Merge tag 'core-build-2020-10-12' of git://git.kernel.org/pub/scm/linux/kernel/git...
[linux-2.6-microblaze.git] / fs / fs-writeback.c
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * fs/fs-writeback.c
4  *
5  * Copyright (C) 2002, Linus Torvalds.
6  *
7  * Contains all the functions related to writing back and waiting
8  * upon dirty inodes against superblocks, and writing back dirty
9  * pages against inodes.  ie: data writeback.  Writeout of the
10  * inode itself is not handled here.
11  *
12  * 10Apr2002    Andrew Morton
13  *              Split out of fs/inode.c
14  *              Additions for address_space-based writeback
15  */
16
17 #include <linux/kernel.h>
18 #include <linux/export.h>
19 #include <linux/spinlock.h>
20 #include <linux/slab.h>
21 #include <linux/sched.h>
22 #include <linux/fs.h>
23 #include <linux/mm.h>
24 #include <linux/pagemap.h>
25 #include <linux/kthread.h>
26 #include <linux/writeback.h>
27 #include <linux/blkdev.h>
28 #include <linux/backing-dev.h>
29 #include <linux/tracepoint.h>
30 #include <linux/device.h>
31 #include <linux/memcontrol.h>
32 #include "internal.h"
33
34 /*
35  * 4MB minimal write chunk size
36  */
37 #define MIN_WRITEBACK_PAGES     (4096UL >> (PAGE_SHIFT - 10))
38
39 /*
40  * Passed into wb_writeback(), essentially a subset of writeback_control
41  */
42 struct wb_writeback_work {
43         long nr_pages;
44         struct super_block *sb;
45         enum writeback_sync_modes sync_mode;
46         unsigned int tagged_writepages:1;
47         unsigned int for_kupdate:1;
48         unsigned int range_cyclic:1;
49         unsigned int for_background:1;
50         unsigned int for_sync:1;        /* sync(2) WB_SYNC_ALL writeback */
51         unsigned int auto_free:1;       /* free on completion */
52         enum wb_reason reason;          /* why was writeback initiated? */
53
54         struct list_head list;          /* pending work list */
55         struct wb_completion *done;     /* set if the caller waits */
56 };
57
58 /*
59  * If an inode is constantly having its pages dirtied, but then the
60  * updates stop dirtytime_expire_interval seconds in the past, it's
61  * possible for the worst case time between when an inode has its
62  * timestamps updated and when they finally get written out to be two
63  * dirtytime_expire_intervals.  We set the default to 12 hours (in
64  * seconds), which means most of the time inodes will have their
65  * timestamps written to disk after 12 hours, but in the worst case a
66  * few inodes might not their timestamps updated for 24 hours.
67  */
68 unsigned int dirtytime_expire_interval = 12 * 60 * 60;
69
70 static inline struct inode *wb_inode(struct list_head *head)
71 {
72         return list_entry(head, struct inode, i_io_list);
73 }
74
75 /*
76  * Include the creation of the trace points after defining the
77  * wb_writeback_work structure and inline functions so that the definition
78  * remains local to this file.
79  */
80 #define CREATE_TRACE_POINTS
81 #include <trace/events/writeback.h>
82
83 EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
84
85 static bool wb_io_lists_populated(struct bdi_writeback *wb)
86 {
87         if (wb_has_dirty_io(wb)) {
88                 return false;
89         } else {
90                 set_bit(WB_has_dirty_io, &wb->state);
91                 WARN_ON_ONCE(!wb->avg_write_bandwidth);
92                 atomic_long_add(wb->avg_write_bandwidth,
93                                 &wb->bdi->tot_write_bandwidth);
94                 return true;
95         }
96 }
97
98 static void wb_io_lists_depopulated(struct bdi_writeback *wb)
99 {
100         if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
101             list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
102                 clear_bit(WB_has_dirty_io, &wb->state);
103                 WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
104                                         &wb->bdi->tot_write_bandwidth) < 0);
105         }
106 }
107
108 /**
109  * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
110  * @inode: inode to be moved
111  * @wb: target bdi_writeback
112  * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
113  *
114  * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
115  * Returns %true if @inode is the first occupant of the !dirty_time IO
116  * lists; otherwise, %false.
117  */
118 static bool inode_io_list_move_locked(struct inode *inode,
119                                       struct bdi_writeback *wb,
120                                       struct list_head *head)
121 {
122         assert_spin_locked(&wb->list_lock);
123
124         list_move(&inode->i_io_list, head);
125
126         /* dirty_time doesn't count as dirty_io until expiration */
127         if (head != &wb->b_dirty_time)
128                 return wb_io_lists_populated(wb);
129
130         wb_io_lists_depopulated(wb);
131         return false;
132 }
133
134 /**
135  * inode_io_list_del_locked - remove an inode from its bdi_writeback IO list
136  * @inode: inode to be removed
137  * @wb: bdi_writeback @inode is being removed from
138  *
139  * Remove @inode which may be on one of @wb->b_{dirty|io|more_io} lists and
140  * clear %WB_has_dirty_io if all are empty afterwards.
141  */
142 static void inode_io_list_del_locked(struct inode *inode,
143                                      struct bdi_writeback *wb)
144 {
145         assert_spin_locked(&wb->list_lock);
146         assert_spin_locked(&inode->i_lock);
147
148         inode->i_state &= ~I_SYNC_QUEUED;
149         list_del_init(&inode->i_io_list);
150         wb_io_lists_depopulated(wb);
151 }
152
153 static void wb_wakeup(struct bdi_writeback *wb)
154 {
155         spin_lock_bh(&wb->work_lock);
156         if (test_bit(WB_registered, &wb->state))
157                 mod_delayed_work(bdi_wq, &wb->dwork, 0);
158         spin_unlock_bh(&wb->work_lock);
159 }
160
161 static void finish_writeback_work(struct bdi_writeback *wb,
162                                   struct wb_writeback_work *work)
163 {
164         struct wb_completion *done = work->done;
165
166         if (work->auto_free)
167                 kfree(work);
168         if (done) {
169                 wait_queue_head_t *waitq = done->waitq;
170
171                 /* @done can't be accessed after the following dec */
172                 if (atomic_dec_and_test(&done->cnt))
173                         wake_up_all(waitq);
174         }
175 }
176
177 static void wb_queue_work(struct bdi_writeback *wb,
178                           struct wb_writeback_work *work)
179 {
180         trace_writeback_queue(wb, work);
181
182         if (work->done)
183                 atomic_inc(&work->done->cnt);
184
185         spin_lock_bh(&wb->work_lock);
186
187         if (test_bit(WB_registered, &wb->state)) {
188                 list_add_tail(&work->list, &wb->work_list);
189                 mod_delayed_work(bdi_wq, &wb->dwork, 0);
190         } else
191                 finish_writeback_work(wb, work);
192
193         spin_unlock_bh(&wb->work_lock);
194 }
195
196 /**
197  * wb_wait_for_completion - wait for completion of bdi_writeback_works
198  * @done: target wb_completion
199  *
200  * Wait for one or more work items issued to @bdi with their ->done field
201  * set to @done, which should have been initialized with
202  * DEFINE_WB_COMPLETION().  This function returns after all such work items
203  * are completed.  Work items which are waited upon aren't freed
204  * automatically on completion.
205  */
206 void wb_wait_for_completion(struct wb_completion *done)
207 {
208         atomic_dec(&done->cnt);         /* put down the initial count */
209         wait_event(*done->waitq, !atomic_read(&done->cnt));
210 }
211
212 #ifdef CONFIG_CGROUP_WRITEBACK
213
214 /*
215  * Parameters for foreign inode detection, see wbc_detach_inode() to see
216  * how they're used.
217  *
218  * These paramters are inherently heuristical as the detection target
219  * itself is fuzzy.  All we want to do is detaching an inode from the
220  * current owner if it's being written to by some other cgroups too much.
221  *
222  * The current cgroup writeback is built on the assumption that multiple
223  * cgroups writing to the same inode concurrently is very rare and a mode
224  * of operation which isn't well supported.  As such, the goal is not
225  * taking too long when a different cgroup takes over an inode while
226  * avoiding too aggressive flip-flops from occasional foreign writes.
227  *
228  * We record, very roughly, 2s worth of IO time history and if more than
229  * half of that is foreign, trigger the switch.  The recording is quantized
230  * to 16 slots.  To avoid tiny writes from swinging the decision too much,
231  * writes smaller than 1/8 of avg size are ignored.
232  */
233 #define WB_FRN_TIME_SHIFT       13      /* 1s = 2^13, upto 8 secs w/ 16bit */
234 #define WB_FRN_TIME_AVG_SHIFT   3       /* avg = avg * 7/8 + new * 1/8 */
235 #define WB_FRN_TIME_CUT_DIV     8       /* ignore rounds < avg / 8 */
236 #define WB_FRN_TIME_PERIOD      (2 * (1 << WB_FRN_TIME_SHIFT))  /* 2s */
237
238 #define WB_FRN_HIST_SLOTS       16      /* inode->i_wb_frn_history is 16bit */
239 #define WB_FRN_HIST_UNIT        (WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
240                                         /* each slot's duration is 2s / 16 */
241 #define WB_FRN_HIST_THR_SLOTS   (WB_FRN_HIST_SLOTS / 2)
242                                         /* if foreign slots >= 8, switch */
243 #define WB_FRN_HIST_MAX_SLOTS   (WB_FRN_HIST_THR_SLOTS / 2 + 1)
244                                         /* one round can affect upto 5 slots */
245 #define WB_FRN_MAX_IN_FLIGHT    1024    /* don't queue too many concurrently */
246
247 static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
248 static struct workqueue_struct *isw_wq;
249
250 void __inode_attach_wb(struct inode *inode, struct page *page)
251 {
252         struct backing_dev_info *bdi = inode_to_bdi(inode);
253         struct bdi_writeback *wb = NULL;
254
255         if (inode_cgwb_enabled(inode)) {
256                 struct cgroup_subsys_state *memcg_css;
257
258                 if (page) {
259                         memcg_css = mem_cgroup_css_from_page(page);
260                         wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
261                 } else {
262                         /* must pin memcg_css, see wb_get_create() */
263                         memcg_css = task_get_css(current, memory_cgrp_id);
264                         wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
265                         css_put(memcg_css);
266                 }
267         }
268
269         if (!wb)
270                 wb = &bdi->wb;
271
272         /*
273          * There may be multiple instances of this function racing to
274          * update the same inode.  Use cmpxchg() to tell the winner.
275          */
276         if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
277                 wb_put(wb);
278 }
279 EXPORT_SYMBOL_GPL(__inode_attach_wb);
280
281 /**
282  * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
283  * @inode: inode of interest with i_lock held
284  *
285  * Returns @inode's wb with its list_lock held.  @inode->i_lock must be
286  * held on entry and is released on return.  The returned wb is guaranteed
287  * to stay @inode's associated wb until its list_lock is released.
288  */
289 static struct bdi_writeback *
290 locked_inode_to_wb_and_lock_list(struct inode *inode)
291         __releases(&inode->i_lock)
292         __acquires(&wb->list_lock)
293 {
294         while (true) {
295                 struct bdi_writeback *wb = inode_to_wb(inode);
296
297                 /*
298                  * inode_to_wb() association is protected by both
299                  * @inode->i_lock and @wb->list_lock but list_lock nests
300                  * outside i_lock.  Drop i_lock and verify that the
301                  * association hasn't changed after acquiring list_lock.
