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.h>
36 #include <linux/interrupt.h>
37 #include <linux/sched.h>
38 #include <linux/nmi.h>
39 #include <linux/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/export.h>
42 #include <linux/completion.h>
43 #include <linux/moduleparam.h>
44 #include <linux/module.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 <linux/prefetch.h>
54 #include <linux/delay.h>
55 #include <linux/stop_machine.h>
56 #include <linux/random.h>
57 #include <linux/ftrace_event.h>
58 #include <linux/suspend.h>
63 MODULE_ALIAS("rcutree");
64 #ifdef MODULE_PARAM_PREFIX
65 #undef MODULE_PARAM_PREFIX
67 #define MODULE_PARAM_PREFIX "rcutree."
69 /* Data structures. */
71 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
72 static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
75 * In order to export the rcu_state name to the tracing tools, it
76 * needs to be added in the __tracepoint_string section.
77 * This requires defining a separate variable tp_<sname>_varname
78 * that points to the string being used, and this will allow
79 * the tracing userspace tools to be able to decipher the string
80 * address to the matching string.
82 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
83 static char sname##_varname[] = #sname; \
84 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
85 struct rcu_state sname##_state = { \
86 .level = { &sname##_state.node[0] }, \
88 .fqs_state = RCU_GP_IDLE, \
89 .gpnum = 0UL - 300UL, \
90 .completed = 0UL - 300UL, \
91 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
92 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
93 .orphan_donetail = &sname##_state.orphan_donelist, \
94 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
95 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
96 .name = sname##_varname, \
99 DEFINE_PER_CPU(struct rcu_data, sname##_data)
101 RCU_STATE_INITIALIZER(rcu_sched, 's', call_rcu_sched);
102 RCU_STATE_INITIALIZER(rcu_bh, 'b', call_rcu_bh);
104 static struct rcu_state *rcu_state;
105 LIST_HEAD(rcu_struct_flavors);
107 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
108 static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
109 module_param(rcu_fanout_leaf, int, 0444);
110 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
111 static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */
118 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
121 * The rcu_scheduler_active variable transitions from zero to one just
122 * before the first task is spawned. So when this variable is zero, RCU
123 * can assume that there is but one task, allowing RCU to (for example)
124 * optimize synchronize_sched() to a simple barrier(). When this variable
125 * is one, RCU must actually do all the hard work required to detect real
126 * grace periods. This variable is also used to suppress boot-time false
127 * positives from lockdep-RCU error checking.
129 int rcu_scheduler_active __read_mostly;
130 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
133 * The rcu_scheduler_fully_active variable transitions from zero to one
134 * during the early_initcall() processing, which is after the scheduler
135 * is capable of creating new tasks. So RCU processing (for example,
136 * creating tasks for RCU priority boosting) must be delayed until after
137 * rcu_scheduler_fully_active transitions from zero to one. We also
138 * currently delay invocation of any RCU callbacks until after this point.
140 * It might later prove better for people registering RCU callbacks during
141 * early boot to take responsibility for these callbacks, but one step at
144 static int rcu_scheduler_fully_active __read_mostly;
146 #ifdef CONFIG_RCU_BOOST
149 * Control variables for per-CPU and per-rcu_node kthreads. These
150 * handle all flavors of RCU.
152 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
153 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
154 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
155 DEFINE_PER_CPU(char, rcu_cpu_has_work);
157 #endif /* #ifdef CONFIG_RCU_BOOST */
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);
164 * Track the rcutorture test sequence number and the update version
165 * number within a given test. The rcutorture_testseq is incremented
166 * on every rcutorture module load and unload, so has an odd value
167 * when a test is running. The rcutorture_vernum is set to zero
168 * when rcutorture starts and is incremented on each rcutorture update.
169 * These variables enable correlating rcutorture output with the
170 * RCU tracing information.
172 unsigned long rcutorture_testseq;
173 unsigned long rcutorture_vernum;
176 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
177 * permit this function to be invoked without holding the root rcu_node
178 * structure's ->lock, but of course results can be subject to change.
180 static int rcu_gp_in_progress(struct rcu_state *rsp)
182 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
186 * Note a quiescent state. Because we do not need to know
187 * how many quiescent states passed, just if there was at least
188 * one since the start of the grace period, this just sets a flag.
189 * The caller must have disabled preemption.
191 void rcu_sched_qs(int cpu)
193 struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
195 if (rdp->passed_quiesce == 0)
196 trace_rcu_grace_period(TPS("rcu_sched"), rdp->gpnum, TPS("cpuqs"));
197 rdp->passed_quiesce = 1;
200 void rcu_bh_qs(int cpu)
202 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
204 if (rdp->passed_quiesce == 0)
205 trace_rcu_grace_period(TPS("rcu_bh"), rdp->gpnum, TPS("cpuqs"));
206 rdp->passed_quiesce = 1;
210 * Note a context switch. This is a quiescent state for RCU-sched,
211 * and requires special handling for preemptible RCU.
212 * The caller must have disabled preemption.
214 void rcu_note_context_switch(int cpu)
216 trace_rcu_utilization(TPS("Start context switch"));
218 rcu_preempt_note_context_switch(cpu);
219 trace_rcu_utilization(TPS("End context switch"));
221 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
223 static DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
224 .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
225 .dynticks = ATOMIC_INIT(1),
226 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
227 .dynticks_idle_nesting = DYNTICK_TASK_NEST_VALUE,
228 .dynticks_idle = ATOMIC_INIT(1),
229 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
232 static long blimit = 10; /* Maximum callbacks per rcu_do_batch. */
233 static long qhimark = 10000; /* If this many pending, ignore blimit. */
234 static long qlowmark = 100; /* Once only this many pending, use blimit. */
236 module_param(blimit, long, 0444);
237 module_param(qhimark, long, 0444);
238 module_param(qlowmark, long, 0444);
240 static ulong jiffies_till_first_fqs = ULONG_MAX;
241 static ulong jiffies_till_next_fqs = ULONG_MAX;
243 module_param(jiffies_till_first_fqs, ulong, 0644);
244 module_param(jiffies_till_next_fqs, ulong, 0644);
246 static bool rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
247 struct rcu_data *rdp);
248 static void force_qs_rnp(struct rcu_state *rsp,
249 int (*f)(struct rcu_data *rsp, bool *isidle,
250 unsigned long *maxj),
251 bool *isidle, unsigned long *maxj);
252 static void force_quiescent_state(struct rcu_state *rsp);
253 static int rcu_pending(int cpu);
256 * Return the number of RCU-sched batches processed thus far for debug & stats.
258 long rcu_batches_completed_sched(void)
260 return rcu_sched_state.completed;
262 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
265 * Return the number of RCU BH batches processed thus far for debug & stats.
267 long rcu_batches_completed_bh(void)
269 return rcu_bh_state.completed;
271 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
274 * Force a quiescent state for RCU BH.
276 void rcu_bh_force_quiescent_state(void)
278 force_quiescent_state(&rcu_bh_state);
280 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
283 * Record the number of times rcutorture tests have been initiated and
284 * terminated. This information allows the debugfs tracing stats to be
285 * correlated to the rcutorture messages, even when the rcutorture module
286 * is being repeatedly loaded and unloaded. In other words, we cannot
287 * store this state in rcutorture itself.
289 void rcutorture_record_test_transition(void)
291 rcutorture_testseq++;
292 rcutorture_vernum = 0;
294 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
297 * Record the number of writer passes through the current rcutorture test.
298 * This is also used to correlate debugfs tracing stats with the rcutorture
301 void rcutorture_record_progress(unsigned long vernum)
305 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
308 * Force a quiescent state for RCU-sched.
310 void rcu_sched_force_quiescent_state(void)
312 force_quiescent_state(&rcu_sched_state);
314 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
317 * Does the CPU have callbacks ready to be invoked?
320 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
322 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL] &&
323 rdp->nxttail[RCU_DONE_TAIL] != NULL;
327 * Return the root node of the specified rcu_state structure.
329 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
331 return &rsp->node[0];
335 * Is there any need for future grace periods?
336 * Interrupts must be disabled. If the caller does not hold the root
337 * rnp_node structure's ->lock, the results are advisory only.
339 static int rcu_future_needs_gp(struct rcu_state *rsp)
341 struct rcu_node *rnp = rcu_get_root(rsp);
342 int idx = (ACCESS_ONCE(rnp->completed) + 1) & 0x1;
343 int *fp = &rnp->need_future_gp[idx];
345 return ACCESS_ONCE(*fp);
349 * Does the current CPU require a not-yet-started grace period?
350 * The caller must have disabled interrupts to prevent races with
351 * normal callback registry.
354 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
358 if (rcu_gp_in_progress(rsp))
359 return 0; /* No, a grace period is already in progress. */
360 if (rcu_future_needs_gp(rsp))
361 return 1; /* Yes, a no-CBs CPU needs one. */
362 if (!rdp->nxttail[RCU_NEXT_TAIL])
363 return 0; /* No, this is a no-CBs (or offline) CPU. */
364 if (*rdp->nxttail[RCU_NEXT_READY_TAIL])
365 return 1; /* Yes, this CPU has newly registered callbacks. */
366 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++)
367 if (rdp->nxttail[i - 1] != rdp->nxttail[i] &&
368 ULONG_CMP_LT(ACCESS_ONCE(rsp->completed),
369 rdp->nxtcompleted[i]))
370 return 1; /* Yes, CBs for future grace period. */
371 return 0; /* No grace period needed. */
375 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
377 * If the new value of the ->dynticks_nesting counter now is zero,
378 * we really have entered idle, and must do the appropriate accounting.
379 * The caller must have disabled interrupts.
381 static void rcu_eqs_enter_common(struct rcu_dynticks *rdtp, long long oldval,
384 struct rcu_state *rsp;
385 struct rcu_data *rdp;
387 trace_rcu_dyntick(TPS("Start"), oldval, rdtp->dynticks_nesting);
388 if (!user && !is_idle_task(current)) {
389 struct task_struct *idle __maybe_unused =
390 idle_task(smp_processor_id());
392 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval, 0);
393 ftrace_dump(DUMP_ORIG);
394 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
395 current->pid, current->comm,
396 idle->pid, idle->comm); /* must be idle task! */
398 for_each_rcu_flavor(rsp) {
399 rdp = this_cpu_ptr(rsp->rda);
400 do_nocb_deferred_wakeup(rdp);
402 rcu_prepare_for_idle(smp_processor_id());
403 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
404 smp_mb__before_atomic_inc(); /* See above. */
405 atomic_inc(&rdtp->dynticks);
406 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
407 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
410 * It is illegal to enter an extended quiescent state while
411 * in an RCU read-side critical section.
413 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
414 "Illegal idle entry in RCU read-side critical section.");
415 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
416 "Illegal idle entry in RCU-bh read-side critical section.");
417 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
418 "Illegal idle entry in RCU-sched read-side critical section.");
422 * Enter an RCU extended quiescent state, which can be either the
423 * idle loop or adaptive-tickless usermode execution.
425 static void rcu_eqs_enter(bool user)
428 struct rcu_dynticks *rdtp;
430 rdtp = this_cpu_ptr(&rcu_dynticks);
431 oldval = rdtp->dynticks_nesting;
432 WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
433 if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE) {
434 rdtp->dynticks_nesting = 0;
435 rcu_eqs_enter_common(rdtp, oldval, user);
437 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
442 * rcu_idle_enter - inform RCU that current CPU is entering idle
444 * Enter idle mode, in other words, -leave- the mode in which RCU
445 * read-side critical sections can occur. (Though RCU read-side
446 * critical sections can occur in irq handlers in idle, a possibility
447 * handled by irq_enter() and irq_exit().)
449 * We crowbar the ->dynticks_nesting field to zero to allow for
450 * the possibility of usermode upcalls having messed up our count
451 * of interrupt nesting level during the prior busy period.
453 void rcu_idle_enter(void)
457 local_irq_save(flags);
458 rcu_eqs_enter(false);
459 rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks), 0);
460 local_irq_restore(flags);
462 EXPORT_SYMBOL_GPL(rcu_idle_enter);
464 #ifdef CONFIG_RCU_USER_QS
466 * rcu_user_enter - inform RCU that we are resuming userspace.
468 * Enter RCU idle mode right before resuming userspace. No use of RCU
469 * is permitted between this call and rcu_user_exit(). This way the
470 * CPU doesn't need to maintain the tick for RCU maintenance purposes
471 * when the CPU runs in userspace.
473 void rcu_user_enter(void)
477 #endif /* CONFIG_RCU_USER_QS */
480 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
482 * Exit from an interrupt handler, which might possibly result in entering
483 * idle mode, in other words, leaving the mode in which read-side critical
484 * sections can occur.
486 * This code assumes that the idle loop never does anything that might
487 * result in unbalanced calls to irq_enter() and irq_exit(). If your
488 * architecture violates this assumption, RCU will give you what you
489 * deserve, good and hard. But very infrequently and irreproducibly.
491 * Use things like work queues to work around this limitation.
493 * You have been warned.
