2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
18 * Copyright IBM Corporation, 2008
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
27 * For detailed explanation of Read-Copy Update mechanism see -
30 #include <linux/types.h>
31 #include <linux/kernel.h>
32 #include <linux/init.h>
33 #include <linux/spinlock.h>
34 #include <linux/smp.h>
35 #include <linux/rcupdate_wait.h>
36 #include <linux/interrupt.h>
37 #include <linux/sched.h>
38 #include <linux/sched/debug.h>
39 #include <linux/nmi.h>
40 #include <linux/atomic.h>
41 #include <linux/bitops.h>
42 #include <linux/export.h>
43 #include <linux/completion.h>
44 #include <linux/moduleparam.h>
45 #include <linux/percpu.h>
46 #include <linux/notifier.h>
47 #include <linux/cpu.h>
48 #include <linux/mutex.h>
49 #include <linux/time.h>
50 #include <linux/kernel_stat.h>
51 #include <linux/wait.h>
52 #include <linux/kthread.h>
53 #include <uapi/linux/sched/types.h>
54 #include <linux/prefetch.h>
55 #include <linux/delay.h>
56 #include <linux/stop_machine.h>
57 #include <linux/random.h>
58 #include <linux/trace_events.h>
59 #include <linux/suspend.h>
60 #include <linux/ftrace.h>
65 #ifdef MODULE_PARAM_PREFIX
66 #undef MODULE_PARAM_PREFIX
68 #define MODULE_PARAM_PREFIX "rcutree."
70 /* Data structures. */
73 * In order to export the rcu_state name to the tracing tools, it
74 * needs to be added in the __tracepoint_string section.
75 * This requires defining a separate variable tp_<sname>_varname
76 * that points to the string being used, and this will allow
77 * the tracing userspace tools to be able to decipher the string
78 * address to the matching string.
81 # define DEFINE_RCU_TPS(sname) \
82 static char sname##_varname[] = #sname; \
83 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname;
84 # define RCU_STATE_NAME(sname) sname##_varname
86 # define DEFINE_RCU_TPS(sname)
87 # define RCU_STATE_NAME(sname) __stringify(sname)
90 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
91 DEFINE_RCU_TPS(sname) \
92 static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, sname##_data); \
93 struct rcu_state sname##_state = { \
94 .level = { &sname##_state.node[0] }, \
95 .rda = &sname##_data, \
97 .gp_state = RCU_GP_IDLE, \
98 .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT, \
99 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
100 .name = RCU_STATE_NAME(sname), \
102 .exp_mutex = __MUTEX_INITIALIZER(sname##_state.exp_mutex), \
103 .exp_wake_mutex = __MUTEX_INITIALIZER(sname##_state.exp_wake_mutex), \
106 RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
107 RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
109 static struct rcu_state *const rcu_state_p;
110 LIST_HEAD(rcu_struct_flavors);
112 /* Dump rcu_node combining tree at boot to verify correct setup. */
113 static bool dump_tree;
114 module_param(dump_tree, bool, 0444);
115 /* Control rcu_node-tree auto-balancing at boot time. */
116 static bool rcu_fanout_exact;
117 module_param(rcu_fanout_exact, bool, 0444);
118 /* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */
119 static int rcu_fanout_leaf = RCU_FANOUT_LEAF;
120 module_param(rcu_fanout_leaf, int, 0444);
121 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
122 /* Number of rcu_nodes at specified level. */
123 int num_rcu_lvl[] = NUM_RCU_LVL_INIT;
124 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
125 /* panic() on RCU Stall sysctl. */
126 int sysctl_panic_on_rcu_stall __read_mostly;
129 * The rcu_scheduler_active variable is initialized to the value
130 * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the
131 * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE,
132 * RCU can assume that there is but one task, allowing RCU to (for example)
133 * optimize synchronize_rcu() to a simple barrier(). When this variable
134 * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required
135 * to detect real grace periods. This variable is also used to suppress
136 * boot-time false positives from lockdep-RCU error checking. Finally, it
137 * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU
138 * is fully initialized, including all of its kthreads having been spawned.
140 int rcu_scheduler_active __read_mostly;
141 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
144 * The rcu_scheduler_fully_active variable transitions from zero to one
145 * during the early_initcall() processing, which is after the scheduler
146 * is capable of creating new tasks. So RCU processing (for example,
147 * creating tasks for RCU priority boosting) must be delayed until after
148 * rcu_scheduler_fully_active transitions from zero to one. We also
149 * currently delay invocation of any RCU callbacks until after this point.
151 * It might later prove better for people registering RCU callbacks during
152 * early boot to take responsibility for these callbacks, but one step at
155 static int rcu_scheduler_fully_active __read_mostly;
157 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
158 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);
159 static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
160 static void invoke_rcu_core(void);
161 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
162 static void rcu_report_exp_rdp(struct rcu_state *rsp,
163 struct rcu_data *rdp, bool wake);
164 static void sync_sched_exp_online_cleanup(int cpu);
166 /* rcuc/rcub kthread realtime priority */
167 static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;
168 module_param(kthread_prio, int, 0644);
170 /* Delay in jiffies for grace-period initialization delays, debug only. */
172 static int gp_preinit_delay;
173 module_param(gp_preinit_delay, int, 0444);
174 static int gp_init_delay;
175 module_param(gp_init_delay, int, 0444);
176 static int gp_cleanup_delay;
177 module_param(gp_cleanup_delay, int, 0444);
180 * Number of grace periods between delays, normalized by the duration of
181 * the delay. The longer the delay, the more the grace periods between
182 * each delay. The reason for this normalization is that it means that,
183 * for non-zero delays, the overall slowdown of grace periods is constant
184 * regardless of the duration of the delay. This arrangement balances
185 * the need for long delays to increase some race probabilities with the
186 * need for fast grace periods to increase other race probabilities.
188 #define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays. */
191 * Track the rcutorture test sequence number and the update version
192 * number within a given test. The rcutorture_testseq is incremented
193 * on every rcutorture module load and unload, so has an odd value
194 * when a test is running. The rcutorture_vernum is set to zero
195 * when rcutorture starts and is incremented on each rcutorture update.
196 * These variables enable correlating rcutorture output with the
197 * RCU tracing information.
199 unsigned long rcutorture_testseq;
200 unsigned long rcutorture_vernum;
203 * Compute the mask of online CPUs for the specified rcu_node structure.
204 * This will not be stable unless the rcu_node structure's ->lock is
205 * held, but the bit corresponding to the current CPU will be stable
208 unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp)
210 return READ_ONCE(rnp->qsmaskinitnext);
214 * Return true if an RCU grace period is in progress. The READ_ONCE()s
215 * permit this function to be invoked without holding the root rcu_node
216 * structure's ->lock, but of course results can be subject to change.
218 static int rcu_gp_in_progress(struct rcu_state *rsp)
220 return rcu_seq_state(rcu_seq_current(&rsp->gp_seq));
224 * Note a quiescent state. Because we do not need to know
225 * how many quiescent states passed, just if there was at least
226 * one since the start of the grace period, this just sets a flag.
227 * The caller must have disabled preemption.
229 void rcu_sched_qs(void)
231 RCU_LOCKDEP_WARN(preemptible(), "rcu_sched_qs() invoked with preemption enabled!!!");
232 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.s))
234 trace_rcu_grace_period(TPS("rcu_sched"),
235 __this_cpu_read(rcu_sched_data.gp_seq),
237 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.norm, false);
238 if (!__this_cpu_read(rcu_sched_data.cpu_no_qs.b.exp))
240 __this_cpu_write(rcu_sched_data.cpu_no_qs.b.exp, false);
241 rcu_report_exp_rdp(&rcu_sched_state,
242 this_cpu_ptr(&rcu_sched_data), true);
247 RCU_LOCKDEP_WARN(preemptible(), "rcu_bh_qs() invoked with preemption enabled!!!");
248 if (__this_cpu_read(rcu_bh_data.cpu_no_qs.s)) {
249 trace_rcu_grace_period(TPS("rcu_bh"),
250 __this_cpu_read(rcu_bh_data.gp_seq),
252 __this_cpu_write(rcu_bh_data.cpu_no_qs.b.norm, false);
257 * Steal a bit from the bottom of ->dynticks for idle entry/exit
258 * control. Initially this is for TLB flushing.
260 #define RCU_DYNTICK_CTRL_MASK 0x1
261 #define RCU_DYNTICK_CTRL_CTR (RCU_DYNTICK_CTRL_MASK + 1)
262 #ifndef rcu_eqs_special_exit
263 #define rcu_eqs_special_exit() do { } while (0)
266 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
267 .dynticks_nesting = 1,
268 .dynticks_nmi_nesting = DYNTICK_IRQ_NONIDLE,
269 .dynticks = ATOMIC_INIT(RCU_DYNTICK_CTRL_CTR),
273 * Record entry into an extended quiescent state. This is only to be
274 * called when not already in an extended quiescent state.
276 static void rcu_dynticks_eqs_enter(void)
278 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
282 * CPUs seeing atomic_add_return() must see prior RCU read-side
283 * critical sections, and we also must force ordering with the
286 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
287 /* Better be in an extended quiescent state! */
288 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
289 (seq & RCU_DYNTICK_CTRL_CTR));
290 /* Better not have special action (TLB flush) pending! */
291 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
292 (seq & RCU_DYNTICK_CTRL_MASK));
296 * Record exit from an extended quiescent state. This is only to be
297 * called from an extended quiescent state.
299 static void rcu_dynticks_eqs_exit(void)
301 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
305 * CPUs seeing atomic_add_return() must see prior idle sojourns,
306 * and we also must force ordering with the next RCU read-side
309 seq = atomic_add_return(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
310 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
311 !(seq & RCU_DYNTICK_CTRL_CTR));
312 if (seq & RCU_DYNTICK_CTRL_MASK) {
313 atomic_andnot(RCU_DYNTICK_CTRL_MASK, &rdtp->dynticks);
314 smp_mb__after_atomic(); /* _exit after clearing mask. */
315 /* Prefer duplicate flushes to losing a flush. */
316 rcu_eqs_special_exit();
321 * Reset the current CPU's ->dynticks counter to indicate that the
322 * newly onlined CPU is no longer in an extended quiescent state.
323 * This will either leave the counter unchanged, or increment it
324 * to the next non-quiescent value.
326 * The non-atomic test/increment sequence works because the upper bits
327 * of the ->dynticks counter are manipulated only by the corresponding CPU,
328 * or when the corresponding CPU is offline.
330 static void rcu_dynticks_eqs_online(void)
332 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
334 if (atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR)
336 atomic_add(RCU_DYNTICK_CTRL_CTR, &rdtp->dynticks);
340 * Is the current CPU in an extended quiescent state?
342 * No ordering, as we are sampling CPU-local information.
344 bool rcu_dynticks_curr_cpu_in_eqs(void)
346 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
348 return !(atomic_read(&rdtp->dynticks) & RCU_DYNTICK_CTRL_CTR);
352 * Snapshot the ->dynticks counter with full ordering so as to allow
353 * stable comparison of this counter with past and future snapshots.
355 int rcu_dynticks_snap(struct rcu_dynticks *rdtp)
357 int snap = atomic_add_return(0, &rdtp->dynticks);
359 return snap & ~RCU_DYNTICK_CTRL_MASK;
363 * Return true if the snapshot returned from rcu_dynticks_snap()
364 * indicates that RCU is in an extended quiescent state.
366 static bool rcu_dynticks_in_eqs(int snap)
368 return !(snap & RCU_DYNTICK_CTRL_CTR);
372 * Return true if the CPU corresponding to the specified rcu_dynticks
373 * structure has spent some time in an extended quiescent state since
374 * rcu_dynticks_snap() returned the specified snapshot.
376 static bool rcu_dynticks_in_eqs_since(struct rcu_dynticks *rdtp, int snap)
378 return snap != rcu_dynticks_snap(rdtp);
382 * Do a double-increment of the ->dynticks counter to emulate a
383 * momentary idle-CPU quiescent state.
385 static void rcu_dynticks_momentary_idle(void)
387 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
388 int special = atomic_add_return(2 * RCU_DYNTICK_CTRL_CTR,
391 /* It is illegal to call this from idle state. */
392 WARN_ON_ONCE(!(special & RCU_DYNTICK_CTRL_CTR));
396 * Set the special (bottom) bit of the specified CPU so that it
397 * will take special action (such as flushing its TLB) on the
398 * next exit from an extended quiescent state. Returns true if
399 * the bit was successfully set, or false if the CPU was not in
400 * an extended quiescent state.
402 bool rcu_eqs_special_set(int cpu)
406 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
409 old = atomic_read(&rdtp->dynticks);
410 if (old & RCU_DYNTICK_CTRL_CTR)
412 new = old | RCU_DYNTICK_CTRL_MASK;
413 } while (atomic_cmpxchg(&rdtp->dynticks, old, new) != old);
418 * Let the RCU core know that this CPU has gone through the scheduler,
419 * which is a quiescent state. This is called when the need for a
420 * quiescent state is urgent, so we burn an atomic operation and full
421 * memory barriers to let the RCU core know about it, regardless of what
422 * this CPU might (or might not) do in the near future.
424 * We inform the RCU core by emulating a zero-duration dyntick-idle period.
426 * The caller must have disabled interrupts.
428 static void rcu_momentary_dyntick_idle(void)
430 raw_cpu_write(rcu_dynticks.rcu_need_heavy_qs, false);
431 rcu_dynticks_momentary_idle();
435 * Note a context switch. This is a quiescent state for RCU-sched,
436 * and requires special handling for preemptible RCU.
437 * The caller must have disabled interrupts.
439 void rcu_note_context_switch(bool preempt)
441 barrier(); /* Avoid RCU read-side critical sections leaking down. */
442 trace_rcu_utilization(TPS("Start context switch"));
444 rcu_preempt_note_context_switch(preempt);
445 /* Load rcu_urgent_qs before other flags. */
446 if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs)))
448 this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
449 if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs)))
450 rcu_momentary_dyntick_idle();
451 this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
453 rcu_note_voluntary_context_switch_lite(current);
455 trace_rcu_utilization(TPS("End context switch"));
456 barrier(); /* Avoid RCU read-side critical sections leaking up. */
458 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
461 * Register a quiescent state for all RCU flavors. If there is an
462 * emergency, invoke rcu_momentary_dyntick_idle() to do a heavy-weight
463 * dyntick-idle quiescent state visible to other CPUs (but only for those
464 * RCU flavors in desperate need of a quiescent state, which will normally
465 * be none of them). Either way, do a lightweight quiescent state for
468 * The barrier() calls are redundant in the common case when this is
469 * called externally, but just in case this is called from within this
473 void rcu_all_qs(void)
477 if (!raw_cpu_read(rcu_dynticks.rcu_urgent_qs))
480 /* Load rcu_urgent_qs before other flags. */
481 if (!smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) {
485 this_cpu_write(rcu_dynticks.rcu_urgent_qs, false);
486 barrier(); /* Avoid RCU read-side critical sections leaking down. */
487 if (unlikely(raw_cpu_read(rcu_dynticks.rcu_need_heavy_qs))) {
488 local_irq_save(flags);
489 rcu_momentary_dyntick_idle();
490 local_irq_restore(flags);
492 if (unlikely(raw_cpu_read(rcu_sched_data.cpu_no_qs.b.exp)))
494 this_cpu_inc(rcu_dynticks.rcu_qs_ctr);
495 barrier(); /* Avoid RCU read-side critical sections leaking up. */
498 EXPORT_SYMBOL_GPL(rcu_all_qs);
500 #define DEFAULT_RCU_BLIMIT 10 /* Maximum callbacks per rcu_do_batch. */
501 static long blimit = DEFAULT_RCU_BLIMIT;
502 #define DEFAULT_RCU_QHIMARK 10000 /* If this many pending, ignore blimit. */
503 static long qhimark = DEFAULT_RCU_QHIMARK;
504 #define DEFAULT_RCU_QLOMARK 100 /* Once only this many pending, use blimit. */
505 static long qlowmark = DEFAULT_RCU_QLOMARK;
507 module_param(blimit, long, 0444);
508 module_param(qhimark, long, 0444);
509 module_param(qlowmark, long, 0444);
511 static ulong jiffies_till_first_fqs = ULONG_MAX;
512 static ulong jiffies_till_next_fqs = ULONG_MAX;
513 static bool rcu_kick_kthreads;
515 module_param(jiffies_till_first_fqs, ulong, 0644);
516 module_param(jiffies_till_next_fqs, ulong, 0644);
517 module_param(rcu_kick_kthreads, bool, 0644);
520 * How long the grace period must be before we start recruiting
521 * quiescent-state help from rcu_note_context_switch().