302                  */
303                 wb_get(wb);
304                 spin_unlock(&inode->i_lock);
305                 spin_lock(&wb->list_lock);
306
307                 /* i_wb may have changed inbetween, can't use inode_to_wb() */
308                 if (likely(wb == inode->i_wb)) {
309                         wb_put(wb);     /* @inode already has ref */
310                         return wb;
311                 }
312
313                 spin_unlock(&wb->list_lock);
314                 wb_put(wb);
315                 cpu_relax();
316                 spin_lock(&inode->i_lock);
317         }
318 }
319
320 /**
321  * inode_to_wb_and_lock_list - determine an inode's wb and lock it
322  * @inode: inode of interest
323  *
324  * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
325  * on entry.
326  */
327 static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
328         __acquires(&wb->list_lock)
329 {
330         spin_lock(&inode->i_lock);
331         return locked_inode_to_wb_and_lock_list(inode);
332 }
333
334 struct inode_switch_wbs_context {
335         struct inode            *inode;
336         struct bdi_writeback    *new_wb;
337
338         struct rcu_head         rcu_head;
339         struct work_struct      work;
340 };
341
342 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
343 {
344         down_write(&bdi->wb_switch_rwsem);
345 }
346
347 static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
348 {
349         up_write(&bdi->wb_switch_rwsem);
350 }
351
352 static void inode_switch_wbs_work_fn(struct work_struct *work)
353 {
354         struct inode_switch_wbs_context *isw =
355                 container_of(work, struct inode_switch_wbs_context, work);
356         struct inode *inode = isw->inode;
357         struct backing_dev_info *bdi = inode_to_bdi(inode);
358         struct address_space *mapping = inode->i_mapping;
359         struct bdi_writeback *old_wb = inode->i_wb;
360         struct bdi_writeback *new_wb = isw->new_wb;
361         XA_STATE(xas, &mapping->i_pages, 0);
362         struct page *page;
363         bool switched = false;
364
365         /*
366          * If @inode switches cgwb membership while sync_inodes_sb() is
367          * being issued, sync_inodes_sb() might miss it.  Synchronize.
368          */
369         down_read(&bdi->wb_switch_rwsem);
370
371         /*
372          * By the time control reaches here, RCU grace period has passed
373          * since I_WB_SWITCH assertion and all wb stat update transactions
374          * between unlocked_inode_to_wb_begin/end() are guaranteed to be
375          * synchronizing against the i_pages lock.
376          *
377          * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
378          * gives us exclusion against all wb related operations on @inode
379          * including IO list manipulations and stat updates.
380          */
381         if (old_wb < new_wb) {
382                 spin_lock(&old_wb->list_lock);
383                 spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
384         } else {
385                 spin_lock(&new_wb->list_lock);
386                 spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
387         }
388         spin_lock(&inode->i_lock);
389         xa_lock_irq(&mapping->i_pages);
390
391         /*
392          * Once I_FREEING is visible under i_lock, the eviction path owns
393          * the inode and we shouldn't modify ->i_io_list.
394          */
395         if (unlikely(inode->i_state & I_FREEING))
396                 goto skip_switch;
397
398         trace_inode_switch_wbs(inode, old_wb, new_wb);
399
400         /*
401          * Count and transfer stats.  Note that PAGECACHE_TAG_DIRTY points
402          * to possibly dirty pages while PAGECACHE_TAG_WRITEBACK points to
403          * pages actually under writeback.
404          */
405         xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
406                 if (PageDirty(page)) {
407                         dec_wb_stat(old_wb, WB_RECLAIMABLE);
408                         inc_wb_stat(new_wb, WB_RECLAIMABLE);
409                 }
410         }
411
412         xas_set(&xas, 0);
413         xas_for_each_marked(&xas, page, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
414                 WARN_ON_ONCE(!PageWriteback(page));
415                 dec_wb_stat(old_wb, WB_WRITEBACK);
416                 inc_wb_stat(new_wb, WB_WRITEBACK);
417         }
418
419         wb_get(new_wb);
420
421         /*
422          * Transfer to @new_wb's IO list if necessary.  The specific list
423          * @inode was on is ignored and the inode is put on ->b_dirty which
424          * is always correct including from ->b_dirty_time.  The transfer
425          * preserves @inode->dirtied_when ordering.
426          */
427         if (!list_empty(&inode->i_io_list)) {
428                 struct inode *pos;
429
430                 inode_io_list_del_locked(inode, old_wb);
431                 inode->i_wb = new_wb;
432                 list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
433                         if (time_after_eq(inode->dirtied_when,
434                                           pos->dirtied_when))
435                                 break;
436                 inode_io_list_move_locked(inode, new_wb, pos->i_io_list.prev);
437         } else {
438                 inode->i_wb = new_wb;
439         }
440
441         /* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
442         inode->i_wb_frn_winner = 0;
443         inode->i_wb_frn_avg_time = 0;
444         inode->i_wb_frn_history = 0;
445         switched = true;
446 skip_switch:
447         /*
448          * Paired with load_acquire in unlocked_inode_to_wb_begin() and
449          * ensures that the new wb is visible if they see !I_WB_SWITCH.
450          */
451         smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
452
453         xa_unlock_irq(&mapping->i_pages);
454         spin_unlock(&inode->i_lock);
455         spin_unlock(&new_wb->list_lock);
456         spin_unlock(&old_wb->list_lock);
457
458         up_read(&bdi->wb_switch_rwsem);
459
460         if (switched) {
461                 wb_wakeup(new_wb);
462                 wb_put(old_wb);
463         }
464         wb_put(new_wb);
465
466         iput(inode);
467         kfree(isw);
468
469         atomic_dec(&isw_nr_in_flight);
470 }
471
472 static void inode_switch_wbs_rcu_fn(struct rcu_head *rcu_head)
473 {
474         struct inode_switch_wbs_context *isw = container_of(rcu_head,
475                                 struct inode_switch_wbs_context, rcu_head);
476
477         /* needs to grab bh-unsafe locks, bounce to work item */
478         INIT_WORK(&isw->work, inode_switch_wbs_work_fn);
479         queue_work(isw_wq, &isw->work);
480 }
481
482 /**
483  * inode_switch_wbs - change the wb association of an inode
484  * @inode: target inode
485  * @new_wb_id: ID of the new wb
486  *
487  * Switch @inode's wb association to the wb identified by @new_wb_id.  The
488  * switching is performed asynchronously and may fail silently.
489  */
490 static void inode_switch_wbs(struct inode *inode, int new_wb_id)
491 {
492         struct backing_dev_info *bdi = inode_to_bdi(inode);
493         struct cgroup_subsys_state *memcg_css;
494         struct inode_switch_wbs_context *isw;
495
496         /* noop if seems to be already in progress */
497         if (inode->i_state & I_WB_SWITCH)
498                 return;
499
500         /* avoid queueing a new switch if too many are already in flight */
501         if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
502                 return;
503
504         isw = kzalloc(sizeof(*isw), GFP_ATOMIC);
505         if (!isw)
506                 return;
507
508         /* find and pin the new wb */
509         rcu_read_lock();
510         memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
511         if (memcg_css)
512                 isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
513         rcu_read_unlock();
514         if (!isw->new_wb)
515                 goto out_free;
516
517         /* while holding I_WB_SWITCH, no one else can update the association */
518         spin_lock(&inode->i_lock);
519         if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
520             inode->i_state & (I_WB_SWITCH | I_FREEING) ||
521             inode_to_wb(inode) == isw->new_wb) {
522                 spin_unlock(&inode->i_lock);
523                 goto out_free;
524         }
525         inode->i_state |= I_WB_SWITCH;
526         __iget(inode);
527         spin_unlock(&inode->i_lock);
528
529         isw->inode = inode;
530
531         /*
532          * In addition to synchronizing among switchers, I_WB_SWITCH tells
533          * the RCU protected stat update paths to grab the i_page
534          * lock so that stat transfer can synchronize against them.
535          * Let's continue after I_WB_SWITCH is guaranteed to be visible.
536          */
537         call_rcu(&isw->rcu_head, inode_switch_wbs_rcu_fn);
538
539         atomic_inc(&isw_nr_in_flight);
540         return;
541
542 out_free:
543         if (isw->new_wb)
544                 wb_put(isw->new_wb);
545         kfree(isw);
546 }
547
548 /**
549  * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
550  * @wbc: writeback_control of interest
551  * @inode: target inode
552  *
553  * @inode is locked and about to be written back under the control of @wbc.
554  * Record @inode's writeback context into @wbc and unlock the i_lock.  On
555  * writeback completion, wbc_detach_inode() should be called.  This is used
556  * to track the cgroup writeback context.
557  */
558 void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
559                                  struct inode *inode)
560 {
561         if (!inode_cgwb_enabled(inode)) {
562                 spin_unlock(&inode->i_lock);
563                 return;
564         }
565
566         wbc->wb = inode_to_wb(inode);
567         wbc->inode = inode;
568
569         wbc->wb_id = wbc->wb->memcg_css->id;
570         wbc->wb_lcand_id = inode->i_wb_frn_winner;
571         wbc->wb_tcand_id = 0;
572         wbc->wb_bytes = 0;
573         wbc->wb_lcand_bytes = 0;
574         wbc->wb_tcand_bytes = 0;
575
576         wb_get(wbc->wb);
577         spin_unlock(&inode->i_lock);
578
579         /*
580          * A dying wb indicates that either the blkcg associated with the
581          * memcg changed or the associated memcg is dying.  In the first
582          * case, a replacement wb should already be available and we should
583          * refresh the wb immediately.  In the second case, trying to
584          * refresh will keep failing.
585          */
586         if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
587                 inode_switch_wbs(inode, wbc->wb_id);
588 }
589 EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
590
591 /**
592  * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
593  * @wbc: writeback_control of the just finished writeback
594  *
595  * To be called after a writeback attempt of an inode finishes and undoes
596  * wbc_attach_and_unlock_inode().  Can be called under any context.
597  *
598  * As concurrent write sharing of an inode is expected to be very rare and
599  * memcg only tracks page ownership on first-use basis severely confining
600  * the usefulness of such sharing, cgroup writeback tracks ownership
601  * per-inode.  While the support for concurrent write sharing of an inode
602  * is deemed unnecessary, an inode being written to by different cgroups at
603  * different points in time is a lot more common, and, more importantly,
604  * charging only by first-use can too readily lead to grossly incorrect
605  * behaviors (single foreign page can lead to gigabytes of writeback to be
606  * incorrectly attributed).
607  *
608  * To resolve this issue, cgroup writeback detects the majority dirtier of
609  * an inode and transfers the ownership to it.  To avoid unnnecessary
610  * oscillation, the detection mechanism keeps track of history and gives
611  * out the switch verdict only if the foreign usage pattern is stable over
612  * a certain amount of time and/or writeback attempts.
613  *
614  * On each writeback attempt, @wbc tries to detect the majority writer
615  * using Boyer-Moore majority vote algorithm.  In addition to the byte
616  * count from the majority voting, it also counts the bytes written for the
617  * current wb and the last round's winner wb (max of last round's current
618  * wb, the winner from two rounds ago, and the last round's majority
619  * candidate).  Keeping track of the historical winner helps the algorithm
620  * to semi-reliably detect the most active writer even when it's not the
621  * absolute majority.
622  *
623  * Once the winner of the round is determined, whether the winner is
624  * foreign or not and how much IO time the round consumed is recorded in
625  * inode->i_wb_frn_history.  If the amount of recorded foreign IO time is
626  * over a certain threshold, the switch verdict is given.