495 void rcu_irq_exit(void)
499 struct rcu_dynticks *rdtp;
501 local_irq_save(flags);
502 rdtp = this_cpu_ptr(&rcu_dynticks);
503 oldval = rdtp->dynticks_nesting;
504 rdtp->dynticks_nesting--;
505 WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
506 if (rdtp->dynticks_nesting)
507 trace_rcu_dyntick(TPS("--="), oldval, rdtp->dynticks_nesting);
509 rcu_eqs_enter_common(rdtp, oldval, true);
510 rcu_sysidle_enter(rdtp, 1);
511 local_irq_restore(flags);
515 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
517 * If the new value of the ->dynticks_nesting counter was previously zero,
518 * we really have exited idle, and must do the appropriate accounting.
519 * The caller must have disabled interrupts.
521 static void rcu_eqs_exit_common(struct rcu_dynticks *rdtp, long long oldval,
524 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
525 atomic_inc(&rdtp->dynticks);
526 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
527 smp_mb__after_atomic_inc(); /* See above. */
528 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
529 rcu_cleanup_after_idle(smp_processor_id());
530 trace_rcu_dyntick(TPS("End"), oldval, rdtp->dynticks_nesting);
531 if (!user && !is_idle_task(current)) {
532 struct task_struct *idle __maybe_unused =
533 idle_task(smp_processor_id());
535 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
536 oldval, rdtp->dynticks_nesting);
537 ftrace_dump(DUMP_ORIG);
538 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
539 current->pid, current->comm,
540 idle->pid, idle->comm); /* must be idle task! */
545 * Exit an RCU extended quiescent state, which can be either the
546 * idle loop or adaptive-tickless usermode execution.
548 static void rcu_eqs_exit(bool user)
550 struct rcu_dynticks *rdtp;
553 rdtp = this_cpu_ptr(&rcu_dynticks);
554 oldval = rdtp->dynticks_nesting;
555 WARN_ON_ONCE(oldval < 0);
556 if (oldval & DYNTICK_TASK_NEST_MASK) {
557 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
559 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
560 rcu_eqs_exit_common(rdtp, oldval, user);
565 * rcu_idle_exit - inform RCU that current CPU is leaving idle
567 * Exit idle mode, in other words, -enter- the mode in which RCU
568 * read-side critical sections can occur.
570 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
571 * allow for the possibility of usermode upcalls messing up our count
572 * of interrupt nesting level during the busy period that is just
575 void rcu_idle_exit(void)
579 local_irq_save(flags);
581 rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks), 0);
582 local_irq_restore(flags);
584 EXPORT_SYMBOL_GPL(rcu_idle_exit);
586 #ifdef CONFIG_RCU_USER_QS
588 * rcu_user_exit - inform RCU that we are exiting userspace.
590 * Exit RCU idle mode while entering the kernel because it can
591 * run a RCU read side critical section anytime.
593 void rcu_user_exit(void)
597 #endif /* CONFIG_RCU_USER_QS */
600 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
602 * Enter an interrupt handler, which might possibly result in exiting
603 * idle mode, in other words, entering the mode in which read-side critical
604 * sections can occur.
606 * Note that the Linux kernel is fully capable of entering an interrupt
607 * handler that it never exits, for example when doing upcalls to
608 * user mode! This code assumes that the idle loop never does upcalls to
609 * user mode. If your architecture does do upcalls from the idle loop (or
610 * does anything else that results in unbalanced calls to the irq_enter()
611 * and irq_exit() functions), RCU will give you what you deserve, good
612 * and hard. But very infrequently and irreproducibly.
614 * Use things like work queues to work around this limitation.
616 * You have been warned.
618 void rcu_irq_enter(void)
621 struct rcu_dynticks *rdtp;
624 local_irq_save(flags);
625 rdtp = this_cpu_ptr(&rcu_dynticks);
626 oldval = rdtp->dynticks_nesting;
627 rdtp->dynticks_nesting++;
628 WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
630 trace_rcu_dyntick(TPS("++="), oldval, rdtp->dynticks_nesting);
632 rcu_eqs_exit_common(rdtp, oldval, true);
633 rcu_sysidle_exit(rdtp, 1);
634 local_irq_restore(flags);
638 * rcu_nmi_enter - inform RCU of entry to NMI context
640 * If the CPU was idle with dynamic ticks active, and there is no
641 * irq handler running, this updates rdtp->dynticks_nmi to let the
642 * RCU grace-period handling know that the CPU is active.
644 void rcu_nmi_enter(void)
646 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
648 if (rdtp->dynticks_nmi_nesting == 0 &&
649 (atomic_read(&rdtp->dynticks) & 0x1))
651 rdtp->dynticks_nmi_nesting++;
652 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
653 atomic_inc(&rdtp->dynticks);
654 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
655 smp_mb__after_atomic_inc(); /* See above. */
656 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
660 * rcu_nmi_exit - inform RCU of exit from NMI context
662 * If the CPU was idle with dynamic ticks active, and there is no
663 * irq handler running, this updates rdtp->dynticks_nmi to let the
664 * RCU grace-period handling know that the CPU is no longer active.
666 void rcu_nmi_exit(void)
668 struct rcu_dynticks *rdtp = this_cpu_ptr(&rcu_dynticks);
670 if (rdtp->dynticks_nmi_nesting == 0 ||
671 --rdtp->dynticks_nmi_nesting != 0)
673 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
674 smp_mb__before_atomic_inc(); /* See above. */
675 atomic_inc(&rdtp->dynticks);
676 smp_mb__after_atomic_inc(); /* Force delay to next write. */
677 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
681 * __rcu_is_watching - are RCU read-side critical sections safe?
683 * Return true if RCU is watching the running CPU, which means that
684 * this CPU can safely enter RCU read-side critical sections. Unlike
685 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
686 * least disabled preemption.
688 bool notrace __rcu_is_watching(void)
690 return atomic_read(this_cpu_ptr(&rcu_dynticks.dynticks)) & 0x1;
694 * rcu_is_watching - see if RCU thinks that the current CPU is idle
696 * If the current CPU is in its idle loop and is neither in an interrupt
697 * or NMI handler, return true.
699 bool notrace rcu_is_watching(void)
704 ret = __rcu_is_watching();
708 EXPORT_SYMBOL_GPL(rcu_is_watching);
710 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
713 * Is the current CPU online? Disable preemption to avoid false positives
714 * that could otherwise happen due to the current CPU number being sampled,
715 * this task being preempted, its old CPU being taken offline, resuming
716 * on some other CPU, then determining that its old CPU is now offline.
717 * It is OK to use RCU on an offline processor during initial boot, hence
718 * the check for rcu_scheduler_fully_active. Note also that it is OK
719 * for a CPU coming online to use RCU for one jiffy prior to marking itself
720 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
721 * offline to continue to use RCU for one jiffy after marking itself
722 * offline in the cpu_online_mask. This leniency is necessary given the
723 * non-atomic nature of the online and offline processing, for example,
724 * the fact that a CPU enters the scheduler after completing the CPU_DYING
727 * This is also why RCU internally marks CPUs online during the
728 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
730 * Disable checking if in an NMI handler because we cannot safely report
731 * errors from NMI handlers anyway.
733 bool rcu_lockdep_current_cpu_online(void)
735 struct rcu_data *rdp;
736 struct rcu_node *rnp;
742 rdp = this_cpu_ptr(&rcu_sched_data);
744 ret = (rdp->grpmask & rnp->qsmaskinit) ||
745 !rcu_scheduler_fully_active;
749 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
751 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
754 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
756 * If the current CPU is idle or running at a first-level (not nested)
757 * interrupt from idle, return true. The caller must have at least
758 * disabled preemption.
760 static int rcu_is_cpu_rrupt_from_idle(void)
762 return __this_cpu_read(rcu_dynticks.dynticks_nesting) <= 1;
766 * Snapshot the specified CPU's dynticks counter so that we can later
767 * credit them with an implicit quiescent state. Return 1 if this CPU
768 * is in dynticks idle mode, which is an extended quiescent state.
770 static int dyntick_save_progress_counter(struct rcu_data *rdp,
771 bool *isidle, unsigned long *maxj)
773 rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
774 rcu_sysidle_check_cpu(rdp, isidle, maxj);
775 return (rdp->dynticks_snap & 0x1) == 0;
779 * This function really isn't for public consumption, but RCU is special in
780 * that context switches can allow the state machine to make progress.
782 extern void resched_cpu(int cpu);
785 * Return true if the specified CPU has passed through a quiescent
786 * state by virtue of being in or having passed through an dynticks
787 * idle state since the last call to dyntick_save_progress_counter()
788 * for this same CPU, or by virtue of having been offline.
790 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp,
791 bool *isidle, unsigned long *maxj)
796 curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
797 snap = (unsigned int)rdp->dynticks_snap;
800 * If the CPU passed through or entered a dynticks idle phase with
801 * no active irq/NMI handlers, then we can safely pretend that the CPU
802 * already acknowledged the request to pass through a quiescent
803 * state. Either way, that CPU cannot possibly be in an RCU
804 * read-side critical section that started before the beginning
805 * of the current RCU grace period.
807 if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
808 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("dti"));
814 * Check for the CPU being offline, but only if the grace period
815 * is old enough. We don't need to worry about the CPU changing
816 * state: If we see it offline even once, it has been through a
819 * The reason for insisting that the grace period be at least
820 * one jiffy old is that CPUs that are not quite online and that
821 * have just gone offline can still execute RCU read-side critical
824 if (ULONG_CMP_GE(rdp->rsp->gp_start + 2, jiffies))
825 return 0; /* Grace period is not old enough. */
827 if (cpu_is_offline(rdp->cpu)) {
828 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, TPS("ofl"));
834 * There is a possibility that a CPU in adaptive-ticks state
835 * might run in the kernel with the scheduling-clock tick disabled
836 * for an extended time period. Invoke rcu_kick_nohz_cpu() to
837 * force the CPU to restart the scheduling-clock tick in this
838 * CPU is in this state.
840 rcu_kick_nohz_cpu(rdp->cpu);
843 * Alternatively, the CPU might be running in the kernel
844 * for an extended period of time without a quiescent state.
845 * Attempt to force the CPU through the scheduler to gain the
846 * needed quiescent state, but only if the grace period has gone
847 * on for an uncommonly long time. If there are many stuck CPUs,
848 * we will beat on the first one until it gets unstuck, then move
849 * to the next. Only do this for the primary flavor of RCU.
851 if (rdp->rsp == rcu_state &&
852 ULONG_CMP_GE(jiffies, rdp->rsp->jiffies_resched)) {
853 rdp->rsp->jiffies_resched += 5;
854 resched_cpu(rdp->cpu);
860 static void record_gp_stall_check_time(struct rcu_state *rsp)
862 unsigned long j = jiffies;
866 smp_wmb(); /* Record start time before stall time. */
867 j1 = rcu_jiffies_till_stall_check();
868 ACCESS_ONCE(rsp->jiffies_stall) = j + j1;
869 rsp->jiffies_resched = j + j1 / 2;
873 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
874 * for architectures that do not implement trigger_all_cpu_backtrace().
875 * The NMI-triggered stack traces are more accurate because they are
876 * printed by the target CPU.
878 static void rcu_dump_cpu_stacks(struct rcu_state *rsp)
882 struct rcu_node *rnp;
884 rcu_for_each_leaf_node(rsp, rnp) {
885 raw_spin_lock_irqsave(&rnp->lock, flags);
886 if (rnp->qsmask != 0) {
887 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
888 if (rnp->qsmask & (1UL << cpu))
889 dump_cpu_task(rnp->grplo + cpu);
891 raw_spin_unlock_irqrestore(&rnp->lock, flags);
895 static void print_other_cpu_stall(struct rcu_state *rsp)
901 struct rcu_node *rnp = rcu_get_root(rsp);
904 /* Only let one CPU complain about others per time interval. */
906 raw_spin_lock_irqsave(&rnp->lock, flags);
907 delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
908 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
909 raw_spin_unlock_irqrestore(&rnp->lock, flags);
912 ACCESS_ONCE(rsp->jiffies_stall) = jiffies + 3 * rcu_jiffies_till_stall_check() + 3;
913 raw_spin_unlock_irqrestore(&rnp->lock, flags);
916 * OK, time to rat on our buddy...
917 * See Documentation/RCU/stallwarn.txt for info on how to debug
918 * RCU CPU stall warnings.
920 pr_err("INFO: %s detected stalls on CPUs/tasks:",
922 print_cpu_stall_info_begin();
923 rcu_for_each_leaf_node(rsp, rnp) {
924 raw_spin_lock_irqsave(&rnp->lock, flags);
925 ndetected += rcu_print_task_stall(rnp);
926 if (rnp->qsmask != 0) {
927 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
928 if (rnp->qsmask & (1UL << cpu)) {
929 print_cpu_stall_info(rsp,
934 raw_spin_unlock_irqrestore(&rnp->lock, flags);
938 * Now rat on any tasks that got kicked up to the root rcu_node
939 * due to CPU offlining.
941 rnp = rcu_get_root(rsp);
942 raw_spin_lock_irqsave(&rnp->lock, flags);
943 ndetected += rcu_print_task_stall(rnp);
944 raw_spin_unlock_irqrestore(&rnp->lock, flags);
946 print_cpu_stall_info_end();
947 for_each_possible_cpu(cpu)
948 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
949 pr_cont("(detected by %d, t=%ld jiffies, g=%ld, c=%ld, q=%lu)\n",
950 smp_processor_id(), (long)(jiffies - rsp->gp_start),
951 (long)rsp->gpnum, (long)rsp->completed, totqlen);
953 pr_err("INFO: Stall ended before state dump start\n");
954 else if (!trigger_all_cpu_backtrace())
955 rcu_dump_cpu_stacks(rsp);
957 /* Complain about tasks blocking the grace period. */
959 rcu_print_detail_task_stall(rsp);
961 force_quiescent_state(rsp); /* Kick them all. */
965 * This function really isn't for public consumption, but RCU is special in
966 * that context switches can allow the state machine to make progress.