523 static ulong jiffies_till_sched_qs = HZ / 10;
524 module_param(jiffies_till_sched_qs, ulong, 0444);
526 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp));
527 static void force_quiescent_state(struct rcu_state *rsp);
528 static int rcu_pending(void);
531 * Return the number of RCU GPs completed thus far for debug & stats.
533 unsigned long rcu_get_gp_seq(void)
535 return READ_ONCE(rcu_state_p->gp_seq);
537 EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
540 * Return the number of RCU-sched GPs completed thus far for debug & stats.
542 unsigned long rcu_sched_get_gp_seq(void)
544 return READ_ONCE(rcu_sched_state.gp_seq);
546 EXPORT_SYMBOL_GPL(rcu_sched_get_gp_seq);
549 * Return the number of RCU-bh GPs completed thus far for debug & stats.
551 unsigned long rcu_bh_get_gp_seq(void)
553 return READ_ONCE(rcu_bh_state.gp_seq);
555 EXPORT_SYMBOL_GPL(rcu_bh_get_gp_seq);
558 * Return the number of RCU expedited batches completed thus far for
559 * debug & stats. Odd numbers mean that a batch is in progress, even
560 * numbers mean idle. The value returned will thus be roughly double
561 * the cumulative batches since boot.
563 unsigned long rcu_exp_batches_completed(void)
565 return rcu_state_p->expedited_sequence;
567 EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
570 * Return the number of RCU-sched expedited batches completed thus far
571 * for debug & stats. Similar to rcu_exp_batches_completed().
573 unsigned long rcu_exp_batches_completed_sched(void)
575 return rcu_sched_state.expedited_sequence;
577 EXPORT_SYMBOL_GPL(rcu_exp_batches_completed_sched);
580 * Force a quiescent state.
582 void rcu_force_quiescent_state(void)
584 force_quiescent_state(rcu_state_p);
586 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
589 * Force a quiescent state for RCU BH.
591 void rcu_bh_force_quiescent_state(void)
593 force_quiescent_state(&rcu_bh_state);
595 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
598 * Force a quiescent state for RCU-sched.
600 void rcu_sched_force_quiescent_state(void)
602 force_quiescent_state(&rcu_sched_state);
604 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
607 * Show the state of the grace-period kthreads.
609 void show_rcu_gp_kthreads(void)
611 struct rcu_state *rsp;
613 for_each_rcu_flavor(rsp) {
614 pr_info("%s: wait state: %d ->state: %#lx\n",
615 rsp->name, rsp->gp_state, rsp->gp_kthread->state);
616 /* sched_show_task(rsp->gp_kthread); */
619 EXPORT_SYMBOL_GPL(show_rcu_gp_kthreads);
622 * Record the number of times rcutorture tests have been initiated and
623 * terminated. This information allows the debugfs tracing stats to be
624 * correlated to the rcutorture messages, even when the rcutorture module
625 * is being repeatedly loaded and unloaded. In other words, we cannot
626 * store this state in rcutorture itself.
628 void rcutorture_record_test_transition(void)
630 rcutorture_testseq++;
631 rcutorture_vernum = 0;
633 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
636 * Send along grace-period-related data for rcutorture diagnostics.
638 void rcutorture_get_gp_data(enum rcutorture_type test_type, int *flags,
639 unsigned long *gp_seq)
641 struct rcu_state *rsp = NULL;
650 case RCU_SCHED_FLAVOR:
651 rsp = &rcu_sched_state;
658 *flags = READ_ONCE(rsp->gp_flags);
659 *gp_seq = rcu_seq_current(&rsp->gp_seq);
661 EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
664 * Record the number of writer passes through the current rcutorture test.
665 * This is also used to correlate debugfs tracing stats with the rcutorture
668 void rcutorture_record_progress(unsigned long vernum)
672 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
675 * Return the root node of the specified rcu_state structure.
677 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
679 return &rsp->node[0];
683 * Enter an RCU extended quiescent state, which can be either the
684 * idle loop or adaptive-tickless usermode execution.
686 * We crowbar the ->dynticks_nmi_nesting field to zero to allow for
687 * the possibility of usermode upcalls having messed up our count
688 * of interrupt nesting level during the prior busy period.
690 static void rcu_eqs_enter(bool user)
692 struct rcu_state *rsp;
693 struct rcu_data *rdp;
694 struct rcu_dynticks *rdtp;
696 rdtp = this_cpu_ptr(&rcu_dynticks);
697 WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0);
698 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) &&
699 rdtp->dynticks_nesting == 0);
700 if (rdtp->dynticks_nesting != 1) {
701 rdtp->dynticks_nesting--;
705 lockdep_assert_irqs_disabled();
706 trace_rcu_dyntick(TPS("Start"), rdtp->dynticks_nesting, 0, rdtp->dynticks);
707 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
708 for_each_rcu_flavor(rsp) {
709 rdp = this_cpu_ptr(rsp->rda);
710 do_nocb_deferred_wakeup(rdp);
712 rcu_prepare_for_idle();
713 WRITE_ONCE(rdtp->dynticks_nesting, 0); /* Avoid irq-access tearing. */
714 rcu_dynticks_eqs_enter();
715 rcu_dynticks_task_enter();
719 * rcu_idle_enter - inform RCU that current CPU is entering idle
721 * Enter idle mode, in other words, -leave- the mode in which RCU
722 * read-side critical sections can occur. (Though RCU read-side
723 * critical sections can occur in irq handlers in idle, a possibility
724 * handled by irq_enter() and irq_exit().)
726 * If you add or remove a call to rcu_idle_enter(), be sure to test with
727 * CONFIG_RCU_EQS_DEBUG=y.
729 void rcu_idle_enter(void)
731 lockdep_assert_irqs_disabled();
732 rcu_eqs_enter(false);
735 #ifdef CONFIG_NO_HZ_FULL
737 * rcu_user_enter - inform RCU that we are resuming userspace.
739 * Enter RCU idle mode right before resuming userspace. No use of RCU
740 * is permitted between this call and rcu_user_exit(). This way the
741 * CPU doesn't need to maintain the tick for RCU maintenance purposes
742 * when the CPU runs in userspace.
744 * If you add or remove a call to rcu_user_enter(), be sure to test with
745 * CONFIG_RCU_EQS_DEBUG=y.
747 void rcu_user_enter(void)
749 lockdep_assert_irqs_disabled();
752 #endif /* CONFIG_NO_HZ_FULL */
755 * rcu_nmi_exit - inform RCU of exit from NMI context
757 * If we are returning from the outermost NMI handler that interrupted an
758 * RCU-idle period, update rdtp->dynticks and rdtp->dynticks_nmi_nesting
759 * to let the RCU grace-period handling know that the CPU is back to
762 * If you add or remove a call to rcu_nmi_exit(), be sure to test
763 * with CONFIG_RCU_EQS_DEBUG=y.
765 void rcu_nmi_exit(void)
767 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
770 * Check for ->dynticks_nmi_nesting underflow and bad ->dynticks.
771 * (We are exiting an NMI handler, so RCU better be paying attention
774 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting <= 0);
775 WARN_ON_ONCE(rcu_dynticks_curr_cpu_in_eqs());
778 * If the nesting level is not 1, the CPU wasn't RCU-idle, so
779 * leave it in non-RCU-idle state.
781 if (rdtp->dynticks_nmi_nesting != 1) {
782 trace_rcu_dyntick(TPS("--="), rdtp->dynticks_nmi_nesting, rdtp->dynticks_nmi_nesting - 2, rdtp->dynticks);
783 WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* No store tearing. */
784 rdtp->dynticks_nmi_nesting - 2);
788 /* This NMI interrupted an RCU-idle CPU, restore RCU-idleness. */
789 trace_rcu_dyntick(TPS("Startirq"), rdtp->dynticks_nmi_nesting, 0, rdtp->dynticks);
790 WRITE_ONCE(rdtp->dynticks_nmi_nesting, 0); /* Avoid store tearing. */
791 rcu_dynticks_eqs_enter();
795 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
797 * Exit from an interrupt handler, which might possibly result in entering
798 * idle mode, in other words, leaving the mode in which read-side critical
799 * sections can occur. The caller must have disabled interrupts.
801 * This code assumes that the idle loop never does anything that might
802 * result in unbalanced calls to irq_enter() and irq_exit(). If your
803 * architecture's idle loop violates this assumption, RCU will give you what
804 * you deserve, good and hard. But very infrequently and irreproducibly.
806 * Use things like work queues to work around this limitation.
808 * You have been warned.
810 * If you add or remove a call to rcu_irq_exit(), be sure to test with
811 * CONFIG_RCU_EQS_DEBUG=y.
813 void rcu_irq_exit(void)
815 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
817 lockdep_assert_irqs_disabled();
818 if (rdtp->dynticks_nmi_nesting == 1)
819 rcu_prepare_for_idle();
821 if (rdtp->dynticks_nmi_nesting == 0)
822 rcu_dynticks_task_enter();
826 * Wrapper for rcu_irq_exit() where interrupts are enabled.
828 * If you add or remove a call to rcu_irq_exit_irqson(), be sure to test
829 * with CONFIG_RCU_EQS_DEBUG=y.
831 void rcu_irq_exit_irqson(void)
835 local_irq_save(flags);
837 local_irq_restore(flags);
841 * Exit an RCU extended quiescent state, which can be either the
842 * idle loop or adaptive-tickless usermode execution.
844 * We crowbar the ->dynticks_nmi_nesting field to DYNTICK_IRQ_NONIDLE to
845 * allow for the possibility of usermode upcalls messing up our count of
846 * interrupt nesting level during the busy period that is just now starting.
848 static void rcu_eqs_exit(bool user)
850 struct rcu_dynticks *rdtp;
853 lockdep_assert_irqs_disabled();
854 rdtp = this_cpu_ptr(&rcu_dynticks);
855 oldval = rdtp->dynticks_nesting;
856 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && oldval < 0);
858 rdtp->dynticks_nesting++;
861 rcu_dynticks_task_exit();
862 rcu_dynticks_eqs_exit();
863 rcu_cleanup_after_idle();
864 trace_rcu_dyntick(TPS("End"), rdtp->dynticks_nesting, 1, rdtp->dynticks);
865 WARN_ON_ONCE(IS_ENABLED(CONFIG_RCU_EQS_DEBUG) && !user && !is_idle_task(current));
866 WRITE_ONCE(rdtp->dynticks_nesting, 1);
867 WRITE_ONCE(rdtp->dynticks_nmi_nesting, DYNTICK_IRQ_NONIDLE);
871 * rcu_idle_exit - inform RCU that current CPU is leaving idle
873 * Exit idle mode, in other words, -enter- the mode in which RCU
874 * read-side critical sections can occur.
876 * If you add or remove a call to rcu_idle_exit(), be sure to test with
877 * CONFIG_RCU_EQS_DEBUG=y.
879 void rcu_idle_exit(void)
883 local_irq_save(flags);
885 local_irq_restore(flags);
888 #ifdef CONFIG_NO_HZ_FULL
890 * rcu_user_exit - inform RCU that we are exiting userspace.
892 * Exit RCU idle mode while entering the kernel because it can
893 * run a RCU read side critical section anytime.
895 * If you add or remove a call to rcu_user_exit(), be sure to test with
896 * CONFIG_RCU_EQS_DEBUG=y.
898 void rcu_user_exit(void)
902 #endif /* CONFIG_NO_HZ_FULL */
905 * rcu_nmi_enter - inform RCU of entry to NMI context
907 * If the CPU was idle from RCU's viewpoint, update rdtp->dynticks and
908 * rdtp->dynticks_nmi_nesting to let the RCU grace-period handling know
909 * that the CPU is active. This implementation permits nested NMIs, as
910 * long as the nesting level does not overflow an int. (You will probably
911 * run out of stack space first.)
913 * If you add or remove a call to rcu_nmi_enter(), be sure to test
914 * with CONFIG_RCU_EQS_DEBUG=y.
916 void rcu_nmi_enter(void)
918 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
921 /* Complain about underflow. */
922 WARN_ON_ONCE(rdtp->dynticks_nmi_nesting < 0);
925 * If idle from RCU viewpoint, atomically increment ->dynticks
926 * to mark non-idle and increment ->dynticks_nmi_nesting by one.
927 * Otherwise, increment ->dynticks_nmi_nesting by two. This means
928 * if ->dynticks_nmi_nesting is equal to one, we are guaranteed
929 * to be in the outermost NMI handler that interrupted an RCU-idle
930 * period (observation due to Andy Lutomirski).
932 if (rcu_dynticks_curr_cpu_in_eqs()) {
933 rcu_dynticks_eqs_exit();
936 trace_rcu_dyntick(incby == 1 ? TPS("Endirq") : TPS("++="),
937 rdtp->dynticks_nmi_nesting,
938 rdtp->dynticks_nmi_nesting + incby, rdtp->dynticks);
939 WRITE_ONCE(rdtp->dynticks_nmi_nesting, /* Prevent store tearing. */
940 rdtp->dynticks_nmi_nesting + incby);
945 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
947 * Enter an interrupt handler, which might possibly result in exiting
948 * idle mode, in other words, entering the mode in which read-side critical
949 * sections can occur. The caller must have disabled interrupts.
951 * Note that the Linux kernel is fully capable of entering an interrupt
952 * handler that it never exits, for example when doing upcalls to user mode!
953 * This code assumes that the idle loop never does upcalls to user mode.
954 * If your architecture's idle loop does do upcalls to user mode (or does
955 * anything else that results in unbalanced calls to the irq_enter() and
956 * irq_exit() functions), RCU will give you what you deserve, good and hard.
957 * But very infrequently and irreproducibly.
959 * Use things like work queues to work around this limitation.
961 * You have been warned.
963 * If you add or remove a call to rcu_irq_enter(), be sure to test with
964 * CONFIG_RCU_EQS_DEBUG=y.
966 void rcu_irq_enter(void)
968 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
970 lockdep_assert_irqs_disabled();
971 if (rdtp->dynticks_nmi_nesting == 0)
972 rcu_dynticks_task_exit();
974 if (rdtp->dynticks_nmi_nesting == 1)
975 rcu_cleanup_after_idle();
979 * Wrapper for rcu_irq_enter() where interrupts are enabled.
981 * If you add or remove a call to rcu_irq_enter_irqson(), be sure to test
982 * with CONFIG_RCU_EQS_DEBUG=y.
984 void rcu_irq_enter_irqson(void)
988 local_irq_save(flags);
990 local_irq_restore(flags);
994 * rcu_is_watching - see if RCU thinks that the current CPU is idle
996 * Return true if RCU is watching the running CPU, which means that this
997 * CPU can safely enter RCU read-side critical sections. In other words,
998 * if the current CPU is in its idle loop and is neither in an interrupt
999 * or NMI handler, return true.
1001 bool notrace rcu_is_watching(void)
1005 preempt_disable_notrace();
1006 ret = !rcu_dynticks_curr_cpu_in_eqs();
1007 preempt_enable_notrace();
1010 EXPORT_SYMBOL_GPL(rcu_is_watching);
1013 * If a holdout task is actually running, request an urgent quiescent
1014 * state from its CPU. This is unsynchronized, so migrations can cause
1015 * the request to go to the wrong CPU. Which is OK, all that will happen
1016 * is that the CPU's next context switch will be a bit slower and next
1017 * time around this task will generate another request.
1019 void rcu_request_urgent_qs_task(struct task_struct *t)
1026 return; /* This task is not running on that CPU. */
1027 smp_store_release(per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, cpu), true);
1030 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
1033 * Is the current CPU online? Disable preemption to avoid false positives
1034 * that could otherwise happen due to the current CPU number being sampled,
1035 * this task being preempted, its old CPU being taken offline, resuming
1036 * on some other CPU, then determining that its old CPU is now offline.
1037 * It is OK to use RCU on an offline processor during initial boot, hence
1038 * the check for rcu_scheduler_fully_active. Note also that it is OK
1039 * for a CPU coming online to use RCU for one jiffy prior to marking itself
1040 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
1041 * offline to continue to use RCU for one jiffy after marking itself
1042 * offline in the cpu_online_mask. This leniency is necessary given the
1043 * non-atomic nature of the online and offline processing, for example,
1044 * the fact that a CPU enters the scheduler after completing the teardown
1047 * This is also why RCU internally marks CPUs online during in the
1048 * preparation phase and offline after the CPU has been taken down.
1050 * Disable checking if in an NMI handler because we cannot safely report
1051 * errors from NMI handlers anyway.
