Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/bwh/sfc-next-2.6
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / rcutree.c
blobdd4aea806f8ef63ba882af3a47d5981b366d4dc7
1 /*
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, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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 -
28 * Documentation/RCU
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 <asm/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/module.h>
42 #include <linux/completion.h>
43 #include <linux/moduleparam.h>
44 #include <linux/percpu.h>
45 #include <linux/notifier.h>
46 #include <linux/cpu.h>
47 #include <linux/mutex.h>
48 #include <linux/time.h>
49 #include <linux/kernel_stat.h>
51 #include "rcutree.h"
53 /* Data structures. */
55 static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
57 #define RCU_STATE_INITIALIZER(structname) { \
58 .level = { &structname.node[0] }, \
59 .levelcnt = { \
60 NUM_RCU_LVL_0, /* root of hierarchy. */ \
61 NUM_RCU_LVL_1, \
62 NUM_RCU_LVL_2, \
63 NUM_RCU_LVL_3, \
64 NUM_RCU_LVL_4, /* == MAX_RCU_LVLS */ \
65 }, \
66 .signaled = RCU_GP_IDLE, \
67 .gpnum = -300, \
68 .completed = -300, \
69 .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&structname.onofflock), \
70 .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \
71 .n_force_qs = 0, \
72 .n_force_qs_ngp = 0, \
73 .name = #structname, \
76 struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
77 DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
79 struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
80 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
82 int rcu_scheduler_active __read_mostly;
83 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
86 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
87 * permit this function to be invoked without holding the root rcu_node
88 * structure's ->lock, but of course results can be subject to change.
90 static int rcu_gp_in_progress(struct rcu_state *rsp)
92 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
96 * Note a quiescent state. Because we do not need to know
97 * how many quiescent states passed, just if there was at least
98 * one since the start of the grace period, this just sets a flag.
100 void rcu_sched_qs(int cpu)
102 struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
104 rdp->passed_quiesc_completed = rdp->gpnum - 1;
105 barrier();
106 rdp->passed_quiesc = 1;
109 void rcu_bh_qs(int cpu)
111 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
113 rdp->passed_quiesc_completed = rdp->gpnum - 1;
114 barrier();
115 rdp->passed_quiesc = 1;
119 * Note a context switch. This is a quiescent state for RCU-sched,
120 * and requires special handling for preemptible RCU.
122 void rcu_note_context_switch(int cpu)
124 rcu_sched_qs(cpu);
125 rcu_preempt_note_context_switch(cpu);
128 #ifdef CONFIG_NO_HZ
129 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
130 .dynticks_nesting = 1,
131 .dynticks = 1,
133 #endif /* #ifdef CONFIG_NO_HZ */
135 static int blimit = 10; /* Maximum callbacks per softirq. */
136 static int qhimark = 10000; /* If this many pending, ignore blimit. */
137 static int qlowmark = 100; /* Once only this many pending, use blimit. */
139 module_param(blimit, int, 0);
140 module_param(qhimark, int, 0);
141 module_param(qlowmark, int, 0);
143 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
144 int rcu_cpu_stall_suppress __read_mostly = RCU_CPU_STALL_SUPPRESS_INIT;
145 module_param(rcu_cpu_stall_suppress, int, 0644);
146 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
148 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
149 static int rcu_pending(int cpu);
152 * Return the number of RCU-sched batches processed thus far for debug & stats.
154 long rcu_batches_completed_sched(void)
156 return rcu_sched_state.completed;
158 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
161 * Return the number of RCU BH batches processed thus far for debug & stats.
163 long rcu_batches_completed_bh(void)
165 return rcu_bh_state.completed;
167 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
170 * Force a quiescent state for RCU BH.
172 void rcu_bh_force_quiescent_state(void)
174 force_quiescent_state(&rcu_bh_state, 0);
176 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
179 * Force a quiescent state for RCU-sched.
181 void rcu_sched_force_quiescent_state(void)
183 force_quiescent_state(&rcu_sched_state, 0);
185 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
188 * Does the CPU have callbacks ready to be invoked?
190 static int
191 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
193 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
197 * Does the current CPU require a yet-as-unscheduled grace period?
199 static int
200 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
202 return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
206 * Return the root node of the specified rcu_state structure.