968 extern void resched_cpu(int cpu);
970 static void print_cpu_stall(struct rcu_state *rsp)
974 struct rcu_node *rnp = rcu_get_root(rsp);
978 * OK, time to rat on ourselves...
979 * See Documentation/RCU/stallwarn.txt for info on how to debug
980 * RCU CPU stall warnings.
982 pr_err("INFO: %s self-detected stall on CPU", rsp->name);
983 print_cpu_stall_info_begin();
984 print_cpu_stall_info(rsp, smp_processor_id());
985 print_cpu_stall_info_end();
986 for_each_possible_cpu(cpu)
987 totqlen += per_cpu_ptr(rsp->rda, cpu)->qlen;
988 pr_cont(" (t=%lu jiffies g=%ld c=%ld q=%lu)\n",
989 jiffies - rsp->gp_start,
990 (long)rsp->gpnum, (long)rsp->completed, totqlen);
991 if (!trigger_all_cpu_backtrace())
994 raw_spin_lock_irqsave(&rnp->lock, flags);
995 if (ULONG_CMP_GE(jiffies, ACCESS_ONCE(rsp->jiffies_stall)))
996 ACCESS_ONCE(rsp->jiffies_stall) = jiffies +
997 3 * rcu_jiffies_till_stall_check() + 3;
998 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1001 * Attempt to revive the RCU machinery by forcing a context switch.
1003 * A context switch would normally allow the RCU state machine to make
1004 * progress and it could be we're stuck in kernel space without context
1005 * switches for an entirely unreasonable amount of time.
1007 resched_cpu(smp_processor_id());
1010 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
1012 unsigned long completed;
1013 unsigned long gpnum;
1017 struct rcu_node *rnp;
1019 if (rcu_cpu_stall_suppress || !rcu_gp_in_progress(rsp))
1024 * Lots of memory barriers to reject false positives.
1026 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1027 * then rsp->gp_start, and finally rsp->completed. These values
1028 * are updated in the opposite order with memory barriers (or
1029 * equivalent) during grace-period initialization and cleanup.
1030 * Now, a false positive can occur if we get an new value of
1031 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1032 * the memory barriers, the only way that this can happen is if one
1033 * grace period ends and another starts between these two fetches.
1034 * Detect this by comparing rsp->completed with the previous fetch
1037 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1038 * and rsp->gp_start suffice to forestall false positives.
1040 gpnum = ACCESS_ONCE(rsp->gpnum);
1041 smp_rmb(); /* Pick up ->gpnum first... */
1042 js = ACCESS_ONCE(rsp->jiffies_stall);
1043 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1044 gps = ACCESS_ONCE(rsp->gp_start);
1045 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1046 completed = ACCESS_ONCE(rsp->completed);
1047 if (ULONG_CMP_GE(completed, gpnum) ||
1048 ULONG_CMP_LT(j, js) ||
1049 ULONG_CMP_GE(gps, js))
1050 return; /* No stall or GP completed since entering function. */
1052 if (rcu_gp_in_progress(rsp) &&
1053 (ACCESS_ONCE(rnp->qsmask) & rdp->grpmask)) {
1055 /* We haven't checked in, so go dump stack. */
1056 print_cpu_stall(rsp);
1058 } else if (rcu_gp_in_progress(rsp) &&
1059 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
1061 /* They had a few time units to dump stack, so complain. */
1062 print_other_cpu_stall(rsp);
1067 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1069 * Set the stall-warning timeout way off into the future, thus preventing
1070 * any RCU CPU stall-warning messages from appearing in the current set of
1071 * RCU grace periods.
1073 * The caller must disable hard irqs.
1075 void rcu_cpu_stall_reset(void)
1077 struct rcu_state *rsp;
1079 for_each_rcu_flavor(rsp)
1080 ACCESS_ONCE(rsp->jiffies_stall) = jiffies + ULONG_MAX / 2;
1084 * Initialize the specified rcu_data structure's callback list to empty.
1086 static void init_callback_list(struct rcu_data *rdp)
1090 if (init_nocb_callback_list(rdp))
1092 rdp->nxtlist = NULL;
1093 for (i = 0; i < RCU_NEXT_SIZE; i++)
1094 rdp->nxttail[i] = &rdp->nxtlist;
1098 * Determine the value that ->completed will have at the end of the
1099 * next subsequent grace period. This is used to tag callbacks so that
1100 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1101 * been dyntick-idle for an extended period with callbacks under the
1102 * influence of RCU_FAST_NO_HZ.
1104 * The caller must hold rnp->lock with interrupts disabled.
1106 static unsigned long rcu_cbs_completed(struct rcu_state *rsp,
1107 struct rcu_node *rnp)
1110 * If RCU is idle, we just wait for the next grace period.
1111 * But we can only be sure that RCU is idle if we are looking
1112 * at the root rcu_node structure -- otherwise, a new grace
1113 * period might have started, but just not yet gotten around
1114 * to initializing the current non-root rcu_node structure.
1116 if (rcu_get_root(rsp) == rnp && rnp->gpnum == rnp->completed)
1117 return rnp->completed + 1;
1120 * Otherwise, wait for a possible partial grace period and
1121 * then the subsequent full grace period.
1123 return rnp->completed + 2;
1127 * Trace-event helper function for rcu_start_future_gp() and
1128 * rcu_nocb_wait_gp().
1130 static void trace_rcu_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1131 unsigned long c, const char *s)
1133 trace_rcu_future_grace_period(rdp->rsp->name, rnp->gpnum,
1134 rnp->completed, c, rnp->level,
1135 rnp->grplo, rnp->grphi, s);
1139 * Start some future grace period, as needed to handle newly arrived
1140 * callbacks. The required future grace periods are recorded in each
1141 * rcu_node structure's ->need_future_gp field. Returns true if there
1142 * is reason to awaken the grace-period kthread.
1144 * The caller must hold the specified rcu_node structure's ->lock.
1146 static bool __maybe_unused
1147 rcu_start_future_gp(struct rcu_node *rnp, struct rcu_data *rdp,
1148 unsigned long *c_out)
1153 struct rcu_node *rnp_root = rcu_get_root(rdp->rsp);
1156 * Pick up grace-period number for new callbacks. If this
1157 * grace period is already marked as needed, return to the caller.
1159 c = rcu_cbs_completed(rdp->rsp, rnp);
1160 trace_rcu_future_gp(rnp, rdp, c, TPS("Startleaf"));
1161 if (rnp->need_future_gp[c & 0x1]) {
1162 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartleaf"));
1167 * If either this rcu_node structure or the root rcu_node structure
1168 * believe that a grace period is in progress, then we must wait
1169 * for the one following, which is in "c". Because our request
1170 * will be noticed at the end of the current grace period, we don't
1171 * need to explicitly start one.
1173 if (rnp->gpnum != rnp->completed ||
1174 ACCESS_ONCE(rnp->gpnum) != ACCESS_ONCE(rnp->completed)) {
1175 rnp->need_future_gp[c & 0x1]++;
1176 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleaf"));
1181 * There might be no grace period in progress. If we don't already
1182 * hold it, acquire the root rcu_node structure's lock in order to
1183 * start one (if needed).
1185 if (rnp != rnp_root) {
1186 raw_spin_lock(&rnp_root->lock);
1187 smp_mb__after_unlock_lock();
1191 * Get a new grace-period number. If there really is no grace
1192 * period in progress, it will be smaller than the one we obtained
1193 * earlier. Adjust callbacks as needed. Note that even no-CBs
1194 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1196 c = rcu_cbs_completed(rdp->rsp, rnp_root);
1197 for (i = RCU_DONE_TAIL; i < RCU_NEXT_TAIL; i++)
1198 if (ULONG_CMP_LT(c, rdp->nxtcompleted[i]))
1199 rdp->nxtcompleted[i] = c;
1202 * If the needed for the required grace period is already
1203 * recorded, trace and leave.
1205 if (rnp_root->need_future_gp[c & 0x1]) {
1206 trace_rcu_future_gp(rnp, rdp, c, TPS("Prestartedroot"));
1210 /* Record the need for the future grace period. */
1211 rnp_root->need_future_gp[c & 0x1]++;
1213 /* If a grace period is not already in progress, start one. */
1214 if (rnp_root->gpnum != rnp_root->completed) {
1215 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedleafroot"));
1217 trace_rcu_future_gp(rnp, rdp, c, TPS("Startedroot"));
1218 ret = rcu_start_gp_advanced(rdp->rsp, rnp_root, rdp);
1221 if (rnp != rnp_root)
1222 raw_spin_unlock(&rnp_root->lock);
1230 * Clean up any old requests for the just-ended grace period. Also return
1231 * whether any additional grace periods have been requested. Also invoke
1232 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1233 * waiting for this grace period to complete.
1235 static int rcu_future_gp_cleanup(struct rcu_state *rsp, struct rcu_node *rnp)
1237 int c = rnp->completed;
1239 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1241 rcu_nocb_gp_cleanup(rsp, rnp);
1242 rnp->need_future_gp[c & 0x1] = 0;
1243 needmore = rnp->need_future_gp[(c + 1) & 0x1];
1244 trace_rcu_future_gp(rnp, rdp, c,
1245 needmore ? TPS("CleanupMore") : TPS("Cleanup"));
1250 * Awaken the grace-period kthread for the specified flavor of RCU.
1251 * Don't do a self-awaken, and don't bother awakening when there is
1252 * nothing for the grace-period kthread to do (as in several CPUs
1253 * raced to awaken, and we lost), and finally don't try to awaken
1254 * a kthread that has not yet been created.
1256 static void rcu_gp_kthread_wake(struct rcu_state *rsp)
1258 if (current == rsp->gp_kthread ||
1259 !ACCESS_ONCE(rsp->gp_flags) ||
1262 wake_up(&rsp->gp_wq);
1266 * If there is room, assign a ->completed number to any callbacks on
1267 * this CPU that have not already been assigned. Also accelerate any
1268 * callbacks that were previously assigned a ->completed number that has
1269 * since proven to be too conservative, which can happen if callbacks get
1270 * assigned a ->completed number while RCU is idle, but with reference to
1271 * a non-root rcu_node structure. This function is idempotent, so it does
1272 * not hurt to call it repeatedly. Returns an flag saying that we should
1273 * awaken the RCU grace-period kthread.
1275 * The caller must hold rnp->lock with interrupts disabled.
1277 static bool rcu_accelerate_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1278 struct rcu_data *rdp)
1284 /* If the CPU has no callbacks, nothing to do. */
1285 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1289 * Starting from the sublist containing the callbacks most
1290 * recently assigned a ->completed number and working down, find the
1291 * first sublist that is not assignable to an upcoming grace period.
1292 * Such a sublist has something in it (first two tests) and has
1293 * a ->completed number assigned that will complete sooner than
1294 * the ->completed number for newly arrived callbacks (last test).
1296 * The key point is that any later sublist can be assigned the
1297 * same ->completed number as the newly arrived callbacks, which
1298 * means that the callbacks in any of these later sublist can be
1299 * grouped into a single sublist, whether or not they have already
1300 * been assigned a ->completed number.
1302 c = rcu_cbs_completed(rsp, rnp);
1303 for (i = RCU_NEXT_TAIL - 1; i > RCU_DONE_TAIL; i--)
1304 if (rdp->nxttail[i] != rdp->nxttail[i - 1] &&
1305 !ULONG_CMP_GE(rdp->nxtcompleted[i], c))
1309 * If there are no sublist for unassigned callbacks, leave.
1310 * At the same time, advance "i" one sublist, so that "i" will
1311 * index into the sublist where all the remaining callbacks should
1314 if (++i >= RCU_NEXT_TAIL)
1318 * Assign all subsequent callbacks' ->completed number to the next
1319 * full grace period and group them all in the sublist initially
1322 for (; i <= RCU_NEXT_TAIL; i++) {
1323 rdp->nxttail[i] = rdp->nxttail[RCU_NEXT_TAIL];
1324 rdp->nxtcompleted[i] = c;
1326 /* Record any needed additional grace periods. */
1327 ret = rcu_start_future_gp(rnp, rdp, NULL);
1329 /* Trace depending on how much we were able to accelerate. */
1330 if (!*rdp->nxttail[RCU_WAIT_TAIL])
1331 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccWaitCB"));
1333 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("AccReadyCB"));
1338 * Move any callbacks whose grace period has completed to the
1339 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1340 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1341 * sublist. This function is idempotent, so it does not hurt to
1342 * invoke it repeatedly. As long as it is not invoked -too- often...
1343 * Returns true if the RCU grace-period kthread needs to be awakened.
1345 * The caller must hold rnp->lock with interrupts disabled.