1053 bool rcu_lockdep_current_cpu_online(void)
1055 struct rcu_data *rdp;
1056 struct rcu_node *rnp;
1062 rdp = this_cpu_ptr(&rcu_sched_data);
1064 ret = (rdp->grpmask & rcu_rnp_online_cpus(rnp)) ||
1065 !rcu_scheduler_fully_active;
1069 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
1071 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
1074 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
1076 * If the current CPU is idle or running at a first-level (not nested)
1077 * interrupt from idle, return true. The caller must have at least
1078 * disabled preemption.
1080 static int rcu_is_cpu_rrupt_from_idle(void)
1082 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 0 &&
1083 __this_cpu_read(rcu_dynticks.dynticks_nmi_nesting) <= 1;
1087 * We are reporting a quiescent state on behalf of some other CPU, so
1088 * it is our responsibility to check for and handle potential overflow
1089 * of the rcu_node ->gp_seq counter with respect to the rcu_data counters.
1090 * After all, the CPU might be in deep idle state, and thus executing no
1093 static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp)
1095 raw_lockdep_assert_held_rcu_node(rnp);
1096 if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + ULONG_MAX / 4,
1098 WRITE_ONCE(rdp->gpwrap, true);
1099 if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq))
1100 rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;
1104 * Snapshot the specified CPU's dynticks counter so that we can later
1105 * credit them with an implicit quiescent state. Return 1 if this CPU
1106 * is in dynticks idle mode, which is an extended quiescent state.
1108 static int dyntick_save_progress_counter(struct rcu_data *rdp)
1110 rdp->dynticks_snap = rcu_dynticks_snap(rdp->dynticks);
1111 if (rcu_dynticks_in_eqs(rdp->dynticks_snap)) {
1112 trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("dti"));
1113 rcu_gpnum_ovf(rdp->mynode, rdp);
1120 * Handler for the irq_work request posted when a grace period has
1121 * gone on for too long, but not yet long enough for an RCU CPU
1122 * stall warning. Set state appropriately, but just complain if
1123 * there is unexpected state on entry.
1125 static void rcu_iw_handler(struct irq_work *iwp)
1127 struct rcu_data *rdp;
1128 struct rcu_node *rnp;
1130 rdp = container_of(iwp, struct rcu_data, rcu_iw);
1132 raw_spin_lock_rcu_node(rnp);
1133 if (!WARN_ON_ONCE(!rdp->rcu_iw_pending)) {
1134 rdp->rcu_iw_gp_seq = rnp->gp_seq;
1135 rdp->rcu_iw_pending = false;
1137 raw_spin_unlock_rcu_node(rnp);
1141 * Return true if the specified CPU has passed through a quiescent
1142 * state by virtue of being in or having passed through an dynticks
1143 * idle state since the last call to dyntick_save_progress_counter()
1144 * for this same CPU, or by virtue of having been offline.
1146 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
1151 struct rcu_node *rnp = rdp->mynode;
1154 * If the CPU passed through or entered a dynticks idle phase with
1155 * no active irq/NMI handlers, then we can safely pretend that the CPU
1156 * already acknowledged the request to pass through a quiescent
1157 * state. Either way, that CPU cannot possibly be in an RCU
1158 * read-side critical section that started before the beginning
1159 * of the current RCU grace period.
1161 if (rcu_dynticks_in_eqs_since(rdp->dynticks, rdp->dynticks_snap)) {
1162 trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("dti"));
1163 rdp->dynticks_fqs++;
1164 rcu_gpnum_ovf(rnp, rdp);
1169 * Has this CPU encountered a cond_resched() since the beginning
1170 * of the grace period? For this to be the case, the CPU has to
1171 * have noticed the current grace period. This might not be the
1172 * case for nohz_full CPUs looping in the kernel.
1174 jtsq = jiffies_till_sched_qs;
1175 ruqp = per_cpu_ptr(&rcu_dynticks.rcu_urgent_qs, rdp->cpu);
1176 if (time_after(jiffies, rdp->rsp->gp_start + jtsq) &&
1177 READ_ONCE(rdp->rcu_qs_ctr_snap) != per_cpu(rcu_dynticks.rcu_qs_ctr, rdp->cpu) &&
1178 rcu_seq_current(&rdp->gp_seq) == rnp->gp_seq && !rdp->gpwrap) {
1179 trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("rqc"));
1180 rcu_gpnum_ovf(rnp, rdp);
1182 } else if (time_after(jiffies, rdp->rsp->gp_start + jtsq)) {
1183 /* Load rcu_qs_ctr before store to rcu_urgent_qs. */
1184 smp_store_release(ruqp, true);
1187 /* Check for the CPU being offline. */
1188 if (!(rdp->grpmask & rcu_rnp_online_cpus(rnp))) {
1189 trace_rcu_fqs(rdp->rsp->name, rdp->gp_seq, rdp->cpu, TPS("ofl"));
1191 rcu_gpnum_ovf(rnp, rdp);
1196 * A CPU running for an extended time within the kernel can
1197 * delay RCU grace periods. When the CPU is in NO_HZ_FULL mode,
1198 * even context-switching back and forth between a pair of
1199 * in-kernel CPU-bound tasks cannot advance grace periods.
1200 * So if the grace period is old enough, make the CPU pay attention.
1201 * Note that the unsynchronized assignments to the per-CPU
1202 * rcu_need_heavy_qs variable are safe. Yes, setting of
1203 * bits can be lost, but they will be set again on the next
1204 * force-quiescent-state pass. So lost bit sets do not result
1205 * in incorrect behavior, merely in a grace period lasting
1206 * a few jiffies longer than it might otherwise. Because
1207 * there are at most four threads involved, and because the
1208 * updates are only once every few jiffies, the probability of
1209 * lossage (and thus of slight grace-period extension) is
1212 rnhqp = &per_cpu(rcu_dynticks.rcu_need_heavy_qs, rdp->cpu);
1213 if (!READ_ONCE(*rnhqp) &&
1214 (time_after(jiffies, rdp->rsp->gp_start + jtsq) ||
1215 time_after(jiffies, rdp->rsp->jiffies_resched))) {
1216 WRITE_ONCE(*rnhqp, true);
1217 /* Store rcu_need_heavy_qs before rcu_urgent_qs. */
1218 smp_store_release(ruqp, true);
1219 rdp->rsp->jiffies_resched += jtsq; /* Re-enable beating. */
1223 * If more than halfway to RCU CPU stall-warning time, do a
1224 * resched_cpu() to try to loosen things up a bit. Also check to
1225 * see if the CPU is getting hammered with interrupts, but only
1226 * once per grace period, just to keep the IPIs down to a dull roar.
1228 if (jiffies - rdp->rsp->gp_start > rcu_jiffies_till_stall_check() / 2) {
1229 resched_cpu(rdp->cpu);
1230 if (IS_ENABLED(CONFIG_IRQ_WORK) &&
1231 !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq &&
1232 (rnp->ffmask & rdp->grpmask)) {
1233 init_irq_work(&rdp->rcu_iw, rcu_iw_handler);
1234 rdp->rcu_iw_pending = true;
1235 rdp->rcu_iw_gp_seq = rnp->gp_seq;
1236 irq_work_queue_on(&rdp->rcu_iw, rdp->cpu);
1243 static void record_gp_stall_check_time(struct rcu_state *rsp)
1245 unsigned long j = jiffies;
1249 smp_wmb(); /* Record start time before stall time. */
1250 j1 = rcu_jiffies_till_stall_check();
1251 WRITE_ONCE(rsp->jiffies_stall, j + j1);
1252 rsp->jiffies_resched = j + j1 / 2;
1253 rsp->n_force_qs_gpstart = READ_ONCE(rsp->n_force_qs);
1257 * Convert a ->gp_state value to a character string.
1259 static const char *gp_state_getname(short gs)
1261 if (gs < 0 || gs >= ARRAY_SIZE(gp_state_names))
1263 return gp_state_names[gs];
1267 * Complain about starvation of grace-period kthread.
1269 static void rcu_check_gp_kthread_starvation(struct rcu_state *rsp)
1275 gpa = READ_ONCE(rsp->gp_activity);
1276 if (j - gpa > 2 * HZ) {
1277 pr_err("%s kthread starved for %ld jiffies! g%ld f%#x %s(%d) ->state=%#lx ->cpu=%d\n",
1279 (long)rcu_seq_current(&rsp->gp_seq),
1281 gp_state_getname(rsp->gp_state), rsp->gp_state,
1282 rsp->gp_kthread ? rsp->gp_kthread->state : ~0,
1283 rsp->gp_kthread ? task_cpu(rsp->gp_kthread) : -1);
1284 if (rsp->gp_kthread) {
1285 pr_err("RCU grace-period kthread stack dump:\n");
1286 sched_show_task(rsp->gp_kthread);
1287 wake_up_process(rsp->gp_kthread);
1293 * Dump stacks of all tasks running on stalled CPUs. First try using
1294 * NMIs, but fall back to manual remote stack tracing on architectures
1295 * that don't support NMI-based stack dumps. The NMI-triggered stack
1296 * traces are more accurate because they are printed by the target CPU.
1298 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
1301 unsigned long flags;
1302 struct rcu_node *rnp;
1304 rcu_for_each_leaf_node(rsp, rnp) {
1305 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1306 for_each_leaf_node_possible_cpu(rnp, cpu)
1307 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu))
1308 if (!trigger_single_cpu_backtrace(cpu))
1310 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1315 * If too much time has passed in the current grace period, and if
1316 * so configured, go kick the relevant kthreads.
1318 static void rcu_stall_kick_kthreads(struct rcu_state *rsp)
1322 if (!rcu_kick_kthreads)
1324 j = READ_ONCE(rsp->jiffies_kick_kthreads);
1325 if (time_after(jiffies, j) && rsp->gp_kthread &&
1326 (rcu_gp_in_progress(rsp) || READ_ONCE(rsp->gp_flags))) {
1327 WARN_ONCE(1, "Kicking %s grace-period kthread\n", rsp->name);
1328 rcu_ftrace_dump(DUMP_ALL);
1329 wake_up_process(rsp->gp_kthread);
1330 WRITE_ONCE(rsp->jiffies_kick_kthreads, j + HZ);
1334 static inline void panic_on_rcu_stall(void)
1336 if (sysctl_panic_on_rcu_stall)
1337 panic("RCU Stall\n");
1340 static void print_other_cpu_stall(struct rcu_state *rsp, unsigned long gp_seq)
1343 unsigned long flags;
1347 struct rcu_node *rnp = rcu_get_root(rsp);
1350 /* Kick and suppress, if so configured. */
1351 rcu_stall_kick_kthreads(rsp);
1352 if (rcu_cpu_stall_suppress)
1356 * OK, time to rat on our buddy...
1357 * See Documentation/RCU/stallwarn.txt for info on how to debug
1358 * RCU CPU stall warnings.
1360 pr_err("INFO: %s detected stalls on CPUs/tasks:",
1362 print_cpu_stall_info_begin();
1363 rcu_for_each_leaf_node(rsp, rnp) {
1364 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1365 ndetected += rcu_print_task_stall(rnp);
1366 if (rnp->qsmask != 0) {
1367 for_each_leaf_node_possible_cpu(rnp, cpu)
1368 if (rnp->qsmask & leaf_node_cpu_bit(rnp, cpu)) {
1369 print_cpu_stall_info(rsp, cpu);
1373 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1376 print_cpu_stall_info_end();
1377 for_each_possible_cpu(cpu)
1378 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
1380 pr_cont("(detected by %d, t=%ld jiffies, g=%ld, q=%lu)\n",
1381 smp_processor_id(), (long)(jiffies - rsp->gp_start),
1382 (long)rcu_seq_current(&rsp->gp_seq), totqlen);
1384 rcu_dump_cpu_stacks(rsp);
1386 /* Complain about tasks blocking the grace period. */
1387 rcu_print_detail_task_stall(rsp);
1389 if (rcu_seq_current(&rsp->gp_seq) != gp_seq) {
1390 pr_err("INFO: Stall ended before state dump start\n");
1393 gpa = READ_ONCE(rsp->gp_activity);
1394 pr_err("All QSes seen, last %s kthread activity %ld (%ld-%ld), jiffies_till_next_fqs=%ld, root ->qsmask %#lx\n",
1395 rsp->name, j - gpa, j, gpa,
1396 jiffies_till_next_fqs,
1397 rcu_get_root(rsp)->qsmask);
1398 /* In this case, the current CPU might be at fault. */
1399 sched_show_task(current);
1402 /* Rewrite if needed in case of slow consoles. */
1403 if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1404 WRITE_ONCE(rsp->jiffies_stall,
1405 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1407 rcu_check_gp_kthread_starvation(rsp);
1409 panic_on_rcu_stall();
1411 force_quiescent_state(rsp); /* Kick them all. */
1414 static void print_cpu_stall(struct rcu_state *rsp)
1417 unsigned long flags;
1418 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1419 struct rcu_node *rnp = rcu_get_root(rsp);
1422 /* Kick and suppress, if so configured. */
1423 rcu_stall_kick_kthreads(rsp);
1424 if (rcu_cpu_stall_suppress)
1428 * OK, time to rat on ourselves...
1429 * See Documentation/RCU/stallwarn.txt for info on how to debug
1430 * RCU CPU stall warnings.
1432 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
1433 print_cpu_stall_info_begin();
1434 raw_spin_lock_irqsave_rcu_node(rdp->mynode, flags);
1435 print_cpu_stall_info(rsp, smp_processor_id());
1436 raw_spin_unlock_irqrestore_rcu_node(rdp->mynode, flags);
1437 print_cpu_stall_info_end();
1438 for_each_possible_cpu(cpu)
1439 totqlen += rcu_segcblist_n_cbs(&per_cpu_ptr(rsp->rda,
1441 pr_cont(" (t=%lu jiffies g=%ld q=%lu)\n",
1442 jiffies - rsp->gp_start,
1443 (long)rcu_seq_current(&rsp->gp_seq), totqlen);
1445 rcu_check_gp_kthread_starvation(rsp);
1447 rcu_dump_cpu_stacks(rsp);
1449 raw_spin_lock_irqsave_rcu_node(rnp, flags);
1450 /* Rewrite if needed in case of slow consoles. */
1451 if (ULONG_CMP_GE(jiffies, READ_ONCE(rsp->jiffies_stall)))
1452 WRITE_ONCE(rsp->jiffies_stall,
1453 jiffies + 3 * rcu_jiffies_till_stall_check() + 3);
1454 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1456 panic_on_rcu_stall();
1459 * Attempt to revive the RCU machinery by forcing a context switch.
1461 * A context switch would normally allow the RCU state machine to make
1462 * progress and it could be we're stuck in kernel space without context
1463 * switches for an entirely unreasonable amount of time.
1465 resched_cpu(smp_processor_id());
1468 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1476 struct rcu_node *rnp;
1478 if ((rcu_cpu_stall_suppress && !rcu_kick_kthreads) ||
1479 !rcu_gp_in_progress(rsp))
1481 rcu_stall_kick_kthreads(rsp);
1485 * Lots of memory barriers to reject false positives.
1487 * The idea is to pick up rsp->gp_seq, then rsp->jiffies_stall,
1488 * then rsp->gp_start, and finally another copy of rsp->gp_seq.
1489 * These values are updated in the opposite order with memory
1490 * barriers (or equivalent) during grace-period initialization
1491 * and cleanup. Now, a false positive can occur if we get an new
1492 * value of rsp->gp_start and a old value of rsp->jiffies_stall.
1493 * But given the memory barriers, the only way that this can happen
1494 * is if one grace period ends and another starts between these
1495 * two fetches. This is detected by comparing the second fetch
1496 * of rsp->gp_seq with the previous fetch from rsp->gp_seq.
1498 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1499 * and rsp->gp_start suffice to forestall false positives.
1501 gs1 = READ_ONCE(rsp->gp_seq);
1502 smp_rmb(); /* Pick up ->gp_seq first... */
1503 js = READ_ONCE(rsp->jiffies_stall);
1504 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1505 gps = READ_ONCE(rsp->gp_start);
1506 smp_rmb(); /* ...and finally ->gp_start before ->gp_seq again. */
1507 gs2 = READ_ONCE(rsp->gp_seq);
1509 ULONG_CMP_LT(j, js) ||
1510 ULONG_CMP_GE(gps, js))
1511 return; /* No stall or GP completed since entering function. */
1513 jn = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
1514 if (rcu_gp_in_progress(rsp) &&
1515 (READ_ONCE(rnp->qsmask) & rdp->grpmask) &&
1516 cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
1518 /* We haven't checked in, so go dump stack. */
1519 print_cpu_stall(rsp);
1521 } else if (rcu_gp_in_progress(rsp) &&
1522 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY) &&
1523 cmpxchg(&rsp->jiffies_stall, js, jn) == js) {
1525 /* They had a few time units to dump stack, so complain. */
1526 print_other_cpu_stall(rsp, gs2);
1531 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1533 * Set the stall-warning timeout way off into the future, thus preventing
1534 * any RCU CPU stall-warning messages from appearing in the current set of
1535 * RCU grace periods.