208 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
210 return &rsp->node[0];
213 #ifdef CONFIG_SMP
216 * If the specified CPU is offline, tell the caller that it is in
217 * a quiescent state. Otherwise, whack it with a reschedule IPI.
218 * Grace periods can end up waiting on an offline CPU when that
219 * CPU is in the process of coming online -- it will be added to the
220 * rcu_node bitmasks before it actually makes it online. The same thing
221 * can happen while a CPU is in the process of coming online. Because this
222 * race is quite rare, we check for it after detecting that the grace
223 * period has been delayed rather than checking each and every CPU
224 * each and every time we start a new grace period.
226 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
229 * If the CPU is offline, it is in a quiescent state. We can
230 * trust its state not to change because interrupts are disabled.
232 if (cpu_is_offline(rdp->cpu)) {
233 rdp->offline_fqs++;
234 return 1;
237 /* If preemptable RCU, no point in sending reschedule IPI. */
238 if (rdp->preemptable)
239 return 0;
241 /* The CPU is online, so send it a reschedule IPI. */
242 if (rdp->cpu != smp_processor_id())
243 smp_send_reschedule(rdp->cpu);
244 else
245 set_need_resched();
246 rdp->resched_ipi++;
247 return 0;
250 #endif /* #ifdef CONFIG_SMP */
252 #ifdef CONFIG_NO_HZ
255 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
257 * Enter nohz mode, in other words, -leave- the mode in which RCU
258 * read-side critical sections can occur. (Though RCU read-side
259 * critical sections can occur in irq handlers in nohz mode, a possibility
260 * handled by rcu_irq_enter() and rcu_irq_exit()).
262 void rcu_enter_nohz(void)
264 unsigned long flags;
265 struct rcu_dynticks *rdtp;
267 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
268 local_irq_save(flags);
269 rdtp = &__get_cpu_var(rcu_dynticks);
270 rdtp->dynticks++;
271 rdtp->dynticks_nesting--;
272 WARN_ON_ONCE(rdtp->dynticks & 0x1);
273 local_irq_restore(flags);
277 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
279 * Exit nohz mode, in other words, -enter- the mode in which RCU
280 * read-side critical sections normally occur.
282 void rcu_exit_nohz(void)
284 unsigned long flags;
285 struct rcu_dynticks *rdtp;
287 local_irq_save(flags);
288 rdtp = &__get_cpu_var(rcu_dynticks);
289 rdtp->dynticks++;
290 rdtp->dynticks_nesting++;
291 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
292 local_irq_restore(flags);
293 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
297 * rcu_nmi_enter - inform RCU of entry to NMI context
299 * If the CPU was idle with dynamic ticks active, and there is no
300 * irq handler running, this updates rdtp->dynticks_nmi to let the
301 * RCU grace-period handling know that the CPU is active.
303 void rcu_nmi_enter(void)
305 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
307 if (rdtp->dynticks & 0x1)
308 return;
309 rdtp->dynticks_nmi++;
310 WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
311 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
315 * rcu_nmi_exit - inform RCU of exit from NMI context
317 * If the CPU was idle with dynamic ticks active, and there is no
318 * irq handler running, this updates rdtp->dynticks_nmi to let the
319 * RCU grace-period handling know that the CPU is no longer active.
321 void rcu_nmi_exit(void)
323 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
325 if (rdtp->dynticks & 0x1)
326 return;
327 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
328 rdtp->dynticks_nmi++;
329 WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
333 * rcu_irq_enter - inform RCU of entry to hard irq context
335 * If the CPU was idle with dynamic ticks active, this updates the
336 * rdtp->dynticks to let the RCU handling know that the CPU is active.
338 void rcu_irq_enter(void)
340 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
342 if (rdtp->dynticks_nesting++)
343 return;
344 rdtp->dynticks++;
345 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
346 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
350 * rcu_irq_exit - inform RCU of exit from hard irq context
352 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
353 * to put let the RCU handling be aware that the CPU is going back to idle
354 * with no ticks.
356 void rcu_irq_exit(void)
358 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
360 if (--rdtp->dynticks_nesting)
361 return;
362 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
363 rdtp->dynticks++;
364 WARN_ON_ONCE(rdtp->dynticks & 0x1);
366 /* If the interrupt queued a callback, get out of dyntick mode. */
367 if (__this_cpu_read(rcu_sched_data.nxtlist) ||
368 __this_cpu_read(rcu_bh_data.nxtlist))
369 set_need_resched();
372 #ifdef CONFIG_SMP
375 * Snapshot the specified CPU's dynticks counter so that we can later
376 * credit them with an implicit quiescent state. Return 1 if this CPU
377 * is in dynticks idle mode, which is an extended quiescent state.