1347 static bool rcu_advance_cbs(struct rcu_state *rsp, struct rcu_node *rnp,
1348 struct rcu_data *rdp)
1352 /* If the CPU has no callbacks, nothing to do. */
1353 if (!rdp->nxttail[RCU_NEXT_TAIL] || !*rdp->nxttail[RCU_DONE_TAIL])
1357 * Find all callbacks whose ->completed numbers indicate that they
1358 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1360 for (i = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++) {
1361 if (ULONG_CMP_LT(rnp->completed, rdp->nxtcompleted[i]))
1363 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[i];
1365 /* Clean up any sublist tail pointers that were misordered above. */
1366 for (j = RCU_WAIT_TAIL; j < i; j++)
1367 rdp->nxttail[j] = rdp->nxttail[RCU_DONE_TAIL];
1369 /* Copy down callbacks to fill in empty sublists. */
1370 for (j = RCU_WAIT_TAIL; i < RCU_NEXT_TAIL; i++, j++) {
1371 if (rdp->nxttail[j] == rdp->nxttail[RCU_NEXT_TAIL])
1373 rdp->nxttail[j] = rdp->nxttail[i];
1374 rdp->nxtcompleted[j] = rdp->nxtcompleted[i];
1377 /* Classify any remaining callbacks. */
1378 return rcu_accelerate_cbs(rsp, rnp, rdp);
1382 * Update CPU-local rcu_data state to record the beginnings and ends of
1383 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1384 * structure corresponding to the current CPU, and must have irqs disabled.
1385 * Returns true if the grace-period kthread needs to be awakened.
1387 static bool __note_gp_changes(struct rcu_state *rsp, struct rcu_node *rnp,
1388 struct rcu_data *rdp)
1392 /* Handle the ends of any preceding grace periods first. */
1393 if (rdp->completed == rnp->completed) {
1395 /* No grace period end, so just accelerate recent callbacks. */
1396 ret = rcu_accelerate_cbs(rsp, rnp, rdp);
1400 /* Advance callbacks. */
1401 ret = rcu_advance_cbs(rsp, rnp, rdp);
1403 /* Remember that we saw this grace-period completion. */
1404 rdp->completed = rnp->completed;
1405 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuend"));
1408 if (rdp->gpnum != rnp->gpnum) {
1410 * If the current grace period is waiting for this CPU,
1411 * set up to detect a quiescent state, otherwise don't
1412 * go looking for one.
1414 rdp->gpnum = rnp->gpnum;
1415 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpustart"));
1416 rdp->passed_quiesce = 0;
1417 rdp->qs_pending = !!(rnp->qsmask & rdp->grpmask);
1418 zero_cpu_stall_ticks(rdp);
1423 static void note_gp_changes(struct rcu_state *rsp, struct rcu_data *rdp)
1425 unsigned long flags;
1427 struct rcu_node *rnp;
1429 local_irq_save(flags);
1431 if ((rdp->gpnum == ACCESS_ONCE(rnp->gpnum) &&
1432 rdp->completed == ACCESS_ONCE(rnp->completed)) || /* w/out lock. */
1433 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
1434 local_irq_restore(flags);
1437 smp_mb__after_unlock_lock();
1438 needwake = __note_gp_changes(rsp, rnp, rdp);
1439 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1441 rcu_gp_kthread_wake(rsp);
1445 * Initialize a new grace period. Return 0 if no grace period required.
1447 static int rcu_gp_init(struct rcu_state *rsp)
1449 struct rcu_data *rdp;
1450 struct rcu_node *rnp = rcu_get_root(rsp);
1452 rcu_bind_gp_kthread();
1453 raw_spin_lock_irq(&rnp->lock);
1454 smp_mb__after_unlock_lock();
1455 if (!ACCESS_ONCE(rsp->gp_flags)) {
1456 /* Spurious wakeup, tell caller to go back to sleep. */
1457 raw_spin_unlock_irq(&rnp->lock);
1460 ACCESS_ONCE(rsp->gp_flags) = 0; /* Clear all flags: New grace period. */
1462 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp))) {
1464 * Grace period already in progress, don't start another.
1465 * Not supposed to be able to happen.
1467 raw_spin_unlock_irq(&rnp->lock);
1471 /* Advance to a new grace period and initialize state. */
1472 record_gp_stall_check_time(rsp);
1473 /* Record GP times before starting GP, hence smp_store_release(). */
1474 smp_store_release(&rsp->gpnum, rsp->gpnum + 1);
1475 trace_rcu_grace_period(rsp->name, rsp->gpnum, TPS("start"));
1476 raw_spin_unlock_irq(&rnp->lock);
1478 /* Exclude any concurrent CPU-hotplug operations. */
1479 mutex_lock(&rsp->onoff_mutex);
1480 smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1483 * Set the quiescent-state-needed bits in all the rcu_node
1484 * structures for all currently online CPUs in breadth-first order,
1485 * starting from the root rcu_node structure, relying on the layout
1486 * of the tree within the rsp->node[] array. Note that other CPUs
1487 * will access only the leaves of the hierarchy, thus seeing that no
1488 * grace period is in progress, at least until the corresponding
1489 * leaf node has been initialized. In addition, we have excluded
1490 * CPU-hotplug operations.
1492 * The grace period cannot complete until the initialization
1493 * process finishes, because this kthread handles both.
1495 rcu_for_each_node_breadth_first(rsp, rnp) {
1496 raw_spin_lock_irq(&rnp->lock);
1497 smp_mb__after_unlock_lock();
1498 rdp = this_cpu_ptr(rsp->rda);
1499 rcu_preempt_check_blocked_tasks(rnp);
1500 rnp->qsmask = rnp->qsmaskinit;
1501 ACCESS_ONCE(rnp->gpnum) = rsp->gpnum;
1502 WARN_ON_ONCE(rnp->completed != rsp->completed);
1503 ACCESS_ONCE(rnp->completed) = rsp->completed;
1504 if (rnp == rdp->mynode)
1505 (void)__note_gp_changes(rsp, rnp, rdp);
1506 rcu_preempt_boost_start_gp(rnp);
1507 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1508 rnp->level, rnp->grplo,
1509 rnp->grphi, rnp->qsmask);
1510 raw_spin_unlock_irq(&rnp->lock);
1511 #ifdef CONFIG_PROVE_RCU_DELAY
1512 if ((prandom_u32() % (rcu_num_nodes + 1)) == 0 &&
1513 system_state == SYSTEM_RUNNING)
1515 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1519 mutex_unlock(&rsp->onoff_mutex);
1524 * Do one round of quiescent-state forcing.
1526 static int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1528 int fqs_state = fqs_state_in;
1529 bool isidle = false;
1531 struct rcu_node *rnp = rcu_get_root(rsp);
1534 if (fqs_state == RCU_SAVE_DYNTICK) {
1535 /* Collect dyntick-idle snapshots. */
1536 if (is_sysidle_rcu_state(rsp)) {
1538 maxj = jiffies - ULONG_MAX / 4;
1540 force_qs_rnp(rsp, dyntick_save_progress_counter,
1542 rcu_sysidle_report_gp(rsp, isidle, maxj);
1543 fqs_state = RCU_FORCE_QS;
1545 /* Handle dyntick-idle and offline CPUs. */
1547 force_qs_rnp(rsp, rcu_implicit_dynticks_qs, &isidle, &maxj);
1549 /* Clear flag to prevent immediate re-entry. */
1550 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1551 raw_spin_lock_irq(&rnp->lock);
1552 smp_mb__after_unlock_lock();
1553 ACCESS_ONCE(rsp->gp_flags) &= ~RCU_GP_FLAG_FQS;
1554 raw_spin_unlock_irq(&rnp->lock);
1560 * Clean up after the old grace period.
1562 static void rcu_gp_cleanup(struct rcu_state *rsp)
1564 unsigned long gp_duration;
1565 bool needgp = false;
1567 struct rcu_data *rdp;
1568 struct rcu_node *rnp = rcu_get_root(rsp);
1570 raw_spin_lock_irq(&rnp->lock);
1571 smp_mb__after_unlock_lock();
1572 gp_duration = jiffies - rsp->gp_start;
1573 if (gp_duration > rsp->gp_max)
1574 rsp->gp_max = gp_duration;
1577 * We know the grace period is complete, but to everyone else
1578 * it appears to still be ongoing. But it is also the case
1579 * that to everyone else it looks like there is nothing that
1580 * they can do to advance the grace period. It is therefore
1581 * safe for us to drop the lock in order to mark the grace
1582 * period as completed in all of the rcu_node structures.
1584 raw_spin_unlock_irq(&rnp->lock);
1587 * Propagate new ->completed value to rcu_node structures so
1588 * that other CPUs don't have to wait until the start of the next
1589 * grace period to process their callbacks. This also avoids
1590 * some nasty RCU grace-period initialization races by forcing
1591 * the end of the current grace period to be completely recorded in
1592 * all of the rcu_node structures before the beginning of the next
1593 * grace period is recorded in any of the rcu_node structures.
1595 rcu_for_each_node_breadth_first(rsp, rnp) {
1596 raw_spin_lock_irq(&rnp->lock);
1597 smp_mb__after_unlock_lock();
1598 ACCESS_ONCE(rnp->completed) = rsp->gpnum;
1599 rdp = this_cpu_ptr(rsp->rda);
1600 if (rnp == rdp->mynode)
1601 needgp = __note_gp_changes(rsp, rnp, rdp) || needgp;
1602 /* smp_mb() provided by prior unlock-lock pair. */
1603 nocb += rcu_future_gp_cleanup(rsp, rnp);
1604 raw_spin_unlock_irq(&rnp->lock);
1607 rnp = rcu_get_root(rsp);
1608 raw_spin_lock_irq(&rnp->lock);
1609 smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1610 rcu_nocb_gp_set(rnp, nocb);
1612 /* Declare grace period done. */
1613 ACCESS_ONCE(rsp->completed) = rsp->gpnum;
1614 trace_rcu_grace_period(rsp->name, rsp->completed, TPS("end"));
1615 rsp->fqs_state = RCU_GP_IDLE;
1616 rdp = this_cpu_ptr(rsp->rda);
1617 /* Advance CBs to reduce false positives below. */
1618 needgp = rcu_advance_cbs(rsp, rnp, rdp) || needgp;
1619 if (needgp || cpu_needs_another_gp(rsp, rdp)) {
1620 ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1621 trace_rcu_grace_period(rsp->name,
1622 ACCESS_ONCE(rsp->gpnum),
1625 raw_spin_unlock_irq(&rnp->lock);
1629 * Body of kthread that handles grace periods.
1631 static int __noreturn rcu_gp_kthread(void *arg)
1637 struct rcu_state *rsp = arg;
1638 struct rcu_node *rnp = rcu_get_root(rsp);
1642 /* Handle grace-period start. */
1644 trace_rcu_grace_period(rsp->name,
1645 ACCESS_ONCE(rsp->gpnum),
1647 wait_event_interruptible(rsp->gp_wq,
1648 ACCESS_ONCE(rsp->gp_flags) &
1650 /* Locking provides needed memory barrier. */
1651 if (rcu_gp_init(rsp))
1654 flush_signals(current);
1655 trace_rcu_grace_period(rsp->name,
1656 ACCESS_ONCE(rsp->gpnum),
1660 /* Handle quiescent-state forcing. */
1661 fqs_state = RCU_SAVE_DYNTICK;
1662 j = jiffies_till_first_fqs;
1665 jiffies_till_first_fqs = HZ;
1670 rsp->jiffies_force_qs = jiffies + j;
1671 trace_rcu_grace_period(rsp->name,
1672 ACCESS_ONCE(rsp->gpnum),
1674 ret = wait_event_interruptible_timeout(rsp->gp_wq,
1675 ((gf = ACCESS_ONCE(rsp->gp_flags)) &
1677 (!ACCESS_ONCE(rnp->qsmask) &&
1678 !rcu_preempt_blocked_readers_cgp(rnp)),
1680 /* Locking provides needed memory barriers. */
1681 /* If grace period done, leave loop. */
1682 if (!ACCESS_ONCE(rnp->qsmask) &&
1683 !rcu_preempt_blocked_readers_cgp(rnp))
1685 /* If time for quiescent-state forcing, do it. */
1686 if (ULONG_CMP_GE(jiffies, rsp->jiffies_force_qs) ||
1687 (gf & RCU_GP_FLAG_FQS)) {
1688 trace_rcu_grace_period(rsp->name,
1689 ACCESS_ONCE(rsp->gpnum),
1691 fqs_state = rcu_gp_fqs(rsp, fqs_state);
1692 trace_rcu_grace_period(rsp->name,
1693 ACCESS_ONCE(rsp->gpnum),
1697 /* Deal with stray signal. */
1699 flush_signals(current);
1700 trace_rcu_grace_period(rsp->name,
1701 ACCESS_ONCE(rsp->gpnum),
1704 j = jiffies_till_next_fqs;
1707 jiffies_till_next_fqs = HZ;
1710 jiffies_till_next_fqs = 1;
1714 /* Handle grace-period end. */
1715 rcu_gp_cleanup(rsp);
1720 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1721 * in preparation for detecting the next grace period. The caller must hold
1722 * the root node's ->lock and hard irqs must be disabled.
1724 * Note that it is legal for a dying CPU (which is marked as offline) to
1725 * invoke this function. This can happen when the dying CPU reports its
1728 * Returns true if the grace-period kthread must be awakened.
1731 rcu_start_gp_advanced(struct rcu_state *rsp, struct rcu_node *rnp,
1732 struct rcu_data *rdp)
1734 if (!rsp->gp_kthread || !cpu_needs_another_gp(rsp, rdp)) {
1736 * Either we have not yet spawned the grace-period
1737 * task, this CPU does not need another grace period,
1738 * or a grace period is already in progress.