1537 * The caller must disable hard irqs.
1539 void rcu_cpu_stall_reset(void)
1541 struct rcu_state *rsp;
1543 for_each_rcu_flavor(rsp)
1544 WRITE_ONCE(rsp->jiffies_stall, jiffies + ULONG_MAX / 2);
1547 /* Trace-event wrapper function for trace_rcu_future_grace_period. */
1548 static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1549 unsigned long gp_seq_req, const char *s)
1551 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gp_seq, gp_seq_req,
1552 rnp->level, rnp->grplo, rnp->grphi, s);
1556 * rcu_start_this_gp - Request the start of a particular grace period
1557 * @rnp: The leaf node of the CPU from which to start.
1558 * @rdp: The rcu_data corresponding to the CPU from which to start.
1559 * @gp_seq_req: The gp_seq of the grace period to start.
1561 * Start the specified grace period, as needed to handle newly arrived
1562 * callbacks. The required future grace periods are recorded in each
1563 * rcu_node structure's ->gp_seq_needed field. Returns true if there
1564 * is reason to awaken the grace-period kthread.
1566 * The caller must hold the specified rcu_node structure's ->lock, which
1567 * is why the caller is responsible for waking the grace-period kthread.
1569 * Returns true if the GP thread needs to be awakened else false.
1571 static bool rcu_start_this_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1572 unsigned long gp_seq_req)
1575 struct rcu_state *rsp = rdp->rsp;
1576 struct rcu_node *rnp_root;
1579 * Use funnel locking to either acquire the root rcu_node
1580 * structure's lock or bail out if the need for this grace period
1581 * has already been recorded -- or has already started. If there
1582 * is already a grace period in progress in a non-leaf node, no
1583 * recording is needed because the end of the grace period will
1584 * scan the leaf rcu_node structures. Note that rnp->lock must
1587 raw_lockdep_assert_held_rcu_node(rnp);
1588 trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startleaf"));
1589 for (rnp_root = rnp; 1; rnp_root = rnp_root->parent) {
1590 if (rnp_root != rnp)
1591 raw_spin_lock_rcu_node(rnp_root);
1592 if (ULONG_CMP_GE(rnp_root->gp_seq_needed, gp_seq_req) ||
1593 rcu_seq_started(&rnp_root->gp_seq, gp_seq_req) ||
1595 rcu_seq_state(rcu_seq_current(&rnp_root->gp_seq)))) {
1596 trace_rcu_this_gp(rnp_root, rdp, gp_seq_req,
1600 rnp_root->gp_seq_needed = gp_seq_req;
1601 if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) {
1603 * We just marked the leaf, and a grace period
1604 * is in progress, which means that rcu_gp_cleanup()
1605 * will see the marking. Bail to reduce contention.
1607 trace_rcu_this_gp(rnp, rdp, gp_seq_req,
1608 TPS("Startedleaf"));
1611 if (rnp_root != rnp && rnp_root->parent != NULL)
1612 raw_spin_unlock_rcu_node(rnp_root);
1613 if (!rnp_root->parent)
1614 break; /* At root, and perhaps also leaf. */
1617 /* If GP already in progress, just leave, otherwise start one. */
1618 if (rcu_gp_in_progress(rsp)) {
1619 trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, TPS("Startedleafroot"));
1622 trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, TPS("Startedroot"));
1623 WRITE_ONCE(rsp->gp_flags, rsp->gp_flags | RCU_GP_FLAG_INIT);
1624 rsp->gp_req_activity = jiffies;
1625 if (!rsp->gp_kthread) {
1626 trace_rcu_this_gp(rnp_root, rdp, gp_seq_req, TPS("NoGPkthread"));
1629 trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq), TPS("newreq"));
1630 ret = true; /* Caller must wake GP kthread. */
1632 /* Push furthest requested GP to leaf node and rcu_data structure. */
1633 if (ULONG_CMP_LT(gp_seq_req, rnp_root->gp_seq_needed)) {
1634 rnp->gp_seq_needed = rnp_root->gp_seq_needed;
1635 rdp->gp_seq_needed = rnp_root->gp_seq_needed;
1637 if (rnp != rnp_root)
1638 raw_spin_unlock_rcu_node(rnp_root);
1643 * Clean up any old requests for the just-ended grace period. Also return
1644 * whether any additional grace periods have been requested.
1646 static bool rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1649 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1651 needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed);
1653 rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */
1654 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq,
1655 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1660 * Awaken the grace-period kthread for the specified flavor of RCU.
1661 * Don't do a self-awaken, and don't bother awakening when there is
1662 * nothing for the grace-period kthread to do (as in several CPUs
1663 * raced to awaken, and we lost), and finally don't try to awaken
1664 * a kthread that has not yet been created.
1666 static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1668 if (current == rsp->gp_kthread ||
1669 !READ_ONCE(rsp->gp_flags) ||
1672 swake_up(&rsp->gp_wq);
1676 * If there is room, assign a ->gp_seq number to any callbacks on this
1677 * CPU that have not already been assigned. Also accelerate any callbacks
1678 * that were previously assigned a ->gp_seq number that has since proven
1679 * to be too conservative, which can happen if callbacks get assigned a
1680 * ->gp_seq number while RCU is idle, but with reference to a non-root
1681 * rcu_node structure. This function is idempotent, so it does not hurt
1682 * to call it repeatedly. Returns an flag saying that we should awaken
1683 * the RCU grace-period kthread.
1685 * The caller must hold rnp->lock with interrupts disabled.
1687 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1688 struct rcu_data *rdp)
1690 unsigned long gp_seq_req;
1693 raw_lockdep_assert_held_rcu_node(rnp);
1695 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1696 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1700 * Callbacks are often registered with incomplete grace-period
1701 * information. Something about the fact that getting exact
1702 * information requires acquiring a global lock... RCU therefore
1703 * makes a conservative estimate of the grace period number at which
1704 * a given callback will become ready to invoke. The following
1705 * code checks this estimate and improves it when possible, thus
1706 * accelerating callback invocation to an earlier grace-period
1709 gp_seq_req = rcu_seq_snap(&rsp->gp_seq);
1710 if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req))
1711 ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
1713 /* Trace depending on how much we were able to accelerate. */
1714 if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL))
1715 trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("AccWaitCB"));
1717 trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("AccReadyCB"));
1722 * Similar to rcu_accelerate_cbs(), but does not require that the leaf
1723 * rcu_node structure's ->lock be held. It consults the cached value
1724 * of ->gp_seq_needed in the rcu_data structure, and if that indicates
1725 * that a new grace-period request be made, invokes rcu_accelerate_cbs()
1726 * while holding the leaf rcu_node structure's ->lock.
1728 static void rcu_accelerate_cbs_unlocked(struct rcu_state *rsp,
1729 struct rcu_node *rnp,
1730 struct rcu_data *rdp)
1735 lockdep_assert_irqs_disabled();
1736 c = rcu_seq_snap(&rsp->gp_seq);
1737 if (!rdp->gpwrap && ULONG_CMP_GE(rdp->gp_seq_needed, c)) {
1738 /* Old request still live, so mark recent callbacks. */
1739 (void)rcu_segcblist_accelerate(&rdp->cblist, c);
1742 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
1743 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1744 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
1746 rcu_gp_kthread_wake(rsp);
1750 * Move any callbacks whose grace period has completed to the
1751 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1752 * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL
1753 * sublist. This function is idempotent, so it does not hurt to
1754 * invoke it repeatedly. As long as it is not invoked -too- often...
1755 * Returns true if the RCU grace-period kthread needs to be awakened.
1757 * The caller must hold rnp->lock with interrupts disabled.
1759 static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1760 struct rcu_data *rdp)
1762 raw_lockdep_assert_held_rcu_node(rnp);
1764 /* If no pending (not yet ready to invoke) callbacks, nothing to do. */
1765 if (!rcu_segcblist_pend_cbs(&rdp->cblist))
1769 * Find all callbacks whose ->gp_seq numbers indicate that they
1770 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1772 rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
1774 /* Classify any remaining callbacks. */
1775 return rcu_accelerate_cbs(rsp, rnp, rdp);
1779 * Update CPU-local rcu_data state to record the beginnings and ends of
1780 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1781 * structure corresponding to the current CPU, and must have irqs disabled.
1782 * Returns true if the grace-period kthread needs to be awakened.
1784 static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1785 struct rcu_data *rdp)
1790 raw_lockdep_assert_held_rcu_node(rnp);
1792 if (rdp->gp_seq == rnp->gp_seq)
1793 return false; /* Nothing to do. */
1795 /* Handle the ends of any preceding grace periods first. */
1796 if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) ||
1797 unlikely(READ_ONCE(rdp->gpwrap))) {
1798 ret = rcu_advance_cbs(rsp, rnp, rdp); /* Advance callbacks. */
1799 trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("cpuend"));
1801 ret = rcu_accelerate_cbs(rsp, rnp, rdp); /* Recent callbacks. */
1804 /* Now handle the beginnings of any new-to-this-CPU grace periods. */
1805 if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) ||
1806 unlikely(READ_ONCE(rdp->gpwrap))) {
1808 * If the current grace period is waiting for this CPU,
1809 * set up to detect a quiescent state, otherwise don't
1810 * go looking for one.
1812 trace_rcu_grace_period(rsp->name, rnp->gp_seq, TPS("cpustart"));
1813 need_gp = !!(rnp->qsmask & rdp->grpmask);
1814 rdp->cpu_no_qs.b.norm = need_gp;
1815 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
1816 rdp->core_needs_qs = need_gp;
1817 zero_cpu_stall_ticks(rdp);
1819 rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */
1820 if (ULONG_CMP_GE(rnp->gp_seq_needed, rdp->gp_seq_needed) || rdp->gpwrap)
1821 rdp->gp_seq_needed = rnp->gp_seq_needed;
1822 WRITE_ONCE(rdp->gpwrap, false);
1823 rcu_gpnum_ovf(rnp, rdp);
1827 static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1829 unsigned long flags;
1831 struct rcu_node *rnp;
1833 local_irq_save(flags);
1835 if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) &&
1836 !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */
1837 !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */
1838 local_irq_restore(flags);
1841 needwake = __note_gp_changes(rsp, rnp, rdp);
1842 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
1844 rcu_gp_kthread_wake(rsp);
1847 static void rcu_gp_slow(struct rcu_state *rsp, int delay)
1850 !(rcu_seq_ctr(rsp->gp_seq) %
1851 (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay)))
1852 schedule_timeout_uninterruptible(delay);
1856 * Initialize a new grace period. Return false if no grace period required.
1858 static bool rcu_gp_init(struct rcu_state *rsp)
1860 unsigned long oldmask;
1861 struct rcu_data *rdp;
1862 struct rcu_node *rnp = rcu_get_root(rsp);
1864 WRITE_ONCE(rsp->gp_activity, jiffies);
1865 raw_spin_lock_irq_rcu_node(rnp);
1866 if (!READ_ONCE(rsp->gp_flags)) {
1867 /* Spurious wakeup, tell caller to go back to sleep. */
1868 raw_spin_unlock_irq_rcu_node(rnp);
1871 WRITE_ONCE(rsp->gp_flags, 0); /* Clear all flags: New grace period. */
1873 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1875 * Grace period already in progress, don't start another.
1876 * Not supposed to be able to happen.
1878 raw_spin_unlock_irq_rcu_node(rnp);
1882 /* Advance to a new grace period and initialize state. */
1883 record_gp_stall_check_time(rsp);
1884 /* Record GP times before starting GP, hence rcu_seq_start(). */
1885 rcu_seq_start(&rsp->gp_seq);
1886 trace_rcu_grace_period(rsp->name, rsp->gp_seq, TPS("start"));
1887 raw_spin_unlock_irq_rcu_node(rnp);
1890 * Apply per-leaf buffered online and offline operations to the
1891 * rcu_node tree. Note that this new grace period need not wait
1892 * for subsequent online CPUs, and that quiescent-state forcing
1893 * will handle subsequent offline CPUs.
1895 rcu_for_each_leaf_node(rsp, rnp) {
1896 rcu_gp_slow(rsp, gp_preinit_delay);
1897 raw_spin_lock_irq_rcu_node(rnp);
1898 if (rnp->qsmaskinit == rnp->qsmaskinitnext &&
1899 !rnp->wait_blkd_tasks) {
1900 /* Nothing to do on this leaf rcu_node structure. */
1901 raw_spin_unlock_irq_rcu_node(rnp);
1905 /* Record old state, apply changes to ->qsmaskinit field. */
1906 oldmask = rnp->qsmaskinit;
1907 rnp->qsmaskinit = rnp->qsmaskinitnext;
1909 /* If zero-ness of ->qsmaskinit changed, propagate up tree. */
1910 if (!oldmask != !rnp->qsmaskinit) {
1911 if (!oldmask) /* First online CPU for this rcu_node. */
1912 rcu_init_new_rnp(rnp);
1913 else if (rcu_preempt_has_tasks(rnp)) /* blocked tasks */
1914 rnp->wait_blkd_tasks = true;
1915 else /* Last offline CPU and can propagate. */
1916 rcu_cleanup_dead_rnp(rnp);
1920 * If all waited-on tasks from prior grace period are
1921 * done, and if all this rcu_node structure's CPUs are
1922 * still offline, propagate up the rcu_node tree and
1923 * clear ->wait_blkd_tasks. Otherwise, if one of this
1924 * rcu_node structure's CPUs has since come back online,
1925 * simply clear ->wait_blkd_tasks (but rcu_cleanup_dead_rnp()
1926 * checks for this, so just call it unconditionally).
1928 if (rnp->wait_blkd_tasks &&
1929 (!rcu_preempt_has_tasks(rnp) ||
1931 rnp->wait_blkd_tasks = false;
1932 rcu_cleanup_dead_rnp(rnp);
1935 raw_spin_unlock_irq_rcu_node(rnp);
1939 * Set the quiescent-state-needed bits in all the rcu_node
1940 * structures for all currently online CPUs in breadth-first order,
1941 * starting from the root rcu_node structure, relying on the layout
1942 * of the tree within the rsp->node[] array. Note that other CPUs
1943 * will access only the leaves of the hierarchy, thus seeing that no
1944 * grace period is in progress, at least until the corresponding
1945 * leaf node has been initialized.
1947 * The grace period cannot complete until the initialization
1948 * process finishes, because this kthread handles both.
1950 rcu_for_each_node_breadth_first(rsp, rnp) {
1951 rcu_gp_slow(rsp, gp_init_delay);
1952 raw_spin_lock_irq_rcu_node(rnp);
1953 rdp = this_cpu_ptr(rsp->rda);
1954 rcu_preempt_check_blocked_tasks(rnp);
1955 rnp->qsmask = rnp->qsmaskinit;
1956 WRITE_ONCE(rnp->gp_seq, rsp->gp_seq);
1957 if (rnp == rdp->mynode)
1958 (void)__note_gp_changes(rsp, rnp, rdp);
1959 rcu_preempt_boost_start_gp(rnp);
1960 trace_rcu_grace_period_init(rsp->name, rnp->gp_seq,
1961 rnp->level, rnp->grplo,
1962 rnp->grphi, rnp->qsmask);
1963 raw_spin_unlock_irq_rcu_node(rnp);
1964 cond_resched_tasks_rcu_qs();
1965 WRITE_ONCE(rsp->gp_activity, jiffies);
1972 * Helper function for swait_event_idle() wakeup at force-quiescent-state
1975 static bool rcu_gp_fqs_check_wake(struct rcu_state *rsp, int *gfp)
1977 struct rcu_node *rnp = rcu_get_root(rsp);
1979 /* Someone like call_rcu() requested a force-quiescent-state scan. */
1980 *gfp = READ_ONCE(rsp->gp_flags);
1981 if (*gfp & RCU_GP_FLAG_FQS)
1984 /* The current grace period has completed. */
1985 if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp))
1992 * Do one round of quiescent-state forcing.