627  */
628 void wbc_detach_inode(struct writeback_control *wbc)
629 {
630         struct bdi_writeback *wb = wbc->wb;
631         struct inode *inode = wbc->inode;
632         unsigned long avg_time, max_bytes, max_time;
633         u16 history;
634         int max_id;
635
636         if (!wb)
637                 return;
638
639         history = inode->i_wb_frn_history;
640         avg_time = inode->i_wb_frn_avg_time;
641
642         /* pick the winner of this round */
643         if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
644             wbc->wb_bytes >= wbc->wb_tcand_bytes) {
645                 max_id = wbc->wb_id;
646                 max_bytes = wbc->wb_bytes;
647         } else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
648                 max_id = wbc->wb_lcand_id;
649                 max_bytes = wbc->wb_lcand_bytes;
650         } else {
651                 max_id = wbc->wb_tcand_id;
652                 max_bytes = wbc->wb_tcand_bytes;
653         }
654
655         /*
656          * Calculate the amount of IO time the winner consumed and fold it
657          * into the running average kept per inode.  If the consumed IO
658          * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
659          * deciding whether to switch or not.  This is to prevent one-off
660          * small dirtiers from skewing the verdict.
661          */
662         max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
663                                 wb->avg_write_bandwidth);
664         if (avg_time)
665                 avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
666                             (avg_time >> WB_FRN_TIME_AVG_SHIFT);
667         else
668                 avg_time = max_time;    /* immediate catch up on first run */
669
670         if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
671                 int slots;
672
673                 /*
674                  * The switch verdict is reached if foreign wb's consume
675                  * more than a certain proportion of IO time in a
676                  * WB_FRN_TIME_PERIOD.  This is loosely tracked by 16 slot
677                  * history mask where each bit represents one sixteenth of
678                  * the period.  Determine the number of slots to shift into
679                  * history from @max_time.
680                  */
681                 slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
682                             (unsigned long)WB_FRN_HIST_MAX_SLOTS);
683                 history <<= slots;
684                 if (wbc->wb_id != max_id)
685                         history |= (1U << slots) - 1;
686
687                 if (history)
688                         trace_inode_foreign_history(inode, wbc, history);
689
690                 /*
691                  * Switch if the current wb isn't the consistent winner.
692                  * If there are multiple closely competing dirtiers, the
693                  * inode may switch across them repeatedly over time, which
694                  * is okay.  The main goal is avoiding keeping an inode on
695                  * the wrong wb for an extended period of time.
696                  */
697                 if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
698                         inode_switch_wbs(inode, max_id);
699         }
700
701         /*
702          * Multiple instances of this function may race to update the
703          * following fields but we don't mind occassional inaccuracies.
704          */
705         inode->i_wb_frn_winner = max_id;
706         inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
707         inode->i_wb_frn_history = history;
708
709         wb_put(wbc->wb);
710         wbc->wb = NULL;
711 }
712 EXPORT_SYMBOL_GPL(wbc_detach_inode);
713
714 /**
715  * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
716  * @wbc: writeback_control of the writeback in progress
717  * @page: page being written out
718  * @bytes: number of bytes being written out
719  *
720  * @bytes from @page are about to written out during the writeback
721  * controlled by @wbc.  Keep the book for foreign inode detection.  See
722  * wbc_detach_inode().
723  */
724 void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
725                               size_t bytes)
726 {
727         struct cgroup_subsys_state *css;
728         int id;
729
730         /*
731          * pageout() path doesn't attach @wbc to the inode being written
732          * out.  This is intentional as we don't want the function to block
733          * behind a slow cgroup.  Ultimately, we want pageout() to kick off
734          * regular writeback instead of writing things out itself.
735          */
736         if (!wbc->wb || wbc->no_cgroup_owner)
737                 return;
738
739         css = mem_cgroup_css_from_page(page);
740         /* dead cgroups shouldn't contribute to inode ownership arbitration */
741         if (!(css->flags & CSS_ONLINE))
742                 return;
743
744         id = css->id;
745
746         if (id == wbc->wb_id) {
747                 wbc->wb_bytes += bytes;
748                 return;
749         }
750
751         if (id == wbc->wb_lcand_id)
752                 wbc->wb_lcand_bytes += bytes;
753
754         /* Boyer-Moore majority vote algorithm */
755         if (!wbc->wb_tcand_bytes)
756                 wbc->wb_tcand_id = id;
757         if (id == wbc->wb_tcand_id)
758                 wbc->wb_tcand_bytes += bytes;
759         else
760                 wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
761 }
762 EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
763
764 /**
765  * inode_congested - test whether an inode is congested
766  * @inode: inode to test for congestion (may be NULL)
767  * @cong_bits: mask of WB_[a]sync_congested bits to test
768  *
769  * Tests whether @inode is congested.  @cong_bits is the mask of congestion
770  * bits to test and the return value is the mask of set bits.
771  *
772  * If cgroup writeback is enabled for @inode, the congestion state is
773  * determined by whether the cgwb (cgroup bdi_writeback) for the blkcg
774  * associated with @inode is congested; otherwise, the root wb's congestion
775  * state is used.
776  *
777  * @inode is allowed to be NULL as this function is often called on
778  * mapping->host which is NULL for the swapper space.
779  */
780 int inode_congested(struct inode *inode, int cong_bits)
781 {
782         /*
783          * Once set, ->i_wb never becomes NULL while the inode is alive.
784          * Start transaction iff ->i_wb is visible.
785          */
786         if (inode && inode_to_wb_is_valid(inode)) {
787                 struct bdi_writeback *wb;
788                 struct wb_lock_cookie lock_cookie = {};
789                 bool congested;
790
791                 wb = unlocked_inode_to_wb_begin(inode, &lock_cookie);
792                 congested = wb_congested(wb, cong_bits);
793                 unlocked_inode_to_wb_end(inode, &lock_cookie);
794                 return congested;
795         }
796
797         return wb_congested(&inode_to_bdi(inode)->wb, cong_bits);
798 }
799 EXPORT_SYMBOL_GPL(inode_congested);
800
801 /**
802  * wb_split_bdi_pages - split nr_pages to write according to bandwidth
803  * @wb: target bdi_writeback to split @nr_pages to
804  * @nr_pages: number of pages to write for the whole bdi
805  *
806  * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
807  * relation to the total write bandwidth of all wb's w/ dirty inodes on
808  * @wb->bdi.
809  */
810 static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
811 {
812         unsigned long this_bw = wb->avg_write_bandwidth;
813         unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
814
815         if (nr_pages == LONG_MAX)
816                 return LONG_MAX;
817
818         /*
819          * This may be called on clean wb's and proportional distribution
820          * may not make sense, just use the original @nr_pages in those
821          * cases.  In general, we wanna err on the side of writing more.
822          */
823         if (!tot_bw || this_bw >= tot_bw)
824                 return nr_pages;
825         else
826                 return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
827 }
828
829 /**
830  * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
831  * @bdi: target backing_dev_info
832  * @base_work: wb_writeback_work to issue
833  * @skip_if_busy: skip wb's which already have writeback in progress
834  *
835  * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
836  * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's
837  * distributed to the busy wbs according to each wb's proportion in the
838  * total active write bandwidth of @bdi.
839  */
840 static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
841                                   struct wb_writeback_work *base_work,
842                                   bool skip_if_busy)
843 {
844         struct bdi_writeback *last_wb = NULL;
845         struct bdi_writeback *wb = list_entry(&bdi->wb_list,
846                                               struct bdi_writeback, bdi_node);
847
848         might_sleep();
849 restart:
850         rcu_read_lock();
851         list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
852                 DEFINE_WB_COMPLETION(fallback_work_done, bdi);
853                 struct wb_writeback_work fallback_work;
854                 struct wb_writeback_work *work;
855                 long nr_pages;
856
857                 if (last_wb) {
858                         wb_put(last_wb);
859                         last_wb = NULL;
860                 }
861
862                 /* SYNC_ALL writes out I_DIRTY_TIME too */
863                 if (!wb_has_dirty_io(wb) &&
864                     (base_work->sync_mode == WB_SYNC_NONE ||
865                      list_empty(&wb->b_dirty_time)))
866                         continue;
867                 if (skip_if_busy && writeback_in_progress(wb))
868                         continue;
869
870                 nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
871
872                 work = kmalloc(sizeof(*work), GFP_ATOMIC);
873                 if (work) {
874                         *work = *base_work;
875                         work->nr_pages = nr_pages;
876                         work->auto_free = 1;
877                         wb_queue_work(wb, work);
878                         continue;
879                 }
880
881                 /* alloc failed, execute synchronously using on-stack fallback */
882                 work = &fallback_work;
883                 *work = *base_work;
884                 work->nr_pages = nr_pages;
885                 work->auto_free = 0;
886                 work->done = &fallback_work_done;
887
888                 wb_queue_work(wb, work);
889
890                 /*
891                  * Pin @wb so that it stays on @bdi->wb_list.  This allows
892                  * continuing iteration from @wb after dropping and
893                  * regrabbing rcu read lock.
894                  */
895                 wb_get(wb);
896                 last_wb = wb;
897
898                 rcu_read_unlock();
899                 wb_wait_for_completion(&fallback_work_done);
900                 goto restart;
901         }
902         rcu_read_unlock();
903
904         if (last_wb)
905                 wb_put(last_wb);
906 }
907
908 /**
909  * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
910  * @bdi_id: target bdi id
911  * @memcg_id: target memcg css id
912  * @nr: number of pages to write, 0 for best-effort dirty flushing
913  * @reason: reason why some writeback work initiated
914  * @done: target wb_completion
915  *
916  * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
917  * with the specified parameters.
918  */
919 int cgroup_writeback_by_id(u64 bdi_id, int memcg_id, unsigned long nr,
920                            enum wb_reason reason, struct wb_completion *done)
921 {
922         struct backing_dev_info *bdi;
923         struct cgroup_subsys_state *memcg_css;
924         struct bdi_writeback *wb;
925         struct wb_writeback_work *work;
926         int ret;
927
928         /* lookup bdi and memcg */
929         bdi = bdi_get_by_id(bdi_id);
930         if (!bdi)
931                 return -ENOENT;
932
933         rcu_read_lock();
934         memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
935         if (memcg_css && !css_tryget(memcg_css))
936                 memcg_css = NULL;
937         rcu_read_unlock();
938         if (!memcg_css) {
939                 ret = -ENOENT;
940                 goto out_bdi_put;
941         }
942
943         /*
944          * And find the associated wb.  If the wb isn't there already
945          * there's nothing to flush, don't create one.
946          */
947         wb = wb_get_lookup(bdi, memcg_css);
948         if (!wb) {
949                 ret = -ENOENT;
950                 goto out_css_put;
951         }
952
953         /*
954          * If @nr is zero, the caller is attempting to write out most of
955          * the currently dirty pages.  Let's take the current dirty page
956          * count and inflate it by 25% which should be large enough to
957          * flush out most dirty pages while avoiding getting livelocked by
958          * concurrent dirtiers.
959          */
960         if (!nr) {
961                 unsigned long filepages, headroom, dirty, writeback;
962
963                 mem_cgroup_wb_stats(wb, &filepages, &headroom, &dirty,
964                                       &writeback);
965                 nr = dirty * 10 / 8;
966         }
967
968         /* issue the writeback work */
969         work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
970         if (work) {
971                 work->nr_pages = nr;
972                 work->sync_mode = WB_SYNC_NONE;
973                 work->range_cyclic = 1;
974                 work->reason = reason;
975                 work->done = done;
976                 work->auto_free = 1;
977                 wb_queue_work(wb, work);
978                 ret = 0;
979         } else {
980                 ret = -ENOMEM;
981         }
982
983         wb_put(wb);
984 out_css_put:
985         css_put(memcg_css);
986 out_bdi_put:
987         bdi_put(bdi);
988         return ret;
989 }
990
991 /**
992  * cgroup_writeback_umount - flush inode wb switches for umount
993  *
994  * This function is called when a super_block is about to be destroyed and
995  * flushes in-flight inode wb switches.  An inode wb switch goes through
996  * RCU and then workqueue, so the two need to be flushed in order to ensure
997  * that all previously scheduled switches are finished.  As wb switches are
998  * rare occurrences and synchronize_rcu() can take a while, perform
999  * flushing iff wb switches are in flight.