379 static int dyntick_save_progress_counter(struct rcu_data *rdp)
381 int ret;
382 int snap;
383 int snap_nmi;
385 snap = rdp->dynticks->dynticks;
386 snap_nmi = rdp->dynticks->dynticks_nmi;
387 smp_mb(); /* Order sampling of snap with end of grace period. */
388 rdp->dynticks_snap = snap;
389 rdp->dynticks_nmi_snap = snap_nmi;
390 ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
391 if (ret)
392 rdp->dynticks_fqs++;
393 return ret;
397 * Return true if the specified CPU has passed through a quiescent
398 * state by virtue of being in or having passed through an dynticks
399 * idle state since the last call to dyntick_save_progress_counter()
400 * for this same CPU.
402 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
404 long curr;
405 long curr_nmi;
406 long snap;
407 long snap_nmi;
409 curr = rdp->dynticks->dynticks;
410 snap = rdp->dynticks_snap;
411 curr_nmi = rdp->dynticks->dynticks_nmi;
412 snap_nmi = rdp->dynticks_nmi_snap;
413 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
416 * If the CPU passed through or entered a dynticks idle phase with
417 * no active irq/NMI handlers, then we can safely pretend that the CPU
418 * already acknowledged the request to pass through a quiescent
419 * state. Either way, that CPU cannot possibly be in an RCU
420 * read-side critical section that started before the beginning
421 * of the current RCU grace period.
423 if ((curr != snap || (curr & 0x1) == 0) &&
424 (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
425 rdp->dynticks_fqs++;
426 return 1;
429 /* Go check for the CPU being offline. */
430 return rcu_implicit_offline_qs(rdp);
433 #endif /* #ifdef CONFIG_SMP */
435 #else /* #ifdef CONFIG_NO_HZ */
437 #ifdef CONFIG_SMP
439 static int dyntick_save_progress_counter(struct rcu_data *rdp)
441 return 0;
444 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
446 return rcu_implicit_offline_qs(rdp);
449 #endif /* #ifdef CONFIG_SMP */
451 #endif /* #else #ifdef CONFIG_NO_HZ */
453 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
455 int rcu_cpu_stall_suppress __read_mostly;
457 static void record_gp_stall_check_time(struct rcu_state *rsp)
459 rsp->gp_start = jiffies;
460 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
463 static void print_other_cpu_stall(struct rcu_state *rsp)
465 int cpu;
466 long delta;
467 unsigned long flags;
468 struct rcu_node *rnp = rcu_get_root(rsp);
470 /* Only let one CPU complain about others per time interval. */
472 raw_spin_lock_irqsave(&rnp->lock, flags);
473 delta = jiffies - rsp->jiffies_stall;
474 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
475 raw_spin_unlock_irqrestore(&rnp->lock, flags);
476 return;
478 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
481 * Now rat on any tasks that got kicked up to the root rcu_node
482 * due to CPU offlining.
484 rcu_print_task_stall(rnp);
485 raw_spin_unlock_irqrestore(&rnp->lock, flags);
488 * OK, time to rat on our buddy...
489 * See Documentation/RCU/stallwarn.txt for info on how to debug
490 * RCU CPU stall warnings.
492 printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
493 rsp->name);
494 rcu_for_each_leaf_node(rsp, rnp) {
495 raw_spin_lock_irqsave(&rnp->lock, flags);
496 rcu_print_task_stall(rnp);
497 raw_spin_unlock_irqrestore(&rnp->lock, flags);
498 if (rnp->qsmask == 0)
499 continue;
500 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
501 if (rnp->qsmask & (1UL << cpu))
502 printk(" %d", rnp->grplo + cpu);
504 printk("} (detected by %d, t=%ld jiffies)\n",
505 smp_processor_id(), (long)(jiffies - rsp->gp_start));
506 trigger_all_cpu_backtrace();
508 /* If so configured, complain about tasks blocking the grace period. */
510 rcu_print_detail_task_stall(rsp);
512 force_quiescent_state(rsp, 0); /* Kick them all. */
515 static void print_cpu_stall(struct rcu_state *rsp)
517 unsigned long flags;
518 struct rcu_node *rnp = rcu_get_root(rsp);
521 * OK, time to rat on ourselves...
