032         struct ring_buffer_per_cpu *cpu_buffer = container_of(work,
2033                         struct ring_buffer_per_cpu, update_pages_work);
2034         rb_update_pages(cpu_buffer);
2035         complete(&cpu_buffer->update_done);
2036 }
2037
2038 /**
2039  * ring_buffer_resize - resize the ring buffer
2040  * @buffer: the buffer to resize.
2041  * @size: the new size.
2042  * @cpu_id: the cpu buffer to resize
2043  *
2044  * Minimum size is 2 * BUF_PAGE_SIZE.
2045  *
2046  * Returns 0 on success and < 0 on failure.
2047  */
2048 int ring_buffer_resize(struct trace_buffer *buffer, unsigned long size,
2049                         int cpu_id)
2050 {
2051         struct ring_buffer_per_cpu *cpu_buffer;
2052         unsigned long nr_pages;
2053         int cpu, err;
2054
2055         /*
2056          * Always succeed at resizing a non-existent buffer:
2057          */
2058         if (!buffer)
2059                 return 0;
2060
2061         /* Make sure the requested buffer exists */
2062         if (cpu_id != RING_BUFFER_ALL_CPUS &&
2063             !cpumask_test_cpu(cpu_id, buffer->cpumask))
2064                 return 0;
2065
2066         nr_pages = DIV_ROUND_UP(size, BUF_PAGE_SIZE);
2067
2068         /* we need a minimum of two pages */
2069         if (nr_pages < 2)
2070                 nr_pages = 2;
2071
2072         /* prevent another thread from changing buffer sizes */
2073         mutex_lock(&buffer->mutex);
2074
2075
2076         if (cpu_id == RING_BUFFER_ALL_CPUS) {
2077                 /*
2078                  * Don't succeed if resizing is disabled, as a reader might be
2079                  * manipulating the ring buffer and is expecting a sane state while
2080                  * this is true.
2081                  */
2082                 for_each_buffer_cpu(buffer, cpu) {
2083                         cpu_buffer = buffer->buffers[cpu];
2084                         if (atomic_read(&cpu_buffer->resize_disabled)) {
2085                                 err = -EBUSY;
2086                                 goto out_err_unlock;
2087                         }
2088                 }
2089
2090                 /* calculate the pages to update */
2091                 for_each_buffer_cpu(buffer, cpu) {
2092                         cpu_buffer = buffer->buffers[cpu];
2093
2094                         cpu_buffer->nr_pages_to_update = nr_pages -
2095                                                         cpu_buffer->nr_pages;
2096                         /*
2097                          * nothing more to do for removing pages or no update
2098                          */
2099                         if (cpu_buffer->nr_pages_to_update <= 0)
2100                                 continue;
2101                         /*
2102                          * to add pages, make sure all new pages can be
2103                          * allocated without receiving ENOMEM
2104                          */
2105                         INIT_LIST_HEAD(&cpu_buffer->new_pages);
2106                         if (__rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
2107                                                 &cpu_buffer->new_pages)) {
2108                                 /* not enough memory for new pages */
2109                                 err = -ENOMEM;
2110                                 goto out_err;
2111                         }
2112                 }
2113
2114                 get_online_cpus();
2115                 /*
2116                  * Fire off all the required work handlers
2117                  * We can't schedule on offline CPUs, but it's not necessary
2118                  * since we can change their buffer sizes without any race.
2119                  */
2120                 for_each_buffer_cpu(buffer, cpu) {
2121                         cpu_buffer = buffer->buffers[cpu];
2122                         if (!cpu_buffer->nr_pages_to_update)
2123                                 continue;
2124
2125                         /* Can't run something on an offline CPU. */
2126                         if (!cpu_online(cpu)) {
2127                                 rb_update_pages(cpu_buffer);
2128                                 cpu_buffer->nr_pages_to_update = 0;
2129                         } else {
2130                                 schedule_work_on(cpu,
2131                                                 &cpu_buffer->update_pages_work);
2132                         }
2133                 }
2134
2135                 /* wait for all the updates to complete */
2136                 for_each_buffer_cpu(buffer, cpu) {
2137                         cpu_buffer = buffer->buffers[cpu];
2138                         if (!cpu_buffer->nr_pages_to_update)
2139                                 continue;
2140
2141                         if (cpu_online(cpu))
2142                                 wait_for_completion(&cpu_buffer->update_done);
2143                         cpu_buffer->nr_pages_to_update = 0;
2144                 }
2145
2146                 put_online_cpus();
2147         } else {
2148                 cpu_buffer = buffer->buffers[cpu_id];
2149
2150                 if (nr_pages == cpu_buffer->nr_pages)
2151                         goto out;
2152
2153                 /*
2154                  * Don't succeed if resizing is disabled, as a reader might be
2155                  * manipulating the ring buffer and is expecting a sane state while
2156                  * this is true.
2157                  */
2158                 if (atomic_read(&cpu_buffer->resize_disabled)) {
2159                         err = -EBUSY;
2160                         goto out_err_unlock;
2161                 }
2162
2163                 cpu_buffer->nr_pages_to_update = nr_pages -
2164                                                 cpu_buffer->nr_pages;
2165
2166                 INIT_LIST_HEAD(&cpu_buffer->new_pages);
2167                 if (cpu_buffer->nr_pages_to_update > 0 &&
2168                         __rb_allocate_pages(cpu_buffer, cpu_buffer->nr_pages_to_update,
2169                                             &cpu_buffer->new_pages)) {
2170                         err = -ENOMEM;
2171                         goto out_err;
2172                 }
2173
2174                 get_online_cpus();
2175
2176                 /* Can't run something on an offline CPU. */
2177                 if (!cpu_online(cpu_id))
2178                         rb_update_pages(cpu_buffer);
2179                 else {
2180                         schedule_work_on(cpu_id,
2181                                          &cpu_buffer->update_pages_work);
2182                         wait_for_completion(&cpu_buffer->update_done);
2183                 }
2184
2185                 cpu_buffer->nr_pages_to_update = 0;
2186                 put_online_cpus();
2187         }
2188
2189  out:
2190         /*
2191          * The ring buffer resize can happen with the ring buffer
2192          * enabled, so that the update disturbs the tracing as little
2193          * as possible. But if the buffer is disabled, we do not need
2194          * to worry about that, and we can take the time to verify
2195          * that the buffer is not corrupt.
2196          */
2197         if (atomic_read(&buffer->record_disabled)) {
2198                 atomic_inc(&buffer->record_disabled);
2199                 /*
2200                  * Even though the buffer was disabled, we must make sure
2201                  * that it is truly disabled before calling rb_check_pages.
2202                  * There could have been a race between checking
2203                  * record_disable and incrementing it.
2204                  */
2205                 synchronize_rcu();
2206                 for_each_buffer_cpu(buffer, cpu) {
2207                         cpu_buffer = buffer->buffers[cpu];
2208                         rb_check_pages(cpu_buffer);
2209                 }
2210                 atomic_dec(&buffer->record_disabled);
2211         }
2212
2213         mutex_unlock(&buffer->mutex);
2214         return 0;
2215
2216  out_err:
2217         for_each_buffer_cpu(buffer, cpu) {
2218                 struct buffer_page *bpage, *tmp;
2219
2220                 cpu_buffer = buffer->buffers[cpu];
2221                 cpu_buffer->nr_pages_to_update = 0;
2222
2223                 if (list_empty(&cpu_buffer->new_pages))
2224                         continue;
2225
2226                 list_for_each_entry_safe(bpage, tmp, &cpu_buffer->new_pages,
2227                                         list) {
2228                         list_del_init(&bpage->list);
2229                         free_buffer_page(bpage);
2230                 }
2231         }
2232  out_err_unlock:
2233         mutex_unlock(&buffer->mutex);
2234         return err;
2235 }
2236 EXPORT_SYMBOL_GPL(ring_buffer_resize);
2237
2238 void ring_buffer_change_overwrite(struct trace_buffer *buffer, int val)
2239 {
2240         mutex_lock(&buffer->mutex);
2241         if (val)
2242                 buffer->flags |= RB_FL_OVERWRITE;
2243         else
2244                 buffer->flags &= ~RB_FL_OVERWRITE;
2245         mutex_unlock(&buffer->mutex);
2246 }
2247 EXPORT_SYMBOL_GPL(ring_buffer_change_overwrite);
2248
2249 static __always_inline void *__rb_page_index(struct buffer_page *bpage, unsigned index)
2250 {
2251         return bpage->page->data + index;
2252 }
2253
2254 static __always_inline struct ring_buffer_event *
2255 rb_reader_event(struct ring_buffer_per_cpu *cpu_buffer)
2256 {
2257         return __rb_page_index(cpu_buffer->reader_page,
2258                                cpu_buffer->reader_page->read);
2259 }
2260
2261 static __always_inline unsigned rb_page_commit(struct buffer_page *bpage)
2262 {
2263         return local_read(&bpage->page->commit);
2264 }
2265
2266 static struct ring_buffer_event *
2267 rb_iter_head_event(struct ring_buffer_iter *iter)
2268 {
2269         struct ring_buffer_event *event;
2270         struct buffer_page *iter_head_page = iter->head_page;
2271         unsigned long commit;
2272         unsigned length;
2273
2274         if (iter->head != iter->next_event)
2275                 return iter->event;
2276
2277         /*
2278          * When the writer goes across pages, it issues a cmpxchg which
2279          * is a mb(), which will synchronize with the rmb here.
2280          * (see rb_tail_page_update() and __rb_reserve_next())
2281          */
2282         commit = rb_page_commit(iter_head_page);
2283         smp_rmb();
2284         event = __rb_page_index(iter_head_page, iter->head);
2285         length = rb_event_length(event);
2286
2287         /*
2288          * READ_ONCE() doesn't work on functions and we don't want the
2289          * compiler doing any crazy optimizations with length.
2290          */
2291         barrier();
2292
2293         if ((iter->head + length) > commit || length > BUF_MAX_DATA_SIZE)
2294                 /* Writer corrupted the read? */
2295                 goto reset;
2296
2297         memcpy(iter->event, event, length);
2298         /*
2299          * If the page stamp is still the same after this rmb() then the
2300          * event was safely copied without the writer entering the page.
2301          */
2302         smp_rmb();
2303
2304         /* Make sure the page didn't change since we read this */
2305         if (iter->page_stamp != iter_head_page->page->time_stamp ||
2306             commit > rb_page_commit(iter_head_page))
2307                 goto reset;
2308
2309         iter->next_event = iter->head + length;
2310         return iter->event;
2311  reset:
2312         /* Reset to the beginning */
2313         iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
2314         iter->head = 0;
2315         iter->next_event = 0;
2316         iter->missed_events = 1;
2317         return NULL;
2318 }
2319
2320 /* Size is determined by what has been committed */
2321 static __always_inline unsigned rb_page_size(struct buffer_page *bpage)
2322 {
2323         return rb_page_commit(bpage);
2324 }
2325
2326 static __always_inline unsigned
2327 rb_commit_index(struct ring_buffer_per_cpu *cpu_buffer)
2328 {
2329         return rb_page_commit(cpu_buffer->commit_page);
2330 }
2331
2332 static __always_inline unsigned
2333 rb_event_index(struct ring_buffer_event *event)
2334 {
2335         unsigned long addr = (unsigned long)event;
2336
2337         return (addr & ~PAGE_MASK) - BUF_PAGE_HDR_SIZE;
2338 }
2339
2340 static void rb_inc_iter(struct ring_buffer_iter *iter)
2341 {
2342         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
2343
2344         /*
2345          * The iterator could be on the reader page (it starts there).
2346          * But the head could have moved, since the reader was
2347          * found. Check for this case and assign the iterator
2348          * to the head page instead of next.
2349          */
2350         if (iter->head_page == cpu_buffer->reader_page)
2351                 iter->head_page = rb_set_head_page(cpu_buffer);
2352         else
2353                 rb_inc_page(&iter->head_page);
2354
2355         iter->page_stamp = iter->read_stamp = iter->head_page->page->time_stamp;
2356         iter->head = 0;
2357         iter->next_event = 0;
2358 }
2359
2360 /*
2361  * rb_handle_head_page - writer hit the head page
2362  *
2363  * Returns: +1 to retry page
2364  *           0 to continue
2365  *          -1 on error
2366  */
2367 static int
2368 rb_handle_head_page(struct ring_buffer_per_cpu *cpu_buffer,
2369                     struct buffer_page *tail_page,
2370                     struct buffer_page *next_page)
2371 {
2372         struct buffer_page *new_head;
2373         int entries;
2374         int type;
2375         int ret;
2376
2377         entries = rb_page_entries(next_page);
2378
2379         /*
2380          * The hard part is here. We need to move the head
2381          * forward, and protect against both readers on
2382          * other CPUs and writers coming in via interrupts.
2383          */
2384         type = rb_head_page_set_update(cpu_buffer, next_page, tail_page,
2385                                        RB_PAGE_HEAD);
2386
2387         /*
2388          * type can be one of four:
2389          *  NORMAL - an interrupt already moved it for us
2390          *  HEAD   - we are the first to get here.
2391          *  UPDATE - we are the interrupt interrupting
2392          *           a current move.
2393          *  MOVED  - a reader on another CPU moved the next
2394          *           pointer to its reader page. Give up
2395          *           and try again.
2396          */
2397
2398         switch (type) {
2399         case RB_PAGE_HEAD:
2400                 /*
2401                  * We changed the head to UPDATE, thus
2402                  * it is our responsibility to update
2403                  * the counters.
2404                  */
2405                 local_add(entries, &cpu_buffer->overrun);
2406                 local_sub(BUF_PAGE_SIZE, &cpu_buffer->entries_bytes);
2407
2408                 /*
2409                  * The entries will be zeroed out when we move the
2410                  * tail page.
2411                  */
2412
2413                 /* still more to do */
2414                 break;
2415
2416         case RB_PAGE_UPDATE:
2417                 /*
2418                  * This is an interrupt that interrupt the
2419                  * previous update. Still more to do.
2420                  */
2421                 break;
2422         case RB_PAGE_NORMAL:
2423                 /*
2424                  * An interrupt came in before the update
2425                  * and processed this for us.
2426                  * Nothing left to do.
2427                  */
2428                 return 1;
2429         case RB_PAGE_MOVED:
2430                 /*
2431                  * The reader is on another CPU and just did
2432                  * a swap with our next_page.
2433                  * Try again.
2434                  */
2435                 return 1;
2436         default:
2437                 RB_WARN_ON(cpu_buffer, 1); /* WTF??? */
2438                 return -1;
2439         }
2440
2441         /*
2442          * Now that we are here, the old head pointer is
2443          * set to UPDATE. This will keep the reader from
2444          * swapping the head page with the reader page.
2445          * The reader (on another CPU) will spin till
2446          * we are finished.
2447          *
2448          * We just need to protect against interrupts
2449          * doing the job. We will set the next pointer
2450          * to HEAD. After that, we set the old pointer
2451          * to NORMAL, but only if it was HEAD before.
2452          * otherwise we are an interrupt, and only
2453          * want the outer most commit to reset it.
2454          */
2455         new_head = next_page;
2456         rb_inc_page(&new_head);
2457
2458         ret = rb_head_page_set_head(cpu_buffer, new_head, next_page,
2459                                     RB_PAGE_NORMAL);
2460
2461         /*
2462          * Valid returns are:
2463          *  HEAD   - an interrupt came in and already set it.
2464          *  NORMAL - One of two things:
2465          *            1) We really set it.
2466          *            2) A bunch of interrupts came in and moved
2467          *               the page forward again.
2468          */
2469         switch (ret) {
2470         case RB_PAGE_HEAD:
2471         case RB_PAGE_NORMAL:
2472                 /* OK */
2473                 break;
2474         default:
2475                 RB_WARN_ON(cpu_buffer, 1);
2476                 return -1;
2477         }
2478
2479         /*
2480          * It is possible that an interrupt came in,
2481          * set the head up, then more interrupts came in
2482          * and moved it again. When we get back here,
2483          * the page would have been set to NORMAL but we
2484          * just set it back to HEAD.
2485          *
2486          * How do you detect this? Well, if that happened
2487          * the tail page would have moved.
2488          */
2489         if (ret == RB_PAGE_NORMAL) {
2490                 struct buffer_page *buffer_tail_page;
2491
2492                 buffer_tail_page = READ_ONCE(cpu_buffer->tail_page);
2493                 /*
2494                  * If the tail had moved passed next, then we need
2495                  * to reset the pointer.
2496                  */
2497                 if (buffer_tail_page != tail_page &&
2498                     buffer_tail_page != next_page)
2499                         rb_head_page_set_normal(cpu_buffer, new_head,
2500                                                 next_page,
2501                                                 RB_PAGE_HEAD);
2502         }
2503
2504         /*
2505          * If this was the outer most commit (the one that
2506          * changed the original pointer from HEAD to UPDATE),
2507          * then it is up to us to reset it to NORMAL.
2508          */
2509         if (type == RB_PAGE_HEAD) {
2510                 ret = rb_head_page_set_normal(cpu_buffer, next_page,
2511                                               tail_page,
2512                                               RB_PAGE_UPDATE);
2513                 if (RB_WARN_ON(cpu_buffer,
2514                                ret != RB_PAGE_UPDATE))
2515                         return -1;
2516         }
2517
2518         return 0;
2519 }
2520
2521 static inline void
2522 rb_reset_tail(struct ring_buffer_per_cpu *cpu_buffer,
2523               unsigned long tail, struct rb_event_info *info)
2524 {
2525         struct buffer_page *tail_page = info->tail_page;
2526         struct ring_buffer_event *event;
2527         unsigned long length = info->length;
2528
2529         /*
2530          * Only the event that crossed the page boundary
2531          * must fill the old tail_page with padding.
2532          */
2533         if (tail >= BUF_PAGE_SIZE) {
2534                 /*
2535                  * If the page was filled, then we still need
2536                  * to update the real_end. Reset it to zero
2537                  * and the reader will ignore it.
2538                  */
2539                 if (tail == BUF_PAGE_SIZE)
2540                         tail_page->real_end = 0;
2541
2542                 local_sub(length, &tail_page->write);
2543                 return;
2544         }
2545
2546         event = __rb_page_index(tail_page, tail);
2547
2548         /* account for padding bytes */
2549         local_add(BUF_PAGE_SIZE - tail, &cpu_buffer->entries_bytes);
2550
2551         /*
2552          * Save the original length to the meta data.