1000  */
1001 void cgroup_writeback_umount(void)
1002 {
1003         if (atomic_read(&isw_nr_in_flight)) {
1004                 /*
1005                  * Use rcu_barrier() to wait for all pending callbacks to
1006                  * ensure that all in-flight wb switches are in the workqueue.
1007                  */
1008                 rcu_barrier();
1009                 flush_workqueue(isw_wq);
1010         }
1011 }
1012
1013 static int __init cgroup_writeback_init(void)
1014 {
1015         isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
1016         if (!isw_wq)
1017                 return -ENOMEM;
1018         return 0;
1019 }
1020 fs_initcall(cgroup_writeback_init);
1021
1022 #else   /* CONFIG_CGROUP_WRITEBACK */
1023
1024 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1025 static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1026
1027 static struct bdi_writeback *
1028 locked_inode_to_wb_and_lock_list(struct inode *inode)
1029         __releases(&inode->i_lock)
1030         __acquires(&wb->list_lock)
1031 {
1032         struct bdi_writeback *wb = inode_to_wb(inode);
1033
1034         spin_unlock(&inode->i_lock);
1035         spin_lock(&wb->list_lock);
1036         return wb;
1037 }
1038
1039 static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1040         __acquires(&wb->list_lock)
1041 {
1042         struct bdi_writeback *wb = inode_to_wb(inode);
1043
1044         spin_lock(&wb->list_lock);
1045         return wb;
1046 }
1047
1048 static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1049 {
1050         return nr_pages;
1051 }
1052
1053 static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1054                                   struct wb_writeback_work *base_work,
1055                                   bool skip_if_busy)
1056 {
1057         might_sleep();
1058
1059         if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1060                 base_work->auto_free = 0;
1061                 wb_queue_work(&bdi->wb, base_work);
1062         }
1063 }
1064
1065 #endif  /* CONFIG_CGROUP_WRITEBACK */
1066
1067 /*
1068  * Add in the number of potentially dirty inodes, because each inode
1069  * write can dirty pagecache in the underlying blockdev.
1070  */
1071 static unsigned long get_nr_dirty_pages(void)
1072 {
1073         return global_node_page_state(NR_FILE_DIRTY) +
1074                 get_nr_dirty_inodes();
1075 }
1076
1077 static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1078 {
1079         if (!wb_has_dirty_io(wb))
1080                 return;
1081
1082         /*
1083          * All callers of this function want to start writeback of all
1084          * dirty pages. Places like vmscan can call this at a very
1085          * high frequency, causing pointless allocations of tons of
1086          * work items and keeping the flusher threads busy retrieving
1087          * that work. Ensure that we only allow one of them pending and
1088          * inflight at the time.
1089          */
1090         if (test_bit(WB_start_all, &wb->state) ||
1091             test_and_set_bit(WB_start_all, &wb->state))
1092                 return;
1093
1094         wb->start_all_reason = reason;
1095         wb_wakeup(wb);
1096 }
1097
1098 /**
1099  * wb_start_background_writeback - start background writeback
1100  * @wb: bdi_writback to write from
1101  *
1102  * Description:
1103  *   This makes sure WB_SYNC_NONE background writeback happens. When
1104  *   this function returns, it is only guaranteed that for given wb
1105  *   some IO is happening if we are over background dirty threshold.
1106  *   Caller need not hold sb s_umount semaphore.
1107  */
1108 void wb_start_background_writeback(struct bdi_writeback *wb)
1109 {
1110         /*
1111          * We just wake up the flusher thread. It will perform background
1112          * writeback as soon as there is no other work to do.
1113          */
1114         trace_writeback_wake_background(wb);
1115         wb_wakeup(wb);
1116 }
1117
1118 /*
1119  * Remove the inode from the writeback list it is on.
1120  */
1121 void inode_io_list_del(struct inode *inode)
1122 {
1123         struct bdi_writeback *wb;
1124
1125         wb = inode_to_wb_and_lock_list(inode);
1126         spin_lock(&inode->i_lock);
1127         inode_io_list_del_locked(inode, wb);
1128         spin_unlock(&inode->i_lock);
1129         spin_unlock(&wb->list_lock);
1130 }
1131 EXPORT_SYMBOL(inode_io_list_del);
1132
1133 /*
1134  * mark an inode as under writeback on the sb
1135  */
1136 void sb_mark_inode_writeback(struct inode *inode)
1137 {
1138         struct super_block *sb = inode->i_sb;
1139         unsigned long flags;
1140
1141         if (list_empty(&inode->i_wb_list)) {
1142                 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1143                 if (list_empty(&inode->i_wb_list)) {
1144                         list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
1145                         trace_sb_mark_inode_writeback(inode);
1146                 }
1147                 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1148         }
1149 }
1150
1151 /*
1152  * clear an inode as under writeback on the sb
1153  */
1154 void sb_clear_inode_writeback(struct inode *inode)
1155 {
1156         struct super_block *sb = inode->i_sb;
1157         unsigned long flags;
1158
1159         if (!list_empty(&inode->i_wb_list)) {
1160                 spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1161                 if (!list_empty(&inode->i_wb_list)) {
1162                         list_del_init(&inode->i_wb_list);
1163                         trace_sb_clear_inode_writeback(inode);
1164                 }
1165                 spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1166         }
1167 }
1168
1169 /*
1170  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1171  * furthest end of its superblock's dirty-inode list.
1172  *
1173  * Before stamping the inode's ->dirtied_when, we check to see whether it is
1174  * already the most-recently-dirtied inode on the b_dirty list.  If that is
1175  * the case then the inode must have been redirtied while it was being written
1176  * out and we don't reset its dirtied_when.
1177  */
1178 static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1179 {
1180         assert_spin_locked(&inode->i_lock);
1181
1182         if (!list_empty(&wb->b_dirty)) {
1183                 struct inode *tail;
1184
1185                 tail = wb_inode(wb->b_dirty.next);
1186                 if (time_before(inode->dirtied_when, tail->dirtied_when))
1187                         inode->dirtied_when = jiffies;
1188         }
1189         inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1190         inode->i_state &= ~I_SYNC_QUEUED;
1191 }
1192
1193 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1194 {
1195         spin_lock(&inode->i_lock);
1196         redirty_tail_locked(inode, wb);
1197         spin_unlock(&inode->i_lock);
1198 }
1199
1200 /*
1201  * requeue inode for re-scanning after bdi->b_io list is exhausted.
1202  */
1203 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1204 {
1205         inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1206 }
1207
1208 static void inode_sync_complete(struct inode *inode)
1209 {
1210         inode->i_state &= ~I_SYNC;
1211         /* If inode is clean an unused, put it into LRU now... */
1212         inode_add_lru(inode);
1213         /* Waiters must see I_SYNC cleared before being woken up */
1214         smp_mb();
1215         wake_up_bit(&inode->i_state, __I_SYNC);
1216 }
1217
1218 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1219 {
1220         bool ret = time_after(inode->dirtied_when, t);
1221 #ifndef CONFIG_64BIT
1222         /*
1223          * For inodes being constantly redirtied, dirtied_when can get stuck.
1224          * It _appears_ to be in the future, but is actually in distant past.
1225          * This test is necessary to prevent such wrapped-around relative times
1226          * from permanently stopping the whole bdi writeback.
1227          */
1228         ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1229 #endif
1230         return ret;
1231 }
1232
1233 #define EXPIRE_DIRTY_ATIME 0x0001
1234
1235 /*
1236  * Move expired (dirtied before dirtied_before) dirty inodes from
1237  * @delaying_queue to @dispatch_queue.
1238  */
1239 static int move_expired_inodes(struct list_head *delaying_queue,
1240                                struct list_head *dispatch_queue,
1241                                unsigned long dirtied_before)
1242 {
1243         LIST_HEAD(tmp);
1244         struct list_head *pos, *node;
1245         struct super_block *sb = NULL;
1246         struct inode *inode;
1247         int do_sb_sort = 0;
1248         int moved = 0;
1249
1250         while (!list_empty(delaying_queue)) {
1251                 inode = wb_inode(delaying_queue->prev);
1252                 if (inode_dirtied_after(inode, dirtied_before))
1253                         break;
1254                 list_move(&inode->i_io_list, &tmp);
1255                 moved++;
1256                 spin_lock(&inode->i_lock);
1257                 inode->i_state |= I_SYNC_QUEUED;
1258                 spin_unlock(&inode->i_lock);
1259                 if (sb_is_blkdev_sb(inode->i_sb))
1260                         continue;
1261                 if (sb && sb != inode->i_sb)
1262                         do_sb_sort = 1;
1263                 sb = inode->i_sb;
1264         }
1265
1266         /* just one sb in list, splice to dispatch_queue and we're done */
1267         if (!do_sb_sort) {
1268                 list_splice(&tmp, dispatch_queue);
1269                 goto out;
1270         }
1271
1272         /* Move inodes from one superblock together */
1273         while (!list_empty(&tmp)) {
1274                 sb = wb_inode(tmp.prev)->i_sb;
1275                 list_for_each_prev_safe(pos, node, &tmp) {
1276                         inode = wb_inode(pos);
1277                         if (inode->i_sb == sb)
1278                                 list_move(&inode->i_io_list, dispatch_queue);
1279                 }
1280         }
1281 out:
1282         return moved;
1283 }
1284
1285 /*
1286  * Queue all expired dirty inodes for io, eldest first.
1287  * Before
1288  *         newly dirtied     b_dirty    b_io    b_more_io
1289  *         =============>    gf         edc     BA
1290  * After
1291  *         newly dirtied     b_dirty    b_io    b_more_io
1292  *         =============>    g          fBAedc
1293  *                                           |
1294  *                                           +--> dequeue for IO
1295  */
1296 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1297                      unsigned long dirtied_before)
1298 {
1299         int moved;
1300         unsigned long time_expire_jif = dirtied_before;
1301
1302         assert_spin_locked(&wb->list_lock);
1303         list_splice_init(&wb->b_more_io, &wb->b_io);
1304         moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
1305         if (!work->for_sync)
1306                 time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1307         moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1308                                      time_expire_jif);
1309         if (moved)
1310                 wb_io_lists_populated(wb);
1311         trace_writeback_queue_io(wb, work, dirtied_before, moved);
1312 }
1313
1314 static int write_inode(struct inode *inode, struct writeback_control *wbc)
1315 {
1316         int ret;
1317
1318         if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1319                 trace_writeback_write_inode_start(inode, wbc);
1320                 ret = inode->i_sb->s_op->write_inode(inode, wbc);
1321                 trace_writeback_write_inode(inode, wbc);
1322                 return ret;
1323         }
1324         return 0;
1325 }
1326
1327 /*
1328  * Wait for writeback on an inode to complete. Called with i_lock held.
1329  * Caller must make sure inode cannot go away when we drop i_lock.