1739 * Either way, don't start a new grace period.
1743 ACCESS_ONCE(rsp->gp_flags) = RCU_GP_FLAG_INIT;
1744 trace_rcu_grace_period(rsp->name, ACCESS_ONCE(rsp->gpnum),
1748 * We can't do wakeups while holding the rnp->lock, as that
1749 * could cause possible deadlocks with the rq->lock. Defer
1750 * the wakeup to our caller.
1756 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
1757 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
1758 * is invoked indirectly from rcu_advance_cbs(), which would result in
1759 * endless recursion -- or would do so if it wasn't for the self-deadlock
1760 * that is encountered beforehand.
1762 * Returns true if the grace-period kthread needs to be awakened.
1764 static bool rcu_start_gp(struct rcu_state *rsp)
1766 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1767 struct rcu_node *rnp = rcu_get_root(rsp);
1771 * If there is no grace period in progress right now, any
1772 * callbacks we have up to this point will be satisfied by the
1773 * next grace period. Also, advancing the callbacks reduces the
1774 * probability of false positives from cpu_needs_another_gp()
1775 * resulting in pointless grace periods. So, advance callbacks
1776 * then start the grace period!
1778 ret = rcu_advance_cbs(rsp, rnp, rdp) || ret;
1779 ret = rcu_start_gp_advanced(rsp, rnp, rdp) || ret;
1784 * Report a full set of quiescent states to the specified rcu_state
1785 * data structure. This involves cleaning up after the prior grace
1786 * period and letting rcu_start_gp() start up the next grace period
1787 * if one is needed. Note that the caller must hold rnp->lock, which
1788 * is released before return.
1790 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1791 __releases(rcu_get_root(rsp)->lock)
1793 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
1794 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
1795 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
1799 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1800 * Allows quiescent states for a group of CPUs to be reported at one go
1801 * to the specified rcu_node structure, though all the CPUs in the group
1802 * must be represented by the same rcu_node structure (which need not be
1803 * a leaf rcu_node structure, though it often will be). That structure's
1804 * lock must be held upon entry, and it is released before return.
1807 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
1808 struct rcu_node *rnp, unsigned long flags)
1809 __releases(rnp->lock)
1811 struct rcu_node *rnp_c;
1813 /* Walk up the rcu_node hierarchy. */
1815 if (!(rnp->qsmask & mask)) {
1817 /* Our bit has already been cleared, so done. */
1818 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1821 rnp->qsmask &= ~mask;
1822 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
1823 mask, rnp->qsmask, rnp->level,
1824 rnp->grplo, rnp->grphi,
1826 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1828 /* Other bits still set at this level, so done. */
1829 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1832 mask = rnp->grpmask;
1833 if (rnp->parent == NULL) {
1835 /* No more levels. Exit loop holding root lock. */
1839 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1842 raw_spin_lock_irqsave(&rnp->lock, flags);
1843 smp_mb__after_unlock_lock();
1844 WARN_ON_ONCE(rnp_c->qsmask);
1848 * Get here if we are the last CPU to pass through a quiescent
1849 * state for this grace period. Invoke rcu_report_qs_rsp()
1850 * to clean up and start the next grace period if one is needed.
1852 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
1856 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1857 * structure. This must be either called from the specified CPU, or
1858 * called when the specified CPU is known to be offline (and when it is
1859 * also known that no other CPU is concurrently trying to help the offline
1860 * CPU). The lastcomp argument is used to make sure we are still in the
1861 * grace period of interest. We don't want to end the current grace period
1862 * based on quiescent states detected in an earlier grace period!
1865 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp)
1867 unsigned long flags;
1870 struct rcu_node *rnp;
1873 raw_spin_lock_irqsave(&rnp->lock, flags);
1874 smp_mb__after_unlock_lock();
1875 if (rdp->passed_quiesce == 0 || rdp->gpnum != rnp->gpnum ||
1876 rnp->completed == rnp->gpnum) {
1879 * The grace period in which this quiescent state was
1880 * recorded has ended, so don't report it upwards.
1881 * We will instead need a new quiescent state that lies
1882 * within the current grace period.
1884 rdp->passed_quiesce = 0; /* need qs for new gp. */
1885 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1888 mask = rdp->grpmask;
1889 if ((rnp->qsmask & mask) == 0) {
1890 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1892 rdp->qs_pending = 0;
1895 * This GP can't end until cpu checks in, so all of our
1896 * callbacks can be processed during the next GP.
1898 needwake = rcu_accelerate_cbs(rsp, rnp, rdp);
1900 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1902 rcu_gp_kthread_wake(rsp);
1907 * Check to see if there is a new grace period of which this CPU
1908 * is not yet aware, and if so, set up local rcu_data state for it.
1909 * Otherwise, see if this CPU has just passed through its first
1910 * quiescent state for this grace period, and record that fact if so.
1913 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
1915 /* Check for grace-period ends and beginnings. */
1916 note_gp_changes(rsp, rdp);
1919 * Does this CPU still need to do its part for current grace period?
1920 * If no, return and let the other CPUs do their part as well.
1922 if (!rdp->qs_pending)
1926 * Was there a quiescent state since the beginning of the grace
1927 * period? If no, then exit and wait for the next call.
1929 if (!rdp->passed_quiesce)
1933 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1936 rcu_report_qs_rdp(rdp->cpu, rsp, rdp);
1939 #ifdef CONFIG_HOTPLUG_CPU
1942 * Send the specified CPU's RCU callbacks to the orphanage. The
1943 * specified CPU must be offline, and the caller must hold the
1947 rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
1948 struct rcu_node *rnp, struct rcu_data *rdp)
1950 /* No-CBs CPUs do not have orphanable callbacks. */
1951 if (rcu_is_nocb_cpu(rdp->cpu))
1955 * Orphan the callbacks. First adjust the counts. This is safe
1956 * because _rcu_barrier() excludes CPU-hotplug operations, so it
1957 * cannot be running now. Thus no memory barrier is required.
1959 if (rdp->nxtlist != NULL) {
1960 rsp->qlen_lazy += rdp->qlen_lazy;
1961 rsp->qlen += rdp->qlen;
1962 rdp->n_cbs_orphaned += rdp->qlen;
1964 ACCESS_ONCE(rdp->qlen) = 0;
1968 * Next, move those callbacks still needing a grace period to
1969 * the orphanage, where some other CPU will pick them up.
1970 * Some of the callbacks might have gone partway through a grace
1971 * period, but that is too bad. They get to start over because we
1972 * cannot assume that grace periods are synchronized across CPUs.
1973 * We don't bother updating the ->nxttail[] array yet, instead
1974 * we just reset the whole thing later on.
1976 if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
1977 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
1978 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
1979 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1983 * Then move the ready-to-invoke callbacks to the orphanage,
1984 * where some other CPU will pick them up. These will not be
1985 * required to pass though another grace period: They are done.
1987 if (rdp->nxtlist != NULL) {
1988 *rsp->orphan_donetail = rdp->nxtlist;
1989 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
1992 /* Finally, initialize the rcu_data structure's list to empty. */
1993 init_callback_list(rdp);
1997 * Adopt the RCU callbacks from the specified rcu_state structure's
1998 * orphanage. The caller must hold the ->orphan_lock.
2000 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp, unsigned long flags)
2003 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2005 /* No-CBs CPUs are handled specially. */
2006 if (rcu_nocb_adopt_orphan_cbs(rsp, rdp, flags))
2009 /* Do the accounting first. */
2010 rdp->qlen_lazy += rsp->qlen_lazy;
2011 rdp->qlen += rsp->qlen;
2012 rdp->n_cbs_adopted += rsp->qlen;
2013 if (rsp->qlen_lazy != rsp->qlen)
2014 rcu_idle_count_callbacks_posted();
2019 * We do not need a memory barrier here because the only way we
2020 * can get here if there is an rcu_barrier() in flight is if
2021 * we are the task doing the rcu_barrier().
2024 /* First adopt the ready-to-invoke callbacks. */
2025 if (rsp->orphan_donelist != NULL) {
2026 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
2027 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
2028 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
2029 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2030 rdp->nxttail[i] = rsp->orphan_donetail;
2031 rsp->orphan_donelist = NULL;
2032 rsp->orphan_donetail = &rsp->orphan_donelist;
2035 /* And then adopt the callbacks that still need a grace period. */
2036 if (rsp->orphan_nxtlist != NULL) {
2037 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
2038 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
2039 rsp->orphan_nxtlist = NULL;
2040 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
2045 * Trace the fact that this CPU is going offline.
2047 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2049 RCU_TRACE(unsigned long mask);
2050 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
2051 RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
2053 RCU_TRACE(mask = rdp->grpmask);
2054 trace_rcu_grace_period(rsp->name,
2055 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
2060 * The CPU has been completely removed, and some other CPU is reporting
2061 * this fact from process context. Do the remainder of the cleanup,
2062 * including orphaning the outgoing CPU's RCU callbacks, and also
2063 * adopting them. There can only be one CPU hotplug operation at a time,
2064 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2066 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2068 unsigned long flags;
2070 int need_report = 0;
2071 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2072 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
2074 /* Adjust any no-longer-needed kthreads. */
2075 rcu_boost_kthread_setaffinity(rnp, -1);
2077 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
2079 /* Exclude any attempts to start a new grace period. */
2080 mutex_lock(&rsp->onoff_mutex);
2081 raw_spin_lock_irqsave(&rsp->orphan_lock, flags);
2083 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2084 rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
2085 rcu_adopt_orphan_cbs(rsp, flags);
2087 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
2088 mask = rdp->grpmask; /* rnp->grplo is constant. */
2090 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
2091 smp_mb__after_unlock_lock();
2092 rnp->qsmaskinit &= ~mask;
2093 if (rnp->qsmaskinit != 0) {
2094 if (rnp != rdp->mynode)
2095 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2098 if (rnp == rdp->mynode)
2099 need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
2101 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2102 mask = rnp->grpmask;
2104 } while (rnp != NULL);
2107 * We still hold the leaf rcu_node structure lock here, and
2108 * irqs are still disabled. The reason for this subterfuge is
2109 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2110 * held leads to deadlock.
2112 raw_spin_unlock(&rsp->orphan_lock); /* irqs remain disabled. */
2114 if (need_report & RCU_OFL_TASKS_NORM_GP)
2115 rcu_report_unblock_qs_rnp(rnp, flags);
2117 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2118 if (need_report & RCU_OFL_TASKS_EXP_GP)
2119 rcu_report_exp_rnp(rsp, rnp, true);
2120 WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
2121 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2122 cpu, rdp->qlen, rdp->nxtlist);
2123 init_callback_list(rdp);
2124 /* Disallow further callbacks on this CPU. */
2125 rdp->nxttail[RCU_NEXT_TAIL] = NULL;
2126 mutex_unlock(&rsp->onoff_mutex);
2129 #else /* #ifdef CONFIG_HOTPLUG_CPU */
2131 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
2135 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
2139 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
2142 * Invoke any RCU callbacks that have made it to the end of their grace
2143 * period. Thottle as specified by rdp->blimit.
2145 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
2147 unsigned long flags;
2148 struct rcu_head *next, *list, **tail;
2149 long bl, count, count_lazy;
2152 /* If no callbacks are ready, just return. */
2153 if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
2154 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
2155 trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
2156 need_resched(), is_idle_task(current),
2157 rcu_is_callbacks_kthread());
2162 * Extract the list of ready callbacks, disabling to prevent
2163 * races with call_rcu() from interrupt handlers.
2165 local_irq_save(flags);
2166 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2168 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
2169 list = rdp->nxtlist;
2170 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
2171 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
2172 tail = rdp->nxttail[RCU_DONE_TAIL];
2173 for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
2174 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
2175 rdp->nxttail[i] = &rdp->nxtlist;
2176 local_irq_restore(flags);
2178 /* Invoke callbacks. */
2179 count = count_lazy = 0;
2183 debug_rcu_head_unqueue(list);
2184 if (__rcu_reclaim(rsp->name, list))
2187 /* Stop only if limit reached and CPU has something to do. */
2188 if (++count >= bl &&
2190 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
2194 local_irq_save(flags);
2195 trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
2196 is_idle_task(current),
2197 rcu_is_callbacks_kthread());
2199 /* Update count, and requeue any remaining callbacks. */
2201 *tail = rdp->nxtlist;
2202 rdp->nxtlist = list;
2203 for (i = 0; i < RCU_NEXT_SIZE; i++)
2204 if (&rdp->nxtlist == rdp->nxttail[i])
2205 rdp->nxttail[i] = tail;
2209 smp_mb(); /* List handling before counting for rcu_barrier(). */
2210 rdp->qlen_lazy -= count_lazy;
2211 ACCESS_ONCE(rdp->qlen) -= count;
2212 rdp->n_cbs_invoked += count;
2214 /* Reinstate batch limit if we have worked down the excess. */
2215 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
2216 rdp->blimit = blimit;
2218 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2219 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
2220 rdp->qlen_last_fqs_check = 0;
2221 rdp->n_force_qs_snap = rsp->n_force_qs;
2222 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
2223 rdp->qlen_last_fqs_check = rdp->qlen;
2224 WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
2226 local_irq_restore(flags);
2228 /* Re-invoke RCU core processing if there are callbacks remaining. */
2229 if (cpu_has_callbacks_ready_to_invoke(rdp))
2234 * Check to see if this CPU is in a non-context-switch quiescent state
2235 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2236 * Also schedule RCU core processing.