1994 static void rcu_gp_fqs(struct rcu_state *rsp, bool first_time)
1996 struct rcu_node *rnp = rcu_get_root(rsp);
1998 WRITE_ONCE(rsp->gp_activity, jiffies);
2001 /* Collect dyntick-idle snapshots. */
2002 force_qs_rnp(rsp, dyntick_save_progress_counter);
2004 /* Handle dyntick-idle and offline CPUs. */
2005 force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
2007 /* Clear flag to prevent immediate re-entry. */
2008 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2009 raw_spin_lock_irq_rcu_node(rnp);
2010 WRITE_ONCE(rsp->gp_flags,
2011 READ_ONCE(rsp->gp_flags) & ~RCU_GP_FLAG_FQS);
2012 raw_spin_unlock_irq_rcu_node(rnp);
2017 * Clean up after the old grace period.
2019 static void rcu_gp_cleanup(struct rcu_state *rsp)
2021 unsigned long gp_duration;
2022 bool needgp = false;
2023 unsigned long new_gp_seq;
2024 struct rcu_data *rdp;
2025 struct rcu_node *rnp = rcu_get_root(rsp);
2026 struct swait_queue_head *sq;
2028 WRITE_ONCE(rsp->gp_activity, jiffies);
2029 raw_spin_lock_irq_rcu_node(rnp);
2030 gp_duration = jiffies - rsp->gp_start;
2031 if (gp_duration > rsp->gp_max)
2032 rsp->gp_max = gp_duration;
2035 * We know the grace period is complete, but to everyone else
2036 * it appears to still be ongoing. But it is also the case
2037 * that to everyone else it looks like there is nothing that
2038 * they can do to advance the grace period. It is therefore
2039 * safe for us to drop the lock in order to mark the grace
2040 * period as completed in all of the rcu_node structures.
2042 raw_spin_unlock_irq_rcu_node(rnp);
2045 * Propagate new ->gp_seq value to rcu_node structures so that
2046 * other CPUs don't have to wait until the start of the next grace
2047 * period to process their callbacks. This also avoids some nasty
2048 * RCU grace-period initialization races by forcing the end of
2049 * the current grace period to be completely recorded in all of
2050 * the rcu_node structures before the beginning of the next grace
2051 * period is recorded in any of the rcu_node structures.
2053 new_gp_seq = rsp->gp_seq;
2054 rcu_seq_end(&new_gp_seq);
2055 rcu_for_each_node_breadth_first(rsp, rnp) {
2056 raw_spin_lock_irq_rcu_node(rnp);
2057 if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)))
2058 dump_blkd_tasks(rnp, 10);
2059 WARN_ON_ONCE(rnp->qsmask);
2060 WRITE_ONCE(rnp->gp_seq, new_gp_seq);
2061 rdp = this_cpu_ptr(rsp->rda);
2062 if (rnp == rdp->mynode)
2063 needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
2064 /* smp_mb() provided by prior unlock-lock pair. */
2065 needgp = rcu_future_gp_cleanup(rsp, rnp) || needgp;
2066 sq = rcu_nocb_gp_get(rnp);
2067 raw_spin_unlock_irq_rcu_node(rnp);
2068 rcu_nocb_gp_cleanup(sq);
2069 cond_resched_tasks_rcu_qs();
2070 WRITE_ONCE(rsp->gp_activity, jiffies);
2071 rcu_gp_slow(rsp, gp_cleanup_delay);
2073 rnp = rcu_get_root(rsp);
2074 raw_spin_lock_irq_rcu_node(rnp); /* GP before rsp->gp_seq update. */
2076 /* Declare grace period done. */
2077 rcu_seq_end(&rsp->gp_seq);
2078 trace_rcu_grace_period(rsp->name, rsp->gp_seq, TPS("end"));
2079 rsp->gp_state = RCU_GP_IDLE;
2080 /* Check for GP requests since above loop. */
2081 rdp = this_cpu_ptr(rsp->rda);
2082 if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) {
2083 trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed,
2084 TPS("CleanupMore"));
2087 /* Advance CBs to reduce false positives below. */
2088 if (!rcu_accelerate_cbs(rsp, rnp, rdp) && needgp) {
2089 WRITE_ONCE(rsp->gp_flags, RCU_GP_FLAG_INIT);
2090 rsp->gp_req_activity = jiffies;
2091 trace_rcu_grace_period(rsp->name, READ_ONCE(rsp->gp_seq),
2094 WRITE_ONCE(rsp->gp_flags, rsp->gp_flags & RCU_GP_FLAG_INIT);
2096 raw_spin_unlock_irq_rcu_node(rnp);
2100 * Body of kthread that handles grace periods.
2102 static int __noreturn rcu_gp_kthread(void *arg)
2108 struct rcu_state *rsp = arg;
2109 struct rcu_node *rnp = rcu_get_root(rsp);
2111 rcu_bind_gp_kthread();
2114 /* Handle grace-period start. */
2116 trace_rcu_grace_period(rsp->name,
2117 READ_ONCE(rsp->gp_seq),
2119 rsp->gp_state = RCU_GP_WAIT_GPS;
2120 swait_event_idle(rsp->gp_wq, READ_ONCE(rsp->gp_flags) &
2122 rsp->gp_state = RCU_GP_DONE_GPS;
2123 /* Locking provides needed memory barrier. */
2124 if (rcu_gp_init(rsp))
2126 cond_resched_tasks_rcu_qs();
2127 WRITE_ONCE(rsp->gp_activity, jiffies);
2128 WARN_ON(signal_pending(current));
2129 trace_rcu_grace_period(rsp->name,
2130 READ_ONCE(rsp->gp_seq),
2134 /* Handle quiescent-state forcing. */
2135 first_gp_fqs = true;
2136 j = jiffies_till_first_fqs;
2139 jiffies_till_first_fqs = HZ;
2144 rsp->jiffies_force_qs = jiffies + j;
2145 WRITE_ONCE(rsp->jiffies_kick_kthreads,
2148 trace_rcu_grace_period(rsp->name,
2149 READ_ONCE(rsp->gp_seq),
2151 rsp->gp_state = RCU_GP_WAIT_FQS;
2152 ret = swait_event_idle_timeout(rsp->gp_wq,
2153 rcu_gp_fqs_check_wake(rsp, &gf), j);
2154 rsp->gp_state = RCU_GP_DOING_FQS;
2155 /* Locking provides needed memory barriers. */
2156 /* If grace period done, leave loop. */
2157 if (!READ_ONCE(rnp->qsmask) &&
2158 !rcu_preempt_blocked_readers_cgp(rnp))
2160 /* If time for quiescent-state forcing, do it. */
2161 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
2162 (gf & RCU_GP_FLAG_FQS)) {
2163 trace_rcu_grace_period(rsp->name,
2164 READ_ONCE(rsp->gp_seq),
2166 rcu_gp_fqs(rsp, first_gp_fqs);
2167 first_gp_fqs = false;
2168 trace_rcu_grace_period(rsp->name,
2169 READ_ONCE(rsp->gp_seq),
2171 cond_resched_tasks_rcu_qs();
2172 WRITE_ONCE(rsp->gp_activity, jiffies);
2173 ret = 0; /* Force full wait till next FQS. */
2174 j = jiffies_till_next_fqs;
2177 jiffies_till_next_fqs = HZ;
2180 jiffies_till_next_fqs = 1;
2183 /* Deal with stray signal. */
2184 cond_resched_tasks_rcu_qs();
2185 WRITE_ONCE(rsp->gp_activity, jiffies);
2186 WARN_ON(signal_pending(current));
2187 trace_rcu_grace_period(rsp->name,
2188 READ_ONCE(rsp->gp_seq),
2190 ret = 1; /* Keep old FQS timing. */
2192 if (time_after(jiffies, rsp->jiffies_force_qs))
2195 j = rsp->jiffies_force_qs - j;
2199 /* Handle grace-period end. */
2200 rsp->gp_state = RCU_GP_CLEANUP;
2201 rcu_gp_cleanup(rsp);
2202 rsp->gp_state = RCU_GP_CLEANED;
2207 * Report a full set of quiescent states to the specified rcu_state data
2208 * structure. Invoke rcu_gp_kthread_wake() to awaken the grace-period
2209 * kthread if another grace period is required. Whether we wake
2210 * the grace-period kthread or it awakens itself for the next round
2211 * of quiescent-state forcing, that kthread will clean up after the
2212 * just-completed grace period. Note that the caller must hold rnp->lock,
2213 * which is released before return.
2215 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
2216 __releases(rcu_get_root(rsp)->lock)
2218 raw_lockdep_assert_held_rcu_node(rcu_get_root(rsp));
2219 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
2220 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2221 raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(rsp), flags);
2222 rcu_gp_kthread_wake(rsp);
2226 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
2227 * Allows quiescent states for a group of CPUs to be reported at one go
2228 * to the specified rcu_node structure, though all the CPUs in the group
2229 * must be represented by the same rcu_node structure (which need not be a
2230 * leaf rcu_node structure, though it often will be). The gps parameter
2231 * is the grace-period snapshot, which means that the quiescent states
2232 * are valid only if rnp->gp_seq is equal to gps. That structure's lock
2233 * must be held upon entry, and it is released before return.
2236 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
2237 struct rcu_node *rnp, unsigned long gps, unsigned long flags)
2238 __releases(rnp->lock)
2240 unsigned long oldmask = 0;
2241 struct rcu_node *rnp_c;
2243 raw_lockdep_assert_held_rcu_node(rnp);
2245 /* Walk up the rcu_node hierarchy. */
2247 if (!(rnp->qsmask & mask) || rnp->gp_seq != gps) {
2250 * Our bit has already been cleared, or the
2251 * relevant grace period is already over, so done.
2253 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2256 WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */
2257 WARN_ON_ONCE(!rcu_is_leaf_node(rnp) &&
2258 rcu_preempt_blocked_readers_cgp(rnp));
2259 rnp->qsmask &= ~mask;
2260 trace_rcu_quiescent_state_report(rsp->name, rnp->gp_seq,
2261 mask, rnp->qsmask, rnp->level,
2262 rnp->grplo, rnp->grphi,
2264 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2266 /* Other bits still set at this level, so done. */
2267 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2270 rnp->completedqs = rnp->gp_seq;
2271 mask = rnp->grpmask;
2272 if (rnp->parent == NULL) {
2274 /* No more levels. Exit loop holding root lock. */
2278 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2281 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2282 oldmask = rnp_c->qsmask;
2286 * Get here if we are the last CPU to pass through a quiescent
2287 * state for this grace period. Invoke rcu_report_qs_rsp()
2288 * to clean up and start the next grace period if one is needed.
2290 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
2294 * Record a quiescent state for all tasks that were previously queued
2295 * on the specified rcu_node structure and that were blocking the current
2296 * RCU grace period. The caller must hold the specified rnp->lock with
2297 * irqs disabled, and this lock is released upon return, but irqs remain
2300 static void rcu_report_unblock_qs_rnp(struct rcu_state *rsp,
2301 struct rcu_node *rnp, unsigned long flags)
2302 __releases(rnp->lock)
2306 struct rcu_node *rnp_p;
2308 raw_lockdep_assert_held_rcu_node(rnp);
2309 if (rcu_state_p == &rcu_sched_state || rsp != rcu_state_p ||
2310 rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
2311 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2312 return; /* Still need more quiescent states! */
2315 rnp_p = rnp->parent;
2316 if (rnp_p == NULL) {
2318 * Only one rcu_node structure in the tree, so don't
2319 * try to report up to its nonexistent parent!
2321 rcu_report_qs_rsp(rsp, flags);
2325 /* Report up the rest of the hierarchy, tracking current ->gp_seq. */
2327 mask = rnp->grpmask;
2328 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2329 raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */
2330 rcu_report_qs_rnp(mask, rsp, rnp_p, gps, flags);
2334 * Record a quiescent state for the specified CPU to that CPU's rcu_data
2335 * structure. This must be called from the specified CPU.
2338 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
2340 unsigned long flags;
2343 struct rcu_node *rnp;
2346 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2347 if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq ||
2351 * The grace period in which this quiescent state was
2352 * recorded has ended, so don't report it upwards.
2353 * We will instead need a new quiescent state that lies
2354 * within the current grace period.
2356 rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */
2357 rdp->rcu_qs_ctr_snap = __this_cpu_read(rcu_dynticks.rcu_qs_ctr);
2358 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2361 mask = rdp->grpmask;
2362 if ((rnp->qsmask & mask) == 0) {
2363 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2365 rdp->core_needs_qs = false;
2368 * This GP can't end until cpu checks in, so all of our
2369 * callbacks can be processed during the next GP.
2371 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
2373 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
2374 /* ^^^ Released rnp->lock */
2376 rcu_gp_kthread_wake(rsp);
2381 * Check to see if there is a new grace period of which this CPU
2382 * is not yet aware, and if so, set up local rcu_data state for it.
2383 * Otherwise, see if this CPU has just passed through its first
2384 * quiescent state for this grace period, and record that fact if so.
2387 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
2389 /* Check for grace-period ends and beginnings. */
2390 note_gp_changes(rsp, rdp);
2393 * Does this CPU still need to do its part for current grace period?
2394 * If no, return and let the other CPUs do their part as well.
2396 if (!rdp->core_needs_qs)
2400 * Was there a quiescent state since the beginning of the grace
2401 * period? If no, then exit and wait for the next call.
2403 if (rdp->cpu_no_qs.b.norm)
2407 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
2410 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
2414 * Trace the fact that this CPU is going offline.
2416 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2418 RCU_TRACE(bool blkd;)
2419 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda);)
2420 RCU_TRACE(struct rcu_node *rnp = rdp->mynode;)
2422 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2425 RCU_TRACE(blkd = !!(rnp->qsmask & rdp->grpmask);)
2426 trace_rcu_grace_period(rsp->name, rnp->gp_seq,
2427 blkd ? TPS("cpuofl") : TPS("cpuofl-bgp"));
2431 * All CPUs for the specified rcu_node structure have gone offline,
2432 * and all tasks that were preempted within an RCU read-side critical
2433 * section while running on one of those CPUs have since exited their RCU
2434 * read-side critical section. Some other CPU is reporting this fact with
2435 * the specified rcu_node structure's ->lock held and interrupts disabled.
2436 * This function therefore goes up the tree of rcu_node structures,
2437 * clearing the corresponding bits in the ->qsmaskinit fields. Note that
2438 * the leaf rcu_node structure's ->qsmaskinit field has already been
2441 * This function does check that the specified rcu_node structure has
2442 * all CPUs offline and no blocked tasks, so it is OK to invoke it
2443 * prematurely. That said, invoking it after the fact will cost you
2444 * a needless lock acquisition. So once it has done its work, don't
2447 static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf)
2450 struct rcu_node *rnp = rnp_leaf;
2452 raw_lockdep_assert_held_rcu_node(rnp);
2453 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) ||
2454 rnp->qsmaskinit || rcu_preempt_has_tasks(rnp))
2457 mask = rnp->grpmask;
2461 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
2462 rnp->qsmaskinit &= ~mask;
2463 rnp->qsmask &= ~mask;
2464 if (rnp->qsmaskinit) {
2465 raw_spin_unlock_rcu_node(rnp);
2466 /* irqs remain disabled. */
2469 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
2474 * The CPU has been completely removed, and some other CPU is reporting
2475 * this fact from process context. Do the remainder of the cleanup.
2476 * There can only be one CPU hotplug operation at a time, so no need for
2479 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2481 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2482 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2484 if (!IS_ENABLED(CONFIG_HOTPLUG_CPU))
2487 /* Adjust any no-longer-needed kthreads. */
2488 rcu_boost_kthread_setaffinity(rnp, -1);
2492 * Invoke any RCU callbacks that have made it to the end of their grace
2493 * period. Thottle as specified by rdp->blimit.
2495 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2497 unsigned long flags;
2498 struct rcu_head *rhp;
2499 struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl);
2502 /* If no callbacks are ready, just return. */
2503 if (!rcu_segcblist_ready_cbs(&rdp->cblist)) {
2504 trace_rcu_batch_start(rsp->name,
2505 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2506 rcu_segcblist_n_cbs(&rdp->cblist), 0);
2507 trace_rcu_batch_end(rsp->name, 0,
2508 !rcu_segcblist_empty(&rdp->cblist),
2509 need_resched(), is_idle_task(current),
2510 rcu_is_callbacks_kthread());
2515 * Extract the list of ready callbacks, disabling to prevent
2516 * races with call_rcu() from interrupt handlers. Leave the
2517 * callback counts, as rcu_barrier() needs to be conservative.
2519 local_irq_save(flags);
2520 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2522 trace_rcu_batch_start(rsp->name, rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2523 rcu_segcblist_n_cbs(&rdp->cblist), bl);
2524 rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl);
2525 local_irq_restore(flags);
2527 /* Invoke callbacks. */
2528 rhp = rcu_cblist_dequeue(&rcl);
2529 for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) {
2530 debug_rcu_head_unqueue(rhp);
2531 if (__rcu_reclaim(rsp->name, rhp))
2532 rcu_cblist_dequeued_lazy(&rcl);
2534 * Stop only if limit reached and CPU has something to do.