1330  */
1331 static void __inode_wait_for_writeback(struct inode *inode)
1332         __releases(inode->i_lock)
1333         __acquires(inode->i_lock)
1334 {
1335         DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1336         wait_queue_head_t *wqh;
1337
1338         wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1339         while (inode->i_state & I_SYNC) {
1340                 spin_unlock(&inode->i_lock);
1341                 __wait_on_bit(wqh, &wq, bit_wait,
1342                               TASK_UNINTERRUPTIBLE);
1343                 spin_lock(&inode->i_lock);
1344         }
1345 }
1346
1347 /*
1348  * Wait for writeback on an inode to complete. Caller must have inode pinned.
1349  */
1350 void inode_wait_for_writeback(struct inode *inode)
1351 {
1352         spin_lock(&inode->i_lock);
1353         __inode_wait_for_writeback(inode);
1354         spin_unlock(&inode->i_lock);
1355 }
1356
1357 /*
1358  * Sleep until I_SYNC is cleared. This function must be called with i_lock
1359  * held and drops it. It is aimed for callers not holding any inode reference
1360  * so once i_lock is dropped, inode can go away.
1361  */
1362 static void inode_sleep_on_writeback(struct inode *inode)
1363         __releases(inode->i_lock)
1364 {
1365         DEFINE_WAIT(wait);
1366         wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1367         int sleep;
1368
1369         prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1370         sleep = inode->i_state & I_SYNC;
1371         spin_unlock(&inode->i_lock);
1372         if (sleep)
1373                 schedule();
1374         finish_wait(wqh, &wait);
1375 }
1376
1377 /*
1378  * Find proper writeback list for the inode depending on its current state and
1379  * possibly also change of its state while we were doing writeback.  Here we
1380  * handle things such as livelock prevention or fairness of writeback among
1381  * inodes. This function can be called only by flusher thread - noone else
1382  * processes all inodes in writeback lists and requeueing inodes behind flusher
1383  * thread's back can have unexpected consequences.
1384  */
1385 static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1386                           struct writeback_control *wbc)
1387 {
1388         if (inode->i_state & I_FREEING)
1389                 return;
1390
1391         /*
1392          * Sync livelock prevention. Each inode is tagged and synced in one
1393          * shot. If still dirty, it will be redirty_tail()'ed below.  Update
1394          * the dirty time to prevent enqueue and sync it again.
1395          */
1396         if ((inode->i_state & I_DIRTY) &&
1397             (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1398                 inode->dirtied_when = jiffies;
1399
1400         if (wbc->pages_skipped) {
1401                 /*
1402                  * writeback is not making progress due to locked
1403                  * buffers. Skip this inode for now.
1404                  */
1405                 redirty_tail_locked(inode, wb);
1406                 return;
1407         }
1408
1409         if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1410                 /*
1411                  * We didn't write back all the pages.  nfs_writepages()
1412                  * sometimes bales out without doing anything.
1413                  */
1414                 if (wbc->nr_to_write <= 0) {
1415                         /* Slice used up. Queue for next turn. */
1416                         requeue_io(inode, wb);
1417                 } else {
1418                         /*
1419                          * Writeback blocked by something other than
1420                          * congestion. Delay the inode for some time to
1421                          * avoid spinning on the CPU (100% iowait)
1422                          * retrying writeback of the dirty page/inode
1423                          * that cannot be performed immediately.
1424                          */
1425                         redirty_tail_locked(inode, wb);
1426                 }
1427         } else if (inode->i_state & I_DIRTY) {
1428                 /*
1429                  * Filesystems can dirty the inode during writeback operations,
1430                  * such as delayed allocation during submission or metadata
1431                  * updates after data IO completion.
1432                  */
1433                 redirty_tail_locked(inode, wb);
1434         } else if (inode->i_state & I_DIRTY_TIME) {
1435                 inode->dirtied_when = jiffies;
1436                 inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1437                 inode->i_state &= ~I_SYNC_QUEUED;
1438         } else {
1439                 /* The inode is clean. Remove from writeback lists. */
1440                 inode_io_list_del_locked(inode, wb);
1441         }
1442 }
1443
1444 /*
1445  * Write out an inode and its dirty pages. Do not update the writeback list
1446  * linkage. That is left to the caller. The caller is also responsible for
1447  * setting I_SYNC flag and calling inode_sync_complete() to clear it.
1448  */
1449 static int
1450 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1451 {
1452         struct address_space *mapping = inode->i_mapping;
1453         long nr_to_write = wbc->nr_to_write;
1454         unsigned dirty;
1455         int ret;
1456
1457         WARN_ON(!(inode->i_state & I_SYNC));
1458
1459         trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1460
1461         ret = do_writepages(mapping, wbc);
1462
1463         /*
1464          * Make sure to wait on the data before writing out the metadata.
1465          * This is important for filesystems that modify metadata on data
1466          * I/O completion. We don't do it for sync(2) writeback because it has a
1467          * separate, external IO completion path and ->sync_fs for guaranteeing
1468          * inode metadata is written back correctly.
1469          */
1470         if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1471                 int err = filemap_fdatawait(mapping);
1472                 if (ret == 0)
1473                         ret = err;
1474         }
1475
1476         /*
1477          * Some filesystems may redirty the inode during the writeback
1478          * due to delalloc, clear dirty metadata flags right before
1479          * write_inode()
1480          */
1481         spin_lock(&inode->i_lock);
1482
1483         dirty = inode->i_state & I_DIRTY;
1484         if ((inode->i_state & I_DIRTY_TIME) &&
1485             ((dirty & I_DIRTY_INODE) ||
1486              wbc->sync_mode == WB_SYNC_ALL || wbc->for_sync ||
1487              time_after(jiffies, inode->dirtied_time_when +
1488                         dirtytime_expire_interval * HZ))) {
1489                 dirty |= I_DIRTY_TIME;
1490                 trace_writeback_lazytime(inode);
1491         }
1492         inode->i_state &= ~dirty;
1493
1494         /*
1495          * Paired with smp_mb() in __mark_inode_dirty().  This allows
1496          * __mark_inode_dirty() to test i_state without grabbing i_lock -
1497          * either they see the I_DIRTY bits cleared or we see the dirtied
1498          * inode.
1499          *
1500          * I_DIRTY_PAGES is always cleared together above even if @mapping
1501          * still has dirty pages.  The flag is reinstated after smp_mb() if
1502          * necessary.  This guarantees that either __mark_inode_dirty()
1503          * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1504          */
1505         smp_mb();
1506
1507         if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1508                 inode->i_state |= I_DIRTY_PAGES;
1509
1510         spin_unlock(&inode->i_lock);
1511
1512         if (dirty & I_DIRTY_TIME)
1513                 mark_inode_dirty_sync(inode);
1514         /* Don't write the inode if only I_DIRTY_PAGES was set */
1515         if (dirty & ~I_DIRTY_PAGES) {
1516                 int err = write_inode(inode, wbc);
1517                 if (ret == 0)
1518                         ret = err;
1519         }
1520         trace_writeback_single_inode(inode, wbc, nr_to_write);
1521         return ret;
1522 }
1523
1524 /*
1525  * Write out an inode's dirty pages. Either the caller has an active reference
1526  * on the inode or the inode has I_WILL_FREE set.
1527  *
1528  * This function is designed to be called for writing back one inode which
1529  * we go e.g. from filesystem. Flusher thread uses __writeback_single_inode()
1530  * and does more profound writeback list handling in writeback_sb_inodes().
1531  */
1532 static int writeback_single_inode(struct inode *inode,
1533                                   struct writeback_control *wbc)
1534 {
1535         struct bdi_writeback *wb;
1536         int ret = 0;
1537
1538         spin_lock(&inode->i_lock);
1539         if (!atomic_read(&inode->i_count))
1540                 WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1541         else
1542                 WARN_ON(inode->i_state & I_WILL_FREE);
1543
1544         if (inode->i_state & I_SYNC) {
1545                 if (wbc->sync_mode != WB_SYNC_ALL)
1546                         goto out;
1547                 /*
1548                  * It's a data-integrity sync. We must wait. Since callers hold
1549                  * inode reference or inode has I_WILL_FREE set, it cannot go
1550                  * away under us.
1551                  */
1552                 __inode_wait_for_writeback(inode);
1553         }
1554         WARN_ON(inode->i_state & I_SYNC);
1555         /*
1556          * Skip inode if it is clean and we have no outstanding writeback in
1557          * WB_SYNC_ALL mode. We don't want to mess with writeback lists in this
1558          * function since flusher thread may be doing for example sync in
1559          * parallel and if we move the inode, it could get skipped. So here we
1560          * make sure inode is on some writeback list and leave it there unless
1561          * we have completely cleaned the inode.
1562          */
1563         if (!(inode->i_state & I_DIRTY_ALL) &&
1564             (wbc->sync_mode != WB_SYNC_ALL ||
1565              !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1566                 goto out;
1567         inode->i_state |= I_SYNC;
1568         wbc_attach_and_unlock_inode(wbc, inode);
1569
1570         ret = __writeback_single_inode(inode, wbc);
1571
1572         wbc_detach_inode(wbc);
1573
1574         wb = inode_to_wb_and_lock_list(inode);
1575         spin_lock(&inode->i_lock);
1576         /*
1577          * If inode is clean, remove it from writeback lists. Otherwise don't
1578          * touch it. See comment above for explanation.
1579          */
1580         if (!(inode->i_state & I_DIRTY_ALL))
1581                 inode_io_list_del_locked(inode, wb);
1582         spin_unlock(&wb->list_lock);
1583         inode_sync_complete(inode);
1584 out:
1585         spin_unlock(&inode->i_lock);
1586         return ret;
1587 }
1588
1589 static long writeback_chunk_size(struct bdi_writeback *wb,
1590                                  struct wb_writeback_work *work)
1591 {
1592         long pages;
1593
1594         /*
1595          * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1596          * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1597          * here avoids calling into writeback_inodes_wb() more than once.
1598          *
1599          * The intended call sequence for WB_SYNC_ALL writeback is:
1600          *
1601          *      wb_writeback()
1602          *          writeback_sb_inodes()       <== called only once
1603          *              write_cache_pages()     <== called once for each inode
1604          *                   (quickly) tag currently dirty pages
1605          *                   (maybe slowly) sync all tagged pages
1606          */
1607         if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1608                 pages = LONG_MAX;
1609         else {
1610                 pages = min(wb->avg_write_bandwidth / 2,
1611                             global_wb_domain.dirty_limit / DIRTY_SCOPE);
1612                 pages = min(pages, work->nr_pages);
1613                 pages = round_down(pages + MIN_WRITEBACK_PAGES,
1614                                    MIN_WRITEBACK_PAGES);
1615         }
1616
1617         return pages;
1618 }
1619
1620 /*
1621  * Write a portion of b_io inodes which belong to @sb.
1622  *
1623  * Return the number of pages and/or inodes written.
1624  *
1625  * NOTE! This is called with wb->list_lock held, and will
1626  * unlock and relock that for each inode it ends up doing
1627  * IO for.
1628  */
1629 static long writeback_sb_inodes(struct super_block *sb,
1630                                 struct bdi_writeback *wb,
1631                                 struct wb_writeback_work *work)
1632 {
1633         struct writeback_control wbc = {
1634                 .sync_mode              = work->sync_mode,
1635                 .tagged_writepages      = work->tagged_writepages,
1636                 .for_kupdate            = work->for_kupdate,
1637                 .for_background         = work->for_background,
1638                 .for_sync               = work->for_sync,
1639                 .range_cyclic           = work->range_cyclic,
1640                 .range_start            = 0,
1641                 .range_end              = LLONG_MAX,
1642         };
1643         unsigned long start_time = jiffies;
1644         long write_chunk;
1645         long wrote = 0;  /* count both pages and inodes */
1646
1647         while (!list_empty(&wb->b_io)) {
1648                 struct inode *inode = wb_inode(wb->b_io.prev);
1649                 struct bdi_writeback *tmp_wb;
1650
1651                 if (inode->i_sb != sb) {
1652                         if (work->sb) {
1653                                 /*
1654                                  * We only want to write back data for this
1655                                  * superblock, move all inodes not belonging
1656                                  * to it back onto the dirty list.