522 * See Documentation/RCU/stallwarn.txt for info on how to debug
523 * RCU CPU stall warnings.
525 printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
526 rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
527 trigger_all_cpu_backtrace();
529 raw_spin_lock_irqsave(&rnp->lock, flags);
530 if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
531 rsp->jiffies_stall =
532 jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
533 raw_spin_unlock_irqrestore(&rnp->lock, flags);
535 set_need_resched(); /* kick ourselves to get things going. */
538 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
540 long delta;
541 struct rcu_node *rnp;
543 if (rcu_cpu_stall_suppress)
544 return;
545 delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
546 rnp = rdp->mynode;
547 if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
549 /* We haven't checked in, so go dump stack. */
550 print_cpu_stall(rsp);
552 } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
554 /* They had two time units to dump stack, so complain. */
555 print_other_cpu_stall(rsp);
559 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
561 rcu_cpu_stall_suppress = 1;
562 return NOTIFY_DONE;
566 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
568 * Set the stall-warning timeout way off into the future, thus preventing
569 * any RCU CPU stall-warning messages from appearing in the current set of
570 * RCU grace periods.
572 * The caller must disable hard irqs.
574 void rcu_cpu_stall_reset(void)
576 rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
577 rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
578 rcu_preempt_stall_reset();
581 static struct notifier_block rcu_panic_block = {
582 .notifier_call = rcu_panic,
585 static void __init check_cpu_stall_init(void)
587 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
590 #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
592 static void record_gp_stall_check_time(struct rcu_state *rsp)
596 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
600 void rcu_cpu_stall_reset(void)
604 static void __init check_cpu_stall_init(void)
608 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
611 * Update CPU-local rcu_data state to record the newly noticed grace period.
612 * This is used both when we started the grace period and when we notice
613 * that someone else started the grace period. The caller must hold the
614 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
615 * and must have irqs disabled.
617 static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
619 if (rdp->gpnum != rnp->gpnum) {
621 * If the current grace period is waiting for this CPU,
622 * set up to detect a quiescent state, otherwise don't
623 * go looking for one.
625 rdp->gpnum = rnp->gpnum;
626 if (rnp->qsmask & rdp->grpmask) {
627 rdp->qs_pending = 1;
628 rdp->passed_quiesc = 0;
629 } else
630 rdp->qs_pending = 0;
634 static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
636 unsigned long flags;
637 struct rcu_node *rnp;
639 local_irq_save(flags);
640 rnp = rdp->mynode;
641 if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
642 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
643 local_irq_restore(flags);
644 return;
646 __note_new_gpnum(rsp, rnp, rdp);
647 raw_spin_unlock_irqrestore(&rnp->lock, flags);
651 * Did someone else start a new RCU grace period start since we last
652 * checked? Update local state appropriately if so. Must be called
653 * on the CPU corresponding to rdp.
655 static int
656 check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
658 unsigned long flags;
659 int ret = 0;
661 local_irq_save(flags);
662 if (rdp->gpnum != rsp->gpnum) {
663 note_new_gpnum(rsp, rdp);
664 ret = 1;
666 local_irq_restore(flags);
667 return ret;
671 * Advance this CPU's callbacks, but only if the current grace period
672 * has ended. This may be called only from the CPU to whom the rdp
673 * belongs. In addition, the corresponding leaf rcu_node structure's
674 * ->lock must be held by the caller, with irqs disabled.
676 static void
677 __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
679 /* Did another grace period end? */
680 if (rdp->completed != rnp->completed) {
682 /* Advance callbacks. No harm if list empty. */
683 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
684 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
685 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
687 /* Remember that we saw this grace-period completion. */
688 rdp->completed = rnp->completed;
691 * If we were in an extended quiescent state, we may have
692 * missed some grace periods that others CPUs handled on
693 * our behalf. Catch up with this state to avoid noting
694 * spurious new grace periods. If another grace period
695 * has started, then rnp->gpnum will have advanced, so
696 * we will detect this later on.
698 if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
699 rdp->gpnum = rdp->completed;
702 * If RCU does not need a quiescent state from this CPU,
703 * then make sure that this CPU doesn't go looking for one.