2553          * This will be used by the reader to add lost event
2554          * counter.
2555          */
2556         tail_page->real_end = tail;
2557
2558         /*
2559          * If this event is bigger than the minimum size, then
2560          * we need to be careful that we don't subtract the
2561          * write counter enough to allow another writer to slip
2562          * in on this page.
2563          * We put in a discarded commit instead, to make sure
2564          * that this space is not used again.
2565          *
2566          * If we are less than the minimum size, we don't need to
2567          * worry about it.
2568          */
2569         if (tail > (BUF_PAGE_SIZE - RB_EVNT_MIN_SIZE)) {
2570                 /* No room for any events */
2571
2572                 /* Mark the rest of the page with padding */
2573                 rb_event_set_padding(event);
2574
2575                 /* Set the write back to the previous setting */
2576                 local_sub(length, &tail_page->write);
2577                 return;
2578         }
2579
2580         /* Put in a discarded event */
2581         event->array[0] = (BUF_PAGE_SIZE - tail) - RB_EVNT_HDR_SIZE;
2582         event->type_len = RINGBUF_TYPE_PADDING;
2583         /* time delta must be non zero */
2584         event->time_delta = 1;
2585
2586         /* Set write to end of buffer */
2587         length = (tail + length) - BUF_PAGE_SIZE;
2588         local_sub(length, &tail_page->write);
2589 }
2590
2591 static inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer);
2592
2593 /*
2594  * This is the slow path, force gcc not to inline it.
2595  */
2596 static noinline struct ring_buffer_event *
2597 rb_move_tail(struct ring_buffer_per_cpu *cpu_buffer,
2598              unsigned long tail, struct rb_event_info *info)
2599 {
2600         struct buffer_page *tail_page = info->tail_page;
2601         struct buffer_page *commit_page = cpu_buffer->commit_page;
2602         struct trace_buffer *buffer = cpu_buffer->buffer;
2603         struct buffer_page *next_page;
2604         int ret;
2605
2606         next_page = tail_page;
2607
2608         rb_inc_page(&next_page);
2609
2610         /*
2611          * If for some reason, we had an interrupt storm that made
2612          * it all the way around the buffer, bail, and warn
2613          * about it.
2614          */
2615         if (unlikely(next_page == commit_page)) {
2616                 local_inc(&cpu_buffer->commit_overrun);
2617                 goto out_reset;
2618         }
2619
2620         /*
2621          * This is where the fun begins!
2622          *
2623          * We are fighting against races between a reader that
2624          * could be on another CPU trying to swap its reader
2625          * page with the buffer head.
2626          *
2627          * We are also fighting against interrupts coming in and
2628          * moving the head or tail on us as well.
2629          *
2630          * If the next page is the head page then we have filled
2631          * the buffer, unless the commit page is still on the
2632          * reader page.
2633          */
2634         if (rb_is_head_page(next_page, &tail_page->list)) {
2635
2636                 /*
2637                  * If the commit is not on the reader page, then
2638                  * move the header page.
2639                  */
2640                 if (!rb_is_reader_page(cpu_buffer->commit_page)) {
2641                         /*
2642                          * If we are not in overwrite mode,
2643                          * this is easy, just stop here.
2644                          */
2645                         if (!(buffer->flags & RB_FL_OVERWRITE)) {
2646                                 local_inc(&cpu_buffer->dropped_events);
2647                                 goto out_reset;
2648                         }
2649
2650                         ret = rb_handle_head_page(cpu_buffer,
2651                                                   tail_page,
2652                                                   next_page);
2653                         if (ret < 0)
2654                                 goto out_reset;
2655                         if (ret)
2656                                 goto out_again;
2657                 } else {
2658                         /*
2659                          * We need to be careful here too. The
2660                          * commit page could still be on the reader
2661                          * page. We could have a small buffer, and
2662                          * have filled up the buffer with events
2663                          * from interrupts and such, and wrapped.
2664                          *
2665                          * Note, if the tail page is also on the
2666                          * reader_page, we let it move out.
2667                          */
2668                         if (unlikely((cpu_buffer->commit_page !=
2669                                       cpu_buffer->tail_page) &&
2670                                      (cpu_buffer->commit_page ==
2671                                       cpu_buffer->reader_page))) {
2672                                 local_inc(&cpu_buffer->commit_overrun);
2673                                 goto out_reset;
2674                         }
2675                 }
2676         }
2677
2678         rb_tail_page_update(cpu_buffer, tail_page, next_page);
2679
2680  out_again:
2681
2682         rb_reset_tail(cpu_buffer, tail, info);
2683
2684         /* Commit what we have for now. */
2685         rb_end_commit(cpu_buffer);
2686         /* rb_end_commit() decs committing */
2687         local_inc(&cpu_buffer->committing);
2688
2689         /* fail and let the caller try again */
2690         return ERR_PTR(-EAGAIN);
2691
2692  out_reset:
2693         /* reset write */
2694         rb_reset_tail(cpu_buffer, tail, info);
2695
2696         return NULL;
2697 }
2698
2699 /* Slow path */
2700 static struct ring_buffer_event *
2701 rb_add_time_stamp(struct ring_buffer_event *event, u64 delta, bool abs)
2702 {
2703         if (abs)
2704                 event->type_len = RINGBUF_TYPE_TIME_STAMP;
2705         else
2706                 event->type_len = RINGBUF_TYPE_TIME_EXTEND;
2707
2708         /* Not the first event on the page, or not delta? */
2709         if (abs || rb_event_index(event)) {
2710                 event->time_delta = delta & TS_MASK;
2711                 event->array[0] = delta >> TS_SHIFT;
2712         } else {
2713                 /* nope, just zero it */
2714                 event->time_delta = 0;
2715                 event->array[0] = 0;
2716         }
2717
2718         return skip_time_extend(event);
2719 }
2720
2721 #ifndef CONFIG_HAVE_UNSTABLE_SCHED_CLOCK
2722 static inline bool sched_clock_stable(void)
2723 {
2724         return true;
2725 }
2726 #endif
2727
2728 static void
2729 rb_check_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2730                    struct rb_event_info *info)
2731 {
2732         u64 write_stamp;
2733
2734         WARN_ONCE(1, "Delta way too big! %llu ts=%llu before=%llu after=%llu write stamp=%llu\n%s",
2735                   (unsigned long long)info->delta,
2736                   (unsigned long long)info->ts,
2737                   (unsigned long long)info->before,
2738                   (unsigned long long)info->after,
2739                   (unsigned long long)(rb_time_read(&cpu_buffer->write_stamp, &write_stamp) ? write_stamp : 0),
2740                   sched_clock_stable() ? "" :
2741                   "If you just came from a suspend/resume,\n"
2742                   "please switch to the trace global clock:\n"
2743                   "  echo global > /sys/kernel/debug/tracing/trace_clock\n"
2744                   "or add trace_clock=global to the kernel command line\n");
2745 }
2746
2747 static void rb_add_timestamp(struct ring_buffer_per_cpu *cpu_buffer,
2748                                       struct ring_buffer_event **event,
2749                                       struct rb_event_info *info,
2750                                       u64 *delta,
2751                                       unsigned int *length)
2752 {
2753         bool abs = info->add_timestamp &
2754                 (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE);
2755
2756         if (unlikely(info->delta > (1ULL << 59))) {
2757                 /* did the clock go backwards */
2758                 if (info->before == info->after && info->before > info->ts) {
2759                         /* not interrupted */
2760                         static int once;
2761
2762                         /*
2763                          * This is possible with a recalibrating of the TSC.
2764                          * Do not produce a call stack, but just report it.
2765                          */
2766                         if (!once) {
2767                                 once++;
2768                                 pr_warn("Ring buffer clock went backwards: %llu -> %llu\n",
2769                                         info->before, info->ts);
2770                         }
2771                 } else
2772                         rb_check_timestamp(cpu_buffer, info);
2773                 if (!abs)
2774                         info->delta = 0;
2775         }
2776         *event = rb_add_time_stamp(*event, info->delta, abs);
2777         *length -= RB_LEN_TIME_EXTEND;
2778         *delta = 0;
2779 }
2780
2781 /**
2782  * rb_update_event - update event type and data
2783  * @cpu_buffer: The per cpu buffer of the @event
2784  * @event: the event to update
2785  * @info: The info to update the @event with (contains length and delta)
2786  *
2787  * Update the type and data fields of the @event. The length
2788  * is the actual size that is written to the ring buffer,
2789  * and with this, we can determine what to place into the
2790  * data field.
2791  */
2792 static void
2793 rb_update_event(struct ring_buffer_per_cpu *cpu_buffer,
2794                 struct ring_buffer_event *event,
2795                 struct rb_event_info *info)
2796 {
2797         unsigned length = info->length;
2798         u64 delta = info->delta;
2799         unsigned int nest = local_read(&cpu_buffer->committing) - 1;
2800
2801         if (!WARN_ON_ONCE(nest >= MAX_NEST))
2802                 cpu_buffer->event_stamp[nest] = info->ts;
2803
2804         /*
2805          * If we need to add a timestamp, then we
2806          * add it to the start of the reserved space.
2807          */
2808         if (unlikely(info->add_timestamp))
2809                 rb_add_timestamp(cpu_buffer, &event, info, &delta, &length);
2810
2811         event->time_delta = delta;
2812         length -= RB_EVNT_HDR_SIZE;
2813         if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT) {
2814                 event->type_len = 0;
2815                 event->array[0] = length;
2816         } else
2817                 event->type_len = DIV_ROUND_UP(length, RB_ALIGNMENT);
2818 }
2819
2820 static unsigned rb_calculate_event_length(unsigned length)
2821 {
2822         struct ring_buffer_event event; /* Used only for sizeof array */
2823
2824         /* zero length can cause confusions */
2825         if (!length)
2826                 length++;
2827
2828         if (length > RB_MAX_SMALL_DATA || RB_FORCE_8BYTE_ALIGNMENT)
2829                 length += sizeof(event.array[0]);
2830
2831         length += RB_EVNT_HDR_SIZE;
2832         length = ALIGN(length, RB_ARCH_ALIGNMENT);
2833
2834         /*
2835          * In case the time delta is larger than the 27 bits for it
2836          * in the header, we need to add a timestamp. If another
2837          * event comes in when trying to discard this one to increase
2838          * the length, then the timestamp will be added in the allocated
2839          * space of this event. If length is bigger than the size needed
2840          * for the TIME_EXTEND, then padding has to be used. The events
2841          * length must be either RB_LEN_TIME_EXTEND, or greater than or equal
2842          * to RB_LEN_TIME_EXTEND + 8, as 8 is the minimum size for padding.
2843          * As length is a multiple of 4, we only need to worry if it
2844          * is 12 (RB_LEN_TIME_EXTEND + 4).
2845          */
2846         if (length == RB_LEN_TIME_EXTEND + RB_ALIGNMENT)
2847                 length += RB_ALIGNMENT;
2848
2849         return length;
2850 }
2851
2852 static u64 rb_time_delta(struct ring_buffer_event *event)
2853 {
2854         switch (event->type_len) {
2855         case RINGBUF_TYPE_PADDING:
2856                 return 0;
2857
2858         case RINGBUF_TYPE_TIME_EXTEND:
2859                 return rb_event_time_stamp(event);
2860
2861         case RINGBUF_TYPE_TIME_STAMP:
2862                 return 0;
2863
2864         case RINGBUF_TYPE_DATA:
2865                 return event->time_delta;
2866         default:
2867                 return 0;
2868         }
2869 }
2870
2871 static inline int
2872 rb_try_to_discard(struct ring_buffer_per_cpu *cpu_buffer,
2873                   struct ring_buffer_event *event)
2874 {
2875         unsigned long new_index, old_index;
2876         struct buffer_page *bpage;
2877         unsigned long index;
2878         unsigned long addr;
2879         u64 write_stamp;
2880         u64 delta;
2881
2882         new_index = rb_event_index(event);
2883         old_index = new_index + rb_event_ts_length(event);
2884         addr = (unsigned long)event;
2885         addr &= PAGE_MASK;
2886
2887         bpage = READ_ONCE(cpu_buffer->tail_page);
2888
2889         delta = rb_time_delta(event);
2890
2891         if (!rb_time_read(&cpu_buffer->write_stamp, &write_stamp))
2892                 return 0;
2893
2894         /* Make sure the write stamp is read before testing the location */
2895         barrier();
2896
2897         if (bpage->page == (void *)addr && rb_page_write(bpage) == old_index) {
2898                 unsigned long write_mask =
2899                         local_read(&bpage->write) & ~RB_WRITE_MASK;
2900                 unsigned long event_length = rb_event_length(event);
2901
2902                 /* Something came in, can't discard */
2903                 if (!rb_time_cmpxchg(&cpu_buffer->write_stamp,
2904                                        write_stamp, write_stamp - delta))
2905                         return 0;
2906
2907                 /*
2908                  * It's possible that the event time delta is zero
2909                  * (has the same time stamp as the previous event)
2910                  * in which case write_stamp and before_stamp could
2911                  * be the same. In such a case, force before_stamp
2912                  * to be different than write_stamp. It doesn't
2913                  * matter what it is, as long as its different.
2914                  */
2915                 if (!delta)
2916                         rb_time_set(&cpu_buffer->before_stamp, 0);
2917
2918                 /*
2919                  * If an event were to come in now, it would see that the
2920                  * write_stamp and the before_stamp are different, and assume
2921                  * that this event just added itself before updating
2922                  * the write stamp. The interrupting event will fix the
2923                  * write stamp for us, and use the before stamp as its delta.
2924                  */
2925
2926                 /*
2927                  * This is on the tail page. It is possible that
2928                  * a write could come in and move the tail page
2929                  * and write to the next page. That is fine
2930                  * because we just shorten what is on this page.
2931                  */
2932                 old_index += write_mask;
2933                 new_index += write_mask;
2934                 index = local_cmpxchg(&bpage->write, old_index, new_index);
2935                 if (index == old_index) {
2936                         /* update counters */
2937                         local_sub(event_length, &cpu_buffer->entries_bytes);
2938                         return 1;
2939                 }
2940         }
2941
2942         /* could not discard */
2943         return 0;
2944 }
2945
2946 static void rb_start_commit(struct ring_buffer_per_cpu *cpu_buffer)
2947 {
2948         local_inc(&cpu_buffer->committing);
2949         local_inc(&cpu_buffer->commits);
2950 }
2951
2952 static __always_inline void
2953 rb_set_commit_to_write(struct ring_buffer_per_cpu *cpu_buffer)
2954 {
2955         unsigned long max_count;
2956
2957         /*
2958          * We only race with interrupts and NMIs on this CPU.
2959          * If we own the commit event, then we can commit
2960          * all others that interrupted us, since the interruptions
2961          * are in stack format (they finish before they come
2962          * back to us). This allows us to do a simple loop to
2963          * assign the commit to the tail.
2964          */
2965  again:
2966         max_count = cpu_buffer->nr_pages * 100;
2967
2968         while (cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)) {
2969                 if (RB_WARN_ON(cpu_buffer, !(--max_count)))
2970                         return;
2971                 if (RB_WARN_ON(cpu_buffer,
2972                                rb_is_reader_page(cpu_buffer->tail_page)))
2973                         return;
2974                 local_set(&cpu_buffer->commit_page->page->commit,
2975                           rb_page_write(cpu_buffer->commit_page));
2976                 rb_inc_page(&cpu_buffer->commit_page);
2977                 /* add barrier to keep gcc from optimizing too much */
2978                 barrier();
2979         }
2980         while (rb_commit_index(cpu_buffer) !=
2981                rb_page_write(cpu_buffer->commit_page)) {
2982
2983                 local_set(&cpu_buffer->commit_page->page->commit,
2984                           rb_page_write(cpu_buffer->commit_page));
2985                 RB_WARN_ON(cpu_buffer,
2986                            local_read(&cpu_buffer->commit_page->page->commit) &
2987                            ~RB_WRITE_MASK);
2988                 barrier();
2989         }
2990
2991         /* again, keep gcc from optimizing */
2992         barrier();
2993
2994         /*
2995          * If an interrupt came in just after the first while loop
2996          * and pushed the tail page forward, we will be left with
2997          * a dangling commit that will never go forward.
2998          */
2999         if (unlikely(cpu_buffer->commit_page != READ_ONCE(cpu_buffer->tail_page)))
3000                 goto again;
3001 }
3002
3003 static __always_inline void rb_end_commit(struct ring_buffer_per_cpu *cpu_buffer)
3004 {
3005         unsigned long commits;
3006
3007         if (RB_WARN_ON(cpu_buffer,
3008                        !local_read(&cpu_buffer->committing)))
3009                 return;
3010
3011  again:
3012         commits = local_read(&cpu_buffer->commits);
3013         /* synchronize with interrupts */
3014         barrier();
3015         if (local_read(&cpu_buffer->committing) == 1)
3016                 rb_set_commit_to_write(cpu_buffer);
3017
3018         local_dec(&cpu_buffer->committing);
3019
3020         /* synchronize with interrupts */
3021         barrier();
3022
3023         /*
3024          * Need to account for interrupts coming in between the
3025          * updating of the commit page and the clearing of the
3026          * committing counter.