1657                                  */
1658                                 redirty_tail(inode, wb);
1659                                 continue;
1660                         }
1661
1662                         /*
1663                          * The inode belongs to a different superblock.
1664                          * Bounce back to the caller to unpin this and
1665                          * pin the next superblock.
1666                          */
1667                         break;
1668                 }
1669
1670                 /*
1671                  * Don't bother with new inodes or inodes being freed, first
1672                  * kind does not need periodic writeout yet, and for the latter
1673                  * kind writeout is handled by the freer.
1674                  */
1675                 spin_lock(&inode->i_lock);
1676                 if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1677                         redirty_tail_locked(inode, wb);
1678                         spin_unlock(&inode->i_lock);
1679                         continue;
1680                 }
1681                 if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1682                         /*
1683                          * If this inode is locked for writeback and we are not
1684                          * doing writeback-for-data-integrity, move it to
1685                          * b_more_io so that writeback can proceed with the
1686                          * other inodes on s_io.
1687                          *
1688                          * We'll have another go at writing back this inode
1689                          * when we completed a full scan of b_io.
1690                          */
1691                         spin_unlock(&inode->i_lock);
1692                         requeue_io(inode, wb);
1693                         trace_writeback_sb_inodes_requeue(inode);
1694                         continue;
1695                 }
1696                 spin_unlock(&wb->list_lock);
1697
1698                 /*
1699                  * We already requeued the inode if it had I_SYNC set and we
1700                  * are doing WB_SYNC_NONE writeback. So this catches only the
1701                  * WB_SYNC_ALL case.
1702                  */
1703                 if (inode->i_state & I_SYNC) {
1704                         /* Wait for I_SYNC. This function drops i_lock... */
1705                         inode_sleep_on_writeback(inode);
1706                         /* Inode may be gone, start again */
1707                         spin_lock(&wb->list_lock);
1708                         continue;
1709                 }
1710                 inode->i_state |= I_SYNC;
1711                 wbc_attach_and_unlock_inode(&wbc, inode);
1712
1713                 write_chunk = writeback_chunk_size(wb, work);
1714                 wbc.nr_to_write = write_chunk;
1715                 wbc.pages_skipped = 0;
1716
1717                 /*
1718                  * We use I_SYNC to pin the inode in memory. While it is set
1719                  * evict_inode() will wait so the inode cannot be freed.
1720                  */
1721                 __writeback_single_inode(inode, &wbc);
1722
1723                 wbc_detach_inode(&wbc);
1724                 work->nr_pages -= write_chunk - wbc.nr_to_write;
1725                 wrote += write_chunk - wbc.nr_to_write;
1726
1727                 if (need_resched()) {
1728                         /*
1729                          * We're trying to balance between building up a nice
1730                          * long list of IOs to improve our merge rate, and
1731                          * getting those IOs out quickly for anyone throttling
1732                          * in balance_dirty_pages().  cond_resched() doesn't
1733                          * unplug, so get our IOs out the door before we
1734                          * give up the CPU.
1735                          */
1736                         blk_flush_plug(current);
1737                         cond_resched();
1738                 }
1739
1740                 /*
1741                  * Requeue @inode if still dirty.  Be careful as @inode may
1742                  * have been switched to another wb in the meantime.
1743                  */
1744                 tmp_wb = inode_to_wb_and_lock_list(inode);
1745                 spin_lock(&inode->i_lock);
1746                 if (!(inode->i_state & I_DIRTY_ALL))
1747                         wrote++;
1748                 requeue_inode(inode, tmp_wb, &wbc);
1749                 inode_sync_complete(inode);
1750                 spin_unlock(&inode->i_lock);
1751
1752                 if (unlikely(tmp_wb != wb)) {
1753                         spin_unlock(&tmp_wb->list_lock);
1754                         spin_lock(&wb->list_lock);
1755                 }
1756
1757                 /*
1758                  * bail out to wb_writeback() often enough to check
1759                  * background threshold and other termination conditions.
1760                  */
1761                 if (wrote) {
1762                         if (time_is_before_jiffies(start_time + HZ / 10UL))
1763                                 break;
1764                         if (work->nr_pages <= 0)
1765                                 break;
1766                 }
1767         }
1768         return wrote;
1769 }
1770
1771 static long __writeback_inodes_wb(struct bdi_writeback *wb,
1772                                   struct wb_writeback_work *work)
1773 {
1774         unsigned long start_time = jiffies;
1775         long wrote = 0;
1776
1777         while (!list_empty(&wb->b_io)) {
1778                 struct inode *inode = wb_inode(wb->b_io.prev);
1779                 struct super_block *sb = inode->i_sb;
1780
1781                 if (!trylock_super(sb)) {
1782                         /*
1783                          * trylock_super() may fail consistently due to
1784                          * s_umount being grabbed by someone else. Don't use
1785                          * requeue_io() to avoid busy retrying the inode/sb.
1786                          */
1787                         redirty_tail(inode, wb);
1788                         continue;
1789                 }
1790                 wrote += writeback_sb_inodes(sb, wb, work);
1791                 up_read(&sb->s_umount);
1792
1793                 /* refer to the same tests at the end of writeback_sb_inodes */
1794                 if (wrote) {
1795                         if (time_is_before_jiffies(start_time + HZ / 10UL))
1796                                 break;
1797                         if (work->nr_pages <= 0)
1798                                 break;
1799                 }
1800         }
1801         /* Leave any unwritten inodes on b_io */
1802         return wrote;
1803 }
1804
1805 static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1806                                 enum wb_reason reason)
1807 {
1808         struct wb_writeback_work work = {
1809                 .nr_pages       = nr_pages,
1810                 .sync_mode      = WB_SYNC_NONE,
1811                 .range_cyclic   = 1,
1812                 .reason         = reason,
1813         };
1814         struct blk_plug plug;
1815
1816         blk_start_plug(&plug);
1817         spin_lock(&wb->list_lock);
1818         if (list_empty(&wb->b_io))
1819                 queue_io(wb, &work, jiffies);
1820         __writeback_inodes_wb(wb, &work);
1821         spin_unlock(&wb->list_lock);
1822         blk_finish_plug(&plug);
1823
1824         return nr_pages - work.nr_pages;
1825 }
1826
1827 /*
1828  * Explicit flushing or periodic writeback of "old" data.
1829  *
1830  * Define "old": the first time one of an inode's pages is dirtied, we mark the
1831  * dirtying-time in the inode's address_space.  So this periodic writeback code
1832  * just walks the superblock inode list, writing back any inodes which are
1833  * older than a specific point in time.
1834  *
1835  * Try to run once per dirty_writeback_interval.  But if a writeback event
1836  * takes longer than a dirty_writeback_interval interval, then leave a
1837  * one-second gap.
1838  *
1839  * dirtied_before takes precedence over nr_to_write.  So we'll only write back
1840  * all dirty pages if they are all attached to "old" mappings.
1841  */
1842 static long wb_writeback(struct bdi_writeback *wb,
1843                          struct wb_writeback_work *work)
1844 {
1845         unsigned long wb_start = jiffies;
1846         long nr_pages = work->nr_pages;
1847         unsigned long dirtied_before = jiffies;
1848         struct inode *inode;
1849         long progress;
1850         struct blk_plug plug;
1851
1852         blk_start_plug(&plug);
1853         spin_lock(&wb->list_lock);
1854         for (;;) {
1855                 /*
1856                  * Stop writeback when nr_pages has been consumed
1857                  */
1858                 if (work->nr_pages <= 0)
1859                         break;
1860
1861                 /*
1862                  * Background writeout and kupdate-style writeback may
1863                  * run forever. Stop them if there is other work to do
1864                  * so that e.g. sync can proceed. They'll be restarted
1865                  * after the other works are all done.
1866                  */
1867                 if ((work->for_background || work->for_kupdate) &&
1868                     !list_empty(&wb->work_list))
1869                         break;
1870
1871                 /*
1872                  * For background writeout, stop when we are below the
1873                  * background dirty threshold
1874                  */
1875                 if (work->for_background && !wb_over_bg_thresh(wb))
1876                         break;
1877
1878                 /*
1879                  * Kupdate and background works are special and we want to
1880                  * include all inodes that need writing. Livelock avoidance is
1881                  * handled by these works yielding to any other work so we are
1882                  * safe.
1883                  */
1884                 if (work->for_kupdate) {
1885                         dirtied_before = jiffies -
1886                                 msecs_to_jiffies(dirty_expire_interval * 10);
1887                 } else if (work->for_background)
1888                         dirtied_before = jiffies;
1889
1890                 trace_writeback_start(wb, work);
1891                 if (list_empty(&wb->b_io))
1892                         queue_io(wb, work, dirtied_before);
1893                 if (work->sb)
1894                         progress = writeback_sb_inodes(work->sb, wb, work);
1895                 else
1896                         progress = __writeback_inodes_wb(wb, work);
1897                 trace_writeback_written(wb, work);
1898
1899                 wb_update_bandwidth(wb, wb_start);
1900
1901                 /*
1902                  * Did we write something? Try for more
1903                  *
1904                  * Dirty inodes are moved to b_io for writeback in batches.
1905                  * The completion of the current batch does not necessarily
1906                  * mean the overall work is done. So we keep looping as long
1907                  * as made some progress on cleaning pages or inodes.
1908                  */
1909                 if (progress)
1910                         continue;
1911                 /*
1912                  * No more inodes for IO, bail
1913                  */
1914                 if (list_empty(&wb->b_more_io))
1915                         break;
1916                 /*
1917                  * Nothing written. Wait for some inode to
1918                  * become available for writeback. Otherwise
1919                  * we'll just busyloop.
1920                  */
1921                 trace_writeback_wait(wb, work);
1922                 inode = wb_inode(wb->b_more_io.prev);
1923                 spin_lock(&inode->i_lock);
1924                 spin_unlock(&wb->list_lock);
1925                 /* This function drops i_lock... */
1926                 inode_sleep_on_writeback(inode);
1927                 spin_lock(&wb->list_lock);
1928         }
1929         spin_unlock(&wb->list_lock);
1930         blk_finish_plug(&plug);
1931
1932         return nr_pages - work->nr_pages;
1933 }
1934
1935 /*
1936  * Return the next wb_writeback_work struct that hasn't been processed yet.