705 if ((rnp->qsmask & rdp->grpmask) == 0)
706 rdp->qs_pending = 0;
711 * Advance this CPU's callbacks, but only if the current grace period
712 * has ended. This may be called only from the CPU to whom the rdp
713 * belongs.
715 static void
716 rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
718 unsigned long flags;
719 struct rcu_node *rnp;
721 local_irq_save(flags);
722 rnp = rdp->mynode;
723 if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
724 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
725 local_irq_restore(flags);
726 return;
728 __rcu_process_gp_end(rsp, rnp, rdp);
729 raw_spin_unlock_irqrestore(&rnp->lock, flags);
733 * Do per-CPU grace-period initialization for running CPU. The caller
734 * must hold the lock of the leaf rcu_node structure corresponding to
735 * this CPU.
737 static void
738 rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
740 /* Prior grace period ended, so advance callbacks for current CPU. */
741 __rcu_process_gp_end(rsp, rnp, rdp);
744 * Because this CPU just now started the new grace period, we know
745 * that all of its callbacks will be covered by this upcoming grace
746 * period, even the ones that were registered arbitrarily recently.
747 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
749 * Other CPUs cannot be sure exactly when the grace period started.
750 * Therefore, their recently registered callbacks must pass through
751 * an additional RCU_NEXT_READY stage, so that they will be handled
752 * by the next RCU grace period.
754 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
755 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
757 /* Set state so that this CPU will detect the next quiescent state. */
758 __note_new_gpnum(rsp, rnp, rdp);
762 * Start a new RCU grace period if warranted, re-initializing the hierarchy
763 * in preparation for detecting the next grace period. The caller must hold
764 * the root node's ->lock, which is released before return. Hard irqs must
765 * be disabled.
767 static void
768 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
769 __releases(rcu_get_root(rsp)->lock)
771 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
772 struct rcu_node *rnp = rcu_get_root(rsp);
774 if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
775 if (cpu_needs_another_gp(rsp, rdp))
776 rsp->fqs_need_gp = 1;
777 if (rnp->completed == rsp->completed) {
778 raw_spin_unlock_irqrestore(&rnp->lock, flags);
779 return;
781 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
784 * Propagate new ->completed value to rcu_node structures
785 * so that other CPUs don't have to wait until the start
786 * of the next grace period to process their callbacks.
788 rcu_for_each_node_breadth_first(rsp, rnp) {
789 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
790 rnp->completed = rsp->completed;
791 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
793 local_irq_restore(flags);
794 return;
797 /* Advance to a new grace period and initialize state. */
798 rsp->gpnum++;
799 WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
800 rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
801 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
802 record_gp_stall_check_time(rsp);
804 /* Special-case the common single-level case. */
805 if (NUM_RCU_NODES == 1) {
806 rcu_preempt_check_blocked_tasks(rnp);
807 rnp->qsmask = rnp->qsmaskinit;
808 rnp->gpnum = rsp->gpnum;
809 rnp->completed = rsp->completed;
810 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
811 rcu_start_gp_per_cpu(rsp, rnp, rdp);
812 raw_spin_unlock_irqrestore(&rnp->lock, flags);
813 return;
816 raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */
819 /* Exclude any concurrent CPU-hotplug operations. */
820 raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
823 * Set the quiescent-state-needed bits in all the rcu_node
824 * structures for all currently online CPUs in breadth-first
825 * order, starting from the root rcu_node structure. This
826 * operation relies on the layout of the hierarchy within the
827 * rsp->node[] array. Note that other CPUs will access only
828 * the leaves of the hierarchy, which still indicate that no
829 * grace period is in progress, at least until the corresponding
830 * leaf node has been initialized. In addition, we have excluded
831 * CPU-hotplug operations.
833 * Note that the grace period cannot complete until we finish
834 * the initialization process, as there will be at least one
835 * qsmask bit set in the root node until that time, namely the
836 * one corresponding to this CPU, due to the fact that we have
837 * irqs disabled.