3027          */
3028         if (unlikely(local_read(&cpu_buffer->commits) != commits) &&
3029             !local_read(&cpu_buffer->committing)) {
3030                 local_inc(&cpu_buffer->committing);
3031                 goto again;
3032         }
3033 }
3034
3035 static inline void rb_event_discard(struct ring_buffer_event *event)
3036 {
3037         if (extended_time(event))
3038                 event = skip_time_extend(event);
3039
3040         /* array[0] holds the actual length for the discarded event */
3041         event->array[0] = rb_event_data_length(event) - RB_EVNT_HDR_SIZE;
3042         event->type_len = RINGBUF_TYPE_PADDING;
3043         /* time delta must be non zero */
3044         if (!event->time_delta)
3045                 event->time_delta = 1;
3046 }
3047
3048 static void rb_commit(struct ring_buffer_per_cpu *cpu_buffer,
3049                       struct ring_buffer_event *event)
3050 {
3051         local_inc(&cpu_buffer->entries);
3052         rb_end_commit(cpu_buffer);
3053 }
3054
3055 static __always_inline void
3056 rb_wakeups(struct trace_buffer *buffer, struct ring_buffer_per_cpu *cpu_buffer)
3057 {
3058         size_t nr_pages;
3059         size_t dirty;
3060         size_t full;
3061
3062         if (buffer->irq_work.waiters_pending) {
3063                 buffer->irq_work.waiters_pending = false;
3064                 /* irq_work_queue() supplies it's own memory barriers */
3065                 irq_work_queue(&buffer->irq_work.work);
3066         }
3067
3068         if (cpu_buffer->irq_work.waiters_pending) {
3069                 cpu_buffer->irq_work.waiters_pending = false;
3070                 /* irq_work_queue() supplies it's own memory barriers */
3071                 irq_work_queue(&cpu_buffer->irq_work.work);
3072         }
3073
3074         if (cpu_buffer->last_pages_touch == local_read(&cpu_buffer->pages_touched))
3075                 return;
3076
3077         if (cpu_buffer->reader_page == cpu_buffer->commit_page)
3078                 return;
3079
3080         if (!cpu_buffer->irq_work.full_waiters_pending)
3081                 return;
3082
3083         cpu_buffer->last_pages_touch = local_read(&cpu_buffer->pages_touched);
3084
3085         full = cpu_buffer->shortest_full;
3086         nr_pages = cpu_buffer->nr_pages;
3087         dirty = ring_buffer_nr_dirty_pages(buffer, cpu_buffer->cpu);
3088         if (full && nr_pages && (dirty * 100) <= full * nr_pages)
3089                 return;
3090
3091         cpu_buffer->irq_work.wakeup_full = true;
3092         cpu_buffer->irq_work.full_waiters_pending = false;
3093         /* irq_work_queue() supplies it's own memory barriers */
3094         irq_work_queue(&cpu_buffer->irq_work.work);
3095 }
3096
3097 #ifdef CONFIG_RING_BUFFER_RECORD_RECURSION
3098 # define do_ring_buffer_record_recursion()      \
3099         do_ftrace_record_recursion(_THIS_IP_, _RET_IP_)
3100 #else
3101 # define do_ring_buffer_record_recursion() do { } while (0)
3102 #endif
3103
3104 /*
3105  * The lock and unlock are done within a preempt disable section.
3106  * The current_context per_cpu variable can only be modified
3107  * by the current task between lock and unlock. But it can
3108  * be modified more than once via an interrupt. To pass this
3109  * information from the lock to the unlock without having to
3110  * access the 'in_interrupt()' functions again (which do show
3111  * a bit of overhead in something as critical as function tracing,
3112  * we use a bitmask trick.
3113  *
3114  *  bit 1 =  NMI context
3115  *  bit 2 =  IRQ context
3116  *  bit 3 =  SoftIRQ context
3117  *  bit 4 =  normal context.
3118  *
3119  * This works because this is the order of contexts that can
3120  * preempt other contexts. A SoftIRQ never preempts an IRQ
3121  * context.
3122  *
3123  * When the context is determined, the corresponding bit is
3124  * checked and set (if it was set, then a recursion of that context
3125  * happened).
3126  *
3127  * On unlock, we need to clear this bit. To do so, just subtract
3128  * 1 from the current_context and AND it to itself.
3129  *
3130  * (binary)
3131  *  101 - 1 = 100
3132  *  101 & 100 = 100 (clearing bit zero)
3133  *
3134  *  1010 - 1 = 1001
3135  *  1010 & 1001 = 1000 (clearing bit 1)
3136  *
3137  * The least significant bit can be cleared this way, and it
3138  * just so happens that it is the same bit corresponding to
3139  * the current context.
3140  *
3141  * Now the TRANSITION bit breaks the above slightly. The TRANSITION bit
3142  * is set when a recursion is detected at the current context, and if
3143  * the TRANSITION bit is already set, it will fail the recursion.
3144  * This is needed because there's a lag between the changing of
3145  * interrupt context and updating the preempt count. In this case,
3146  * a false positive will be found. To handle this, one extra recursion
3147  * is allowed, and this is done by the TRANSITION bit. If the TRANSITION
3148  * bit is already set, then it is considered a recursion and the function
3149  * ends. Otherwise, the TRANSITION bit is set, and that bit is returned.
3150  *
3151  * On the trace_recursive_unlock(), the TRANSITION bit will be the first
3152  * to be cleared. Even if it wasn't the context that set it. That is,
3153  * if an interrupt comes in while NORMAL bit is set and the ring buffer
3154  * is called before preempt_count() is updated, since the check will
3155  * be on the NORMAL bit, the TRANSITION bit will then be set. If an
3156  * NMI then comes in, it will set the NMI bit, but when the NMI code
3157  * does the trace_recursive_unlock() it will clear the TRANSITION bit
3158  * and leave the NMI bit set. But this is fine, because the interrupt
3159  * code that set the TRANSITION bit will then clear the NMI bit when it
3160  * calls trace_recursive_unlock(). If another NMI comes in, it will
3161  * set the TRANSITION bit and continue.
3162  *
3163  * Note: The TRANSITION bit only handles a single transition between context.
3164  */
3165
3166 static __always_inline int
3167 trace_recursive_lock(struct ring_buffer_per_cpu *cpu_buffer)
3168 {
3169         unsigned int val = cpu_buffer->current_context;
3170         unsigned long pc = preempt_count();
3171         int bit;
3172
3173         if (!(pc & (NMI_MASK | HARDIRQ_MASK | SOFTIRQ_OFFSET)))
3174                 bit = RB_CTX_NORMAL;
3175         else
3176                 bit = pc & NMI_MASK ? RB_CTX_NMI :
3177                         pc & HARDIRQ_MASK ? RB_CTX_IRQ : RB_CTX_SOFTIRQ;
3178
3179         if (unlikely(val & (1 << (bit + cpu_buffer->nest)))) {
3180                 /*
3181                  * It is possible that this was called by transitioning
3182                  * between interrupt context, and preempt_count() has not
3183                  * been updated yet. In this case, use the TRANSITION bit.
3184                  */
3185                 bit = RB_CTX_TRANSITION;
3186                 if (val & (1 << (bit + cpu_buffer->nest))) {
3187                         do_ring_buffer_record_recursion();
3188                         return 1;
3189                 }
3190         }
3191
3192         val |= (1 << (bit + cpu_buffer->nest));
3193         cpu_buffer->current_context = val;
3194
3195         return 0;
3196 }
3197
3198 static __always_inline void
3199 trace_recursive_unlock(struct ring_buffer_per_cpu *cpu_buffer)
3200 {
3201         cpu_buffer->current_context &=
3202                 cpu_buffer->current_context - (1 << cpu_buffer->nest);
3203 }
3204
3205 /* The recursive locking above uses 5 bits */
3206 #define NESTED_BITS 5
3207
3208 /**
3209  * ring_buffer_nest_start - Allow to trace while nested
3210  * @buffer: The ring buffer to modify
3211  *
3212  * The ring buffer has a safety mechanism to prevent recursion.
3213  * But there may be a case where a trace needs to be done while
3214  * tracing something else. In this case, calling this function
3215  * will allow this function to nest within a currently active
3216  * ring_buffer_lock_reserve().
3217  *
3218  * Call this function before calling another ring_buffer_lock_reserve() and
3219  * call ring_buffer_nest_end() after the nested ring_buffer_unlock_commit().
3220  */
3221 void ring_buffer_nest_start(struct trace_buffer *buffer)
3222 {
3223         struct ring_buffer_per_cpu *cpu_buffer;
3224         int cpu;
3225
3226         /* Enabled by ring_buffer_nest_end() */
3227         preempt_disable_notrace();
3228         cpu = raw_smp_processor_id();
3229         cpu_buffer = buffer->buffers[cpu];
3230         /* This is the shift value for the above recursive locking */
3231         cpu_buffer->nest += NESTED_BITS;
3232 }
3233
3234 /**
3235  * ring_buffer_nest_end - Allow to trace while nested
3236  * @buffer: The ring buffer to modify
3237  *
3238  * Must be called after ring_buffer_nest_start() and after the
3239  * ring_buffer_unlock_commit().
3240  */
3241 void ring_buffer_nest_end(struct trace_buffer *buffer)
3242 {
3243         struct ring_buffer_per_cpu *cpu_buffer;
3244         int cpu;
3245
3246         /* disabled by ring_buffer_nest_start() */
3247         cpu = raw_smp_processor_id();
3248         cpu_buffer = buffer->buffers[cpu];
3249         /* This is the shift value for the above recursive locking */
3250         cpu_buffer->nest -= NESTED_BITS;
3251         preempt_enable_notrace();
3252 }
3253
3254 /**
3255  * ring_buffer_unlock_commit - commit a reserved
3256  * @buffer: The buffer to commit to
3257  * @event: The event pointer to commit.
3258  *
3259  * This commits the data to the ring buffer, and releases any locks held.
3260  *
3261  * Must be paired with ring_buffer_lock_reserve.
3262  */
3263 int ring_buffer_unlock_commit(struct trace_buffer *buffer,
3264                               struct ring_buffer_event *event)
3265 {
3266         struct ring_buffer_per_cpu *cpu_buffer;
3267         int cpu = raw_smp_processor_id();
3268
3269         cpu_buffer = buffer->buffers[cpu];
3270
3271         rb_commit(cpu_buffer, event);
3272
3273         rb_wakeups(buffer, cpu_buffer);
3274
3275         trace_recursive_unlock(cpu_buffer);
3276
3277         preempt_enable_notrace();
3278
3279         return 0;
3280 }
3281 EXPORT_SYMBOL_GPL(ring_buffer_unlock_commit);
3282
3283 /* Special value to validate all deltas on a page. */
3284 #define CHECK_FULL_PAGE         1L
3285
3286 #ifdef CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS
3287 static void dump_buffer_page(struct buffer_data_page *bpage,
3288                              struct rb_event_info *info,
3289                              unsigned long tail)
3290 {
3291         struct ring_buffer_event *event;
3292         u64 ts, delta;
3293         int e;
3294
3295         ts = bpage->time_stamp;
3296         pr_warn("  [%lld] PAGE TIME STAMP\n", ts);
3297
3298         for (e = 0; e < tail; e += rb_event_length(event)) {
3299
3300                 event = (struct ring_buffer_event *)(bpage->data + e);
3301
3302                 switch (event->type_len) {
3303
3304                 case RINGBUF_TYPE_TIME_EXTEND:
3305                         delta = rb_event_time_stamp(event);
3306                         ts += delta;
3307                         pr_warn("  [%lld] delta:%lld TIME EXTEND\n", ts, delta);
3308                         break;
3309
3310                 case RINGBUF_TYPE_TIME_STAMP:
3311                         delta = rb_event_time_stamp(event);
3312                         ts = delta;
3313                         pr_warn("  [%lld] absolute:%lld TIME STAMP\n", ts, delta);
3314                         break;
3315
3316                 case RINGBUF_TYPE_PADDING:
3317                         ts += event->time_delta;
3318                         pr_warn("  [%lld] delta:%d PADDING\n", ts, event->time_delta);
3319                         break;
3320
3321                 case RINGBUF_TYPE_DATA:
3322                         ts += event->time_delta;
3323                         pr_warn("  [%lld] delta:%d\n", ts, event->time_delta);
3324                         break;
3325
3326                 default:
3327                         break;
3328                 }
3329         }
3330 }
3331
3332 static DEFINE_PER_CPU(atomic_t, checking);
3333 static atomic_t ts_dump;
3334
3335 /*
3336  * Check if the current event time stamp matches the deltas on
3337  * the buffer page.
3338  */
3339 static void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
3340                          struct rb_event_info *info,
3341                          unsigned long tail)
3342 {
3343         struct ring_buffer_event *event;
3344         struct buffer_data_page *bpage;
3345         u64 ts, delta;
3346         bool full = false;
3347         int e;
3348
3349         bpage = info->tail_page->page;
3350
3351         if (tail == CHECK_FULL_PAGE) {
3352                 full = true;
3353                 tail = local_read(&bpage->commit);
3354         } else if (info->add_timestamp &
3355                    (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE)) {
3356                 /* Ignore events with absolute time stamps */
3357                 return;
3358         }
3359
3360         /*
3361          * Do not check the first event (skip possible extends too).
3362          * Also do not check if previous events have not been committed.
3363          */
3364         if (tail <= 8 || tail > local_read(&bpage->commit))
3365                 return;
3366
3367         /*
3368          * If this interrupted another event, 
3369          */
3370         if (atomic_inc_return(this_cpu_ptr(&checking)) != 1)
3371                 goto out;
3372
3373         ts = bpage->time_stamp;
3374
3375         for (e = 0; e < tail; e += rb_event_length(event)) {
3376
3377                 event = (struct ring_buffer_event *)(bpage->data + e);
3378
3379                 switch (event->type_len) {
3380
3381                 case RINGBUF_TYPE_TIME_EXTEND:
3382                         delta = rb_event_time_stamp(event);
3383                         ts += delta;
3384                         break;
3385
3386                 case RINGBUF_TYPE_TIME_STAMP:
3387                         delta = rb_event_time_stamp(event);
3388                         ts = delta;
3389                         break;
3390
3391                 case RINGBUF_TYPE_PADDING:
3392                         if (event->time_delta == 1)
3393                                 break;
3394                         /* fall through */
3395                 case RINGBUF_TYPE_DATA:
3396                         ts += event->time_delta;
3397                         break;
3398
3399                 default:
3400                         RB_WARN_ON(cpu_buffer, 1);
3401                 }
3402         }
3403         if ((full && ts > info->ts) ||
3404             (!full && ts + info->delta != info->ts)) {
3405                 /* If another report is happening, ignore this one */
3406                 if (atomic_inc_return(&ts_dump) != 1) {
3407                         atomic_dec(&ts_dump);
3408                         goto out;
3409                 }
3410                 atomic_inc(&cpu_buffer->record_disabled);
3411                 /* There's some cases in boot up that this can happen */
3412                 WARN_ON_ONCE(system_state != SYSTEM_BOOTING);
3413                 pr_warn("[CPU: %d]TIME DOES NOT MATCH expected:%lld actual:%lld delta:%lld before:%lld after:%lld%s\n",
3414                         cpu_buffer->cpu,
3415                         ts + info->delta, info->ts, info->delta,
3416                         info->before, info->after,
3417                         full ? " (full)" : "");
3418                 dump_buffer_page(bpage, info, tail);
3419                 atomic_dec(&ts_dump);
3420                 /* Do not re-enable checking */
3421                 return;
3422         }
3423 out:
3424         atomic_dec(this_cpu_ptr(&checking));
3425 }
3426 #else
3427 static inline void check_buffer(struct ring_buffer_per_cpu *cpu_buffer,
3428                          struct rb_event_info *info,
3429                          unsigned long tail)
3430 {
3431 }
3432 #endif /* CONFIG_RING_BUFFER_VALIDATE_TIME_DELTAS */
3433
3434 static struct ring_buffer_event *
3435 __rb_reserve_next(struct ring_buffer_per_cpu *cpu_buffer,
3436                   struct rb_event_info *info)
3437 {
3438         struct ring_buffer_event *event;
3439         struct buffer_page *tail_page;
3440         unsigned long tail, write, w;
3441         bool a_ok;
3442         bool b_ok;
3443
3444         /* Don't let the compiler play games with cpu_buffer->tail_page */
3445         tail_page = info->tail_page = READ_ONCE(cpu_buffer->tail_page);
3446
3447  /*A*/  w = local_read(&tail_page->write) & RB_WRITE_MASK;
3448         barrier();
3449         b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
3450         a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3451         barrier();
3452         info->ts = rb_time_stamp(cpu_buffer->buffer);
3453
3454         if ((info->add_timestamp & RB_ADD_STAMP_ABSOLUTE)) {
3455                 info->delta = info->ts;
3456         } else {
3457                 /*
3458                  * If interrupting an event time update, we may need an
3459                  * absolute timestamp.
3460                  * Don't bother if this is the start of a new page (w == 0).
3461                  */
3462                 if (unlikely(!a_ok || !b_ok || (info->before != info->after && w))) {
3463                         info->add_timestamp |= RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND;
3464                         info->length += RB_LEN_TIME_EXTEND;
3465                 } else {
3466                         info->delta = info->ts - info->after;
3467                         if (unlikely(test_time_stamp(info->delta))) {
3468                                 info->add_timestamp |= RB_ADD_STAMP_EXTEND;
3469                                 info->length += RB_LEN_TIME_EXTEND;
3470                         }
3471                 }
3472         }
3473
3474  /*B*/  rb_time_set(&cpu_buffer->before_stamp, info->ts);
3475
3476  /*C*/  write = local_add_return(info->length, &tail_page->write);
3477
3478         /* set write to only the index of the write */
3479         write &= RB_WRITE_MASK;
3480
3481         tail = write - info->length;
3482
3483         /* See if we shot pass the end of this buffer page */
3484         if (unlikely(write > BUF_PAGE_SIZE)) {
3485                 /* before and after may now different, fix it up*/
3486                 b_ok = rb_time_read(&cpu_buffer->before_stamp, &info->before);
3487                 a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3488                 if (a_ok && b_ok && info->before != info->after)
3489                         (void)rb_time_cmpxchg(&cpu_buffer->before_stamp,
3490                                               info->before, info->after);
3491                 if (a_ok && b_ok)
3492                         check_buffer(cpu_buffer, info, CHECK_FULL_PAGE);
3493                 return rb_move_tail(cpu_buffer, tail, info);
3494         }
3495
3496         if (likely(tail == w)) {
3497                 u64 save_before;
3498                 bool s_ok;
3499
3500                 /* Nothing interrupted us between A and C */
3501  /*D*/          rb_time_set(&cpu_buffer->write_stamp, info->ts);
3502                 barrier();
3503  /*E*/          s_ok = rb_time_read(&cpu_buffer->before_stamp, &save_before);
3504                 RB_WARN_ON(cpu_buffer, !s_ok);
3505                 if (likely(!(info->add_timestamp &
3506                              (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
3507                         /* This did not interrupt any time update */
3508                         info->delta = info->ts - info->after;
3509                 else
3510                         /* Just use full timestamp for interrupting event */
3511                         info->delta = info->ts;
3512                 barrier();
3513                 check_buffer(cpu_buffer, info, tail);
3514                 if (unlikely(info->ts != save_before)) {
3515                         /* SLOW PATH - Interrupted between C and E */
3516
3517                         a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3518                         RB_WARN_ON(cpu_buffer, !a_ok);
3519
3520                         /* Write stamp must only go forward */
3521                         if (save_before > info->after) {
3522                                 /*
3523                                  * We do not care about the result, only that
3524                                  * it gets updated atomically.