2535 * Note: The rcl structure counts down from zero.
2537 if (-rcl.len >= bl &&
2539 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2543 local_irq_save(flags);
2545 trace_rcu_batch_end(rsp->name, count, !!rcl.head, need_resched(),
2546 is_idle_task(current), rcu_is_callbacks_kthread());
2548 /* Update counts and requeue any remaining callbacks. */
2549 rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl);
2550 smp_mb(); /* List handling before counting for rcu_barrier(). */
2551 rcu_segcblist_insert_count(&rdp->cblist, &rcl);
2553 /* Reinstate batch limit if we have worked down the excess. */
2554 count = rcu_segcblist_n_cbs(&rdp->cblist);
2555 if (rdp->blimit == LONG_MAX && count <= qlowmark)
2556 rdp->blimit = blimit;
2558 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2559 if (count == 0 && rdp->qlen_last_fqs_check != 0) {
2560 rdp->qlen_last_fqs_check = 0;
2561 rdp->n_force_qs_snap = rsp->n_force_qs;
2562 } else if (count < rdp->qlen_last_fqs_check - qhimark)
2563 rdp->qlen_last_fqs_check = count;
2566 * The following usually indicates a double call_rcu(). To track
2567 * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y.
2569 WARN_ON_ONCE(rcu_segcblist_empty(&rdp->cblist) != (count == 0));
2571 local_irq_restore(flags);
2573 /* Re-invoke RCU core processing if there are callbacks remaining. */
2574 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2579 * Check to see if this CPU is in a non-context-switch quiescent state
2580 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2581 * Also schedule RCU core processing.
2583 * This function must be called from hardirq context. It is normally
2584 * invoked from the scheduling-clock interrupt.
2586 void rcu_check_callbacks(int user)
2588 trace_rcu_utilization(TPS("Start scheduler-tick"));
2589 increment_cpu_stall_ticks();
2590 if (user || rcu_is_cpu_rrupt_from_idle()) {
2593 * Get here if this CPU took its interrupt from user
2594 * mode or from the idle loop, and if this is not a
2595 * nested interrupt. In this case, the CPU is in
2596 * a quiescent state, so note it.
2598 * No memory barrier is required here because both
2599 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2600 * variables that other CPUs neither access nor modify,
2601 * at least not while the corresponding CPU is online.
2607 } else if (!in_softirq()) {
2610 * Get here if this CPU did not take its interrupt from
2611 * softirq, in other words, if it is not interrupting
2612 * a rcu_bh read-side critical section. This is an _bh
2613 * critical section, so note it.
2618 rcu_preempt_check_callbacks();
2622 rcu_note_voluntary_context_switch(current);
2623 trace_rcu_utilization(TPS("End scheduler-tick"));
2627 * Scan the leaf rcu_node structures, processing dyntick state for any that
2628 * have not yet encountered a quiescent state, using the function specified.
2629 * Also initiate boosting for any threads blocked on the root rcu_node.
2631 * The caller must have suppressed start of new grace periods.
2633 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *rsp))
2636 unsigned long flags;
2638 struct rcu_node *rnp;
2640 rcu_for_each_leaf_node(rsp, rnp) {
2641 cond_resched_tasks_rcu_qs();
2643 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2644 if (rnp->qsmask == 0) {
2645 if (rcu_state_p == &rcu_sched_state ||
2646 rsp != rcu_state_p ||
2647 rcu_preempt_blocked_readers_cgp(rnp)) {
2649 * No point in scanning bits because they
2650 * are all zero. But we might need to
2651 * priority-boost blocked readers.
2653 rcu_initiate_boost(rnp, flags);
2654 /* rcu_initiate_boost() releases rnp->lock */
2658 (rnp->parent->qsmask & rnp->grpmask)) {
2660 * Race between grace-period
2661 * initialization and task exiting RCU
2662 * read-side critical section: Report.
2664 rcu_report_unblock_qs_rnp(rsp, rnp, flags);
2665 /* rcu_report_unblock_qs_rnp() rlses ->lock */
2669 for_each_leaf_node_possible_cpu(rnp, cpu) {
2670 unsigned long bit = leaf_node_cpu_bit(rnp, cpu);
2671 if ((rnp->qsmask & bit) != 0) {
2672 if (f(per_cpu_ptr(rsp->rda, cpu)))
2677 /* Idle/offline CPUs, report (releases rnp->lock). */
2678 rcu_report_qs_rnp(mask, rsp, rnp, rnp->gp_seq, flags);
2680 /* Nothing to do here, so just drop the lock. */
2681 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2687 * Force quiescent states on reluctant CPUs, and also detect which
2688 * CPUs are in dyntick-idle mode.
2690 static void force_quiescent_state(struct rcu_state *rsp)
2692 unsigned long flags;
2694 struct rcu_node *rnp;
2695 struct rcu_node *rnp_old = NULL;
2697 /* Funnel through hierarchy to reduce memory contention. */
2698 rnp = __this_cpu_read(rsp->rda->mynode);
2699 for (; rnp != NULL; rnp = rnp->parent) {
2700 ret = (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2701 !raw_spin_trylock(&rnp->fqslock);
2702 if (rnp_old != NULL)
2703 raw_spin_unlock(&rnp_old->fqslock);
2708 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2710 /* Reached the root of the rcu_node tree, acquire lock. */
2711 raw_spin_lock_irqsave_rcu_node(rnp_old, flags);
2712 raw_spin_unlock(&rnp_old->fqslock);
2713 if (READ_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2714 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2715 return; /* Someone beat us to it. */
2717 WRITE_ONCE(rsp->gp_flags, READ_ONCE(rsp->gp_flags) | RCU_GP_FLAG_FQS);
2718 raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags);
2719 rcu_gp_kthread_wake(rsp);
2723 * This function checks for grace-period requests that fail to motivate
2724 * RCU to come out of its idle mode.
2727 rcu_check_gp_start_stall(struct rcu_state *rsp, struct rcu_node *rnp,
2728 struct rcu_data *rdp)
2730 unsigned long flags;
2732 struct rcu_node *rnp_root = rcu_get_root(rsp);
2733 static atomic_t warned = ATOMIC_INIT(0);
2735 if (!IS_ENABLED(CONFIG_PROVE_RCU) || rcu_gp_in_progress(rsp) ||
2736 ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed))
2738 j = jiffies; /* Expensive access, and in common case don't get here. */
2739 if (time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
2740 time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
2741 atomic_read(&warned))
2744 raw_spin_lock_irqsave_rcu_node(rnp, flags);
2746 if (rcu_gp_in_progress(rsp) ||
2747 ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
2748 time_before(j, READ_ONCE(rsp->gp_req_activity) + HZ) ||
2749 time_before(j, READ_ONCE(rsp->gp_activity) + HZ) ||
2750 atomic_read(&warned)) {
2751 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2754 /* Hold onto the leaf lock to make others see warned==1. */
2756 if (rnp_root != rnp)
2757 raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
2759 if (rcu_gp_in_progress(rsp) ||
2760 ULONG_CMP_GE(rnp_root->gp_seq, rnp_root->gp_seq_needed) ||
2761 time_before(j, rsp->gp_req_activity + HZ) ||
2762 time_before(j, rsp->gp_activity + HZ) ||
2763 atomic_xchg(&warned, 1)) {
2764 raw_spin_unlock_rcu_node(rnp_root); /* irqs remain disabled. */
2765 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2768 pr_alert("%s: g%ld->%ld gar:%lu ga:%lu f%#x %s->state:%#lx\n",
2769 __func__, (long)READ_ONCE(rsp->gp_seq),
2770 (long)READ_ONCE(rnp_root->gp_seq_needed),
2771 j - rsp->gp_req_activity, j - rsp->gp_activity,
2772 rsp->gp_flags, rsp->name,
2773 rsp->gp_kthread ? rsp->gp_kthread->state : 0x1ffffL);
2775 if (rnp_root != rnp)
2776 raw_spin_unlock_rcu_node(rnp_root);
2777 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
2781 * This does the RCU core processing work for the specified rcu_state
2782 * and rcu_data structures. This may be called only from the CPU to
2783 * whom the rdp belongs.
2786 __rcu_process_callbacks(struct rcu_state *rsp)
2788 unsigned long flags;
2789 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
2790 struct rcu_node *rnp = rdp->mynode;
2792 WARN_ON_ONCE(!rdp->beenonline);
2794 /* Update RCU state based on any recent quiescent states. */
2795 rcu_check_quiescent_state(rsp, rdp);
2797 /* No grace period and unregistered callbacks? */
2798 if (!rcu_gp_in_progress(rsp) &&
2799 rcu_segcblist_is_enabled(&rdp->cblist)) {
2800 local_irq_save(flags);
2801 if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
2802 rcu_accelerate_cbs_unlocked(rsp, rnp, rdp);
2803 local_irq_restore(flags);
2806 rcu_check_gp_start_stall(rsp, rnp, rdp);
2808 /* If there are callbacks ready, invoke them. */
2809 if (rcu_segcblist_ready_cbs(&rdp->cblist))
2810 invoke_rcu_callbacks(rsp, rdp);
2812 /* Do any needed deferred wakeups of rcuo kthreads. */
2813 do_nocb_deferred_wakeup(rdp);
2817 * Do RCU core processing for the current CPU.
2819 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
2821 struct rcu_state *rsp;
2823 if (cpu_is_offline(smp_processor_id()))
2825 trace_rcu_utilization(TPS("Start RCU core"));
2826 for_each_rcu_flavor(rsp)
2827 __rcu_process_callbacks(rsp);
2828 trace_rcu_utilization(TPS("End RCU core"));
2832 * Schedule RCU callback invocation. If the specified type of RCU
2833 * does not support RCU priority boosting, just do a direct call,
2834 * otherwise wake up the per-CPU kernel kthread. Note that because we
2835 * are running on the current CPU with softirqs disabled, the
2836 * rcu_cpu_kthread_task cannot disappear out from under us.
2838 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2840 if (unlikely(!READ_ONCE(rcu_scheduler_fully_active)))
2842 if (likely(!rsp->boost)) {
2843 rcu_do_batch(rsp, rdp);
2846 invoke_rcu_callbacks_kthread();
2849 static void invoke_rcu_core(void)
2851 if (cpu_online(smp_processor_id()))
2852 raise_softirq(RCU_SOFTIRQ);
2856 * Handle any core-RCU processing required by a call_rcu() invocation.
2858 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2859 struct rcu_head *head, unsigned long flags)
2862 * If called from an extended quiescent state, invoke the RCU
2863 * core in order to force a re-evaluation of RCU's idleness.
2865 if (!rcu_is_watching())
2868 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2869 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2873 * Force the grace period if too many callbacks or too long waiting.
2874 * Enforce hysteresis, and don't invoke force_quiescent_state()
2875 * if some other CPU has recently done so. Also, don't bother
2876 * invoking force_quiescent_state() if the newly enqueued callback
2877 * is the only one waiting for a grace period to complete.
2879 if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) >
2880 rdp->qlen_last_fqs_check + qhimark)) {
2882 /* Are we ignoring a completed grace period? */
2883 note_gp_changes(rsp, rdp);
2885 /* Start a new grace period if one not already started. */
2886 if (!rcu_gp_in_progress(rsp)) {
2887 rcu_accelerate_cbs_unlocked(rsp, rdp->mynode, rdp);
2889 /* Give the grace period a kick. */
2890 rdp->blimit = LONG_MAX;
2891 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
2892 rcu_segcblist_first_pend_cb(&rdp->cblist) != head)
2893 force_quiescent_state(rsp);
2894 rdp->n_force_qs_snap = rsp->n_force_qs;
2895 rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
2901 * RCU callback function to leak a callback.
2903 static void rcu_leak_callback(struct rcu_head *rhp)
2908 * Helper function for call_rcu() and friends. The cpu argument will
2909 * normally be -1, indicating "currently running CPU". It may specify
2910 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2911 * is expected to specify a CPU.
2914 __call_rcu(struct rcu_head *head, rcu_callback_t func,
2915 struct rcu_state *rsp, int cpu, bool lazy)
2917 unsigned long flags;
2918 struct rcu_data *rdp;
2920 /* Misaligned rcu_head! */
2921 WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
2923 if (debug_rcu_head_queue(head)) {
2925 * Probable double call_rcu(), so leak the callback.
2926 * Use rcu:rcu_callback trace event to find the previous
2927 * time callback was passed to __call_rcu().
2929 WARN_ONCE(1, "__call_rcu(): Double-freed CB %p->%pF()!!!\n",
2931 WRITE_ONCE(head->func, rcu_leak_callback);
2936 local_irq_save(flags);
2937 rdp = this_cpu_ptr(rsp->rda);
2939 /* Add the callback to our list. */
2940 if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist)) || cpu != -1) {
2944 rdp = per_cpu_ptr(rsp->rda, cpu);
2945 if (likely(rdp->mynode)) {
2946 /* Post-boot, so this should be for a no-CBs CPU. */
2947 offline = !__call_rcu_nocb(rdp, head, lazy, flags);
2948 WARN_ON_ONCE(offline);
2949 /* Offline CPU, _call_rcu() illegal, leak callback. */
2950 local_irq_restore(flags);
2954 * Very early boot, before rcu_init(). Initialize if needed
2955 * and then drop through to queue the callback.
2958 WARN_ON_ONCE(!rcu_is_watching());
2959 if (rcu_segcblist_empty(&rdp->cblist))
2960 rcu_segcblist_init(&rdp->cblist);
2962 rcu_segcblist_enqueue(&rdp->cblist, head, lazy);
2964 rcu_idle_count_callbacks_posted();
2966 if (__is_kfree_rcu_offset((unsigned long)func))
2967 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2968 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2969 rcu_segcblist_n_cbs(&rdp->cblist));
2971 trace_rcu_callback(rsp->name, head,
2972 rcu_segcblist_n_lazy_cbs(&rdp->cblist),
2973 rcu_segcblist_n_cbs(&rdp->cblist));
2975 /* Go handle any RCU core processing required. */
2976 __call_rcu_core(rsp, rdp, head, flags);
2977 local_irq_restore(flags);
2981 * call_rcu_sched() - Queue an RCU for invocation after sched grace period.
2982 * @head: structure to be used for queueing the RCU updates.
2983 * @func: actual callback function to be invoked after the grace period
2985 * The callback function will be invoked some time after a full grace
2986 * period elapses, in other words after all currently executing RCU
2987 * read-side critical sections have completed. call_rcu_sched() assumes
2988 * that the read-side critical sections end on enabling of preemption
2989 * or on voluntary preemption.
2990 * RCU read-side critical sections are delimited by:
2992 * - rcu_read_lock_sched() and rcu_read_unlock_sched(), OR
2993 * - anything that disables preemption.
2995 * These may be nested.
2997 * See the description of call_rcu() for more detailed information on
2998 * memory ordering guarantees.
3000 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
3002 __call_rcu(head, func, &rcu_sched_state, -1, 0);
3004 EXPORT_SYMBOL_GPL(call_rcu_sched);
3007 * call_rcu_bh() - Queue an RCU for invocation after a quicker grace period.
3008 * @head: structure to be used for queueing the RCU updates.
3009 * @func: actual callback function to be invoked after the grace period
3011 * The callback function will be invoked some time after a full grace
3012 * period elapses, in other words after all currently executing RCU
3013 * read-side critical sections have completed. call_rcu_bh() assumes
3014 * that the read-side critical sections end on completion of a softirq
3015 * handler. This means that read-side critical sections in process
3016 * context must not be interrupted by softirqs. This interface is to be
3017 * used when most of the read-side critical sections are in softirq context.
3018 * RCU read-side critical sections are delimited by:
3020 * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context, OR
3021 * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
3023 * These may be nested.
3025 * See the description of call_rcu() for more detailed information on
3026 * memory ordering guarantees.
3028 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
3030 __call_rcu(head, func, &rcu_bh_state, -1, 0);
3032 EXPORT_SYMBOL_GPL(call_rcu_bh);
3035 * Queue an RCU callback for lazy invocation after a grace period.
3036 * This will likely be later named something like "call_rcu_lazy()",
3037 * but this change will require some way of tagging the lazy RCU
3038 * callbacks in the list of pending callbacks. Until then, this
3039 * function may only be called from __kfree_rcu().