839 rcu_for_each_node_breadth_first(rsp, rnp) {
840 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
841 rcu_preempt_check_blocked_tasks(rnp);
842 rnp->qsmask = rnp->qsmaskinit;
843 rnp->gpnum = rsp->gpnum;
844 rnp->completed = rsp->completed;
845 if (rnp == rdp->mynode)
846 rcu_start_gp_per_cpu(rsp, rnp, rdp);
847 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
850 rnp = rcu_get_root(rsp);
851 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
852 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
853 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
854 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
858 * Report a full set of quiescent states to the specified rcu_state
859 * data structure. This involves cleaning up after the prior grace
860 * period and letting rcu_start_gp() start up the next grace period
861 * if one is needed. Note that the caller must hold rnp->lock, as
862 * required by rcu_start_gp(), which will release it.
864 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
865 __releases(rcu_get_root(rsp)->lock)
867 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
868 rsp->completed = rsp->gpnum;
869 rsp->signaled = RCU_GP_IDLE;
870 rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
874 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
875 * Allows quiescent states for a group of CPUs to be reported at one go
876 * to the specified rcu_node structure, though all the CPUs in the group
877 * must be represented by the same rcu_node structure (which need not be
878 * a leaf rcu_node structure, though it often will be). That structure's
879 * lock must be held upon entry, and it is released before return.
881 static void
882 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
883 struct rcu_node *rnp, unsigned long flags)
884 __releases(rnp->lock)
886 struct rcu_node *rnp_c;
888 /* Walk up the rcu_node hierarchy. */
889 for (;;) {
890 if (!(rnp->qsmask & mask)) {
892 /* Our bit has already been cleared, so done. */
893 raw_spin_unlock_irqrestore(&rnp->lock, flags);
894 return;
896 rnp->qsmask &= ~mask;
897 if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
899 /* Other bits still set at this level, so done. */
900 raw_spin_unlock_irqrestore(&rnp->lock, flags);
901 return;
903 mask = rnp->grpmask;
904 if (rnp->parent == NULL) {
906 /* No more levels. Exit loop holding root lock. */
908 break;
910 raw_spin_unlock_irqrestore(&rnp->lock, flags);
911 rnp_c = rnp;
912 rnp = rnp->parent;
913 raw_spin_lock_irqsave(&rnp->lock, flags);
914 WARN_ON_ONCE(rnp_c->qsmask);
918 * Get here if we are the last CPU to pass through a quiescent
919 * state for this grace period. Invoke rcu_report_qs_rsp()
920 * to clean up and start the next grace period if one is needed.
922 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
926 * Record a quiescent state for the specified CPU to that CPU's rcu_data
927 * structure. This must be either called from the specified CPU, or
928 * called when the specified CPU is known to be offline (and when it is
929 * also known that no other CPU is concurrently trying to help the offline
930 * CPU). The lastcomp argument is used to make sure we are still in the
931 * grace period of interest. We don't want to end the current grace period
932 * based on quiescent states detected in an earlier grace period!
934 static void
935 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
937 unsigned long flags;
938 unsigned long mask;
939 struct rcu_node *rnp;
941 rnp = rdp->mynode;
942 raw_spin_lock_irqsave(&rnp->lock, flags);
943 if (lastcomp != rnp->completed) {
946 * Someone beat us to it for this grace period, so leave.
947 * The race with GP start is resolved by the fact that we
948 * hold the leaf rcu_node lock, so that the per-CPU bits
949 * cannot yet be initialized -- so we would simply find our
950 * CPU's bit already cleared in rcu_report_qs_rnp() if this
951 * race occurred.
953 rdp->passed_quiesc = 0; /* try again later! */
954 raw_spin_unlock_irqrestore(&rnp->lock, flags);
955 return;
957 mask = rdp->grpmask;
958 if ((rnp->qsmask & mask) == 0) {
959 raw_spin_unlock_irqrestore(&rnp->lock, flags);
960 } else {
961 rdp->qs_pending = 0;
964 * This GP can't end until cpu checks in, so all of our
965 * callbacks can be processed during the next GP.
967 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
969 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
974 * Check to see if there is a new grace period of which this CPU
975 * is not yet aware, and if so, set up local rcu_data state for it.
976 * Otherwise, see if this CPU has just passed through its first
977 * quiescent state for this grace period, and record that fact if so.
979 static void
980 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
982 /* If there is now a new grace period, record and return. */
983 if (check_for_new_grace_period(rsp, rdp))
984 return;
987 * Does this CPU still need to do its part for current grace period?
988 * If no, return and let the other CPUs do their part as well.