3525                                  */
3526                                 (void)rb_time_cmpxchg(&cpu_buffer->write_stamp,
3527                                                       info->after, save_before);
3528                         }
3529                 }
3530         } else {
3531                 u64 ts;
3532                 /* SLOW PATH - Interrupted between A and C */
3533                 a_ok = rb_time_read(&cpu_buffer->write_stamp, &info->after);
3534                 /* Was interrupted before here, write_stamp must be valid */
3535                 RB_WARN_ON(cpu_buffer, !a_ok);
3536                 ts = rb_time_stamp(cpu_buffer->buffer);
3537                 barrier();
3538  /*E*/          if (write == (local_read(&tail_page->write) & RB_WRITE_MASK) &&
3539                     info->after < ts &&
3540                     rb_time_cmpxchg(&cpu_buffer->write_stamp,
3541                                     info->after, ts)) {
3542                         /* Nothing came after this event between C and E */
3543                         info->delta = ts - info->after;
3544                 } else {
3545                         /*
3546                          * Interrupted between C and E:
3547                          * Lost the previous events time stamp. Just set the
3548                          * delta to zero, and this will be the same time as
3549                          * the event this event interrupted. And the events that
3550                          * came after this will still be correct (as they would
3551                          * have built their delta on the previous event.
3552                          */
3553                         info->delta = 0;
3554                 }
3555                 info->ts = ts;
3556                 info->add_timestamp &= ~RB_ADD_STAMP_FORCE;
3557         }
3558
3559         /*
3560          * If this is the first commit on the page, then it has the same
3561          * timestamp as the page itself.
3562          */
3563         if (unlikely(!tail && !(info->add_timestamp &
3564                                 (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_ABSOLUTE))))
3565                 info->delta = 0;
3566
3567         /* We reserved something on the buffer */
3568
3569         event = __rb_page_index(tail_page, tail);
3570         rb_update_event(cpu_buffer, event, info);
3571
3572         local_inc(&tail_page->entries);
3573
3574         /*
3575          * If this is the first commit on the page, then update
3576          * its timestamp.
3577          */
3578         if (unlikely(!tail))
3579                 tail_page->page->time_stamp = info->ts;
3580
3581         /* account for these added bytes */
3582         local_add(info->length, &cpu_buffer->entries_bytes);
3583
3584         return event;
3585 }
3586
3587 static __always_inline struct ring_buffer_event *
3588 rb_reserve_next_event(struct trace_buffer *buffer,
3589                       struct ring_buffer_per_cpu *cpu_buffer,
3590                       unsigned long length)
3591 {
3592         struct ring_buffer_event *event;
3593         struct rb_event_info info;
3594         int nr_loops = 0;
3595         int add_ts_default;
3596
3597         rb_start_commit(cpu_buffer);
3598         /* The commit page can not change after this */
3599
3600 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
3601         /*
3602          * Due to the ability to swap a cpu buffer from a buffer
3603          * it is possible it was swapped before we committed.
3604          * (committing stops a swap). We check for it here and
3605          * if it happened, we have to fail the write.
3606          */
3607         barrier();
3608         if (unlikely(READ_ONCE(cpu_buffer->buffer) != buffer)) {
3609                 local_dec(&cpu_buffer->committing);
3610                 local_dec(&cpu_buffer->commits);
3611                 return NULL;
3612         }
3613 #endif
3614
3615         info.length = rb_calculate_event_length(length);
3616
3617         if (ring_buffer_time_stamp_abs(cpu_buffer->buffer)) {
3618                 add_ts_default = RB_ADD_STAMP_ABSOLUTE;
3619                 info.length += RB_LEN_TIME_EXTEND;
3620         } else {
3621                 add_ts_default = RB_ADD_STAMP_NONE;
3622         }
3623
3624  again:
3625         info.add_timestamp = add_ts_default;
3626         info.delta = 0;
3627
3628         /*
3629          * We allow for interrupts to reenter here and do a trace.
3630          * If one does, it will cause this original code to loop
3631          * back here. Even with heavy interrupts happening, this
3632          * should only happen a few times in a row. If this happens
3633          * 1000 times in a row, there must be either an interrupt
3634          * storm or we have something buggy.
3635          * Bail!
3636          */
3637         if (RB_WARN_ON(cpu_buffer, ++nr_loops > 1000))
3638                 goto out_fail;
3639
3640         event = __rb_reserve_next(cpu_buffer, &info);
3641
3642         if (unlikely(PTR_ERR(event) == -EAGAIN)) {
3643                 if (info.add_timestamp & (RB_ADD_STAMP_FORCE | RB_ADD_STAMP_EXTEND))
3644                         info.length -= RB_LEN_TIME_EXTEND;
3645                 goto again;
3646         }
3647
3648         if (likely(event))
3649                 return event;
3650  out_fail:
3651         rb_end_commit(cpu_buffer);
3652         return NULL;
3653 }
3654
3655 /**
3656  * ring_buffer_lock_reserve - reserve a part of the buffer
3657  * @buffer: the ring buffer to reserve from
3658  * @length: the length of the data to reserve (excluding event header)
3659  *
3660  * Returns a reserved event on the ring buffer to copy directly to.
3661  * The user of this interface will need to get the body to write into
3662  * and can use the ring_buffer_event_data() interface.
3663  *
3664  * The length is the length of the data needed, not the event length
3665  * which also includes the event header.
3666  *
3667  * Must be paired with ring_buffer_unlock_commit, unless NULL is returned.
3668  * If NULL is returned, then nothing has been allocated or locked.
3669  */
3670 struct ring_buffer_event *
3671 ring_buffer_lock_reserve(struct trace_buffer *buffer, unsigned long length)
3672 {
3673         struct ring_buffer_per_cpu *cpu_buffer;
3674         struct ring_buffer_event *event;
3675         int cpu;
3676
3677         /* If we are tracing schedule, we don't want to recurse */
3678         preempt_disable_notrace();
3679
3680         if (unlikely(atomic_read(&buffer->record_disabled)))
3681                 goto out;
3682
3683         cpu = raw_smp_processor_id();
3684
3685         if (unlikely(!cpumask_test_cpu(cpu, buffer->cpumask)))
3686                 goto out;
3687
3688         cpu_buffer = buffer->buffers[cpu];
3689
3690         if (unlikely(atomic_read(&cpu_buffer->record_disabled)))
3691                 goto out;
3692
3693         if (unlikely(length > BUF_MAX_DATA_SIZE))
3694                 goto out;
3695
3696         if (unlikely(trace_recursive_lock(cpu_buffer)))
3697                 goto out;
3698
3699         event = rb_reserve_next_event(buffer, cpu_buffer, length);
3700         if (!event)
3701                 goto out_unlock;
3702
3703         return event;
3704
3705  out_unlock:
3706         trace_recursive_unlock(cpu_buffer);
3707  out:
3708         preempt_enable_notrace();
3709         return NULL;
3710 }
3711 EXPORT_SYMBOL_GPL(ring_buffer_lock_reserve);
3712
3713 /*
3714  * Decrement the entries to the page that an event is on.
3715  * The event does not even need to exist, only the pointer
3716  * to the page it is on. This may only be called before the commit
3717  * takes place.
3718  */
3719 static inline void
3720 rb_decrement_entry(struct ring_buffer_per_cpu *cpu_buffer,
3721                    struct ring_buffer_event *event)
3722 {
3723         unsigned long addr = (unsigned long)event;
3724         struct buffer_page *bpage = cpu_buffer->commit_page;
3725         struct buffer_page *start;
3726
3727         addr &= PAGE_MASK;
3728
3729         /* Do the likely case first */
3730         if (likely(bpage->page == (void *)addr)) {
3731                 local_dec(&bpage->entries);
3732                 return;
3733         }
3734
3735         /*
3736          * Because the commit page may be on the reader page we
3737          * start with the next page and check the end loop there.
3738          */
3739         rb_inc_page(&bpage);
3740         start = bpage;
3741         do {
3742                 if (bpage->page == (void *)addr) {
3743                         local_dec(&bpage->entries);
3744                         return;
3745                 }
3746                 rb_inc_page(&bpage);
3747         } while (bpage != start);
3748
3749         /* commit not part of this buffer?? */
3750         RB_WARN_ON(cpu_buffer, 1);
3751 }
3752
3753 /**
3754  * ring_buffer_discard_commit - discard an event that has not been committed
3755  * @buffer: the ring buffer
3756  * @event: non committed event to discard
3757  *
3758  * Sometimes an event that is in the ring buffer needs to be ignored.
3759  * This function lets the user discard an event in the ring buffer
3760  * and then that event will not be read later.
3761  *
3762  * This function only works if it is called before the item has been
3763  * committed. It will try to free the event from the ring buffer
3764  * if another event has not been added behind it.
3765  *
3766  * If another event has been added behind it, it will set the event
3767  * up as discarded, and perform the commit.
3768  *
3769  * If this function is called, do not call ring_buffer_unlock_commit on
3770  * the event.
3771  */
3772 void ring_buffer_discard_commit(struct trace_buffer *buffer,
3773                                 struct ring_buffer_event *event)
3774 {
3775         struct ring_buffer_per_cpu *cpu_buffer;
3776         int cpu;
3777
3778         /* The event is discarded regardless */
3779         rb_event_discard(event);
3780
3781         cpu = smp_processor_id();
3782         cpu_buffer = buffer->buffers[cpu];
3783
3784         /*
3785          * This must only be called if the event has not been
3786          * committed yet. Thus we can assume that preemption
3787          * is still disabled.
3788          */
3789         RB_WARN_ON(buffer, !local_read(&cpu_buffer->committing));
3790
3791         rb_decrement_entry(cpu_buffer, event);
3792         if (rb_try_to_discard(cpu_buffer, event))
3793                 goto out;
3794
3795  out:
3796         rb_end_commit(cpu_buffer);
3797
3798         trace_recursive_unlock(cpu_buffer);
3799
3800         preempt_enable_notrace();
3801
3802 }
3803 EXPORT_SYMBOL_GPL(ring_buffer_discard_commit);
3804
3805 /**
3806  * ring_buffer_write - write data to the buffer without reserving
3807  * @buffer: The ring buffer to write to.
3808  * @length: The length of the data being written (excluding the event header)
3809  * @data: The data to write to the buffer.
3810  *
3811  * This is like ring_buffer_lock_reserve and ring_buffer_unlock_commit as
3812  * one function. If you already have the data to write to the buffer, it
3813  * may be easier to simply call this function.
3814  *
3815  * Note, like ring_buffer_lock_reserve, the length is the length of the data
3816  * and not the length of the event which would hold the header.
3817  */
3818 int ring_buffer_write(struct trace_buffer *buffer,
3819                       unsigned long length,
3820                       void *data)
3821 {
3822         struct ring_buffer_per_cpu *cpu_buffer;
3823         struct ring_buffer_event *event;
3824         void *body;
3825         int ret = -EBUSY;
3826         int cpu;
3827
3828         preempt_disable_notrace();
3829
3830         if (atomic_read(&buffer->record_disabled))
3831                 goto out;
3832
3833         cpu = raw_smp_processor_id();
3834
3835         if (!cpumask_test_cpu(cpu, buffer->cpumask))
3836                 goto out;
3837
3838         cpu_buffer = buffer->buffers[cpu];
3839
3840         if (atomic_read(&cpu_buffer->record_disabled))
3841                 goto out;
3842
3843         if (length > BUF_MAX_DATA_SIZE)
3844                 goto out;
3845
3846         if (unlikely(trace_recursive_lock(cpu_buffer)))
3847                 goto out;
3848
3849         event = rb_reserve_next_event(buffer, cpu_buffer, length);
3850         if (!event)
3851                 goto out_unlock;
3852
3853         body = rb_event_data(event);
3854
3855         memcpy(body, data, length);
3856
3857         rb_commit(cpu_buffer, event);
3858
3859         rb_wakeups(buffer, cpu_buffer);
3860
3861         ret = 0;
3862
3863  out_unlock:
3864         trace_recursive_unlock(cpu_buffer);
3865
3866  out:
3867         preempt_enable_notrace();
3868
3869         return ret;
3870 }
3871 EXPORT_SYMBOL_GPL(ring_buffer_write);
3872
3873 static bool rb_per_cpu_empty(struct ring_buffer_per_cpu *cpu_buffer)
3874 {
3875         struct buffer_page *reader = cpu_buffer->reader_page;
3876         struct buffer_page *head = rb_set_head_page(cpu_buffer);
3877         struct buffer_page *commit = cpu_buffer->commit_page;
3878
3879         /* In case of error, head will be NULL */
3880         if (unlikely(!head))
3881                 return true;
3882
3883         return reader->read == rb_page_commit(reader) &&
3884                 (commit == reader ||
3885                  (commit == head &&
3886                   head->read == rb_page_commit(commit)));
3887 }
3888
3889 /**
3890  * ring_buffer_record_disable - stop all writes into the buffer
3891  * @buffer: The ring buffer to stop writes to.
3892  *
3893  * This prevents all writes to the buffer. Any attempt to write
3894  * to the buffer after this will fail and return NULL.
3895  *
3896  * The caller should call synchronize_rcu() after this.
3897  */
3898 void ring_buffer_record_disable(struct trace_buffer *buffer)
3899 {
3900         atomic_inc(&buffer->record_disabled);
3901 }
3902 EXPORT_SYMBOL_GPL(ring_buffer_record_disable);
3903
3904 /**
3905  * ring_buffer_record_enable - enable writes to the buffer
3906  * @buffer: The ring buffer to enable writes
3907  *
3908  * Note, multiple disables will need the same number of enables
3909  * to truly enable the writing (much like preempt_disable).
3910  */
3911 void ring_buffer_record_enable(struct trace_buffer *buffer)
3912 {
3913         atomic_dec(&buffer->record_disabled);
3914 }
3915 EXPORT_SYMBOL_GPL(ring_buffer_record_enable);
3916
3917 /**
3918  * ring_buffer_record_off - stop all writes into the buffer
3919  * @buffer: The ring buffer to stop writes to.
3920  *
3921  * This prevents all writes to the buffer. Any attempt to write
3922  * to the buffer after this will fail and return NULL.
3923  *
3924  * This is different than ring_buffer_record_disable() as
3925  * it works like an on/off switch, where as the disable() version
3926  * must be paired with a enable().
3927  */
3928 void ring_buffer_record_off(struct trace_buffer *buffer)
3929 {
3930         unsigned int rd;
3931         unsigned int new_rd;
3932
3933         do {
3934                 rd = atomic_read(&buffer->record_disabled);
3935                 new_rd = rd | RB_BUFFER_OFF;
3936         } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3937 }
3938 EXPORT_SYMBOL_GPL(ring_buffer_record_off);
3939
3940 /**
3941  * ring_buffer_record_on - restart writes into the buffer
3942  * @buffer: The ring buffer to start writes to.
3943  *
3944  * This enables all writes to the buffer that was disabled by
3945  * ring_buffer_record_off().
3946  *
3947  * This is different than ring_buffer_record_enable() as
3948  * it works like an on/off switch, where as the enable() version
3949  * must be paired with a disable().
3950  */
3951 void ring_buffer_record_on(struct trace_buffer *buffer)
3952 {
3953         unsigned int rd;
3954         unsigned int new_rd;
3955
3956         do {
3957                 rd = atomic_read(&buffer->record_disabled);
3958                 new_rd = rd & ~RB_BUFFER_OFF;
3959         } while (atomic_cmpxchg(&buffer->record_disabled, rd, new_rd) != rd);
3960 }
3961 EXPORT_SYMBOL_GPL(ring_buffer_record_on);
3962
3963 /**
3964  * ring_buffer_record_is_on - return true if the ring buffer can write
3965  * @buffer: The ring buffer to see if write is enabled
3966  *
3967  * Returns true if the ring buffer is in a state that it accepts writes.
3968  */
3969 bool ring_buffer_record_is_on(struct trace_buffer *buffer)
3970 {
3971         return !atomic_read(&buffer->record_disabled);
3972 }
3973
3974 /**
3975  * ring_buffer_record_is_set_on - return true if the ring buffer is set writable
3976  * @buffer: The ring buffer to see if write is set enabled
3977  *
3978  * Returns true if the ring buffer is set writable by ring_buffer_record_on().
3979  * Note that this does NOT mean it is in a writable state.
3980  *
3981  * It may return true when the ring buffer has been disabled by
3982  * ring_buffer_record_disable(), as that is a temporary disabling of
3983  * the ring buffer.
3984  */
3985 bool ring_buffer_record_is_set_on(struct trace_buffer *buffer)
3986 {
3987         return !(atomic_read(&buffer->record_disabled) & RB_BUFFER_OFF);
3988 }
3989
3990 /**
3991  * ring_buffer_record_disable_cpu - stop all writes into the cpu_buffer
3992  * @buffer: The ring buffer to stop writes to.
3993  * @cpu: The CPU buffer to stop
3994  *
3995  * This prevents all writes to the buffer. Any attempt to write
3996  * to the buffer after this will fail and return NULL.
3997  *
3998  * The caller should call synchronize_rcu() after this.
3999  */
4000 void ring_buffer_record_disable_cpu(struct trace_buffer *buffer, int cpu)
4001 {
4002         struct ring_buffer_per_cpu *cpu_buffer;
4003
4004         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4005                 return;
4006
4007         cpu_buffer = buffer->buffers[cpu];
4008         atomic_inc(&cpu_buffer->record_disabled);
4009 }
4010 EXPORT_SYMBOL_GPL(ring_buffer_record_disable_cpu);
4011
4012 /**
4013  * ring_buffer_record_enable_cpu - enable writes to the buffer
4014  * @buffer: The ring buffer to enable writes
4015  * @cpu: The CPU to enable.