1937  */
1938 static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
1939 {
1940         struct wb_writeback_work *work = NULL;
1941
1942         spin_lock_bh(&wb->work_lock);
1943         if (!list_empty(&wb->work_list)) {
1944                 work = list_entry(wb->work_list.next,
1945                                   struct wb_writeback_work, list);
1946                 list_del_init(&work->list);
1947         }
1948         spin_unlock_bh(&wb->work_lock);
1949         return work;
1950 }
1951
1952 static long wb_check_background_flush(struct bdi_writeback *wb)
1953 {
1954         if (wb_over_bg_thresh(wb)) {
1955
1956                 struct wb_writeback_work work = {
1957                         .nr_pages       = LONG_MAX,
1958                         .sync_mode      = WB_SYNC_NONE,
1959                         .for_background = 1,
1960                         .range_cyclic   = 1,
1961                         .reason         = WB_REASON_BACKGROUND,
1962                 };
1963
1964                 return wb_writeback(wb, &work);
1965         }
1966
1967         return 0;
1968 }
1969
1970 static long wb_check_old_data_flush(struct bdi_writeback *wb)
1971 {
1972         unsigned long expired;
1973         long nr_pages;
1974
1975         /*
1976          * When set to zero, disable periodic writeback
1977          */
1978         if (!dirty_writeback_interval)
1979                 return 0;
1980
1981         expired = wb->last_old_flush +
1982                         msecs_to_jiffies(dirty_writeback_interval * 10);
1983         if (time_before(jiffies, expired))
1984                 return 0;
1985
1986         wb->last_old_flush = jiffies;
1987         nr_pages = get_nr_dirty_pages();
1988
1989         if (nr_pages) {
1990                 struct wb_writeback_work work = {
1991                         .nr_pages       = nr_pages,
1992                         .sync_mode      = WB_SYNC_NONE,
1993                         .for_kupdate    = 1,
1994                         .range_cyclic   = 1,
1995                         .reason         = WB_REASON_PERIODIC,
1996                 };
1997
1998                 return wb_writeback(wb, &work);
1999         }
2000
2001         return 0;
2002 }
2003
2004 static long wb_check_start_all(struct bdi_writeback *wb)
2005 {
2006         long nr_pages;
2007
2008         if (!test_bit(WB_start_all, &wb->state))
2009                 return 0;
2010
2011         nr_pages = get_nr_dirty_pages();
2012         if (nr_pages) {
2013                 struct wb_writeback_work work = {
2014                         .nr_pages       = wb_split_bdi_pages(wb, nr_pages),
2015                         .sync_mode      = WB_SYNC_NONE,
2016                         .range_cyclic   = 1,
2017                         .reason         = wb->start_all_reason,
2018                 };
2019
2020                 nr_pages = wb_writeback(wb, &work);
2021         }
2022
2023         clear_bit(WB_start_all, &wb->state);
2024         return nr_pages;
2025 }
2026
2027
2028 /*
2029  * Retrieve work items and do the writeback they describe
2030  */
2031 static long wb_do_writeback(struct bdi_writeback *wb)
2032 {
2033         struct wb_writeback_work *work;
2034         long wrote = 0;
2035
2036         set_bit(WB_writeback_running, &wb->state);
2037         while ((work = get_next_work_item(wb)) != NULL) {
2038                 trace_writeback_exec(wb, work);
2039                 wrote += wb_writeback(wb, work);
2040                 finish_writeback_work(wb, work);
2041         }
2042
2043         /*
2044          * Check for a flush-everything request
2045          */
2046         wrote += wb_check_start_all(wb);
2047
2048         /*
2049          * Check for periodic writeback, kupdated() style
2050          */
2051         wrote += wb_check_old_data_flush(wb);
2052         wrote += wb_check_background_flush(wb);
2053         clear_bit(WB_writeback_running, &wb->state);
2054
2055         return wrote;
2056 }
2057
2058 /*
2059  * Handle writeback of dirty data for the device backed by this bdi. Also
2060  * reschedules periodically and does kupdated style flushing.
2061  */
2062 void wb_workfn(struct work_struct *work)
2063 {
2064         struct bdi_writeback *wb = container_of(to_delayed_work(work),
2065                                                 struct bdi_writeback, dwork);
2066         long pages_written;
2067
2068         set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
2069         current->flags |= PF_SWAPWRITE;
2070
2071         if (likely(!current_is_workqueue_rescuer() ||
2072                    !test_bit(WB_registered, &wb->state))) {
2073                 /*
2074                  * The normal path.  Keep writing back @wb until its
2075                  * work_list is empty.  Note that this path is also taken
2076                  * if @wb is shutting down even when we're running off the
2077                  * rescuer as work_list needs to be drained.
2078                  */
2079                 do {
2080                         pages_written = wb_do_writeback(wb);
2081                         trace_writeback_pages_written(pages_written);
2082                 } while (!list_empty(&wb->work_list));
2083         } else {
2084                 /*
2085                  * bdi_wq can't get enough workers and we're running off
2086                  * the emergency worker.  Don't hog it.  Hopefully, 1024 is
2087                  * enough for efficient IO.
2088                  */
2089                 pages_written = writeback_inodes_wb(wb, 1024,
2090                                                     WB_REASON_FORKER_THREAD);
2091                 trace_writeback_pages_written(pages_written);
2092         }
2093
2094         if (!list_empty(&wb->work_list))
2095                 wb_wakeup(wb);
2096         else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2097                 wb_wakeup_delayed(wb);
2098
2099         current->flags &= ~PF_SWAPWRITE;
2100 }
2101
2102 /*
2103  * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2104  * write back the whole world.
2105  */
2106 static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2107                                          enum wb_reason reason)
2108 {
2109         struct bdi_writeback *wb;
2110
2111         if (!bdi_has_dirty_io(bdi))
2112                 return;
2113
2114         list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2115                 wb_start_writeback(wb, reason);
2116 }
2117
2118 void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2119                                 enum wb_reason reason)
2120 {
2121         rcu_read_lock();
2122         __wakeup_flusher_threads_bdi(bdi, reason);
2123         rcu_read_unlock();
2124 }
2125
2126 /*
2127  * Wakeup the flusher threads to start writeback of all currently dirty pages
2128  */
2129 void wakeup_flusher_threads(enum wb_reason reason)
2130 {
2131         struct backing_dev_info *bdi;
2132
2133         /*
2134          * If we are expecting writeback progress we must submit plugged IO.
2135          */
2136         if (blk_needs_flush_plug(current))
2137                 blk_schedule_flush_plug(current);
2138
2139         rcu_read_lock();
2140         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2141                 __wakeup_flusher_threads_bdi(bdi, reason);
2142         rcu_read_unlock();
2143 }
2144
2145 /*
2146  * Wake up bdi's periodically to make sure dirtytime inodes gets
2147  * written back periodically.  We deliberately do *not* check the
2148  * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2149  * kernel to be constantly waking up once there are any dirtytime
2150  * inodes on the system.  So instead we define a separate delayed work
2151  * function which gets called much more rarely.  (By default, only
2152  * once every 12 hours.)
2153  *
2154  * If there is any other write activity going on in the file system,
2155  * this function won't be necessary.  But if the only thing that has
2156  * happened on the file system is a dirtytime inode caused by an atime
2157  * update, we need this infrastructure below to make sure that inode
2158  * eventually gets pushed out to disk.
2159  */
2160 static void wakeup_dirtytime_writeback(struct work_struct *w);
2161 static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2162
2163 static void wakeup_dirtytime_writeback(struct work_struct *w)
2164 {
2165         struct backing_dev_info *bdi;
2166
2167         rcu_read_lock();
2168         list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2169                 struct bdi_writeback *wb;
2170
2171                 list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2172                         if (!list_empty(&wb->b_dirty_time))
2173                                 wb_wakeup(wb);
2174         }
2175         rcu_read_unlock();
2176         schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2177 }
2178
2179 static int __init start_dirtytime_writeback(void)
2180 {
2181         schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2182         return 0;
2183 }
2184 __initcall(start_dirtytime_writeback);
2185
2186 int dirtytime_interval_handler(struct ctl_table *table, int write,
2187                                void *buffer, size_t *lenp, loff_t *ppos)
2188 {
2189         int ret;
2190
2191         ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2192         if (ret == 0 && write)
2193                 mod_delayed_work(system_wq, &dirtytime_work, 0);
2194         return ret;
2195 }
2196
2197 static noinline void block_dump___mark_inode_dirty(struct inode *inode)
2198 {
2199         if (inode->i_ino || strcmp(inode->i_sb->s_id, "bdev")) {
2200                 struct dentry *dentry;
2201                 const char *name = "?";
2202
2203                 dentry = d_find_alias(inode);
2204                 if (dentry) {
2205                         spin_lock(&dentry->d_lock);
2206                         name = (const char *) dentry->d_name.name;
2207                 }
2208                 printk(KERN_DEBUG
2209                        "%s(%d): dirtied inode %lu (%s) on %s\n",
2210                        current->comm, task_pid_nr(current), inode->i_ino,
2211                        name, inode->i_sb->s_id);
2212                 if (dentry) {
2213                         spin_unlock(&dentry->d_lock);
2214                         dput(dentry);
2215                 }
2216         }
2217 }
2218
2219 /**
2220  * __mark_inode_dirty - internal function
2221  *
2222  * @inode: inode to mark
2223  * @flags: what kind of dirty (i.e. I_DIRTY_SYNC)
2224  *
2225  * Mark an inode as dirty. Callers should use mark_inode_dirty or
2226  * mark_inode_dirty_sync.
2227  *
2228  * Put the inode on the super block's dirty list.
2229  *
2230  * CAREFUL! We mark it dirty unconditionally, but move it onto the
2231  * dirty list only if it is hashed or if it refers to a blockdev.
2232  * If it was not hashed, it will never be added to the dirty list
2233  * even if it is later hashed, as it will have been marked dirty already.
2234  *
2235  * In short, make sure you hash any inodes _before_ you start marking
2236  * them dirty.
2237  *
2238  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2239  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
2240  * the kernel-internal blockdev inode represents the dirtying time of the
2241  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
2242  * page->mapping->host, so the page-dirtying time is recorded in the internal
2243  * blockdev inode.
2244  */
2245 void __mark_inode_dirty(struct inode *inode, int flags)
2246 {
2247         struct super_block *sb = inode->i_sb;
2248         int dirtytime;
2249
2250         trace_writeback_mark_inode_dirty(inode, flags);
2251
2252         /*
2253          * Don't do this for I_DIRTY_PAGES - that doesn't actually
2254          * dirty the inode itself
2255          */
2256         if (flags & (I_DIRTY_INODE | I_DIRTY_TIME)) {
2257                 trace_writeback_dirty_inode_start(inode, flags);
2258
2259                 if (sb->s_op->dirty_inode)
2260                         sb->s_op->dirty_inode(inode, flags);
2261
2262                 trace_writeback_dirty_inode(inode, flags);
2263         }
2264         if (flags & I_DIRTY_INODE)
2265                 flags &= ~I_DIRTY_TIME;
2266         dirtytime = flags & I_DIRTY_TIME;
2267
2268         /*
2269          * Paired with smp_mb() in __writeback_single_inode() for the
2270          * following lockless i_state test.  See there for details.
2271          */
2272         smp_mb();
2273
2274         if (((inode->i_state & flags) == flags) ||
2275             (dirtytime && (inode->i_state & I_DIRTY_INODE)))
2276                 return;
2277
2278         if (unlikely(block_dump))
2279                 block_dump___mark_inode_dirty(inode);
2280
2281         spin_lock(&inode->i_lock);
2282         if (dirtytime && (inode->i_state & I_DIRTY_INODE))
2283                 goto out_unlock_inode;
2284         if ((inode->i_state & flags) != flags) {
2285                 const int was_dirty = inode->i_state & I_DIRTY;
2286
2287                 inode_attach_wb(inode, NULL);
2288
2289                 if (flags & I_DIRTY_INODE)
2290                         inode->i_state &= ~I_DIRTY_TIME;
2291                 inode->i_state |= flags;
2292
2293                 /*
2294                  * If the inode is queued for writeback by flush worker, just
2295                  * update its dirty state. Once the flush worker is done with
2296                  * the inode it will place it on the appropriate superblock
2297                  * list, based upon its state.
2298                  */
2299                 if (inode->i_state & I_SYNC_QUEUED)
2300                         goto out_unlock_inode;
2301
2302                 /*
2303                  * Only add valid (hashed) inodes to the superblock's
2304                  * dirty list.  Add blockdev inodes as well.