2238 * This function must be called from hardirq context. It is normally
2239 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2240 * false, there is no point in invoking rcu_check_callbacks().
2242 void rcu_check_callbacks(int cpu, int user)
2244 trace_rcu_utilization(TPS("Start scheduler-tick"));
2245 increment_cpu_stall_ticks();
2246 if (user || rcu_is_cpu_rrupt_from_idle()) {
2249 * Get here if this CPU took its interrupt from user
2250 * mode or from the idle loop, and if this is not a
2251 * nested interrupt. In this case, the CPU is in
2252 * a quiescent state, so note it.
2254 * No memory barrier is required here because both
2255 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2256 * variables that other CPUs neither access nor modify,
2257 * at least not while the corresponding CPU is online.
2263 } else if (!in_softirq()) {
2266 * Get here if this CPU did not take its interrupt from
2267 * softirq, in other words, if it is not interrupting
2268 * a rcu_bh read-side critical section. This is an _bh
2269 * critical section, so note it.
2274 rcu_preempt_check_callbacks(cpu);
2275 if (rcu_pending(cpu))
2277 trace_rcu_utilization(TPS("End scheduler-tick"));
2281 * Scan the leaf rcu_node structures, processing dyntick state for any that
2282 * have not yet encountered a quiescent state, using the function specified.
2283 * Also initiate boosting for any threads blocked on the root rcu_node.
2285 * The caller must have suppressed start of new grace periods.
2287 static void force_qs_rnp(struct rcu_state *rsp,
2288 int (*f)(struct rcu_data *rsp, bool *isidle,
2289 unsigned long *maxj),
2290 bool *isidle, unsigned long *maxj)
2294 unsigned long flags;
2296 struct rcu_node *rnp;
2298 rcu_for_each_leaf_node(rsp, rnp) {
2301 raw_spin_lock_irqsave(&rnp->lock, flags);
2302 smp_mb__after_unlock_lock();
2303 if (!rcu_gp_in_progress(rsp)) {
2304 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2307 if (rnp->qsmask == 0) {
2308 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
2313 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
2314 if ((rnp->qsmask & bit) != 0) {
2315 if ((rnp->qsmaskinit & bit) != 0)
2317 if (f(per_cpu_ptr(rsp->rda, cpu), isidle, maxj))
2323 /* rcu_report_qs_rnp() releases rnp->lock. */
2324 rcu_report_qs_rnp(mask, rsp, rnp, flags);
2327 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2329 rnp = rcu_get_root(rsp);
2330 if (rnp->qsmask == 0) {
2331 raw_spin_lock_irqsave(&rnp->lock, flags);
2332 smp_mb__after_unlock_lock();
2333 rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
2338 * Force quiescent states on reluctant CPUs, and also detect which
2339 * CPUs are in dyntick-idle mode.
2341 static void force_quiescent_state(struct rcu_state *rsp)
2343 unsigned long flags;
2345 struct rcu_node *rnp;
2346 struct rcu_node *rnp_old = NULL;
2348 /* Funnel through hierarchy to reduce memory contention. */
2349 rnp = per_cpu_ptr(rsp->rda, raw_smp_processor_id())->mynode;
2350 for (; rnp != NULL; rnp = rnp->parent) {
2351 ret = (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) ||
2352 !raw_spin_trylock(&rnp->fqslock);
2353 if (rnp_old != NULL)
2354 raw_spin_unlock(&rnp_old->fqslock);
2356 ACCESS_ONCE(rsp->n_force_qs_lh)++;
2361 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2363 /* Reached the root of the rcu_node tree, acquire lock. */
2364 raw_spin_lock_irqsave(&rnp_old->lock, flags);
2365 smp_mb__after_unlock_lock();
2366 raw_spin_unlock(&rnp_old->fqslock);
2367 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
2368 ACCESS_ONCE(rsp->n_force_qs_lh)++;
2369 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2370 return; /* Someone beat us to it. */
2372 ACCESS_ONCE(rsp->gp_flags) |= RCU_GP_FLAG_FQS;
2373 raw_spin_unlock_irqrestore(&rnp_old->lock, flags);
2374 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
2378 * This does the RCU core processing work for the specified rcu_state
2379 * and rcu_data structures. This may be called only from the CPU to
2380 * whom the rdp belongs.
2383 __rcu_process_callbacks(struct rcu_state *rsp)
2385 unsigned long flags;
2387 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2389 WARN_ON_ONCE(rdp->beenonline == 0);
2391 /* Update RCU state based on any recent quiescent states. */
2392 rcu_check_quiescent_state(rsp, rdp);
2394 /* Does this CPU require a not-yet-started grace period? */
2395 local_irq_save(flags);
2396 if (cpu_needs_another_gp(rsp, rdp)) {
2397 raw_spin_lock(&rcu_get_root(rsp)->lock); /* irqs disabled. */
2398 needwake = rcu_start_gp(rsp);
2399 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
2401 rcu_gp_kthread_wake(rsp);
2403 local_irq_restore(flags);
2406 /* If there are callbacks ready, invoke them. */
2407 if (cpu_has_callbacks_ready_to_invoke(rdp))
2408 invoke_rcu_callbacks(rsp, rdp);
2410 /* Do any needed deferred wakeups of rcuo kthreads. */
2411 do_nocb_deferred_wakeup(rdp);
2415 * Do RCU core processing for the current CPU.
2417 static void rcu_process_callbacks(struct softirq_action *unused)
2419 struct rcu_state *rsp;
2421 if (cpu_is_offline(smp_processor_id()))
2423 trace_rcu_utilization(TPS("Start RCU core"));
2424 for_each_rcu_flavor(rsp)
2425 __rcu_process_callbacks(rsp);
2426 trace_rcu_utilization(TPS("End RCU core"));
2430 * Schedule RCU callback invocation. If the specified type of RCU
2431 * does not support RCU priority boosting, just do a direct call,
2432 * otherwise wake up the per-CPU kernel kthread. Note that because we
2433 * are running on the current CPU with interrupts disabled, the
2434 * rcu_cpu_kthread_task cannot disappear out from under us.
2436 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
2438 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
2440 if (likely(!rsp->boost)) {
2441 rcu_do_batch(rsp, rdp);
2444 invoke_rcu_callbacks_kthread();
2447 static void invoke_rcu_core(void)
2449 if (cpu_online(smp_processor_id()))
2450 raise_softirq(RCU_SOFTIRQ);
2454 * Handle any core-RCU processing required by a call_rcu() invocation.
2456 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
2457 struct rcu_head *head, unsigned long flags)
2462 * If called from an extended quiescent state, invoke the RCU
2463 * core in order to force a re-evaluation of RCU's idleness.
2465 if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2468 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2469 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
2473 * Force the grace period if too many callbacks or too long waiting.
2474 * Enforce hysteresis, and don't invoke force_quiescent_state()
2475 * if some other CPU has recently done so. Also, don't bother
2476 * invoking force_quiescent_state() if the newly enqueued callback
2477 * is the only one waiting for a grace period to complete.
2479 if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
2481 /* Are we ignoring a completed grace period? */
2482 note_gp_changes(rsp, rdp);
2484 /* Start a new grace period if one not already started. */
2485 if (!rcu_gp_in_progress(rsp)) {
2486 struct rcu_node *rnp_root = rcu_get_root(rsp);
2488 raw_spin_lock(&rnp_root->lock);
2489 smp_mb__after_unlock_lock();
2490 needwake = rcu_start_gp(rsp);
2491 raw_spin_unlock(&rnp_root->lock);
2493 rcu_gp_kthread_wake(rsp);
2495 /* Give the grace period a kick. */
2496 rdp->blimit = LONG_MAX;
2497 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
2498 *rdp->nxttail[RCU_DONE_TAIL] != head)
2499 force_quiescent_state(rsp);
2500 rdp->n_force_qs_snap = rsp->n_force_qs;
2501 rdp->qlen_last_fqs_check = rdp->qlen;
2507 * RCU callback function to leak a callback.
2509 static void rcu_leak_callback(struct rcu_head *rhp)
2514 * Helper function for call_rcu() and friends. The cpu argument will
2515 * normally be -1, indicating "currently running CPU". It may specify
2516 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2517 * is expected to specify a CPU.
2520 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
2521 struct rcu_state *rsp, int cpu, bool lazy)
2523 unsigned long flags;
2524 struct rcu_data *rdp;
2526 WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
2527 if (debug_rcu_head_queue(head)) {
2528 /* Probable double call_rcu(), so leak the callback. */
2529 ACCESS_ONCE(head->func) = rcu_leak_callback;
2530 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
2537 * Opportunistically note grace-period endings and beginnings.
2538 * Note that we might see a beginning right after we see an
2539 * end, but never vice versa, since this CPU has to pass through
2540 * a quiescent state betweentimes.
2542 local_irq_save(flags);
2543 rdp = this_cpu_ptr(rsp->rda);
2545 /* Add the callback to our list. */
2546 if (unlikely(rdp->nxttail[RCU_NEXT_TAIL] == NULL) || cpu != -1) {
2550 rdp = per_cpu_ptr(rsp->rda, cpu);
2551 offline = !__call_rcu_nocb(rdp, head, lazy, flags);
2552 WARN_ON_ONCE(offline);
2553 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2554 local_irq_restore(flags);
2557 ACCESS_ONCE(rdp->qlen)++;
2561 rcu_idle_count_callbacks_posted();
2562 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2563 *rdp->nxttail[RCU_NEXT_TAIL] = head;
2564 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
2566 if (__is_kfree_rcu_offset((unsigned long)func))
2567 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
2568 rdp->qlen_lazy, rdp->qlen);
2570 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
2572 /* Go handle any RCU core processing required. */
2573 __call_rcu_core(rsp, rdp, head, flags);
2574 local_irq_restore(flags);
2578 * Queue an RCU-sched callback for invocation after a grace period.
2580 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2582 __call_rcu(head, func, &rcu_sched_state, -1, 0);
2584 EXPORT_SYMBOL_GPL(call_rcu_sched);
2587 * Queue an RCU callback for invocation after a quicker grace period.
2589 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2591 __call_rcu(head, func, &rcu_bh_state, -1, 0);
2593 EXPORT_SYMBOL_GPL(call_rcu_bh);
2596 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2597 * any blocking grace-period wait automatically implies a grace period
2598 * if there is only one CPU online at any point time during execution
2599 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2600 * occasionally incorrectly indicate that there are multiple CPUs online
2601 * when there was in fact only one the whole time, as this just adds
2602 * some overhead: RCU still operates correctly.
2604 static inline int rcu_blocking_is_gp(void)
2608 might_sleep(); /* Check for RCU read-side critical section. */
2610 ret = num_online_cpus() <= 1;
2616 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2618 * Control will return to the caller some time after a full rcu-sched
2619 * grace period has elapsed, in other words after all currently executing
2620 * rcu-sched read-side critical sections have completed. These read-side
2621 * critical sections are delimited by rcu_read_lock_sched() and
2622 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2623 * local_irq_disable(), and so on may be used in place of
2624 * rcu_read_lock_sched().
2626 * This means that all preempt_disable code sequences, including NMI and
2627 * non-threaded hardware-interrupt handlers, in progress on entry will
2628 * have completed before this primitive returns. However, this does not
2629 * guarantee that softirq handlers will have completed, since in some
2630 * kernels, these handlers can run in process context, and can block.
2632 * Note that this guarantee implies further memory-ordering guarantees.
2633 * On systems with more than one CPU, when synchronize_sched() returns,
2634 * each CPU is guaranteed to have executed a full memory barrier since the
2635 * end of its last RCU-sched read-side critical section whose beginning
2636 * preceded the call to synchronize_sched(). In addition, each CPU having
2637 * an RCU read-side critical section that extends beyond the return from
2638 * synchronize_sched() is guaranteed to have executed a full memory barrier
2639 * after the beginning of synchronize_sched() and before the beginning of
2640 * that RCU read-side critical section. Note that these guarantees include
2641 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2642 * that are executing in the kernel.
2644 * Furthermore, if CPU A invoked synchronize_sched(), which returned
2645 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2646 * to have executed a full memory barrier during the execution of
2647 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
2648 * again only if the system has more than one CPU).
2650 * This primitive provides the guarantees made by the (now removed)
2651 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2652 * guarantees that rcu_read_lock() sections will have completed.
2653 * In "classic RCU", these two guarantees happen to be one and
2654 * the same, but can differ in realtime RCU implementations.
2656 void synchronize_sched(void)
2658 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2659 !lock_is_held(&rcu_lock_map) &&
2660 !lock_is_held(&rcu_sched_lock_map),
2661 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2662 if (rcu_blocking_is_gp())
2665 synchronize_sched_expedited();
2667 wait_rcu_gp(call_rcu_sched);
2669 EXPORT_SYMBOL_GPL(synchronize_sched);
2672 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2674 * Control will return to the caller some time after a full rcu_bh grace
2675 * period has elapsed, in other words after all currently executing rcu_bh
2676 * read-side critical sections have completed. RCU read-side critical
2677 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2678 * and may be nested.
2680 * See the description of synchronize_sched() for more detailed information
2681 * on memory ordering guarantees.