4016  *
4017  * Note, multiple disables will need the same number of enables
4018  * to truly enable the writing (much like preempt_disable).
4019  */
4020 void ring_buffer_record_enable_cpu(struct trace_buffer *buffer, int cpu)
4021 {
4022         struct ring_buffer_per_cpu *cpu_buffer;
4023
4024         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4025                 return;
4026
4027         cpu_buffer = buffer->buffers[cpu];
4028         atomic_dec(&cpu_buffer->record_disabled);
4029 }
4030 EXPORT_SYMBOL_GPL(ring_buffer_record_enable_cpu);
4031
4032 /*
4033  * The total entries in the ring buffer is the running counter
4034  * of entries entered into the ring buffer, minus the sum of
4035  * the entries read from the ring buffer and the number of
4036  * entries that were overwritten.
4037  */
4038 static inline unsigned long
4039 rb_num_of_entries(struct ring_buffer_per_cpu *cpu_buffer)
4040 {
4041         return local_read(&cpu_buffer->entries) -
4042                 (local_read(&cpu_buffer->overrun) + cpu_buffer->read);
4043 }
4044
4045 /**
4046  * ring_buffer_oldest_event_ts - get the oldest event timestamp from the buffer
4047  * @buffer: The ring buffer
4048  * @cpu: The per CPU buffer to read from.
4049  */
4050 u64 ring_buffer_oldest_event_ts(struct trace_buffer *buffer, int cpu)
4051 {
4052         unsigned long flags;
4053         struct ring_buffer_per_cpu *cpu_buffer;
4054         struct buffer_page *bpage;
4055         u64 ret = 0;
4056
4057         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4058                 return 0;
4059
4060         cpu_buffer = buffer->buffers[cpu];
4061         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4062         /*
4063          * if the tail is on reader_page, oldest time stamp is on the reader
4064          * page
4065          */
4066         if (cpu_buffer->tail_page == cpu_buffer->reader_page)
4067                 bpage = cpu_buffer->reader_page;
4068         else
4069                 bpage = rb_set_head_page(cpu_buffer);
4070         if (bpage)
4071                 ret = bpage->page->time_stamp;
4072         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4073
4074         return ret;
4075 }
4076 EXPORT_SYMBOL_GPL(ring_buffer_oldest_event_ts);
4077
4078 /**
4079  * ring_buffer_bytes_cpu - get the number of bytes consumed in a cpu buffer
4080  * @buffer: The ring buffer
4081  * @cpu: The per CPU buffer to read from.
4082  */
4083 unsigned long ring_buffer_bytes_cpu(struct trace_buffer *buffer, int cpu)
4084 {
4085         struct ring_buffer_per_cpu *cpu_buffer;
4086         unsigned long ret;
4087
4088         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4089                 return 0;
4090
4091         cpu_buffer = buffer->buffers[cpu];
4092         ret = local_read(&cpu_buffer->entries_bytes) - cpu_buffer->read_bytes;
4093
4094         return ret;
4095 }
4096 EXPORT_SYMBOL_GPL(ring_buffer_bytes_cpu);
4097
4098 /**
4099  * ring_buffer_entries_cpu - get the number of entries in a cpu buffer
4100  * @buffer: The ring buffer
4101  * @cpu: The per CPU buffer to get the entries from.
4102  */
4103 unsigned long ring_buffer_entries_cpu(struct trace_buffer *buffer, int cpu)
4104 {
4105         struct ring_buffer_per_cpu *cpu_buffer;
4106
4107         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4108                 return 0;
4109
4110         cpu_buffer = buffer->buffers[cpu];
4111
4112         return rb_num_of_entries(cpu_buffer);
4113 }
4114 EXPORT_SYMBOL_GPL(ring_buffer_entries_cpu);
4115
4116 /**
4117  * ring_buffer_overrun_cpu - get the number of overruns caused by the ring
4118  * buffer wrapping around (only if RB_FL_OVERWRITE is on).
4119  * @buffer: The ring buffer
4120  * @cpu: The per CPU buffer to get the number of overruns from
4121  */
4122 unsigned long ring_buffer_overrun_cpu(struct trace_buffer *buffer, int cpu)
4123 {
4124         struct ring_buffer_per_cpu *cpu_buffer;
4125         unsigned long ret;
4126
4127         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4128                 return 0;
4129
4130         cpu_buffer = buffer->buffers[cpu];
4131         ret = local_read(&cpu_buffer->overrun);
4132
4133         return ret;
4134 }
4135 EXPORT_SYMBOL_GPL(ring_buffer_overrun_cpu);
4136
4137 /**
4138  * ring_buffer_commit_overrun_cpu - get the number of overruns caused by
4139  * commits failing due to the buffer wrapping around while there are uncommitted
4140  * events, such as during an interrupt storm.
4141  * @buffer: The ring buffer
4142  * @cpu: The per CPU buffer to get the number of overruns from
4143  */
4144 unsigned long
4145 ring_buffer_commit_overrun_cpu(struct trace_buffer *buffer, int cpu)
4146 {
4147         struct ring_buffer_per_cpu *cpu_buffer;
4148         unsigned long ret;
4149
4150         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4151                 return 0;
4152
4153         cpu_buffer = buffer->buffers[cpu];
4154         ret = local_read(&cpu_buffer->commit_overrun);
4155
4156         return ret;
4157 }
4158 EXPORT_SYMBOL_GPL(ring_buffer_commit_overrun_cpu);
4159
4160 /**
4161  * ring_buffer_dropped_events_cpu - get the number of dropped events caused by
4162  * the ring buffer filling up (only if RB_FL_OVERWRITE is off).
4163  * @buffer: The ring buffer
4164  * @cpu: The per CPU buffer to get the number of overruns from
4165  */
4166 unsigned long
4167 ring_buffer_dropped_events_cpu(struct trace_buffer *buffer, int cpu)
4168 {
4169         struct ring_buffer_per_cpu *cpu_buffer;
4170         unsigned long ret;
4171
4172         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4173                 return 0;
4174
4175         cpu_buffer = buffer->buffers[cpu];
4176         ret = local_read(&cpu_buffer->dropped_events);
4177
4178         return ret;
4179 }
4180 EXPORT_SYMBOL_GPL(ring_buffer_dropped_events_cpu);
4181
4182 /**
4183  * ring_buffer_read_events_cpu - get the number of events successfully read
4184  * @buffer: The ring buffer
4185  * @cpu: The per CPU buffer to get the number of events read
4186  */
4187 unsigned long
4188 ring_buffer_read_events_cpu(struct trace_buffer *buffer, int cpu)
4189 {
4190         struct ring_buffer_per_cpu *cpu_buffer;
4191
4192         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4193                 return 0;
4194
4195         cpu_buffer = buffer->buffers[cpu];
4196         return cpu_buffer->read;
4197 }
4198 EXPORT_SYMBOL_GPL(ring_buffer_read_events_cpu);
4199
4200 /**
4201  * ring_buffer_entries - get the number of entries in a buffer
4202  * @buffer: The ring buffer
4203  *
4204  * Returns the total number of entries in the ring buffer
4205  * (all CPU entries)
4206  */
4207 unsigned long ring_buffer_entries(struct trace_buffer *buffer)
4208 {
4209         struct ring_buffer_per_cpu *cpu_buffer;
4210         unsigned long entries = 0;
4211         int cpu;
4212
4213         /* if you care about this being correct, lock the buffer */
4214         for_each_buffer_cpu(buffer, cpu) {
4215                 cpu_buffer = buffer->buffers[cpu];
4216                 entries += rb_num_of_entries(cpu_buffer);
4217         }
4218
4219         return entries;
4220 }
4221 EXPORT_SYMBOL_GPL(ring_buffer_entries);
4222
4223 /**
4224  * ring_buffer_overruns - get the number of overruns in buffer
4225  * @buffer: The ring buffer
4226  *
4227  * Returns the total number of overruns in the ring buffer
4228  * (all CPU entries)
4229  */
4230 unsigned long ring_buffer_overruns(struct trace_buffer *buffer)
4231 {
4232         struct ring_buffer_per_cpu *cpu_buffer;
4233         unsigned long overruns = 0;
4234         int cpu;
4235
4236         /* if you care about this being correct, lock the buffer */
4237         for_each_buffer_cpu(buffer, cpu) {
4238                 cpu_buffer = buffer->buffers[cpu];
4239                 overruns += local_read(&cpu_buffer->overrun);
4240         }
4241
4242         return overruns;
4243 }
4244 EXPORT_SYMBOL_GPL(ring_buffer_overruns);
4245
4246 static void rb_iter_reset(struct ring_buffer_iter *iter)
4247 {
4248         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4249
4250         /* Iterator usage is expected to have record disabled */
4251         iter->head_page = cpu_buffer->reader_page;
4252         iter->head = cpu_buffer->reader_page->read;
4253         iter->next_event = iter->head;
4254
4255         iter->cache_reader_page = iter->head_page;
4256         iter->cache_read = cpu_buffer->read;
4257
4258         if (iter->head) {
4259                 iter->read_stamp = cpu_buffer->read_stamp;
4260                 iter->page_stamp = cpu_buffer->reader_page->page->time_stamp;
4261         } else {
4262                 iter->read_stamp = iter->head_page->page->time_stamp;
4263                 iter->page_stamp = iter->read_stamp;
4264         }
4265 }
4266
4267 /**
4268  * ring_buffer_iter_reset - reset an iterator
4269  * @iter: The iterator to reset
4270  *
4271  * Resets the iterator, so that it will start from the beginning
4272  * again.
4273  */
4274 void ring_buffer_iter_reset(struct ring_buffer_iter *iter)
4275 {
4276         struct ring_buffer_per_cpu *cpu_buffer;
4277         unsigned long flags;
4278
4279         if (!iter)
4280                 return;
4281
4282         cpu_buffer = iter->cpu_buffer;
4283
4284         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4285         rb_iter_reset(iter);
4286         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4287 }
4288 EXPORT_SYMBOL_GPL(ring_buffer_iter_reset);
4289
4290 /**
4291  * ring_buffer_iter_empty - check if an iterator has no more to read
4292  * @iter: The iterator to check
4293  */
4294 int ring_buffer_iter_empty(struct ring_buffer_iter *iter)
4295 {
4296         struct ring_buffer_per_cpu *cpu_buffer;
4297         struct buffer_page *reader;
4298         struct buffer_page *head_page;
4299         struct buffer_page *commit_page;
4300         struct buffer_page *curr_commit_page;
4301         unsigned commit;
4302         u64 curr_commit_ts;
4303         u64 commit_ts;
4304
4305         cpu_buffer = iter->cpu_buffer;
4306         reader = cpu_buffer->reader_page;
4307         head_page = cpu_buffer->head_page;
4308         commit_page = cpu_buffer->commit_page;
4309         commit_ts = commit_page->page->time_stamp;
4310
4311         /*
4312          * When the writer goes across pages, it issues a cmpxchg which
4313          * is a mb(), which will synchronize with the rmb here.
4314          * (see rb_tail_page_update())
4315          */
4316         smp_rmb();
4317         commit = rb_page_commit(commit_page);
4318         /* We want to make sure that the commit page doesn't change */
4319         smp_rmb();
4320
4321         /* Make sure commit page didn't change */
4322         curr_commit_page = READ_ONCE(cpu_buffer->commit_page);
4323         curr_commit_ts = READ_ONCE(curr_commit_page->page->time_stamp);
4324
4325         /* If the commit page changed, then there's more data */
4326         if (curr_commit_page != commit_page ||
4327             curr_commit_ts != commit_ts)
4328                 return 0;
4329
4330         /* Still racy, as it may return a false positive, but that's OK */
4331         return ((iter->head_page == commit_page && iter->head >= commit) ||
4332                 (iter->head_page == reader && commit_page == head_page &&
4333                  head_page->read == commit &&
4334                  iter->head == rb_page_commit(cpu_buffer->reader_page)));
4335 }
4336 EXPORT_SYMBOL_GPL(ring_buffer_iter_empty);
4337
4338 static void
4339 rb_update_read_stamp(struct ring_buffer_per_cpu *cpu_buffer,
4340                      struct ring_buffer_event *event)
4341 {
4342         u64 delta;
4343
4344         switch (event->type_len) {
4345         case RINGBUF_TYPE_PADDING:
4346                 return;
4347
4348         case RINGBUF_TYPE_TIME_EXTEND:
4349                 delta = rb_event_time_stamp(event);
4350                 cpu_buffer->read_stamp += delta;
4351                 return;
4352
4353         case RINGBUF_TYPE_TIME_STAMP:
4354                 delta = rb_event_time_stamp(event);
4355                 cpu_buffer->read_stamp = delta;
4356                 return;
4357
4358         case RINGBUF_TYPE_DATA:
4359                 cpu_buffer->read_stamp += event->time_delta;
4360                 return;
4361
4362         default:
4363                 RB_WARN_ON(cpu_buffer, 1);
4364         }
4365         return;
4366 }
4367
4368 static void
4369 rb_update_iter_read_stamp(struct ring_buffer_iter *iter,
4370                           struct ring_buffer_event *event)
4371 {
4372         u64 delta;
4373
4374         switch (event->type_len) {
4375         case RINGBUF_TYPE_PADDING:
4376                 return;
4377
4378         case RINGBUF_TYPE_TIME_EXTEND:
4379                 delta = rb_event_time_stamp(event);
4380                 iter->read_stamp += delta;
4381                 return;
4382
4383         case RINGBUF_TYPE_TIME_STAMP:
4384                 delta = rb_event_time_stamp(event);
4385                 iter->read_stamp = delta;
4386                 return;
4387
4388         case RINGBUF_TYPE_DATA:
4389                 iter->read_stamp += event->time_delta;
4390                 return;
4391
4392         default:
4393                 RB_WARN_ON(iter->cpu_buffer, 1);
4394         }
4395         return;
4396 }
4397
4398 static struct buffer_page *
4399 rb_get_reader_page(struct ring_buffer_per_cpu *cpu_buffer)
4400 {
4401         struct buffer_page *reader = NULL;
4402         unsigned long overwrite;
4403         unsigned long flags;
4404         int nr_loops = 0;
4405         int ret;
4406
4407         local_irq_save(flags);
4408         arch_spin_lock(&cpu_buffer->lock);
4409
4410  again:
4411         /*
4412          * This should normally only loop twice. But because the
4413          * start of the reader inserts an empty page, it causes
4414          * a case where we will loop three times. There should be no
4415          * reason to loop four times (that I know of).
4416          */
4417         if (RB_WARN_ON(cpu_buffer, ++nr_loops > 3)) {
4418                 reader = NULL;
4419                 goto out;
4420         }
4421
4422         reader = cpu_buffer->reader_page;
4423
4424         /* If there's more to read, return this page */
4425         if (cpu_buffer->reader_page->read < rb_page_size(reader))
4426                 goto out;
4427
4428         /* Never should we have an index greater than the size */
4429         if (RB_WARN_ON(cpu_buffer,
4430                        cpu_buffer->reader_page->read > rb_page_size(reader)))
4431                 goto out;
4432
4433         /* check if we caught up to the tail */
4434         reader = NULL;
4435         if (cpu_buffer->commit_page == cpu_buffer->reader_page)
4436                 goto out;
4437
4438         /* Don't bother swapping if the ring buffer is empty */
4439         if (rb_num_of_entries(cpu_buffer) == 0)
4440                 goto out;
4441
4442         /*
4443          * Reset the reader page to size zero.
4444          */
4445         local_set(&cpu_buffer->reader_page->write, 0);
4446         local_set(&cpu_buffer->reader_page->entries, 0);
4447         local_set(&cpu_buffer->reader_page->page->commit, 0);
4448         cpu_buffer->reader_page->real_end = 0;
4449
4450  spin:
4451         /*
4452          * Splice the empty reader page into the list around the head.
4453          */
4454         reader = rb_set_head_page(cpu_buffer);
4455         if (!reader)
4456                 goto out;
4457         cpu_buffer->reader_page->list.next = rb_list_head(reader->list.next);
4458         cpu_buffer->reader_page->list.prev = reader->list.prev;
4459
4460         /*
4461          * cpu_buffer->pages just needs to point to the buffer, it
4462          *  has no specific buffer page to point to. Lets move it out
4463          *  of our way so we don't accidentally swap it.
4464          */
4465         cpu_buffer->pages = reader->list.prev;
4466
4467         /* The reader page will be pointing to the new head */
4468         rb_set_list_to_head(&cpu_buffer->reader_page->list);
4469
4470         /*
4471          * We want to make sure we read the overruns after we set up our
4472          * pointers to the next object. The writer side does a
4473          * cmpxchg to cross pages which acts as the mb on the writer
4474          * side. Note, the reader will constantly fail the swap
4475          * while the writer is updating the pointers, so this
4476          * guarantees that the overwrite recorded here is the one we
4477          * want to compare with the last_overrun.
4478          */
4479         smp_mb();
4480         overwrite = local_read(&(cpu_buffer->overrun));
4481
4482         /*
4483          * Here's the tricky part.
4484          *
4485          * We need to move the pointer past the header page.
4486          * But we can only do that if a writer is not currently
4487          * moving it. The page before the header page has the
4488          * flag bit '1' set if it is pointing to the page we want.
4489          * but if the writer is in the process of moving it
4490          * than it will be '2' or already moved '0'.
4491          */
4492
4493         ret = rb_head_page_replace(reader, cpu_buffer->reader_page);
4494
4495         /*
4496          * If we did not convert it, then we must try again.
4497          */
4498         if (!ret)
4499                 goto spin;
4500
4501         /*
4502          * Yay! We succeeded in replacing the page.
4503          *
4504          * Now make the new head point back to the reader page.