3041 void kfree_call_rcu(struct rcu_head *head,
3042 rcu_callback_t func)
3044 __call_rcu(head, func, rcu_state_p, -1, 1);
3046 EXPORT_SYMBOL_GPL(kfree_call_rcu);
3049 * Because a context switch is a grace period for RCU-sched and RCU-bh,
3050 * any blocking grace-period wait automatically implies a grace period
3051 * if there is only one CPU online at any point time during execution
3052 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
3053 * occasionally incorrectly indicate that there are multiple CPUs online
3054 * when there was in fact only one the whole time, as this just adds
3055 * some overhead: RCU still operates correctly.
3057 static inline int rcu_blocking_is_gp(void)
3061 might_sleep(); /* Check for RCU read-side critical section. */
3063 ret = num_online_cpus() <= 1;
3069 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
3071 * Control will return to the caller some time after a full rcu-sched
3072 * grace period has elapsed, in other words after all currently executing
3073 * rcu-sched read-side critical sections have completed. These read-side
3074 * critical sections are delimited by rcu_read_lock_sched() and
3075 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
3076 * local_irq_disable(), and so on may be used in place of
3077 * rcu_read_lock_sched().
3079 * This means that all preempt_disable code sequences, including NMI and
3080 * non-threaded hardware-interrupt handlers, in progress on entry will
3081 * have completed before this primitive returns. However, this does not
3082 * guarantee that softirq handlers will have completed, since in some
3083 * kernels, these handlers can run in process context, and can block.
3085 * Note that this guarantee implies further memory-ordering guarantees.
3086 * On systems with more than one CPU, when synchronize_sched() returns,
3087 * each CPU is guaranteed to have executed a full memory barrier since the
3088 * end of its last RCU-sched read-side critical section whose beginning
3089 * preceded the call to synchronize_sched(). In addition, each CPU having
3090 * an RCU read-side critical section that extends beyond the return from
3091 * synchronize_sched() is guaranteed to have executed a full memory barrier
3092 * after the beginning of synchronize_sched() and before the beginning of
3093 * that RCU read-side critical section. Note that these guarantees include
3094 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
3095 * that are executing in the kernel.
3097 * Furthermore, if CPU A invoked synchronize_sched(), which returned
3098 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
3099 * to have executed a full memory barrier during the execution of
3100 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
3101 * again only if the system has more than one CPU).
3103 void synchronize_sched(void)
3105 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3106 lock_is_held(&rcu_lock_map) ||
3107 lock_is_held(&rcu_sched_lock_map),
3108 "Illegal synchronize_sched() in RCU-sched read-side critical section");
3109 if (rcu_blocking_is_gp())
3111 if (rcu_gp_is_expedited())
3112 synchronize_sched_expedited();
3114 wait_rcu_gp(call_rcu_sched);
3116 EXPORT_SYMBOL_GPL(synchronize_sched);
3119 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
3121 * Control will return to the caller some time after a full rcu_bh grace
3122 * period has elapsed, in other words after all currently executing rcu_bh
3123 * read-side critical sections have completed. RCU read-side critical
3124 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
3125 * and may be nested.
3127 * See the description of synchronize_sched() for more detailed information
3128 * on memory ordering guarantees.
3130 void synchronize_rcu_bh(void)
3132 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
3133 lock_is_held(&rcu_lock_map) ||
3134 lock_is_held(&rcu_sched_lock_map),
3135 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
3136 if (rcu_blocking_is_gp())
3138 if (rcu_gp_is_expedited())
3139 synchronize_rcu_bh_expedited();
3141 wait_rcu_gp(call_rcu_bh);
3143 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
3146 * get_state_synchronize_rcu - Snapshot current RCU state
3148 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
3149 * to determine whether or not a full grace period has elapsed in the
3152 unsigned long get_state_synchronize_rcu(void)
3155 * Any prior manipulation of RCU-protected data must happen
3156 * before the load from ->gp_seq.
3159 return rcu_seq_snap(&rcu_state_p->gp_seq);
3161 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
3164 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
3166 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
3168 * If a full RCU grace period has elapsed since the earlier call to
3169 * get_state_synchronize_rcu(), just return. Otherwise, invoke
3170 * synchronize_rcu() to wait for a full grace period.
3172 * Yes, this function does not take counter wrap into account. But
3173 * counter wrap is harmless. If the counter wraps, we have waited for
3174 * more than 2 billion grace periods (and way more on a 64-bit system!),
3175 * so waiting for one additional grace period should be just fine.
3177 void cond_synchronize_rcu(unsigned long oldstate)
3179 if (!rcu_seq_done(&rcu_state_p->gp_seq, oldstate))
3182 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3184 EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
3187 * get_state_synchronize_sched - Snapshot current RCU-sched state
3189 * Returns a cookie that is used by a later call to cond_synchronize_sched()
3190 * to determine whether or not a full grace period has elapsed in the
3193 unsigned long get_state_synchronize_sched(void)
3196 * Any prior manipulation of RCU-protected data must happen
3197 * before the load from ->gp_seq.
3200 return rcu_seq_snap(&rcu_sched_state.gp_seq);
3202 EXPORT_SYMBOL_GPL(get_state_synchronize_sched);
3205 * cond_synchronize_sched - Conditionally wait for an RCU-sched grace period
3207 * @oldstate: return value from earlier call to get_state_synchronize_sched()
3209 * If a full RCU-sched grace period has elapsed since the earlier call to
3210 * get_state_synchronize_sched(), just return. Otherwise, invoke
3211 * synchronize_sched() to wait for a full grace period.
3213 * Yes, this function does not take counter wrap into account. But
3214 * counter wrap is harmless. If the counter wraps, we have waited for
3215 * more than 2 billion grace periods (and way more on a 64-bit system!),
3216 * so waiting for one additional grace period should be just fine.
3218 void cond_synchronize_sched(unsigned long oldstate)
3220 if (!rcu_seq_done(&rcu_sched_state.gp_seq, oldstate))
3221 synchronize_sched();
3223 smp_mb(); /* Ensure GP ends before subsequent accesses. */
3225 EXPORT_SYMBOL_GPL(cond_synchronize_sched);
3228 * Check to see if there is any immediate RCU-related work to be done
3229 * by the current CPU, for the specified type of RCU, returning 1 if so.
3230 * The checks are in order of increasing expense: checks that can be
3231 * carried out against CPU-local state are performed first. However,
3232 * we must check for CPU stalls first, else we might not get a chance.
3234 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
3236 struct rcu_node *rnp = rdp->mynode;
3238 /* Check for CPU stalls, if enabled. */
3239 check_cpu_stall(rsp, rdp);
3241 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
3242 if (rcu_nohz_full_cpu(rsp))
3245 /* Is the RCU core waiting for a quiescent state from this CPU? */
3246 if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm)
3249 /* Does this CPU have callbacks ready to invoke? */
3250 if (rcu_segcblist_ready_cbs(&rdp->cblist))
3253 /* Has RCU gone idle with this CPU needing another grace period? */
3254 if (!rcu_gp_in_progress(rsp) &&
3255 rcu_segcblist_is_enabled(&rdp->cblist) &&
3256 !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL))
3259 /* Have RCU grace period completed or started? */
3260 if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq ||
3261 unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */
3264 /* Does this CPU need a deferred NOCB wakeup? */
3265 if (rcu_nocb_need_deferred_wakeup(rdp))
3273 * Check to see if there is any immediate RCU-related work to be done
3274 * by the current CPU, returning 1 if so. This function is part of the
3275 * RCU implementation; it is -not- an exported member of the RCU API.
3277 static int rcu_pending(void)
3279 struct rcu_state *rsp;
3281 for_each_rcu_flavor(rsp)
3282 if (__rcu_pending(rsp, this_cpu_ptr(rsp->rda)))
3288 * Return true if the specified CPU has any callback. If all_lazy is
3289 * non-NULL, store an indication of whether all callbacks are lazy.
3290 * (If there are no callbacks, all of them are deemed to be lazy.)
3292 static bool __maybe_unused rcu_cpu_has_callbacks(bool *all_lazy)
3296 struct rcu_data *rdp;
3297 struct rcu_state *rsp;
3299 for_each_rcu_flavor(rsp) {
3300 rdp = this_cpu_ptr(rsp->rda);
3301 if (rcu_segcblist_empty(&rdp->cblist))
3304 if (rcu_segcblist_n_nonlazy_cbs(&rdp->cblist) || !all_lazy) {
3315 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
3316 * the compiler is expected to optimize this away.
3318 static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3319 int cpu, unsigned long done)
3321 trace_rcu_barrier(rsp->name, s, cpu,
3322 atomic_read(&rsp->barrier_cpu_count), done);
3326 * RCU callback function for _rcu_barrier(). If we are last, wake
3327 * up the task executing _rcu_barrier().
3329 static void rcu_barrier_callback(struct rcu_head *rhp)
3331 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3332 struct rcu_state *rsp = rdp->rsp;
3334 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
3335 _rcu_barrier_trace(rsp, TPS("LastCB"), -1,
3336 rsp->barrier_sequence);
3337 complete(&rsp->barrier_completion);
3339 _rcu_barrier_trace(rsp, TPS("CB"), -1, rsp->barrier_sequence);
3344 * Called with preemption disabled, and from cross-cpu IRQ context.
3346 static void rcu_barrier_func(void *type)
3348 struct rcu_state *rsp = type;
3349 struct rcu_data *rdp = raw_cpu_ptr(rsp->rda);
3351 _rcu_barrier_trace(rsp, TPS("IRQ"), -1, rsp->barrier_sequence);
3352 rdp->barrier_head.func = rcu_barrier_callback;
3353 debug_rcu_head_queue(&rdp->barrier_head);
3354 if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head, 0)) {
3355 atomic_inc(&rsp->barrier_cpu_count);
3357 debug_rcu_head_unqueue(&rdp->barrier_head);
3358 _rcu_barrier_trace(rsp, TPS("IRQNQ"), -1,
3359 rsp->barrier_sequence);
3364 * Orchestrate the specified type of RCU barrier, waiting for all
3365 * RCU callbacks of the specified type to complete.
3367 static void _rcu_barrier(struct rcu_state *rsp)
3370 struct rcu_data *rdp;
3371 unsigned long s = rcu_seq_snap(&rsp->barrier_sequence);
3373 _rcu_barrier_trace(rsp, TPS("Begin"), -1, s);
3375 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3376 mutex_lock(&rsp->barrier_mutex);
3378 /* Did someone else do our work for us? */
3379 if (rcu_seq_done(&rsp->barrier_sequence, s)) {
3380 _rcu_barrier_trace(rsp, TPS("EarlyExit"), -1,
3381 rsp->barrier_sequence);
3382 smp_mb(); /* caller's subsequent code after above check. */
3383 mutex_unlock(&rsp->barrier_mutex);
3387 /* Mark the start of the barrier operation. */
3388 rcu_seq_start(&rsp->barrier_sequence);
3389 _rcu_barrier_trace(rsp, TPS("Inc1"), -1, rsp->barrier_sequence);
3392 * Initialize the count to one rather than to zero in order to
3393 * avoid a too-soon return to zero in case of a short grace period
3394 * (or preemption of this task). Exclude CPU-hotplug operations
3395 * to ensure that no offline CPU has callbacks queued.
3397 init_completion(&rsp->barrier_completion);
3398 atomic_set(&rsp->barrier_cpu_count, 1);
3402 * Force each CPU with callbacks to register a new callback.
3403 * When that callback is invoked, we will know that all of the
3404 * corresponding CPU's preceding callbacks have been invoked.
3406 for_each_possible_cpu(cpu) {
3407 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
3409 rdp = per_cpu_ptr(rsp->rda, cpu);
3410 if (rcu_is_nocb_cpu(cpu)) {
3411 if (!rcu_nocb_cpu_needs_barrier(rsp, cpu)) {
3412 _rcu_barrier_trace(rsp, TPS("OfflineNoCB"), cpu,
3413 rsp->barrier_sequence);
3415 _rcu_barrier_trace(rsp, TPS("OnlineNoCB"), cpu,
3416 rsp->barrier_sequence);
3417 smp_mb__before_atomic();
3418 atomic_inc(&rsp->barrier_cpu_count);
3419 __call_rcu(&rdp->barrier_head,
3420 rcu_barrier_callback, rsp, cpu, 0);
3422 } else if (rcu_segcblist_n_cbs(&rdp->cblist)) {
3423 _rcu_barrier_trace(rsp, TPS("OnlineQ"), cpu,
3424 rsp->barrier_sequence);
3425 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3427 _rcu_barrier_trace(rsp, TPS("OnlineNQ"), cpu,
3428 rsp->barrier_sequence);
3434 * Now that we have an rcu_barrier_callback() callback on each
3435 * CPU, and thus each counted, remove the initial count.
3437 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3438 complete(&rsp->barrier_completion);
3440 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3441 wait_for_completion(&rsp->barrier_completion);
3443 /* Mark the end of the barrier operation. */
3444 _rcu_barrier_trace(rsp, TPS("Inc2"), -1, rsp->barrier_sequence);
3445 rcu_seq_end(&rsp->barrier_sequence);
3447 /* Other rcu_barrier() invocations can now safely proceed. */
3448 mutex_unlock(&rsp->barrier_mutex);
3452 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3454 void rcu_barrier_bh(void)
3456 _rcu_barrier(&rcu_bh_state);
3458 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
3461 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3463 void rcu_barrier_sched(void)
3465 _rcu_barrier(&rcu_sched_state);
3467 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
3470 * Propagate ->qsinitmask bits up the rcu_node tree to account for the
3471 * first CPU in a given leaf rcu_node structure coming online. The caller
3472 * must hold the corresponding leaf rcu_node ->lock with interrrupts
3475 static void rcu_init_new_rnp(struct rcu_node *rnp_leaf)
3478 struct rcu_node *rnp = rnp_leaf;
3480 raw_lockdep_assert_held_rcu_node(rnp);
3482 mask = rnp->grpmask;
3486 raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */
3487 rnp->qsmaskinit |= mask;
3488 raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */
3493 * Do boot-time initialization of a CPU's per-CPU RCU data.
3496 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3498 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3500 /* Set up local state, ensuring consistent view of global state. */
3501 rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu);
3502 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3503 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != 1);
3504 WARN_ON_ONCE(rcu_dynticks_in_eqs(rcu_dynticks_snap(rdp->dynticks)));
3507 rcu_boot_init_nocb_percpu_data(rdp);
3511 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3512 * offline event can be happening at a given time. Note also that we can
3513 * accept some slop in the rsp->gp_seq access due to the fact that this
3514 * CPU cannot possibly have any RCU callbacks in flight yet.
3517 rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3519 unsigned long flags;
3520 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3521 struct rcu_node *rnp = rcu_get_root(rsp);
3523 /* Set up local state, ensuring consistent view of global state. */
3524 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3525 rdp->qlen_last_fqs_check = 0;
3526 rdp->n_force_qs_snap = rsp->n_force_qs;
3527 rdp->blimit = blimit;
3528 if (rcu_segcblist_empty(&rdp->cblist) && /* No early-boot CBs? */
3529 !init_nocb_callback_list(rdp))
3530 rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
3531 rdp->dynticks->dynticks_nesting = 1; /* CPU not up, no tearing. */
3532 rcu_dynticks_eqs_online();
3533 raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
3536 * Add CPU to leaf rcu_node pending-online bitmask. Any needed
3537 * propagation up the rcu_node tree will happen at the beginning
3538 * of the next grace period.
3541 raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
3542 rdp->beenonline = true; /* We have now been online. */
3543 rdp->gp_seq = rnp->gp_seq;
3544 rdp->gp_seq_needed = rnp->gp_seq;
3545 rdp->cpu_no_qs.b.norm = true;
3546 rdp->rcu_qs_ctr_snap = per_cpu(rcu_dynticks.rcu_qs_ctr, cpu);
3547 rdp->core_needs_qs = false;
3548 rdp->rcu_iw_pending = false;
3549 rdp->rcu_iw_gp_seq = rnp->gp_seq - 1;
3550 trace_rcu_grace_period(rsp->name, rdp->gp_seq, TPS("cpuonl"));
3551 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3555 * Invoked early in the CPU-online process, when pretty much all
3556 * services are available. The incoming CPU is not present.
3558 int rcutree_prepare_cpu(unsigned int cpu)
3560 struct rcu_state *rsp;
3562 for_each_rcu_flavor(rsp)
3563 rcu_init_percpu_data(cpu, rsp);
3565 rcu_prepare_kthreads(cpu);
3566 rcu_spawn_all_nocb_kthreads(cpu);
3572 * Update RCU priority boot kthread affinity for CPU-hotplug changes.