2683 void synchronize_rcu_bh(void)
2685 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2686 !lock_is_held(&rcu_lock_map) &&
2687 !lock_is_held(&rcu_sched_lock_map),
2688 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2689 if (rcu_blocking_is_gp())
2692 synchronize_rcu_bh_expedited();
2694 wait_rcu_gp(call_rcu_bh);
2696 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
2699 * get_state_synchronize_rcu - Snapshot current RCU state
2701 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
2702 * to determine whether or not a full grace period has elapsed in the
2705 unsigned long get_state_synchronize_rcu(void)
2708 * Any prior manipulation of RCU-protected data must happen
2709 * before the load from ->gpnum.
2714 * Make sure this load happens before the purportedly
2715 * time-consuming work between get_state_synchronize_rcu()
2716 * and cond_synchronize_rcu().
2718 return smp_load_acquire(&rcu_state->gpnum);
2720 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
2723 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
2725 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
2727 * If a full RCU grace period has elapsed since the earlier call to
2728 * get_state_synchronize_rcu(), just return. Otherwise, invoke
2729 * synchronize_rcu() to wait for a full grace period.
2731 * Yes, this function does not take counter wrap into account. But
2732 * counter wrap is harmless. If the counter wraps, we have waited for
2733 * more than 2 billion grace periods (and way more on a 64-bit system!),
2734 * so waiting for one additional grace period should be just fine.
2736 void cond_synchronize_rcu(unsigned long oldstate)
2738 unsigned long newstate;
2741 * Ensure that this load happens before any RCU-destructive
2742 * actions the caller might carry out after we return.
2744 newstate = smp_load_acquire(&rcu_state->completed);
2745 if (ULONG_CMP_GE(oldstate, newstate))
2748 EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
2750 static int synchronize_sched_expedited_cpu_stop(void *data)
2753 * There must be a full memory barrier on each affected CPU
2754 * between the time that try_stop_cpus() is called and the
2755 * time that it returns.
2757 * In the current initial implementation of cpu_stop, the
2758 * above condition is already met when the control reaches
2759 * this point and the following smp_mb() is not strictly
2760 * necessary. Do smp_mb() anyway for documentation and
2761 * robustness against future implementation changes.
2763 smp_mb(); /* See above comment block. */
2768 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2770 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2771 * approach to force the grace period to end quickly. This consumes
2772 * significant time on all CPUs and is unfriendly to real-time workloads,
2773 * so is thus not recommended for any sort of common-case code. In fact,
2774 * if you are using synchronize_sched_expedited() in a loop, please
2775 * restructure your code to batch your updates, and then use a single
2776 * synchronize_sched() instead.
2778 * Note that it is illegal to call this function while holding any lock
2779 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2780 * to call this function from a CPU-hotplug notifier. Failing to observe
2781 * these restriction will result in deadlock.
2783 * This implementation can be thought of as an application of ticket
2784 * locking to RCU, with sync_sched_expedited_started and
2785 * sync_sched_expedited_done taking on the roles of the halves
2786 * of the ticket-lock word. Each task atomically increments
2787 * sync_sched_expedited_started upon entry, snapshotting the old value,
2788 * then attempts to stop all the CPUs. If this succeeds, then each
2789 * CPU will have executed a context switch, resulting in an RCU-sched
2790 * grace period. We are then done, so we use atomic_cmpxchg() to
2791 * update sync_sched_expedited_done to match our snapshot -- but
2792 * only if someone else has not already advanced past our snapshot.
2794 * On the other hand, if try_stop_cpus() fails, we check the value
2795 * of sync_sched_expedited_done. If it has advanced past our
2796 * initial snapshot, then someone else must have forced a grace period
2797 * some time after we took our snapshot. In this case, our work is
2798 * done for us, and we can simply return. Otherwise, we try again,
2799 * but keep our initial snapshot for purposes of checking for someone
2800 * doing our work for us.
2802 * If we fail too many times in a row, we fall back to synchronize_sched().
2804 void synchronize_sched_expedited(void)
2806 long firstsnap, s, snap;
2808 struct rcu_state *rsp = &rcu_sched_state;
2811 * If we are in danger of counter wrap, just do synchronize_sched().
2812 * By allowing sync_sched_expedited_started to advance no more than
2813 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
2814 * that more than 3.5 billion CPUs would be required to force a
2815 * counter wrap on a 32-bit system. Quite a few more CPUs would of
2816 * course be required on a 64-bit system.
2818 if (ULONG_CMP_GE((ulong)atomic_long_read(&rsp->expedited_start),
2819 (ulong)atomic_long_read(&rsp->expedited_done) +
2821 synchronize_sched();
2822 atomic_long_inc(&rsp->expedited_wrap);
2827 * Take a ticket. Note that atomic_inc_return() implies a
2828 * full memory barrier.
2830 snap = atomic_long_inc_return(&rsp->expedited_start);
2833 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2836 * Each pass through the following loop attempts to force a
2837 * context switch on each CPU.
2839 while (try_stop_cpus(cpu_online_mask,
2840 synchronize_sched_expedited_cpu_stop,
2843 atomic_long_inc(&rsp->expedited_tryfail);
2845 /* Check to see if someone else did our work for us. */
2846 s = atomic_long_read(&rsp->expedited_done);
2847 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2848 /* ensure test happens before caller kfree */
2849 smp_mb__before_atomic_inc(); /* ^^^ */
2850 atomic_long_inc(&rsp->expedited_workdone1);
2854 /* No joy, try again later. Or just synchronize_sched(). */
2855 if (trycount++ < 10) {
2856 udelay(trycount * num_online_cpus());
2858 wait_rcu_gp(call_rcu_sched);
2859 atomic_long_inc(&rsp->expedited_normal);
2863 /* Recheck to see if someone else did our work for us. */
2864 s = atomic_long_read(&rsp->expedited_done);
2865 if (ULONG_CMP_GE((ulong)s, (ulong)firstsnap)) {
2866 /* ensure test happens before caller kfree */
2867 smp_mb__before_atomic_inc(); /* ^^^ */
2868 atomic_long_inc(&rsp->expedited_workdone2);
2873 * Refetching sync_sched_expedited_started allows later
2874 * callers to piggyback on our grace period. We retry
2875 * after they started, so our grace period works for them,
2876 * and they started after our first try, so their grace
2877 * period works for us.
2880 snap = atomic_long_read(&rsp->expedited_start);
2881 smp_mb(); /* ensure read is before try_stop_cpus(). */
2883 atomic_long_inc(&rsp->expedited_stoppedcpus);
2886 * Everyone up to our most recent fetch is covered by our grace
2887 * period. Update the counter, but only if our work is still
2888 * relevant -- which it won't be if someone who started later
2889 * than we did already did their update.
2892 atomic_long_inc(&rsp->expedited_done_tries);
2893 s = atomic_long_read(&rsp->expedited_done);
2894 if (ULONG_CMP_GE((ulong)s, (ulong)snap)) {
2895 /* ensure test happens before caller kfree */
2896 smp_mb__before_atomic_inc(); /* ^^^ */
2897 atomic_long_inc(&rsp->expedited_done_lost);
2900 } while (atomic_long_cmpxchg(&rsp->expedited_done, s, snap) != s);
2901 atomic_long_inc(&rsp->expedited_done_exit);
2905 EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
2908 * Check to see if there is any immediate RCU-related work to be done
2909 * by the current CPU, for the specified type of RCU, returning 1 if so.
2910 * The checks are in order of increasing expense: checks that can be
2911 * carried out against CPU-local state are performed first. However,
2912 * we must check for CPU stalls first, else we might not get a chance.
2914 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
2916 struct rcu_node *rnp = rdp->mynode;
2918 rdp->n_rcu_pending++;
2920 /* Check for CPU stalls, if enabled. */
2921 check_cpu_stall(rsp, rdp);
2923 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
2924 if (rcu_nohz_full_cpu(rsp))
2927 /* Is the RCU core waiting for a quiescent state from this CPU? */
2928 if (rcu_scheduler_fully_active &&
2929 rdp->qs_pending && !rdp->passed_quiesce) {
2930 rdp->n_rp_qs_pending++;
2931 } else if (rdp->qs_pending && rdp->passed_quiesce) {
2932 rdp->n_rp_report_qs++;
2936 /* Does this CPU have callbacks ready to invoke? */
2937 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
2938 rdp->n_rp_cb_ready++;
2942 /* Has RCU gone idle with this CPU needing another grace period? */
2943 if (cpu_needs_another_gp(rsp, rdp)) {
2944 rdp->n_rp_cpu_needs_gp++;
2948 /* Has another RCU grace period completed? */
2949 if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
2950 rdp->n_rp_gp_completed++;
2954 /* Has a new RCU grace period started? */
2955 if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
2956 rdp->n_rp_gp_started++;
2960 /* Does this CPU need a deferred NOCB wakeup? */
2961 if (rcu_nocb_need_deferred_wakeup(rdp)) {
2962 rdp->n_rp_nocb_defer_wakeup++;
2967 rdp->n_rp_need_nothing++;
2972 * Check to see if there is any immediate RCU-related work to be done
2973 * by the current CPU, returning 1 if so. This function is part of the
2974 * RCU implementation; it is -not- an exported member of the RCU API.
2976 static int rcu_pending(int cpu)
2978 struct rcu_state *rsp;
2980 for_each_rcu_flavor(rsp)
2981 if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
2987 * Return true if the specified CPU has any callback. If all_lazy is
2988 * non-NULL, store an indication of whether all callbacks are lazy.
2989 * (If there are no callbacks, all of them are deemed to be lazy.)
2991 static int __maybe_unused rcu_cpu_has_callbacks(int cpu, bool *all_lazy)
2995 struct rcu_data *rdp;
2996 struct rcu_state *rsp;
2998 for_each_rcu_flavor(rsp) {
2999 rdp = per_cpu_ptr(rsp->rda, cpu);
3003 if (rdp->qlen != rdp->qlen_lazy || !all_lazy) {
3014 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
3015 * the compiler is expected to optimize this away.
3017 static void _rcu_barrier_trace(struct rcu_state *rsp, const char *s,
3018 int cpu, unsigned long done)
3020 trace_rcu_barrier(rsp->name, s, cpu,
3021 atomic_read(&rsp->barrier_cpu_count), done);
3025 * RCU callback function for _rcu_barrier(). If we are last, wake
3026 * up the task executing _rcu_barrier().
3028 static void rcu_barrier_callback(struct rcu_head *rhp)
3030 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
3031 struct rcu_state *rsp = rdp->rsp;
3033 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
3034 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
3035 complete(&rsp->barrier_completion);
3037 _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
3042 * Called with preemption disabled, and from cross-cpu IRQ context.
3044 static void rcu_barrier_func(void *type)
3046 struct rcu_state *rsp = type;
3047 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
3049 _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
3050 atomic_inc(&rsp->barrier_cpu_count);
3051 rsp->call(&rdp->barrier_head, rcu_barrier_callback);
3055 * Orchestrate the specified type of RCU barrier, waiting for all
3056 * RCU callbacks of the specified type to complete.
3058 static void _rcu_barrier(struct rcu_state *rsp)
3061 struct rcu_data *rdp;
3062 unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
3063 unsigned long snap_done;
3065 _rcu_barrier_trace(rsp, "Begin", -1, snap);
3067 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3068 mutex_lock(&rsp->barrier_mutex);
3071 * Ensure that all prior references, including to ->n_barrier_done,
3072 * are ordered before the _rcu_barrier() machinery.
3074 smp_mb(); /* See above block comment. */
3077 * Recheck ->n_barrier_done to see if others did our work for us.
3078 * This means checking ->n_barrier_done for an even-to-odd-to-even
3079 * transition. The "if" expression below therefore rounds the old
3080 * value up to the next even number and adds two before comparing.
3082 snap_done = rsp->n_barrier_done;
3083 _rcu_barrier_trace(rsp, "Check", -1, snap_done);
3086 * If the value in snap is odd, we needed to wait for the current
3087 * rcu_barrier() to complete, then wait for the next one, in other
3088 * words, we need the value of snap_done to be three larger than
3089 * the value of snap. On the other hand, if the value in snap is
3090 * even, we only had to wait for the next rcu_barrier() to complete,
3091 * in other words, we need the value of snap_done to be only two
3092 * greater than the value of snap. The "(snap + 3) & ~0x1" computes
3093 * this for us (thank you, Linus!).
3095 if (ULONG_CMP_GE(snap_done, (snap + 3) & ~0x1)) {
3096 _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
3097 smp_mb(); /* caller's subsequent code after above check. */
3098 mutex_unlock(&rsp->barrier_mutex);
3103 * Increment ->n_barrier_done to avoid duplicate work. Use
3104 * ACCESS_ONCE() to prevent the compiler from speculating
3105 * the increment to precede the early-exit check.
3107 ACCESS_ONCE(rsp->n_barrier_done)++;
3108 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
3109 _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
3110 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3113 * Initialize the count to one rather than to zero in order to
3114 * avoid a too-soon return to zero in case of a short grace period
3115 * (or preemption of this task). Exclude CPU-hotplug operations
3116 * to ensure that no offline CPU has callbacks queued.
3118 init_completion(&rsp->barrier_completion);
3119 atomic_set(&rsp->barrier_cpu_count, 1);
3123 * Force each CPU with callbacks to register a new callback.
3124 * When that callback is invoked, we will know that all of the
3125 * corresponding CPU's preceding callbacks have been invoked.