4505          */
4506         rb_list_head(reader->list.next)->prev = &cpu_buffer->reader_page->list;
4507         rb_inc_page(&cpu_buffer->head_page);
4508
4509         local_inc(&cpu_buffer->pages_read);
4510
4511         /* Finally update the reader page to the new head */
4512         cpu_buffer->reader_page = reader;
4513         cpu_buffer->reader_page->read = 0;
4514
4515         if (overwrite != cpu_buffer->last_overrun) {
4516                 cpu_buffer->lost_events = overwrite - cpu_buffer->last_overrun;
4517                 cpu_buffer->last_overrun = overwrite;
4518         }
4519
4520         goto again;
4521
4522  out:
4523         /* Update the read_stamp on the first event */
4524         if (reader && reader->read == 0)
4525                 cpu_buffer->read_stamp = reader->page->time_stamp;
4526
4527         arch_spin_unlock(&cpu_buffer->lock);
4528         local_irq_restore(flags);
4529
4530         return reader;
4531 }
4532
4533 static void rb_advance_reader(struct ring_buffer_per_cpu *cpu_buffer)
4534 {
4535         struct ring_buffer_event *event;
4536         struct buffer_page *reader;
4537         unsigned length;
4538
4539         reader = rb_get_reader_page(cpu_buffer);
4540
4541         /* This function should not be called when buffer is empty */
4542         if (RB_WARN_ON(cpu_buffer, !reader))
4543                 return;
4544
4545         event = rb_reader_event(cpu_buffer);
4546
4547         if (event->type_len <= RINGBUF_TYPE_DATA_TYPE_LEN_MAX)
4548                 cpu_buffer->read++;
4549
4550         rb_update_read_stamp(cpu_buffer, event);
4551
4552         length = rb_event_length(event);
4553         cpu_buffer->reader_page->read += length;
4554 }
4555
4556 static void rb_advance_iter(struct ring_buffer_iter *iter)
4557 {
4558         struct ring_buffer_per_cpu *cpu_buffer;
4559
4560         cpu_buffer = iter->cpu_buffer;
4561
4562         /* If head == next_event then we need to jump to the next event */
4563         if (iter->head == iter->next_event) {
4564                 /* If the event gets overwritten again, there's nothing to do */
4565                 if (rb_iter_head_event(iter) == NULL)
4566                         return;
4567         }
4568
4569         iter->head = iter->next_event;
4570
4571         /*
4572          * Check if we are at the end of the buffer.
4573          */
4574         if (iter->next_event >= rb_page_size(iter->head_page)) {
4575                 /* discarded commits can make the page empty */
4576                 if (iter->head_page == cpu_buffer->commit_page)
4577                         return;
4578                 rb_inc_iter(iter);
4579                 return;
4580         }
4581
4582         rb_update_iter_read_stamp(iter, iter->event);
4583 }
4584
4585 static int rb_lost_events(struct ring_buffer_per_cpu *cpu_buffer)
4586 {
4587         return cpu_buffer->lost_events;
4588 }
4589
4590 static struct ring_buffer_event *
4591 rb_buffer_peek(struct ring_buffer_per_cpu *cpu_buffer, u64 *ts,
4592                unsigned long *lost_events)
4593 {
4594         struct ring_buffer_event *event;
4595         struct buffer_page *reader;
4596         int nr_loops = 0;
4597
4598         if (ts)
4599                 *ts = 0;
4600  again:
4601         /*
4602          * We repeat when a time extend is encountered.
4603          * Since the time extend is always attached to a data event,
4604          * we should never loop more than once.
4605          * (We never hit the following condition more than twice).
4606          */
4607         if (RB_WARN_ON(cpu_buffer, ++nr_loops > 2))
4608                 return NULL;
4609
4610         reader = rb_get_reader_page(cpu_buffer);
4611         if (!reader)
4612                 return NULL;
4613
4614         event = rb_reader_event(cpu_buffer);
4615
4616         switch (event->type_len) {
4617         case RINGBUF_TYPE_PADDING:
4618                 if (rb_null_event(event))
4619                         RB_WARN_ON(cpu_buffer, 1);
4620                 /*
4621                  * Because the writer could be discarding every
4622                  * event it creates (which would probably be bad)
4623                  * if we were to go back to "again" then we may never
4624                  * catch up, and will trigger the warn on, or lock
4625                  * the box. Return the padding, and we will release
4626                  * the current locks, and try again.
4627                  */
4628                 return event;
4629
4630         case RINGBUF_TYPE_TIME_EXTEND:
4631                 /* Internal data, OK to advance */
4632                 rb_advance_reader(cpu_buffer);
4633                 goto again;
4634
4635         case RINGBUF_TYPE_TIME_STAMP:
4636                 if (ts) {
4637                         *ts = rb_event_time_stamp(event);
4638                         ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4639                                                          cpu_buffer->cpu, ts);
4640                 }
4641                 /* Internal data, OK to advance */
4642                 rb_advance_reader(cpu_buffer);
4643                 goto again;
4644
4645         case RINGBUF_TYPE_DATA:
4646                 if (ts && !(*ts)) {
4647                         *ts = cpu_buffer->read_stamp + event->time_delta;
4648                         ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4649                                                          cpu_buffer->cpu, ts);
4650                 }
4651                 if (lost_events)
4652                         *lost_events = rb_lost_events(cpu_buffer);
4653                 return event;
4654
4655         default:
4656                 RB_WARN_ON(cpu_buffer, 1);
4657         }
4658
4659         return NULL;
4660 }
4661 EXPORT_SYMBOL_GPL(ring_buffer_peek);
4662
4663 static struct ring_buffer_event *
4664 rb_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
4665 {
4666         struct trace_buffer *buffer;
4667         struct ring_buffer_per_cpu *cpu_buffer;
4668         struct ring_buffer_event *event;
4669         int nr_loops = 0;
4670
4671         if (ts)
4672                 *ts = 0;
4673
4674         cpu_buffer = iter->cpu_buffer;
4675         buffer = cpu_buffer->buffer;
4676
4677         /*
4678          * Check if someone performed a consuming read to
4679          * the buffer. A consuming read invalidates the iterator
4680          * and we need to reset the iterator in this case.
4681          */
4682         if (unlikely(iter->cache_read != cpu_buffer->read ||
4683                      iter->cache_reader_page != cpu_buffer->reader_page))
4684                 rb_iter_reset(iter);
4685
4686  again:
4687         if (ring_buffer_iter_empty(iter))
4688                 return NULL;
4689
4690         /*
4691          * As the writer can mess with what the iterator is trying
4692          * to read, just give up if we fail to get an event after
4693          * three tries. The iterator is not as reliable when reading
4694          * the ring buffer with an active write as the consumer is.
4695          * Do not warn if the three failures is reached.
4696          */
4697         if (++nr_loops > 3)
4698                 return NULL;
4699
4700         if (rb_per_cpu_empty(cpu_buffer))
4701                 return NULL;
4702
4703         if (iter->head >= rb_page_size(iter->head_page)) {
4704                 rb_inc_iter(iter);
4705                 goto again;
4706         }
4707
4708         event = rb_iter_head_event(iter);
4709         if (!event)
4710                 goto again;
4711
4712         switch (event->type_len) {
4713         case RINGBUF_TYPE_PADDING:
4714                 if (rb_null_event(event)) {
4715                         rb_inc_iter(iter);
4716                         goto again;
4717                 }
4718                 rb_advance_iter(iter);
4719                 return event;
4720
4721         case RINGBUF_TYPE_TIME_EXTEND:
4722                 /* Internal data, OK to advance */
4723                 rb_advance_iter(iter);
4724                 goto again;
4725
4726         case RINGBUF_TYPE_TIME_STAMP:
4727                 if (ts) {
4728                         *ts = rb_event_time_stamp(event);
4729                         ring_buffer_normalize_time_stamp(cpu_buffer->buffer,
4730                                                          cpu_buffer->cpu, ts);
4731                 }
4732                 /* Internal data, OK to advance */
4733                 rb_advance_iter(iter);
4734                 goto again;
4735
4736         case RINGBUF_TYPE_DATA:
4737                 if (ts && !(*ts)) {
4738                         *ts = iter->read_stamp + event->time_delta;
4739                         ring_buffer_normalize_time_stamp(buffer,
4740                                                          cpu_buffer->cpu, ts);
4741                 }
4742                 return event;
4743
4744         default:
4745                 RB_WARN_ON(cpu_buffer, 1);
4746         }
4747
4748         return NULL;
4749 }
4750 EXPORT_SYMBOL_GPL(ring_buffer_iter_peek);
4751
4752 static inline bool rb_reader_lock(struct ring_buffer_per_cpu *cpu_buffer)
4753 {
4754         if (likely(!in_nmi())) {
4755                 raw_spin_lock(&cpu_buffer->reader_lock);
4756                 return true;
4757         }
4758
4759         /*
4760          * If an NMI die dumps out the content of the ring buffer
4761          * trylock must be used to prevent a deadlock if the NMI
4762          * preempted a task that holds the ring buffer locks. If
4763          * we get the lock then all is fine, if not, then continue
4764          * to do the read, but this can corrupt the ring buffer,
4765          * so it must be permanently disabled from future writes.
4766          * Reading from NMI is a oneshot deal.
4767          */
4768         if (raw_spin_trylock(&cpu_buffer->reader_lock))
4769                 return true;
4770
4771         /* Continue without locking, but disable the ring buffer */
4772         atomic_inc(&cpu_buffer->record_disabled);
4773         return false;
4774 }
4775
4776 static inline void
4777 rb_reader_unlock(struct ring_buffer_per_cpu *cpu_buffer, bool locked)
4778 {
4779         if (likely(locked))
4780                 raw_spin_unlock(&cpu_buffer->reader_lock);
4781         return;
4782 }
4783
4784 /**
4785  * ring_buffer_peek - peek at the next event to be read
4786  * @buffer: The ring buffer to read
4787  * @cpu: The cpu to peak at
4788  * @ts: The timestamp counter of this event.
4789  * @lost_events: a variable to store if events were lost (may be NULL)
4790  *
4791  * This will return the event that will be read next, but does
4792  * not consume the data.
4793  */
4794 struct ring_buffer_event *
4795 ring_buffer_peek(struct trace_buffer *buffer, int cpu, u64 *ts,
4796                  unsigned long *lost_events)
4797 {
4798         struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
4799         struct ring_buffer_event *event;
4800         unsigned long flags;
4801         bool dolock;
4802
4803         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4804                 return NULL;
4805
4806  again:
4807         local_irq_save(flags);
4808         dolock = rb_reader_lock(cpu_buffer);
4809         event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4810         if (event && event->type_len == RINGBUF_TYPE_PADDING)
4811                 rb_advance_reader(cpu_buffer);
4812         rb_reader_unlock(cpu_buffer, dolock);
4813         local_irq_restore(flags);
4814
4815         if (event && event->type_len == RINGBUF_TYPE_PADDING)
4816                 goto again;
4817
4818         return event;
4819 }
4820
4821 /** ring_buffer_iter_dropped - report if there are dropped events
4822  * @iter: The ring buffer iterator
4823  *
4824  * Returns true if there was dropped events since the last peek.
4825  */
4826 bool ring_buffer_iter_dropped(struct ring_buffer_iter *iter)
4827 {
4828         bool ret = iter->missed_events != 0;
4829
4830         iter->missed_events = 0;
4831         return ret;
4832 }
4833 EXPORT_SYMBOL_GPL(ring_buffer_iter_dropped);
4834
4835 /**
4836  * ring_buffer_iter_peek - peek at the next event to be read
4837  * @iter: The ring buffer iterator
4838  * @ts: The timestamp counter of this event.
4839  *
4840  * This will return the event that will be read next, but does
4841  * not increment the iterator.
4842  */
4843 struct ring_buffer_event *
4844 ring_buffer_iter_peek(struct ring_buffer_iter *iter, u64 *ts)
4845 {
4846         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
4847         struct ring_buffer_event *event;
4848         unsigned long flags;
4849
4850  again:
4851         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4852         event = rb_iter_peek(iter, ts);
4853         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
4854
4855         if (event && event->type_len == RINGBUF_TYPE_PADDING)
4856                 goto again;
4857
4858         return event;
4859 }
4860
4861 /**
4862  * ring_buffer_consume - return an event and consume it
4863  * @buffer: The ring buffer to get the next event from
4864  * @cpu: the cpu to read the buffer from
4865  * @ts: a variable to store the timestamp (may be NULL)
4866  * @lost_events: a variable to store if events were lost (may be NULL)
4867  *
4868  * Returns the next event in the ring buffer, and that event is consumed.
4869  * Meaning, that sequential reads will keep returning a different event,
4870  * and eventually empty the ring buffer if the producer is slower.
4871  */
4872 struct ring_buffer_event *
4873 ring_buffer_consume(struct trace_buffer *buffer, int cpu, u64 *ts,
4874                     unsigned long *lost_events)
4875 {
4876         struct ring_buffer_per_cpu *cpu_buffer;
4877         struct ring_buffer_event *event = NULL;
4878         unsigned long flags;
4879         bool dolock;
4880
4881  again:
4882         /* might be called in atomic */
4883         preempt_disable();
4884
4885         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4886                 goto out;
4887
4888         cpu_buffer = buffer->buffers[cpu];
4889         local_irq_save(flags);
4890         dolock = rb_reader_lock(cpu_buffer);
4891
4892         event = rb_buffer_peek(cpu_buffer, ts, lost_events);
4893         if (event) {
4894                 cpu_buffer->lost_events = 0;
4895                 rb_advance_reader(cpu_buffer);
4896         }
4897
4898         rb_reader_unlock(cpu_buffer, dolock);
4899         local_irq_restore(flags);
4900
4901  out:
4902         preempt_enable();
4903
4904         if (event && event->type_len == RINGBUF_TYPE_PADDING)
4905                 goto again;
4906
4907         return event;
4908 }
4909 EXPORT_SYMBOL_GPL(ring_buffer_consume);
4910
4911 /**
4912  * ring_buffer_read_prepare - Prepare for a non consuming read of the buffer
4913  * @buffer: The ring buffer to read from
4914  * @cpu: The cpu buffer to iterate over
4915  * @flags: gfp flags to use for memory allocation
4916  *
4917  * This performs the initial preparations necessary to iterate
4918  * through the buffer.  Memory is allocated, buffer recording
4919  * is disabled, and the iterator pointer is returned to the caller.
4920  *
4921  * Disabling buffer recording prevents the reading from being
4922  * corrupted. This is not a consuming read, so a producer is not
4923  * expected.
4924  *
4925  * After a sequence of ring_buffer_read_prepare calls, the user is
4926  * expected to make at least one call to ring_buffer_read_prepare_sync.
4927  * Afterwards, ring_buffer_read_start is invoked to get things going
4928  * for real.
4929  *
4930  * This overall must be paired with ring_buffer_read_finish.
4931  */
4932 struct ring_buffer_iter *
4933 ring_buffer_read_prepare(struct trace_buffer *buffer, int cpu, gfp_t flags)
4934 {
4935         struct ring_buffer_per_cpu *cpu_buffer;
4936         struct ring_buffer_iter *iter;
4937
4938         if (!cpumask_test_cpu(cpu, buffer->cpumask))
4939                 return NULL;
4940
4941         iter = kzalloc(sizeof(*iter), flags);
4942         if (!iter)
4943                 return NULL;
4944
4945         iter->event = kmalloc(BUF_MAX_DATA_SIZE, flags);
4946         if (!iter->event) {
4947                 kfree(iter);
4948                 return NULL;
4949         }
4950
4951         cpu_buffer = buffer->buffers[cpu];
4952
4953         iter->cpu_buffer = cpu_buffer;
4954
4955         atomic_inc(&cpu_buffer->resize_disabled);
4956
4957         return iter;
4958 }
4959 EXPORT_SYMBOL_GPL(ring_buffer_read_prepare);
4960
4961 /**
4962  * ring_buffer_read_prepare_sync - Synchronize a set of prepare calls
4963  *
4964  * All previously invoked ring_buffer_read_prepare calls to prepare
4965  * iterators will be synchronized.  Afterwards, read_buffer_read_start
4966  * calls on those iterators are allowed.
4967  */
4968 void
4969 ring_buffer_read_prepare_sync(void)
4970 {
4971         synchronize_rcu();
4972 }
4973 EXPORT_SYMBOL_GPL(ring_buffer_read_prepare_sync);
4974
4975 /**
4976  * ring_buffer_read_start - start a non consuming read of the buffer
4977  * @iter: The iterator returned by ring_buffer_read_prepare
4978  *
4979  * This finalizes the startup of an iteration through the buffer.
4980  * The iterator comes from a call to ring_buffer_read_prepare and
4981  * an intervening ring_buffer_read_prepare_sync must have been
4982  * performed.
4983  *
4984  * Must be paired with ring_buffer_read_finish.
4985  */
4986 void
4987 ring_buffer_read_start(struct ring_buffer_iter *iter)
4988 {
4989         struct ring_buffer_per_cpu *cpu_buffer;
4990         unsigned long flags;
4991
4992         if (!iter)
4993                 return;
4994
4995         cpu_buffer = iter->cpu_buffer;
4996
4997         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
4998         arch_spin_lock(&cpu_buffer->lock);
4999         rb_iter_reset(iter);
5000         arch_spin_unlock(&cpu_buffer->lock);
5001         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5002 }
5003 EXPORT_SYMBOL_GPL(ring_buffer_read_start);
5004
5005 /**
5006  * ring_buffer_read_finish - finish reading the iterator of the buffer
5007  * @iter: The iterator retrieved by ring_buffer_start
5008  *
5009  * This re-enables the recording to the buffer, and frees the
5010  * iterator.
5011  */
5012 void
5013 ring_buffer_read_finish(struct ring_buffer_iter *iter)
5014 {
5015         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
5016         unsigned long flags;
5017
5018         /*
5019          * Ring buffer is disabled from recording, here's a good place
5020          * to check the integrity of the ring buffer.
5021          * Must prevent readers from trying to read, as the check
5022          * clears the HEAD page and readers require it.
5023          */
5024         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5025         rb_check_pages(cpu_buffer);
5026         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5027
5028         atomic_dec(&cpu_buffer->resize_disabled);
5029         kfree(iter->event);
5030         kfree(iter);
5031 }
5032 EXPORT_SYMBOL_GPL(ring_buffer_read_finish);
5033
5034 /**
5035  * ring_buffer_iter_advance - advance the iterator to the next location
5036  * @iter: The ring buffer iterator
5037  *
5038  * Move the location of the iterator such that the next read will
5039  * be the next location of the iterator.
5040  */
5041 void ring_buffer_iter_advance(struct ring_buffer_iter *iter)
5042 {
5043         struct ring_buffer_per_cpu *cpu_buffer = iter->cpu_buffer;
5044         unsigned long flags;
5045
5046         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5047
5048         rb_advance_iter(iter);
5049
5050         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5051 }
5052 EXPORT_SYMBOL_GPL(ring_buffer_iter_advance);
5053
5054 /**
5055  * ring_buffer_size - return the size of the ring buffer (in bytes)
5056  * @buffer: The ring buffer.