3574 static void rcutree_affinity_setting(unsigned int cpu, int outgoing)
3576 struct rcu_data *rdp = per_cpu_ptr(rcu_state_p->rda, cpu);
3578 rcu_boost_kthread_setaffinity(rdp->mynode, outgoing);
3582 * Near the end of the CPU-online process. Pretty much all services
3583 * enabled, and the CPU is now very much alive.
3585 int rcutree_online_cpu(unsigned int cpu)
3587 unsigned long flags;
3588 struct rcu_data *rdp;
3589 struct rcu_node *rnp;
3590 struct rcu_state *rsp;
3592 for_each_rcu_flavor(rsp) {
3593 rdp = per_cpu_ptr(rsp->rda, cpu);
3595 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3596 rnp->ffmask |= rdp->grpmask;
3597 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3599 if (IS_ENABLED(CONFIG_TREE_SRCU))
3600 srcu_online_cpu(cpu);
3601 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
3602 return 0; /* Too early in boot for scheduler work. */
3603 sync_sched_exp_online_cleanup(cpu);
3604 rcutree_affinity_setting(cpu, -1);
3609 * Near the beginning of the process. The CPU is still very much alive
3610 * with pretty much all services enabled.
3612 int rcutree_offline_cpu(unsigned int cpu)
3614 unsigned long flags;
3615 struct rcu_data *rdp;
3616 struct rcu_node *rnp;
3617 struct rcu_state *rsp;
3619 for_each_rcu_flavor(rsp) {
3620 rdp = per_cpu_ptr(rsp->rda, cpu);
3622 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3623 rnp->ffmask &= ~rdp->grpmask;
3624 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3627 rcutree_affinity_setting(cpu, cpu);
3628 if (IS_ENABLED(CONFIG_TREE_SRCU))
3629 srcu_offline_cpu(cpu);
3634 * Near the end of the offline process. We do only tracing here.
3636 int rcutree_dying_cpu(unsigned int cpu)
3638 struct rcu_state *rsp;
3640 for_each_rcu_flavor(rsp)
3641 rcu_cleanup_dying_cpu(rsp);
3646 * The outgoing CPU is gone and we are running elsewhere.
3648 int rcutree_dead_cpu(unsigned int cpu)
3650 struct rcu_state *rsp;
3652 for_each_rcu_flavor(rsp) {
3653 rcu_cleanup_dead_cpu(cpu, rsp);
3654 do_nocb_deferred_wakeup(per_cpu_ptr(rsp->rda, cpu));
3659 static DEFINE_PER_CPU(int, rcu_cpu_started);
3662 * Mark the specified CPU as being online so that subsequent grace periods
3663 * (both expedited and normal) will wait on it. Note that this means that
3664 * incoming CPUs are not allowed to use RCU read-side critical sections
3665 * until this function is called. Failing to observe this restriction
3666 * will result in lockdep splats.
3668 * Note that this function is special in that it is invoked directly
3669 * from the incoming CPU rather than from the cpuhp_step mechanism.
3670 * This is because this function must be invoked at a precise location.
3672 void rcu_cpu_starting(unsigned int cpu)
3674 unsigned long flags;
3677 unsigned long oldmask;
3678 struct rcu_data *rdp;
3679 struct rcu_node *rnp;
3680 struct rcu_state *rsp;
3682 if (per_cpu(rcu_cpu_started, cpu))
3685 per_cpu(rcu_cpu_started, cpu) = 1;
3687 for_each_rcu_flavor(rsp) {
3688 rdp = per_cpu_ptr(rsp->rda, cpu);
3690 mask = rdp->grpmask;
3691 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3692 rnp->qsmaskinitnext |= mask;
3693 oldmask = rnp->expmaskinitnext;
3694 rnp->expmaskinitnext |= mask;
3695 oldmask ^= rnp->expmaskinitnext;
3696 nbits = bitmap_weight(&oldmask, BITS_PER_LONG);
3697 /* Allow lockless access for expedited grace periods. */
3698 smp_store_release(&rsp->ncpus, rsp->ncpus + nbits); /* ^^^ */
3699 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3701 smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
3704 #ifdef CONFIG_HOTPLUG_CPU
3706 * The CPU is exiting the idle loop into the arch_cpu_idle_dead()
3707 * function. We now remove it from the rcu_node tree's ->qsmaskinit
3710 static void rcu_cleanup_dying_idle_cpu(int cpu, struct rcu_state *rsp)
3712 unsigned long flags;
3714 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3715 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
3717 /* Remove outgoing CPU from mask in the leaf rcu_node structure. */
3718 mask = rdp->grpmask;
3719 raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */
3720 rnp->qsmaskinitnext &= ~mask;
3721 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3725 * The outgoing function has no further need of RCU, so remove it from
3726 * the list of CPUs that RCU must track.
3728 * Note that this function is special in that it is invoked directly
3729 * from the outgoing CPU rather than from the cpuhp_step mechanism.
3730 * This is because this function must be invoked at a precise location.
3732 void rcu_report_dead(unsigned int cpu)
3734 struct rcu_state *rsp;
3736 /* QS for any half-done expedited RCU-sched GP. */
3738 rcu_report_exp_rdp(&rcu_sched_state,
3739 this_cpu_ptr(rcu_sched_state.rda), true);
3741 for_each_rcu_flavor(rsp)
3742 rcu_cleanup_dying_idle_cpu(cpu, rsp);
3744 per_cpu(rcu_cpu_started, cpu) = 0;
3747 /* Migrate the dead CPU's callbacks to the current CPU. */
3748 static void rcu_migrate_callbacks(int cpu, struct rcu_state *rsp)
3750 unsigned long flags;
3751 struct rcu_data *my_rdp;
3752 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3753 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
3756 if (rcu_is_nocb_cpu(cpu) || rcu_segcblist_empty(&rdp->cblist))
3757 return; /* No callbacks to migrate. */
3759 local_irq_save(flags);
3760 my_rdp = this_cpu_ptr(rsp->rda);
3761 if (rcu_nocb_adopt_orphan_cbs(my_rdp, rdp, flags)) {
3762 local_irq_restore(flags);
3765 raw_spin_lock_rcu_node(rnp_root); /* irqs already disabled. */
3766 /* Leverage recent GPs and set GP for new callbacks. */
3767 needwake = rcu_advance_cbs(rsp, rnp_root, rdp) ||
3768 rcu_advance_cbs(rsp, rnp_root, my_rdp);
3769 rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist);
3770 WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) !=
3771 !rcu_segcblist_n_cbs(&my_rdp->cblist));
3772 raw_spin_unlock_irqrestore_rcu_node(rnp_root, flags);
3774 rcu_gp_kthread_wake(rsp);
3775 WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 ||
3776 !rcu_segcblist_empty(&rdp->cblist),
3777 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n",
3778 cpu, rcu_segcblist_n_cbs(&rdp->cblist),
3779 rcu_segcblist_first_cb(&rdp->cblist));
3783 * The outgoing CPU has just passed through the dying-idle state,
3784 * and we are being invoked from the CPU that was IPIed to continue the
3785 * offline operation. We need to migrate the outgoing CPU's callbacks.
3787 void rcutree_migrate_callbacks(int cpu)
3789 struct rcu_state *rsp;
3791 for_each_rcu_flavor(rsp)
3792 rcu_migrate_callbacks(cpu, rsp);
3797 * On non-huge systems, use expedited RCU grace periods to make suspend
3798 * and hibernation run faster.
3800 static int rcu_pm_notify(struct notifier_block *self,
3801 unsigned long action, void *hcpu)
3804 case PM_HIBERNATION_PREPARE:
3805 case PM_SUSPEND_PREPARE:
3806 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3809 case PM_POST_HIBERNATION:
3810 case PM_POST_SUSPEND:
3811 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3812 rcu_unexpedite_gp();
3821 * Spawn the kthreads that handle each RCU flavor's grace periods.
3823 static int __init rcu_spawn_gp_kthread(void)
3825 unsigned long flags;
3826 int kthread_prio_in = kthread_prio;
3827 struct rcu_node *rnp;
3828 struct rcu_state *rsp;
3829 struct sched_param sp;
3830 struct task_struct *t;
3832 /* Force priority into range. */
3833 if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1)
3835 else if (kthread_prio < 0)
3837 else if (kthread_prio > 99)
3839 if (kthread_prio != kthread_prio_in)
3840 pr_alert("rcu_spawn_gp_kthread(): Limited prio to %d from %d\n",
3841 kthread_prio, kthread_prio_in);
3843 rcu_scheduler_fully_active = 1;
3844 for_each_rcu_flavor(rsp) {
3845 t = kthread_create(rcu_gp_kthread, rsp, "%s", rsp->name);
3847 rnp = rcu_get_root(rsp);
3848 raw_spin_lock_irqsave_rcu_node(rnp, flags);
3849 rsp->gp_kthread = t;
3851 sp.sched_priority = kthread_prio;
3852 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
3854 raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
3857 rcu_spawn_nocb_kthreads();
3858 rcu_spawn_boost_kthreads();
3861 early_initcall(rcu_spawn_gp_kthread);
3864 * This function is invoked towards the end of the scheduler's
3865 * initialization process. Before this is called, the idle task might
3866 * contain synchronous grace-period primitives (during which time, this idle
3867 * task is booting the system, and such primitives are no-ops). After this
3868 * function is called, any synchronous grace-period primitives are run as
3869 * expedited, with the requesting task driving the grace period forward.
3870 * A later core_initcall() rcu_set_runtime_mode() will switch to full
3871 * runtime RCU functionality.
3873 void rcu_scheduler_starting(void)
3875 WARN_ON(num_online_cpus() != 1);
3876 WARN_ON(nr_context_switches() > 0);
3877 rcu_test_sync_prims();
3878 rcu_scheduler_active = RCU_SCHEDULER_INIT;
3879 rcu_test_sync_prims();
3883 * Helper function for rcu_init() that initializes one rcu_state structure.
3885 static void __init rcu_init_one(struct rcu_state *rsp)
3887 static const char * const buf[] = RCU_NODE_NAME_INIT;
3888 static const char * const fqs[] = RCU_FQS_NAME_INIT;
3889 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
3890 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
3892 int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */
3896 struct rcu_node *rnp;
3898 BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
3900 /* Silence gcc 4.8 false positive about array index out of range. */
3901 if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS)
3902 panic("rcu_init_one: rcu_num_lvls out of range");
3904 /* Initialize the level-tracking arrays. */
3906 for (i = 1; i < rcu_num_lvls; i++)
3907 rsp->level[i] = rsp->level[i - 1] + num_rcu_lvl[i - 1];
3908 rcu_init_levelspread(levelspread, num_rcu_lvl);
3910 /* Initialize the elements themselves, starting from the leaves. */
3912 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3913 cpustride *= levelspread[i];
3914 rnp = rsp->level[i];
3915 for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) {
3916 raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock));
3917 lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock),
3918 &rcu_node_class[i], buf[i]);
3919 raw_spin_lock_init(&rnp->fqslock);
3920 lockdep_set_class_and_name(&rnp->fqslock,
3921 &rcu_fqs_class[i], fqs[i]);
3922 rnp->gp_seq = rsp->gp_seq;
3923 rnp->gp_seq_needed = rsp->gp_seq;
3924 rnp->completedqs = rsp->gp_seq;
3926 rnp->qsmaskinit = 0;
3927 rnp->grplo = j * cpustride;
3928 rnp->grphi = (j + 1) * cpustride - 1;
3929 if (rnp->grphi >= nr_cpu_ids)
3930 rnp->grphi = nr_cpu_ids - 1;
3936 rnp->grpnum = j % levelspread[i - 1];
3937 rnp->grpmask = 1UL << rnp->grpnum;
3938 rnp->parent = rsp->level[i - 1] +
3939 j / levelspread[i - 1];
3942 INIT_LIST_HEAD(&rnp->blkd_tasks);
3943 rcu_init_one_nocb(rnp);
3944 init_waitqueue_head(&rnp->exp_wq[0]);
3945 init_waitqueue_head(&rnp->exp_wq[1]);
3946 init_waitqueue_head(&rnp->exp_wq[2]);
3947 init_waitqueue_head(&rnp->exp_wq[3]);
3948 spin_lock_init(&rnp->exp_lock);
3952 init_swait_queue_head(&rsp->gp_wq);
3953 init_swait_queue_head(&rsp->expedited_wq);
3954 rnp = rcu_first_leaf_node(rsp);
3955 for_each_possible_cpu(i) {
3956 while (i > rnp->grphi)
3958 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3959 rcu_boot_init_percpu_data(i, rsp);
3961 list_add(&rsp->flavors, &rcu_struct_flavors);
3965 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3966 * replace the definitions in tree.h because those are needed to size
3967 * the ->node array in the rcu_state structure.
3969 static void __init rcu_init_geometry(void)
3973 int rcu_capacity[RCU_NUM_LVLS];
3976 * Initialize any unspecified boot parameters.
3977 * The default values of jiffies_till_first_fqs and
3978 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3979 * value, which is a function of HZ, then adding one for each
3980 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3982 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
3983 if (jiffies_till_first_fqs == ULONG_MAX)
3984 jiffies_till_first_fqs = d;
3985 if (jiffies_till_next_fqs == ULONG_MAX)
3986 jiffies_till_next_fqs = d;
3988 /* If the compile-time values are accurate, just leave. */
3989 if (rcu_fanout_leaf == RCU_FANOUT_LEAF &&
3990 nr_cpu_ids == NR_CPUS)
3992 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n",
3993 rcu_fanout_leaf, nr_cpu_ids);
3996 * The boot-time rcu_fanout_leaf parameter must be at least two
3997 * and cannot exceed the number of bits in the rcu_node masks.
3998 * Complain and fall back to the compile-time values if this
3999 * limit is exceeded.
4001 if (rcu_fanout_leaf < 2 ||
4002 rcu_fanout_leaf > sizeof(unsigned long) * 8) {
4003 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4009 * Compute number of nodes that can be handled an rcu_node tree
4010 * with the given number of levels.
4012 rcu_capacity[0] = rcu_fanout_leaf;
4013 for (i = 1; i < RCU_NUM_LVLS; i++)
4014 rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
4017 * The tree must be able to accommodate the configured number of CPUs.
4018 * If this limit is exceeded, fall back to the compile-time values.
4020 if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) {
4021 rcu_fanout_leaf = RCU_FANOUT_LEAF;
4026 /* Calculate the number of levels in the tree. */
4027 for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) {
4029 rcu_num_lvls = i + 1;
4031 /* Calculate the number of rcu_nodes at each level of the tree. */
4032 for (i = 0; i < rcu_num_lvls; i++) {
4033 int cap = rcu_capacity[(rcu_num_lvls - 1) - i];
4034 num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap);
4037 /* Calculate the total number of rcu_node structures. */
4039 for (i = 0; i < rcu_num_lvls; i++)
4040 rcu_num_nodes += num_rcu_lvl[i];
4044 * Dump out the structure of the rcu_node combining tree associated
4045 * with the rcu_state structure referenced by rsp.
4047 static void __init rcu_dump_rcu_node_tree(struct rcu_state *rsp)
4050 struct rcu_node *rnp;
4052 pr_info("rcu_node tree layout dump\n");
4054 rcu_for_each_node_breadth_first(rsp, rnp) {
4055 if (rnp->level != level) {
4060 pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum);
4065 struct workqueue_struct *rcu_gp_wq;
4066 struct workqueue_struct *rcu_par_gp_wq;
4068 void __init rcu_init(void)
4072 rcu_early_boot_tests();
4074 rcu_bootup_announce();
4075 rcu_init_geometry();
4076 rcu_init_one(&rcu_bh_state);
4077 rcu_init_one(&rcu_sched_state);
4079 rcu_dump_rcu_node_tree(&rcu_sched_state);
4080 __rcu_init_preempt();
4081 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
4084 * We don't need protection against CPU-hotplug here because
4085 * this is called early in boot, before either interrupts
4086 * or the scheduler are operational.
4088 pm_notifier(rcu_pm_notify, 0);
4089 for_each_online_cpu(cpu) {
4090 rcutree_prepare_cpu(cpu);
4091 rcu_cpu_starting(cpu);
4092 rcutree_online_cpu(cpu);
4095 /* Create workqueue for expedited GPs and for Tree SRCU. */
4096 rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM, 0);
4097 WARN_ON(!rcu_gp_wq);
4098 rcu_par_gp_wq = alloc_workqueue("rcu_par_gp", WQ_MEM_RECLAIM, 0);
4099 WARN_ON(!rcu_par_gp_wq);
4102 #include "tree_exp.h"
4103 #include "tree_plugin.h"