2305                  */
2306                 if (!S_ISBLK(inode->i_mode)) {
2307                         if (inode_unhashed(inode))
2308                                 goto out_unlock_inode;
2309                 }
2310                 if (inode->i_state & I_FREEING)
2311                         goto out_unlock_inode;
2312
2313                 /*
2314                  * If the inode was already on b_dirty/b_io/b_more_io, don't
2315                  * reposition it (that would break b_dirty time-ordering).
2316                  */
2317                 if (!was_dirty) {
2318                         struct bdi_writeback *wb;
2319                         struct list_head *dirty_list;
2320                         bool wakeup_bdi = false;
2321
2322                         wb = locked_inode_to_wb_and_lock_list(inode);
2323
2324                         WARN(bdi_cap_writeback_dirty(wb->bdi) &&
2325                              !test_bit(WB_registered, &wb->state),
2326                              "bdi-%s not registered\n", bdi_dev_name(wb->bdi));
2327
2328                         inode->dirtied_when = jiffies;
2329                         if (dirtytime)
2330                                 inode->dirtied_time_when = jiffies;
2331
2332                         if (inode->i_state & I_DIRTY)
2333                                 dirty_list = &wb->b_dirty;
2334                         else
2335                                 dirty_list = &wb->b_dirty_time;
2336
2337                         wakeup_bdi = inode_io_list_move_locked(inode, wb,
2338                                                                dirty_list);
2339
2340                         spin_unlock(&wb->list_lock);
2341                         trace_writeback_dirty_inode_enqueue(inode);
2342
2343                         /*
2344                          * If this is the first dirty inode for this bdi,
2345                          * we have to wake-up the corresponding bdi thread
2346                          * to make sure background write-back happens
2347                          * later.
2348                          */
2349                         if (bdi_cap_writeback_dirty(wb->bdi) && wakeup_bdi)
2350                                 wb_wakeup_delayed(wb);
2351                         return;
2352                 }
2353         }
2354 out_unlock_inode:
2355         spin_unlock(&inode->i_lock);
2356 }
2357 EXPORT_SYMBOL(__mark_inode_dirty);
2358
2359 /*
2360  * The @s_sync_lock is used to serialise concurrent sync operations
2361  * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2362  * Concurrent callers will block on the s_sync_lock rather than doing contending
2363  * walks. The queueing maintains sync(2) required behaviour as all the IO that
2364  * has been issued up to the time this function is enter is guaranteed to be
2365  * completed by the time we have gained the lock and waited for all IO that is
2366  * in progress regardless of the order callers are granted the lock.
2367  */
2368 static void wait_sb_inodes(struct super_block *sb)
2369 {
2370         LIST_HEAD(sync_list);
2371
2372         /*
2373          * We need to be protected against the filesystem going from
2374          * r/o to r/w or vice versa.
2375          */
2376         WARN_ON(!rwsem_is_locked(&sb->s_umount));
2377
2378         mutex_lock(&sb->s_sync_lock);
2379
2380         /*
2381          * Splice the writeback list onto a temporary list to avoid waiting on
2382          * inodes that have started writeback after this point.
2383          *
2384          * Use rcu_read_lock() to keep the inodes around until we have a
2385          * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2386          * the local list because inodes can be dropped from either by writeback
2387          * completion.
2388          */
2389         rcu_read_lock();
2390         spin_lock_irq(&sb->s_inode_wblist_lock);
2391         list_splice_init(&sb->s_inodes_wb, &sync_list);
2392
2393         /*
2394          * Data integrity sync. Must wait for all pages under writeback, because
2395          * there may have been pages dirtied before our sync call, but which had
2396          * writeout started before we write it out.  In which case, the inode
2397          * may not be on the dirty list, but we still have to wait for that
2398          * writeout.
2399          */
2400         while (!list_empty(&sync_list)) {
2401                 struct inode *inode = list_first_entry(&sync_list, struct inode,
2402                                                        i_wb_list);
2403                 struct address_space *mapping = inode->i_mapping;
2404
2405                 /*
2406                  * Move each inode back to the wb list before we drop the lock
2407                  * to preserve consistency between i_wb_list and the mapping
2408                  * writeback tag. Writeback completion is responsible to remove
2409                  * the inode from either list once the writeback tag is cleared.
2410                  */
2411                 list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2412
2413                 /*
2414                  * The mapping can appear untagged while still on-list since we
2415                  * do not have the mapping lock. Skip it here, wb completion
2416                  * will remove it.
2417                  */
2418                 if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2419                         continue;
2420
2421                 spin_unlock_irq(&sb->s_inode_wblist_lock);
2422
2423                 spin_lock(&inode->i_lock);
2424                 if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2425                         spin_unlock(&inode->i_lock);
2426
2427                         spin_lock_irq(&sb->s_inode_wblist_lock);
2428                         continue;
2429                 }
2430                 __iget(inode);
2431                 spin_unlock(&inode->i_lock);
2432                 rcu_read_unlock();
2433
2434                 /*
2435                  * We keep the error status of individual mapping so that
2436                  * applications can catch the writeback error using fsync(2).
2437                  * See filemap_fdatawait_keep_errors() for details.
2438                  */
2439                 filemap_fdatawait_keep_errors(mapping);
2440
2441                 cond_resched();
2442
2443                 iput(inode);
2444
2445                 rcu_read_lock();
2446                 spin_lock_irq(&sb->s_inode_wblist_lock);
2447         }
2448         spin_unlock_irq(&sb->s_inode_wblist_lock);
2449         rcu_read_unlock();
2450         mutex_unlock(&sb->s_sync_lock);
2451 }
2452
2453 static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2454                                      enum wb_reason reason, bool skip_if_busy)
2455 {
2456         struct backing_dev_info *bdi = sb->s_bdi;
2457         DEFINE_WB_COMPLETION(done, bdi);
2458         struct wb_writeback_work work = {
2459                 .sb                     = sb,
2460                 .sync_mode              = WB_SYNC_NONE,
2461                 .tagged_writepages      = 1,
2462                 .done                   = &done,
2463                 .nr_pages               = nr,
2464                 .reason                 = reason,
2465         };
2466
2467         if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2468                 return;
2469         WARN_ON(!rwsem_is_locked(&sb->s_umount));
2470
2471         bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2472         wb_wait_for_completion(&done);
2473 }
2474
2475 /**
2476  * writeback_inodes_sb_nr -     writeback dirty inodes from given super_block
2477  * @sb: the superblock
2478  * @nr: the number of pages to write
2479  * @reason: reason why some writeback work initiated
2480  *
2481  * Start writeback on some inodes on this super_block. No guarantees are made
2482  * on how many (if any) will be written, and this function does not wait
2483  * for IO completion of submitted IO.
2484  */
2485 void writeback_inodes_sb_nr(struct super_block *sb,
2486                             unsigned long nr,
2487                             enum wb_reason reason)
2488 {
2489         __writeback_inodes_sb_nr(sb, nr, reason, false);
2490 }
2491 EXPORT_SYMBOL(writeback_inodes_sb_nr);
2492
2493 /**
2494  * writeback_inodes_sb  -       writeback dirty inodes from given super_block
2495  * @sb: the superblock
2496  * @reason: reason why some writeback work was initiated
2497  *
2498  * Start writeback on some inodes on this super_block. No guarantees are made
2499  * on how many (if any) will be written, and this function does not wait
2500  * for IO completion of submitted IO.
2501  */
2502 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2503 {
2504         return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2505 }
2506 EXPORT_SYMBOL(writeback_inodes_sb);
2507
2508 /**
2509  * try_to_writeback_inodes_sb - try to start writeback if none underway
2510  * @sb: the superblock
2511  * @reason: reason why some writeback work was initiated
2512  *
2513  * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2514  */
2515 void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2516 {
2517         if (!down_read_trylock(&sb->s_umount))
2518                 return;
2519
2520         __writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2521         up_read(&sb->s_umount);
2522 }
2523 EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2524
2525 /**
2526  * sync_inodes_sb       -       sync sb inode pages
2527  * @sb: the superblock
2528  *
2529  * This function writes and waits on any dirty inode belonging to this
2530  * super_block.
2531  */
2532 void sync_inodes_sb(struct super_block *sb)
2533 {
2534         struct backing_dev_info *bdi = sb->s_bdi;
2535         DEFINE_WB_COMPLETION(done, bdi);
2536         struct wb_writeback_work work = {
2537                 .sb             = sb,
2538                 .sync_mode      = WB_SYNC_ALL,
2539                 .nr_pages       = LONG_MAX,
2540                 .range_cyclic   = 0,
2541                 .done           = &done,
2542                 .reason         = WB_REASON_SYNC,
2543                 .for_sync       = 1,
2544         };
2545
2546         /*
2547          * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2548          * inodes under writeback and I_DIRTY_TIME inodes ignored by
2549          * bdi_has_dirty() need to be written out too.
2550          */
2551         if (bdi == &noop_backing_dev_info)
2552                 return;
2553         WARN_ON(!rwsem_is_locked(&sb->s_umount));
2554
2555         /* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2556         bdi_down_write_wb_switch_rwsem(bdi);
2557         bdi_split_work_to_wbs(bdi, &work, false);
2558         wb_wait_for_completion(&done);
2559         bdi_up_write_wb_switch_rwsem(bdi);
2560
2561         wait_sb_inodes(sb);
2562 }
2563 EXPORT_SYMBOL(sync_inodes_sb);
2564
2565 /**
2566  * write_inode_now      -       write an inode to disk
2567  * @inode: inode to write to disk
2568  * @sync: whether the write should be synchronous or not
2569  *
2570  * This function commits an inode to disk immediately if it is dirty. This is
2571  * primarily needed by knfsd.
2572  *
2573  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2574  */
2575 int write_inode_now(struct inode *inode, int sync)
2576 {
2577         struct writeback_control wbc = {
2578                 .nr_to_write = LONG_MAX,
2579                 .sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2580                 .range_start = 0,
2581                 .range_end = LLONG_MAX,
2582         };
2583
2584         if (!mapping_cap_writeback_dirty(inode->i_mapping))
2585                 wbc.nr_to_write = 0;
2586
2587         might_sleep();
2588         return writeback_single_inode(inode, &wbc);
2589 }
2590 EXPORT_SYMBOL(write_inode_now);
2591
2592 /**
2593  * sync_inode - write an inode and its pages to disk.
2594  * @inode: the inode to sync
2595  * @wbc: controls the writeback mode
2596  *
2597  * sync_inode() will write an inode and its pages to disk.  It will also
2598  * correctly update the inode on its superblock's dirty inode lists and will
2599  * update inode->i_state.
2600  *
2601  * The caller must have a ref on the inode.
2602  */
2603 int sync_inode(struct inode *inode, struct writeback_control *wbc)
2604 {
2605         return writeback_single_inode(inode, wbc);
2606 }
2607 EXPORT_SYMBOL(sync_inode);
2608
2609 /**
2610  * sync_inode_metadata - write an inode to disk
2611  * @inode: the inode to sync
2612  * @wait: wait for I/O to complete.
2613  *
2614  * Write an inode to disk and adjust its dirty state after completion.
2615  *
2616  * Note: only writes the actual inode, no associated data or other metadata.
2617  */
2618 int sync_inode_metadata(struct inode *inode, int wait)
2619 {
2620         struct writeback_control wbc = {
2621                 .sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2622                 .nr_to_write = 0, /* metadata-only */
2623         };
2624
2625         return sync_inode(inode, &wbc);
2626 }
2627 EXPORT_SYMBOL(sync_inode_metadata);