5057  * @cpu: The CPU to get ring buffer size from.
5058  */
5059 unsigned long ring_buffer_size(struct trace_buffer *buffer, int cpu)
5060 {
5061         /*
5062          * Earlier, this method returned
5063          *      BUF_PAGE_SIZE * buffer->nr_pages
5064          * Since the nr_pages field is now removed, we have converted this to
5065          * return the per cpu buffer value.
5066          */
5067         if (!cpumask_test_cpu(cpu, buffer->cpumask))
5068                 return 0;
5069
5070         return BUF_PAGE_SIZE * buffer->buffers[cpu]->nr_pages;
5071 }
5072 EXPORT_SYMBOL_GPL(ring_buffer_size);
5073
5074 static void
5075 rb_reset_cpu(struct ring_buffer_per_cpu *cpu_buffer)
5076 {
5077         rb_head_page_deactivate(cpu_buffer);
5078
5079         cpu_buffer->head_page
5080                 = list_entry(cpu_buffer->pages, struct buffer_page, list);
5081         local_set(&cpu_buffer->head_page->write, 0);
5082         local_set(&cpu_buffer->head_page->entries, 0);
5083         local_set(&cpu_buffer->head_page->page->commit, 0);
5084
5085         cpu_buffer->head_page->read = 0;
5086
5087         cpu_buffer->tail_page = cpu_buffer->head_page;
5088         cpu_buffer->commit_page = cpu_buffer->head_page;
5089
5090         INIT_LIST_HEAD(&cpu_buffer->reader_page->list);
5091         INIT_LIST_HEAD(&cpu_buffer->new_pages);
5092         local_set(&cpu_buffer->reader_page->write, 0);
5093         local_set(&cpu_buffer->reader_page->entries, 0);
5094         local_set(&cpu_buffer->reader_page->page->commit, 0);
5095         cpu_buffer->reader_page->read = 0;
5096
5097         local_set(&cpu_buffer->entries_bytes, 0);
5098         local_set(&cpu_buffer->overrun, 0);
5099         local_set(&cpu_buffer->commit_overrun, 0);
5100         local_set(&cpu_buffer->dropped_events, 0);
5101         local_set(&cpu_buffer->entries, 0);
5102         local_set(&cpu_buffer->committing, 0);
5103         local_set(&cpu_buffer->commits, 0);
5104         local_set(&cpu_buffer->pages_touched, 0);
5105         local_set(&cpu_buffer->pages_read, 0);
5106         cpu_buffer->last_pages_touch = 0;
5107         cpu_buffer->shortest_full = 0;
5108         cpu_buffer->read = 0;
5109         cpu_buffer->read_bytes = 0;
5110
5111         rb_time_set(&cpu_buffer->write_stamp, 0);
5112         rb_time_set(&cpu_buffer->before_stamp, 0);
5113
5114         memset(cpu_buffer->event_stamp, 0, sizeof(cpu_buffer->event_stamp));
5115
5116         cpu_buffer->lost_events = 0;
5117         cpu_buffer->last_overrun = 0;
5118
5119         rb_head_page_activate(cpu_buffer);
5120 }
5121
5122 /* Must have disabled the cpu buffer then done a synchronize_rcu */
5123 static void reset_disabled_cpu_buffer(struct ring_buffer_per_cpu *cpu_buffer)
5124 {
5125         unsigned long flags;
5126
5127         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5128
5129         if (RB_WARN_ON(cpu_buffer, local_read(&cpu_buffer->committing)))
5130                 goto out;
5131
5132         arch_spin_lock(&cpu_buffer->lock);
5133
5134         rb_reset_cpu(cpu_buffer);
5135
5136         arch_spin_unlock(&cpu_buffer->lock);
5137
5138  out:
5139         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5140 }
5141
5142 /**
5143  * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
5144  * @buffer: The ring buffer to reset a per cpu buffer of
5145  * @cpu: The CPU buffer to be reset
5146  */
5147 void ring_buffer_reset_cpu(struct trace_buffer *buffer, int cpu)
5148 {
5149         struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
5150
5151         if (!cpumask_test_cpu(cpu, buffer->cpumask))
5152                 return;
5153
5154         /* prevent another thread from changing buffer sizes */
5155         mutex_lock(&buffer->mutex);
5156
5157         atomic_inc(&cpu_buffer->resize_disabled);
5158         atomic_inc(&cpu_buffer->record_disabled);
5159
5160         /* Make sure all commits have finished */
5161         synchronize_rcu();
5162
5163         reset_disabled_cpu_buffer(cpu_buffer);
5164
5165         atomic_dec(&cpu_buffer->record_disabled);
5166         atomic_dec(&cpu_buffer->resize_disabled);
5167
5168         mutex_unlock(&buffer->mutex);
5169 }
5170 EXPORT_SYMBOL_GPL(ring_buffer_reset_cpu);
5171
5172 /**
5173  * ring_buffer_reset_cpu - reset a ring buffer per CPU buffer
5174  * @buffer: The ring buffer to reset a per cpu buffer of
5175  * @cpu: The CPU buffer to be reset
5176  */
5177 void ring_buffer_reset_online_cpus(struct trace_buffer *buffer)
5178 {
5179         struct ring_buffer_per_cpu *cpu_buffer;
5180         int cpu;
5181
5182         /* prevent another thread from changing buffer sizes */
5183         mutex_lock(&buffer->mutex);
5184
5185         for_each_online_buffer_cpu(buffer, cpu) {
5186                 cpu_buffer = buffer->buffers[cpu];
5187
5188                 atomic_inc(&cpu_buffer->resize_disabled);
5189                 atomic_inc(&cpu_buffer->record_disabled);
5190         }
5191
5192         /* Make sure all commits have finished */
5193         synchronize_rcu();
5194
5195         for_each_online_buffer_cpu(buffer, cpu) {
5196                 cpu_buffer = buffer->buffers[cpu];
5197
5198                 reset_disabled_cpu_buffer(cpu_buffer);
5199
5200                 atomic_dec(&cpu_buffer->record_disabled);
5201                 atomic_dec(&cpu_buffer->resize_disabled);
5202         }
5203
5204         mutex_unlock(&buffer->mutex);
5205 }
5206
5207 /**
5208  * ring_buffer_reset - reset a ring buffer
5209  * @buffer: The ring buffer to reset all cpu buffers
5210  */
5211 void ring_buffer_reset(struct trace_buffer *buffer)
5212 {
5213         struct ring_buffer_per_cpu *cpu_buffer;
5214         int cpu;
5215
5216         for_each_buffer_cpu(buffer, cpu) {
5217                 cpu_buffer = buffer->buffers[cpu];
5218
5219                 atomic_inc(&cpu_buffer->resize_disabled);
5220                 atomic_inc(&cpu_buffer->record_disabled);
5221         }
5222
5223         /* Make sure all commits have finished */
5224         synchronize_rcu();
5225
5226         for_each_buffer_cpu(buffer, cpu) {
5227                 cpu_buffer = buffer->buffers[cpu];
5228
5229                 reset_disabled_cpu_buffer(cpu_buffer);
5230
5231                 atomic_dec(&cpu_buffer->record_disabled);
5232                 atomic_dec(&cpu_buffer->resize_disabled);
5233         }
5234 }
5235 EXPORT_SYMBOL_GPL(ring_buffer_reset);
5236
5237 /**
5238  * rind_buffer_empty - is the ring buffer empty?
5239  * @buffer: The ring buffer to test
5240  */
5241 bool ring_buffer_empty(struct trace_buffer *buffer)
5242 {
5243         struct ring_buffer_per_cpu *cpu_buffer;
5244         unsigned long flags;
5245         bool dolock;
5246         int cpu;
5247         int ret;
5248
5249         /* yes this is racy, but if you don't like the race, lock the buffer */
5250         for_each_buffer_cpu(buffer, cpu) {
5251                 cpu_buffer = buffer->buffers[cpu];
5252                 local_irq_save(flags);
5253                 dolock = rb_reader_lock(cpu_buffer);
5254                 ret = rb_per_cpu_empty(cpu_buffer);
5255                 rb_reader_unlock(cpu_buffer, dolock);
5256                 local_irq_restore(flags);
5257
5258                 if (!ret)
5259                         return false;
5260         }
5261
5262         return true;
5263 }
5264 EXPORT_SYMBOL_GPL(ring_buffer_empty);
5265
5266 /**
5267  * ring_buffer_empty_cpu - is a cpu buffer of a ring buffer empty?
5268  * @buffer: The ring buffer
5269  * @cpu: The CPU buffer to test
5270  */
5271 bool ring_buffer_empty_cpu(struct trace_buffer *buffer, int cpu)
5272 {
5273         struct ring_buffer_per_cpu *cpu_buffer;
5274         unsigned long flags;
5275         bool dolock;
5276         int ret;
5277
5278         if (!cpumask_test_cpu(cpu, buffer->cpumask))
5279                 return true;
5280
5281         cpu_buffer = buffer->buffers[cpu];
5282         local_irq_save(flags);
5283         dolock = rb_reader_lock(cpu_buffer);
5284         ret = rb_per_cpu_empty(cpu_buffer);
5285         rb_reader_unlock(cpu_buffer, dolock);
5286         local_irq_restore(flags);
5287
5288         return ret;
5289 }
5290 EXPORT_SYMBOL_GPL(ring_buffer_empty_cpu);
5291
5292 #ifdef CONFIG_RING_BUFFER_ALLOW_SWAP
5293 /**
5294  * ring_buffer_swap_cpu - swap a CPU buffer between two ring buffers
5295  * @buffer_a: One buffer to swap with
5296  * @buffer_b: The other buffer to swap with
5297  * @cpu: the CPU of the buffers to swap
5298  *
5299  * This function is useful for tracers that want to take a "snapshot"
5300  * of a CPU buffer and has another back up buffer lying around.
5301  * it is expected that the tracer handles the cpu buffer not being
5302  * used at the moment.
5303  */
5304 int ring_buffer_swap_cpu(struct trace_buffer *buffer_a,
5305                          struct trace_buffer *buffer_b, int cpu)
5306 {
5307         struct ring_buffer_per_cpu *cpu_buffer_a;
5308         struct ring_buffer_per_cpu *cpu_buffer_b;
5309         int ret = -EINVAL;
5310
5311         if (!cpumask_test_cpu(cpu, buffer_a->cpumask) ||
5312             !cpumask_test_cpu(cpu, buffer_b->cpumask))
5313                 goto out;
5314
5315         cpu_buffer_a = buffer_a->buffers[cpu];
5316         cpu_buffer_b = buffer_b->buffers[cpu];
5317
5318         /* At least make sure the two buffers are somewhat the same */
5319         if (cpu_buffer_a->nr_pages != cpu_buffer_b->nr_pages)
5320                 goto out;
5321
5322         ret = -EAGAIN;
5323
5324         if (atomic_read(&buffer_a->record_disabled))
5325                 goto out;
5326
5327         if (atomic_read(&buffer_b->record_disabled))
5328                 goto out;
5329
5330         if (atomic_read(&cpu_buffer_a->record_disabled))
5331                 goto out;
5332
5333         if (atomic_read(&cpu_buffer_b->record_disabled))
5334                 goto out;
5335
5336         /*
5337          * We can't do a synchronize_rcu here because this
5338          * function can be called in atomic context.
5339          * Normally this will be called from the same CPU as cpu.
5340          * If not it's up to the caller to protect this.
5341          */
5342         atomic_inc(&cpu_buffer_a->record_disabled);
5343         atomic_inc(&cpu_buffer_b->record_disabled);
5344
5345         ret = -EBUSY;
5346         if (local_read(&cpu_buffer_a->committing))
5347                 goto out_dec;
5348         if (local_read(&cpu_buffer_b->committing))
5349                 goto out_dec;
5350
5351         buffer_a->buffers[cpu] = cpu_buffer_b;
5352         buffer_b->buffers[cpu] = cpu_buffer_a;
5353
5354         cpu_buffer_b->buffer = buffer_a;
5355         cpu_buffer_a->buffer = buffer_b;
5356
5357         ret = 0;
5358
5359 out_dec:
5360         atomic_dec(&cpu_buffer_a->record_disabled);
5361         atomic_dec(&cpu_buffer_b->record_disabled);
5362 out:
5363         return ret;
5364 }
5365 EXPORT_SYMBOL_GPL(ring_buffer_swap_cpu);
5366 #endif /* CONFIG_RING_BUFFER_ALLOW_SWAP */
5367
5368 /**
5369  * ring_buffer_alloc_read_page - allocate a page to read from buffer
5370  * @buffer: the buffer to allocate for.
5371  * @cpu: the cpu buffer to allocate.
5372  *
5373  * This function is used in conjunction with ring_buffer_read_page.
5374  * When reading a full page from the ring buffer, these functions
5375  * can be used to speed up the process. The calling function should
5376  * allocate a few pages first with this function. Then when it
5377  * needs to get pages from the ring buffer, it passes the result
5378  * of this function into ring_buffer_read_page, which will swap
5379  * the page that was allocated, with the read page of the buffer.
5380  *
5381  * Returns:
5382  *  The page allocated, or ERR_PTR
5383  */
5384 void *ring_buffer_alloc_read_page(struct trace_buffer *buffer, int cpu)
5385 {
5386         struct ring_buffer_per_cpu *cpu_buffer;
5387         struct buffer_data_page *bpage = NULL;
5388         unsigned long flags;
5389         struct page *page;
5390
5391         if (!cpumask_test_cpu(cpu, buffer->cpumask))
5392                 return ERR_PTR(-ENODEV);
5393
5394         cpu_buffer = buffer->buffers[cpu];
5395         local_irq_save(flags);
5396         arch_spin_lock(&cpu_buffer->lock);
5397
5398         if (cpu_buffer->free_page) {
5399                 bpage = cpu_buffer->free_page;
5400                 cpu_buffer->free_page = NULL;
5401         }
5402
5403         arch_spin_unlock(&cpu_buffer->lock);
5404         local_irq_restore(flags);
5405
5406         if (bpage)
5407                 goto out;
5408
5409         page = alloc_pages_node(cpu_to_node(cpu),
5410                                 GFP_KERNEL | __GFP_NORETRY, 0);
5411         if (!page)
5412                 return ERR_PTR(-ENOMEM);
5413
5414         bpage = page_address(page);
5415
5416  out:
5417         rb_init_page(bpage);
5418
5419         return bpage;
5420 }
5421 EXPORT_SYMBOL_GPL(ring_buffer_alloc_read_page);
5422
5423 /**
5424  * ring_buffer_free_read_page - free an allocated read page
5425  * @buffer: the buffer the page was allocate for
5426  * @cpu: the cpu buffer the page came from
5427  * @data: the page to free
5428  *
5429  * Free a page allocated from ring_buffer_alloc_read_page.
5430  */
5431 void ring_buffer_free_read_page(struct trace_buffer *buffer, int cpu, void *data)
5432 {
5433         struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
5434         struct buffer_data_page *bpage = data;
5435         struct page *page = virt_to_page(bpage);
5436         unsigned long flags;
5437
5438         /* If the page is still in use someplace else, we can't reuse it */
5439         if (page_ref_count(page) > 1)
5440                 goto out;
5441
5442         local_irq_save(flags);
5443         arch_spin_lock(&cpu_buffer->lock);
5444
5445         if (!cpu_buffer->free_page) {
5446                 cpu_buffer->free_page = bpage;
5447                 bpage = NULL;
5448         }
5449
5450         arch_spin_unlock(&cpu_buffer->lock);
5451         local_irq_restore(flags);
5452
5453  out:
5454         free_page((unsigned long)bpage);
5455 }
5456 EXPORT_SYMBOL_GPL(ring_buffer_free_read_page);
5457
5458 /**
5459  * ring_buffer_read_page - extract a page from the ring buffer
5460  * @buffer: buffer to extract from
5461  * @data_page: the page to use allocated from ring_buffer_alloc_read_page
5462  * @len: amount to extract
5463  * @cpu: the cpu of the buffer to extract
5464  * @full: should the extraction only happen when the page is full.
5465  *
5466  * This function will pull out a page from the ring buffer and consume it.
5467  * @data_page must be the address of the variable that was returned
5468  * from ring_buffer_alloc_read_page. This is because the page might be used
5469  * to swap with a page in the ring buffer.
5470  *
5471  * for example:
5472  *      rpage = ring_buffer_alloc_read_page(buffer, cpu);
5473  *      if (IS_ERR(rpage))
5474  *              return PTR_ERR(rpage);
5475  *      ret = ring_buffer_read_page(buffer, &rpage, len, cpu, 0);
5476  *      if (ret >= 0)
5477  *              process_page(rpage, ret);
5478  *
5479  * When @full is set, the function will not return true unless
5480  * the writer is off the reader page.
5481  *
5482  * Note: it is up to the calling functions to handle sleeps and wakeups.
5483  *  The ring buffer can be used anywhere in the kernel and can not
5484  *  blindly call wake_up. The layer that uses the ring buffer must be
5485  *  responsible for that.
5486  *
5487  * Returns:
5488  *  >=0 if data has been transferred, returns the offset of consumed data.
5489  *  <0 if no data has been transferred.
5490  */
5491 int ring_buffer_read_page(struct trace_buffer *buffer,
5492                           void **data_page, size_t len, int cpu, int full)
5493 {
5494         struct ring_buffer_per_cpu *cpu_buffer = buffer->buffers[cpu];
5495         struct ring_buffer_event *event;
5496         struct buffer_data_page *bpage;
5497         struct buffer_page *reader;
5498         unsigned long missed_events;
5499         unsigned long flags;
5500         unsigned int commit;
5501         unsigned int read;
5502         u64 save_timestamp;
5503         int ret = -1;
5504
5505         if (!cpumask_test_cpu(cpu, buffer->cpumask))
5506                 goto out;
5507
5508         /*
5509          * If len is not big enough to hold the page header, then
5510          * we can not copy anything.