3127 for_each_possible_cpu(cpu) {
3128 if (!cpu_online(cpu) && !rcu_is_nocb_cpu(cpu))
3130 rdp = per_cpu_ptr(rsp->rda, cpu);
3131 if (rcu_is_nocb_cpu(cpu)) {
3132 _rcu_barrier_trace(rsp, "OnlineNoCB", cpu,
3133 rsp->n_barrier_done);
3134 atomic_inc(&rsp->barrier_cpu_count);
3135 __call_rcu(&rdp->barrier_head, rcu_barrier_callback,
3137 } else if (ACCESS_ONCE(rdp->qlen)) {
3138 _rcu_barrier_trace(rsp, "OnlineQ", cpu,
3139 rsp->n_barrier_done);
3140 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
3142 _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
3143 rsp->n_barrier_done);
3149 * Now that we have an rcu_barrier_callback() callback on each
3150 * CPU, and thus each counted, remove the initial count.
3152 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
3153 complete(&rsp->barrier_completion);
3155 /* Increment ->n_barrier_done to prevent duplicate work. */
3156 smp_mb(); /* Keep increment after above mechanism. */
3157 ACCESS_ONCE(rsp->n_barrier_done)++;
3158 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
3159 _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
3160 smp_mb(); /* Keep increment before caller's subsequent code. */
3162 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3163 wait_for_completion(&rsp->barrier_completion);
3165 /* Other rcu_barrier() invocations can now safely proceed. */
3166 mutex_unlock(&rsp->barrier_mutex);
3170 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3172 void rcu_barrier_bh(void)
3174 _rcu_barrier(&rcu_bh_state);
3176 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
3179 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3181 void rcu_barrier_sched(void)
3183 _rcu_barrier(&rcu_sched_state);
3185 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
3188 * Do boot-time initialization of a CPU's per-CPU RCU data.
3191 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
3193 unsigned long flags;
3194 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3195 struct rcu_node *rnp = rcu_get_root(rsp);
3197 /* Set up local state, ensuring consistent view of global state. */
3198 raw_spin_lock_irqsave(&rnp->lock, flags);
3199 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
3200 init_callback_list(rdp);
3202 ACCESS_ONCE(rdp->qlen) = 0;
3203 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
3204 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
3205 WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
3208 rcu_boot_init_nocb_percpu_data(rdp);
3209 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3213 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3214 * offline event can be happening at a given time. Note also that we
3215 * can accept some slop in the rsp->completed access due to the fact
3216 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3219 rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
3221 unsigned long flags;
3223 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
3224 struct rcu_node *rnp = rcu_get_root(rsp);
3226 /* Exclude new grace periods. */
3227 mutex_lock(&rsp->onoff_mutex);
3229 /* Set up local state, ensuring consistent view of global state. */
3230 raw_spin_lock_irqsave(&rnp->lock, flags);
3231 rdp->beenonline = 1; /* We have now been online. */
3232 rdp->qlen_last_fqs_check = 0;
3233 rdp->n_force_qs_snap = rsp->n_force_qs;
3234 rdp->blimit = blimit;
3235 init_callback_list(rdp); /* Re-enable callbacks on this CPU. */
3236 rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
3237 rcu_sysidle_init_percpu_data(rdp->dynticks);
3238 atomic_set(&rdp->dynticks->dynticks,
3239 (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
3240 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
3242 /* Add CPU to rcu_node bitmasks. */
3244 mask = rdp->grpmask;
3246 /* Exclude any attempts to start a new GP on small systems. */
3247 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
3248 rnp->qsmaskinit |= mask;
3249 mask = rnp->grpmask;
3250 if (rnp == rdp->mynode) {
3252 * If there is a grace period in progress, we will
3253 * set up to wait for it next time we run the
3256 rdp->gpnum = rnp->completed;
3257 rdp->completed = rnp->completed;
3258 rdp->passed_quiesce = 0;
3259 rdp->qs_pending = 0;
3260 trace_rcu_grace_period(rsp->name, rdp->gpnum, TPS("cpuonl"));
3262 raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
3264 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
3265 local_irq_restore(flags);
3267 mutex_unlock(&rsp->onoff_mutex);
3270 static void rcu_prepare_cpu(int cpu)
3272 struct rcu_state *rsp;
3274 for_each_rcu_flavor(rsp)
3275 rcu_init_percpu_data(cpu, rsp);
3279 * Handle CPU online/offline notification events.
3281 static int rcu_cpu_notify(struct notifier_block *self,
3282 unsigned long action, void *hcpu)
3284 long cpu = (long)hcpu;
3285 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
3286 struct rcu_node *rnp = rdp->mynode;
3287 struct rcu_state *rsp;
3289 trace_rcu_utilization(TPS("Start CPU hotplug"));
3291 case CPU_UP_PREPARE:
3292 case CPU_UP_PREPARE_FROZEN:
3293 rcu_prepare_cpu(cpu);
3294 rcu_prepare_kthreads(cpu);
3297 case CPU_DOWN_FAILED:
3298 rcu_boost_kthread_setaffinity(rnp, -1);
3300 case CPU_DOWN_PREPARE:
3301 rcu_boost_kthread_setaffinity(rnp, cpu);
3304 case CPU_DYING_FROZEN:
3305 for_each_rcu_flavor(rsp)
3306 rcu_cleanup_dying_cpu(rsp);
3309 case CPU_DEAD_FROZEN:
3310 case CPU_UP_CANCELED:
3311 case CPU_UP_CANCELED_FROZEN:
3312 for_each_rcu_flavor(rsp)
3313 rcu_cleanup_dead_cpu(cpu, rsp);
3318 trace_rcu_utilization(TPS("End CPU hotplug"));
3322 static int rcu_pm_notify(struct notifier_block *self,
3323 unsigned long action, void *hcpu)
3326 case PM_HIBERNATION_PREPARE:
3327 case PM_SUSPEND_PREPARE:
3328 if (nr_cpu_ids <= 256) /* Expediting bad for large systems. */
3331 case PM_POST_HIBERNATION:
3332 case PM_POST_SUSPEND:
3342 * Spawn the kthread that handles this RCU flavor's grace periods.
3344 static int __init rcu_spawn_gp_kthread(void)
3346 unsigned long flags;
3347 struct rcu_node *rnp;
3348 struct rcu_state *rsp;
3349 struct task_struct *t;
3351 for_each_rcu_flavor(rsp) {
3352 t = kthread_run(rcu_gp_kthread, rsp, "%s", rsp->name);
3354 rnp = rcu_get_root(rsp);
3355 raw_spin_lock_irqsave(&rnp->lock, flags);
3356 rsp->gp_kthread = t;
3357 raw_spin_unlock_irqrestore(&rnp->lock, flags);
3358 rcu_spawn_nocb_kthreads(rsp);
3362 early_initcall(rcu_spawn_gp_kthread);
3365 * This function is invoked towards the end of the scheduler's initialization
3366 * process. Before this is called, the idle task might contain
3367 * RCU read-side critical sections (during which time, this idle
3368 * task is booting the system). After this function is called, the
3369 * idle tasks are prohibited from containing RCU read-side critical
3370 * sections. This function also enables RCU lockdep checking.
3372 void rcu_scheduler_starting(void)
3374 WARN_ON(num_online_cpus() != 1);
3375 WARN_ON(nr_context_switches() > 0);
3376 rcu_scheduler_active = 1;
3380 * Compute the per-level fanout, either using the exact fanout specified
3381 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
3383 #ifdef CONFIG_RCU_FANOUT_EXACT
3384 static void __init rcu_init_levelspread(struct rcu_state *rsp)
3388 rsp->levelspread[rcu_num_lvls - 1] = rcu_fanout_leaf;
3389 for (i = rcu_num_lvls - 2; i >= 0; i--)
3390 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
3392 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
3393 static void __init rcu_init_levelspread(struct rcu_state *rsp)
3400 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3401 ccur = rsp->levelcnt[i];
3402 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
3406 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
3409 * Helper function for rcu_init() that initializes one rcu_state structure.
3411 static void __init rcu_init_one(struct rcu_state *rsp,
3412 struct rcu_data __percpu *rda)
3414 static char *buf[] = { "rcu_node_0",
3417 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
3418 static char *fqs[] = { "rcu_node_fqs_0",
3421 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
3425 struct rcu_node *rnp;
3427 BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
3429 /* Silence gcc 4.8 warning about array index out of range. */
3430 if (rcu_num_lvls > RCU_NUM_LVLS)
3431 panic("rcu_init_one: rcu_num_lvls overflow");
3433 /* Initialize the level-tracking arrays. */
3435 for (i = 0; i < rcu_num_lvls; i++)
3436 rsp->levelcnt[i] = num_rcu_lvl[i];
3437 for (i = 1; i < rcu_num_lvls; i++)
3438 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
3439 rcu_init_levelspread(rsp);
3441 /* Initialize the elements themselves, starting from the leaves. */
3443 for (i = rcu_num_lvls - 1; i >= 0; i--) {
3444 cpustride *= rsp->levelspread[i];
3445 rnp = rsp->level[i];
3446 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
3447 raw_spin_lock_init(&rnp->lock);
3448 lockdep_set_class_and_name(&rnp->lock,
3449 &rcu_node_class[i], buf[i]);
3450 raw_spin_lock_init(&rnp->fqslock);
3451 lockdep_set_class_and_name(&rnp->fqslock,
3452 &rcu_fqs_class[i], fqs[i]);
3453 rnp->gpnum = rsp->gpnum;
3454 rnp->completed = rsp->completed;
3456 rnp->qsmaskinit = 0;
3457 rnp->grplo = j * cpustride;
3458 rnp->grphi = (j + 1) * cpustride - 1;
3459 if (rnp->grphi >= NR_CPUS)
3460 rnp->grphi = NR_CPUS - 1;
3466 rnp->grpnum = j % rsp->levelspread[i - 1];
3467 rnp->grpmask = 1UL << rnp->grpnum;
3468 rnp->parent = rsp->level[i - 1] +
3469 j / rsp->levelspread[i - 1];
3472 INIT_LIST_HEAD(&rnp->blkd_tasks);
3473 rcu_init_one_nocb(rnp);
3478 init_waitqueue_head(&rsp->gp_wq);
3479 rnp = rsp->level[rcu_num_lvls - 1];
3480 for_each_possible_cpu(i) {
3481 while (i > rnp->grphi)
3483 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
3484 rcu_boot_init_percpu_data(i, rsp);
3486 list_add(&rsp->flavors, &rcu_struct_flavors);
3490 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3491 * replace the definitions in tree.h because those are needed to size
3492 * the ->node array in the rcu_state structure.
3494 static void __init rcu_init_geometry(void)
3500 int rcu_capacity[MAX_RCU_LVLS + 1];
3503 * Initialize any unspecified boot parameters.
3504 * The default values of jiffies_till_first_fqs and
3505 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3506 * value, which is a function of HZ, then adding one for each
3507 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3509 d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV;
3510 if (jiffies_till_first_fqs == ULONG_MAX)
3511 jiffies_till_first_fqs = d;
3512 if (jiffies_till_next_fqs == ULONG_MAX)
3513 jiffies_till_next_fqs = d;
3515 /* If the compile-time values are accurate, just leave. */
3516 if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF &&
3517 nr_cpu_ids == NR_CPUS)
3519 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
3520 rcu_fanout_leaf, nr_cpu_ids);
3523 * Compute number of nodes that can be handled an rcu_node tree
3524 * with the given number of levels. Setting rcu_capacity[0] makes
3525 * some of the arithmetic easier.
3527 rcu_capacity[0] = 1;
3528 rcu_capacity[1] = rcu_fanout_leaf;
3529 for (i = 2; i <= MAX_RCU_LVLS; i++)
3530 rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
3533 * The boot-time rcu_fanout_leaf parameter is only permitted
3534 * to increase the leaf-level fanout, not decrease it. Of course,
3535 * the leaf-level fanout cannot exceed the number of bits in
3536 * the rcu_node masks. Finally, the tree must be able to accommodate
3537 * the configured number of CPUs. Complain and fall back to the
3538 * compile-time values if these limits are exceeded.
3540 if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
3541 rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
3542 n > rcu_capacity[MAX_RCU_LVLS]) {
3547 /* Calculate the number of rcu_nodes at each level of the tree. */
3548 for (i = 1; i <= MAX_RCU_LVLS; i++)
3549 if (n <= rcu_capacity[i]) {
3550 for (j = 0; j <= i; j++)
3552 DIV_ROUND_UP(n, rcu_capacity[i - j]);
3554 for (j = i + 1; j <= MAX_RCU_LVLS; j++)
3559 /* Calculate the total number of rcu_node structures. */
3561 for (i = 0; i <= MAX_RCU_LVLS; i++)
3562 rcu_num_nodes += num_rcu_lvl[i];
3566 void __init rcu_init(void)
3570 rcu_bootup_announce();
3571 rcu_init_geometry();
3572 rcu_init_one(&rcu_bh_state, &rcu_bh_data);
3573 rcu_init_one(&rcu_sched_state, &rcu_sched_data);
3574 __rcu_init_preempt();
3575 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
3578 * We don't need protection against CPU-hotplug here because
3579 * this is called early in boot, before either interrupts
3580 * or the scheduler are operational.
3582 cpu_notifier(rcu_cpu_notify, 0);
3583 pm_notifier(rcu_pm_notify, 0);
3584 for_each_online_cpu(cpu)
3585 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
3588 #include "tree_plugin.h"