5511          */
5512         if (len <= BUF_PAGE_HDR_SIZE)
5513                 goto out;
5514
5515         len -= BUF_PAGE_HDR_SIZE;
5516
5517         if (!data_page)
5518                 goto out;
5519
5520         bpage = *data_page;
5521         if (!bpage)
5522                 goto out;
5523
5524         raw_spin_lock_irqsave(&cpu_buffer->reader_lock, flags);
5525
5526         reader = rb_get_reader_page(cpu_buffer);
5527         if (!reader)
5528                 goto out_unlock;
5529
5530         event = rb_reader_event(cpu_buffer);
5531
5532         read = reader->read;
5533         commit = rb_page_commit(reader);
5534
5535         /* Check if any events were dropped */
5536         missed_events = cpu_buffer->lost_events;
5537
5538         /*
5539          * If this page has been partially read or
5540          * if len is not big enough to read the rest of the page or
5541          * a writer is still on the page, then
5542          * we must copy the data from the page to the buffer.
5543          * Otherwise, we can simply swap the page with the one passed in.
5544          */
5545         if (read || (len < (commit - read)) ||
5546             cpu_buffer->reader_page == cpu_buffer->commit_page) {
5547                 struct buffer_data_page *rpage = cpu_buffer->reader_page->page;
5548                 unsigned int rpos = read;
5549                 unsigned int pos = 0;
5550                 unsigned int size;
5551
5552                 if (full)
5553                         goto out_unlock;
5554
5555                 if (len > (commit - read))
5556                         len = (commit - read);
5557
5558                 /* Always keep the time extend and data together */
5559                 size = rb_event_ts_length(event);
5560
5561                 if (len < size)
5562                         goto out_unlock;
5563
5564                 /* save the current timestamp, since the user will need it */
5565                 save_timestamp = cpu_buffer->read_stamp;
5566
5567                 /* Need to copy one event at a time */
5568                 do {
5569                         /* We need the size of one event, because
5570                          * rb_advance_reader only advances by one event,
5571                          * whereas rb_event_ts_length may include the size of
5572                          * one or two events.
5573                          * We have already ensured there's enough space if this
5574                          * is a time extend. */
5575                         size = rb_event_length(event);
5576                         memcpy(bpage->data + pos, rpage->data + rpos, size);
5577
5578                         len -= size;
5579
5580                         rb_advance_reader(cpu_buffer);
5581                         rpos = reader->read;
5582                         pos += size;
5583
5584                         if (rpos >= commit)
5585                                 break;
5586
5587                         event = rb_reader_event(cpu_buffer);
5588                         /* Always keep the time extend and data together */
5589                         size = rb_event_ts_length(event);
5590                 } while (len >= size);
5591
5592                 /* update bpage */
5593                 local_set(&bpage->commit, pos);
5594                 bpage->time_stamp = save_timestamp;
5595
5596                 /* we copied everything to the beginning */
5597                 read = 0;
5598         } else {
5599                 /* update the entry counter */
5600                 cpu_buffer->read += rb_page_entries(reader);
5601                 cpu_buffer->read_bytes += BUF_PAGE_SIZE;
5602
5603                 /* swap the pages */
5604                 rb_init_page(bpage);
5605                 bpage = reader->page;
5606                 reader->page = *data_page;
5607                 local_set(&reader->write, 0);
5608                 local_set(&reader->entries, 0);
5609                 reader->read = 0;
5610                 *data_page = bpage;
5611
5612                 /*
5613                  * Use the real_end for the data size,
5614                  * This gives us a chance to store the lost events
5615                  * on the page.
5616                  */
5617                 if (reader->real_end)
5618                         local_set(&bpage->commit, reader->real_end);
5619         }
5620         ret = read;
5621
5622         cpu_buffer->lost_events = 0;
5623
5624         commit = local_read(&bpage->commit);
5625         /*
5626          * Set a flag in the commit field if we lost events
5627          */
5628         if (missed_events) {
5629                 /* If there is room at the end of the page to save the
5630                  * missed events, then record it there.
5631                  */
5632                 if (BUF_PAGE_SIZE - commit >= sizeof(missed_events)) {
5633                         memcpy(&bpage->data[commit], &missed_events,
5634                                sizeof(missed_events));
5635                         local_add(RB_MISSED_STORED, &bpage->commit);
5636                         commit += sizeof(missed_events);
5637                 }
5638                 local_add(RB_MISSED_EVENTS, &bpage->commit);
5639         }
5640
5641         /*
5642          * This page may be off to user land. Zero it out here.
5643          */
5644         if (commit < BUF_PAGE_SIZE)
5645                 memset(&bpage->data[commit], 0, BUF_PAGE_SIZE - commit);
5646
5647  out_unlock:
5648         raw_spin_unlock_irqrestore(&cpu_buffer->reader_lock, flags);
5649
5650  out:
5651         return ret;
5652 }
5653 EXPORT_SYMBOL_GPL(ring_buffer_read_page);
5654
5655 /*
5656  * We only allocate new buffers, never free them if the CPU goes down.
5657  * If we were to free the buffer, then the user would lose any trace that was in
5658  * the buffer.
5659  */
5660 int trace_rb_cpu_prepare(unsigned int cpu, struct hlist_node *node)
5661 {
5662         struct trace_buffer *buffer;
5663         long nr_pages_same;
5664         int cpu_i;
5665         unsigned long nr_pages;
5666
5667         buffer = container_of(node, struct trace_buffer, node);
5668         if (cpumask_test_cpu(cpu, buffer->cpumask))
5669                 return 0;
5670
5671         nr_pages = 0;
5672         nr_pages_same = 1;
5673         /* check if all cpu sizes are same */
5674         for_each_buffer_cpu(buffer, cpu_i) {
5675                 /* fill in the size from first enabled cpu */
5676                 if (nr_pages == 0)
5677                         nr_pages = buffer->buffers[cpu_i]->nr_pages;
5678                 if (nr_pages != buffer->buffers[cpu_i]->nr_pages) {
5679                         nr_pages_same = 0;
5680                         break;
5681                 }
5682         }
5683         /* allocate minimum pages, user can later expand it */
5684         if (!nr_pages_same)
5685                 nr_pages = 2;
5686         buffer->buffers[cpu] =
5687                 rb_allocate_cpu_buffer(buffer, nr_pages, cpu);
5688         if (!buffer->buffers[cpu]) {
5689                 WARN(1, "failed to allocate ring buffer on CPU %u\n",
5690                      cpu);
5691                 return -ENOMEM;
5692         }
5693         smp_wmb();
5694         cpumask_set_cpu(cpu, buffer->cpumask);
5695         return 0;
5696 }
5697
5698 #ifdef CONFIG_RING_BUFFER_STARTUP_TEST
5699 /*
5700  * This is a basic integrity check of the ring buffer.
5701  * Late in the boot cycle this test will run when configured in.
5702  * It will kick off a thread per CPU that will go into a loop
5703  * writing to the per cpu ring buffer various sizes of data.
5704  * Some of the data will be large items, some small.
5705  *
5706  * Another thread is created that goes into a spin, sending out
5707  * IPIs to the other CPUs to also write into the ring buffer.
5708  * this is to test the nesting ability of the buffer.
5709  *
5710  * Basic stats are recorded and reported. If something in the
5711  * ring buffer should happen that's not expected, a big warning
5712  * is displayed and all ring buffers are disabled.
5713  */
5714 static struct task_struct *rb_threads[NR_CPUS] __initdata;
5715
5716 struct rb_test_data {
5717         struct trace_buffer *buffer;
5718         unsigned long           events;
5719         unsigned long           bytes_written;
5720         unsigned long           bytes_alloc;
5721         unsigned long           bytes_dropped;
5722         unsigned long           events_nested;
5723         unsigned long           bytes_written_nested;
5724         unsigned long           bytes_alloc_nested;
5725         unsigned long           bytes_dropped_nested;
5726         int                     min_size_nested;
5727         int                     max_size_nested;
5728         int                     max_size;
5729         int                     min_size;
5730         int                     cpu;
5731         int                     cnt;
5732 };
5733
5734 static struct rb_test_data rb_data[NR_CPUS] __initdata;
5735
5736 /* 1 meg per cpu */
5737 #define RB_TEST_BUFFER_SIZE     1048576
5738
5739 static char rb_string[] __initdata =
5740         "abcdefghijklmnopqrstuvwxyz1234567890!@#$%^&*()?+\\"
5741         "?+|:';\",.<>/?abcdefghijklmnopqrstuvwxyz1234567890"
5742         "!@#$%^&*()?+\\?+|:';\",.<>/?abcdefghijklmnopqrstuv";
5743
5744 static bool rb_test_started __initdata;
5745
5746 struct rb_item {
5747         int size;
5748         char str[];
5749 };
5750
5751 static __init int rb_write_something(struct rb_test_data *data, bool nested)
5752 {
5753         struct ring_buffer_event *event;
5754         struct rb_item *item;
5755         bool started;
5756         int event_len;
5757         int size;
5758         int len;
5759         int cnt;
5760
5761         /* Have nested writes different that what is written */
5762         cnt = data->cnt + (nested ? 27 : 0);
5763
5764         /* Multiply cnt by ~e, to make some unique increment */
5765         size = (cnt * 68 / 25) % (sizeof(rb_string) - 1);
5766
5767         len = size + sizeof(struct rb_item);
5768
5769         started = rb_test_started;
5770         /* read rb_test_started before checking buffer enabled */
5771         smp_rmb();
5772
5773         event = ring_buffer_lock_reserve(data->buffer, len);
5774         if (!event) {
5775                 /* Ignore dropped events before test starts. */
5776                 if (started) {
5777                         if (nested)
5778                                 data->bytes_dropped += len;
5779                         else
5780                                 data->bytes_dropped_nested += len;
5781                 }
5782                 return len;
5783         }
5784
5785         event_len = ring_buffer_event_length(event);
5786
5787         if (RB_WARN_ON(data->buffer, event_len < len))
5788                 goto out;
5789
5790         item = ring_buffer_event_data(event);
5791         item->size = size;
5792         memcpy(item->str, rb_string, size);
5793
5794         if (nested) {
5795                 data->bytes_alloc_nested += event_len;
5796                 data->bytes_written_nested += len;
5797                 data->events_nested++;
5798                 if (!data->min_size_nested || len < data->min_size_nested)
5799                         data->min_size_nested = len;
5800                 if (len > data->max_size_nested)
5801                         data->max_size_nested = len;
5802         } else {
5803                 data->bytes_alloc += event_len;
5804                 data->bytes_written += len;
5805                 data->events++;
5806                 if (!data->min_size || len < data->min_size)
5807                         data->max_size = len;
5808                 if (len > data->max_size)
5809                         data->max_size = len;
5810         }
5811
5812  out:
5813         ring_buffer_unlock_commit(data->buffer, event);
5814
5815         return 0;
5816 }
5817
5818 static __init int rb_test(void *arg)
5819 {
5820         struct rb_test_data *data = arg;
5821
5822         while (!kthread_should_stop()) {
5823                 rb_write_something(data, false);
5824                 data->cnt++;
5825
5826                 set_current_state(TASK_INTERRUPTIBLE);
5827                 /* Now sleep between a min of 100-300us and a max of 1ms */
5828                 usleep_range(((data->cnt % 3) + 1) * 100, 1000);
5829         }
5830
5831         return 0;
5832 }
5833
5834 static __init void rb_ipi(void *ignore)
5835 {
5836         struct rb_test_data *data;
5837         int cpu = smp_processor_id();
5838
5839         data = &rb_data[cpu];
5840         rb_write_something(data, true);
5841 }
5842
5843 static __init int rb_hammer_test(void *arg)
5844 {
5845         while (!kthread_should_stop()) {
5846
5847                 /* Send an IPI to all cpus to write data! */
5848                 smp_call_function(rb_ipi, NULL, 1);
5849                 /* No sleep, but for non preempt, let others run */
5850                 schedule();
5851         }
5852
5853         return 0;
5854 }
5855
5856 static __init int test_ringbuffer(void)
5857 {
5858         struct task_struct *rb_hammer;
5859         struct trace_buffer *buffer;
5860         int cpu;
5861         int ret = 0;
5862
5863         if (security_locked_down(LOCKDOWN_TRACEFS)) {
5864                 pr_warn("Lockdown is enabled, skipping ring buffer tests\n");
5865                 return 0;
5866         }
5867
5868         pr_info("Running ring buffer tests...\n");
5869
5870         buffer = ring_buffer_alloc(RB_TEST_BUFFER_SIZE, RB_FL_OVERWRITE);
5871         if (WARN_ON(!buffer))
5872                 return 0;
5873
5874         /* Disable buffer so that threads can't write to it yet */
5875         ring_buffer_record_off(buffer);
5876
5877         for_each_online_cpu(cpu) {
5878                 rb_data[cpu].buffer = buffer;
5879                 rb_data[cpu].cpu = cpu;
5880                 rb_data[cpu].cnt = cpu;
5881                 rb_threads[cpu] = kthread_create(rb_test, &rb_data[cpu],
5882                                                  "rbtester/%d", cpu);
5883                 if (WARN_ON(IS_ERR(rb_threads[cpu]))) {
5884                         pr_cont("FAILED\n");
5885                         ret = PTR_ERR(rb_threads[cpu]);
5886                         goto out_free;
5887                 }
5888
5889                 kthread_bind(rb_threads[cpu], cpu);
5890                 wake_up_process(rb_threads[cpu]);
5891         }
5892
5893         /* Now create the rb hammer! */
5894         rb_hammer = kthread_run(rb_hammer_test, NULL, "rbhammer");
5895         if (WARN_ON(IS_ERR(rb_hammer))) {
5896                 pr_cont("FAILED\n");
5897                 ret = PTR_ERR(rb_hammer);
5898                 goto out_free;
5899         }
5900
5901         ring_buffer_record_on(buffer);
5902         /*
5903          * Show buffer is enabled before setting rb_test_started.
5904          * Yes there's a small race window where events could be
5905          * dropped and the thread wont catch it. But when a ring
5906          * buffer gets enabled, there will always be some kind of
5907          * delay before other CPUs see it. Thus, we don't care about
5908          * those dropped events. We care about events dropped after
5909          * the threads see that the buffer is active.
5910          */
5911         smp_wmb();
5912         rb_test_started = true;
5913
5914         set_current_state(TASK_INTERRUPTIBLE);
5915         /* Just run for 10 seconds */;
5916         schedule_timeout(10 * HZ);
5917
5918         kthread_stop(rb_hammer);
5919
5920  out_free:
5921         for_each_online_cpu(cpu) {
5922                 if (!rb_threads[cpu])
5923                         break;
5924                 kthread_stop(rb_threads[cpu]);
5925         }
5926         if (ret) {
5927                 ring_buffer_free(buffer);
5928                 return ret;
5929         }
5930
5931         /* Report! */
5932         pr_info("finished\n");
5933         for_each_online_cpu(cpu) {
5934                 struct ring_buffer_event *event;
5935                 struct rb_test_data *data = &rb_data[cpu];
5936                 struct rb_item *item;
5937                 unsigned long total_events;
5938                 unsigned long total_dropped;
5939                 unsigned long total_written;
5940                 unsigned long total_alloc;
5941                 unsigned long total_read = 0;
5942                 unsigned long total_size = 0;
5943                 unsigned long total_len = 0;
5944                 unsigned long total_lost = 0;
5945                 unsigned long lost;
5946                 int big_event_size;
5947                 int small_event_size;
5948
5949                 ret = -1;
5950
5951                 total_events = data->events + data->events_nested;
5952                 total_written = data->bytes_written + data->bytes_written_nested;
5953                 total_alloc = data->bytes_alloc + data->bytes_alloc_nested;
5954                 total_dropped = data->bytes_dropped + data->bytes_dropped_nested;
5955
5956                 big_event_size = data->max_size + data->max_size_nested;
5957                 small_event_size = data->min_size + data->min_size_nested;
5958
5959                 pr_info("CPU %d:\n", cpu);
5960                 pr_info("              events:    %ld\n", total_events);
5961                 pr_info("       dropped bytes:    %ld\n", total_dropped);
5962                 pr_info("       alloced bytes:    %ld\n", total_alloc);
5963                 pr_info("       written bytes:    %ld\n", total_written);
5964                 pr_info("       biggest event:    %d\n", big_event_size);
5965                 pr_info("      smallest event:    %d\n", small_event_size);
5966
5967                 if (RB_WARN_ON(buffer, total_dropped))
5968                         break;
5969
5970                 ret = 0;
5971
5972                 while ((event = ring_buffer_consume(buffer, cpu, NULL, &lost))) {
5973                         total_lost += lost;
5974                         item = ring_buffer_event_data(event);
5975                         total_len += ring_buffer_event_length(event);
5976                         total_size += item->size + sizeof(struct rb_item);
5977                         if (memcmp(&item->str[0], rb_string, item->size) != 0) {
5978                                 pr_info("FAILED!\n");
5979                                 pr_info("buffer had: %.*s\n", item->size, item->str);
5980                                 pr_info("expected:   %.*s\n", item->size, rb_string);
5981                                 RB_WARN_ON(buffer, 1);
5982                                 ret = -1;
5983                                 break;
5984                         }
5985                         total_read++;
5986                 }
5987                 if (ret)
5988                         break;
5989
5990                 ret = -1;
5991
5992                 pr_info("         read events:   %ld\n", total_read);
5993                 pr_info("         lost events:   %ld\n", total_lost);
5994                 pr_info("        total events:   %ld\n", total_lost + total_read);
5995                 pr_info("  recorded len bytes:   %ld\n", total_len);
5996                 pr_info(" recorded size bytes:   %ld\n", total_size);
5997                 if (total_lost)
5998                         pr_info(" With dropped events, record len and size may not match\n"
5999                                 " alloced and written from above\n");
6000                 if (!total_lost) {
6001                         if (RB_WARN_ON(buffer, total_len != total_alloc ||
6002                                        total_size != total_written))
6003                                 break;
6004                 }
6005                 if (RB_WARN_ON(buffer, total_lost + total_read != total_events))
6006                         break;
6007
6008                 ret = 0;
6009         }
6010         if (!ret)
6011                 pr_info("Ring buffer PASSED!\n");
6012
6013         ring_buffer_free(buffer);
6014         return 0;
6015 }
6016
6017 late_initcall(test_ringbuffer);
6018 #endif /* CONFIG_RING_BUFFER_STARTUP_TEST */