990 if (!rdp->qs_pending)
991 return;
994 * Was there a quiescent state since the beginning of the grace
995 * period? If no, then exit and wait for the next call.
997 if (!rdp->passed_quiesc)
998 return;
1001 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1002 * judge of that).
1004 rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
1007 #ifdef CONFIG_HOTPLUG_CPU
1010 * Move a dying CPU's RCU callbacks to online CPU's callback list.
1011 * Synchronization is not required because this function executes
1012 * in stop_machine() context.
1014 static void rcu_send_cbs_to_online(struct rcu_state *rsp)
1016 int i;
1017 /* current DYING CPU is cleared in the cpu_online_mask */
1018 int receive_cpu = cpumask_any(cpu_online_mask);
1019 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1020 struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
1022 if (rdp->nxtlist == NULL)
1023 return; /* irqs disabled, so comparison is stable. */
1025 *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
1026 receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
1027 receive_rdp->qlen += rdp->qlen;
1028 receive_rdp->n_cbs_adopted += rdp->qlen;
1029 rdp->n_cbs_orphaned += rdp->qlen;
1031 rdp->nxtlist = NULL;
1032 for (i = 0; i < RCU_NEXT_SIZE; i++)
1033 rdp->nxttail[i] = &rdp->nxtlist;
1034 rdp->qlen = 0;
1038 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
1039 * and move all callbacks from the outgoing CPU to the current one.
1041 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
1043 unsigned long flags;
1044 unsigned long mask;
1045 int need_report = 0;
1046 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1047 struct rcu_node *rnp;
1049 /* Exclude any attempts to start a new grace period. */
1050 raw_spin_lock_irqsave(&rsp->onofflock, flags);
1052 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1053 rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
1054 mask = rdp->grpmask; /* rnp->grplo is constant. */
1055 do {
1056 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1057 rnp->qsmaskinit &= ~mask;
1058 if (rnp->qsmaskinit != 0) {
1059 if (rnp != rdp->mynode)
1060 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1061 break;
1063 if (rnp == rdp->mynode)
1064 need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
1065 else
1066 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1067 mask = rnp->grpmask;
1068 rnp = rnp->parent;
1069 } while (rnp != NULL);
1072 * We still hold the leaf rcu_node structure lock here, and
1073 * irqs are still disabled. The reason for this subterfuge is
1074 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1075 * held leads to deadlock.
1077 raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
1078 rnp = rdp->mynode;
1079 if (need_report & RCU_OFL_TASKS_NORM_GP)
1080 rcu_report_unblock_qs_rnp(rnp, flags);
1081 else
1082 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1083 if (need_report & RCU_OFL_TASKS_EXP_GP)
1084 rcu_report_exp_rnp(rsp, rnp);
1088 * Remove the specified CPU from the RCU hierarchy and move any pending
1089 * callbacks that it might have to the current CPU. This code assumes
1090 * that at least one CPU in the system will remain running at all times.
1091 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1093 static void rcu_offline_cpu(int cpu)
1095 __rcu_offline_cpu(cpu, &rcu_sched_state);
1096 __rcu_offline_cpu(cpu, &rcu_bh_state);
1097 rcu_preempt_offline_cpu(cpu);
1100 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1102 static void rcu_send_cbs_to_online(struct rcu_state *rsp)
1106 static void rcu_offline_cpu(int cpu)
1110 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1113 * Invoke any RCU callbacks that have made it to the end of their grace
1114 * period. Thottle as specified by rdp->blimit.
1116 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1118 unsigned long flags;
1119 struct rcu_head *next, *list, **tail;
1120 int count;
1122 /* If no callbacks are ready, just return.*/
1123 if (!cpu_has_callbacks_ready_to_invoke(rdp))
1124 return;
1127 * Extract the list of ready callbacks, disabling to prevent
1128 * races with call_rcu() from interrupt handlers.
1130 local_irq_save(flags);
1131 list = rdp->nxtlist;
1132 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
1133 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1134 tail = rdp->nxttail[RCU_DONE_TAIL];
1135 for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
1136 if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
1137 rdp->nxttail[count] = &rdp->nxtlist;
1138 local_irq_restore(flags);
1140 /* Invoke callbacks. */
1141 count = 0;
1142 while (list) {
1143 next = list->next;
1144 prefetch(next);
1145 debug_rcu_head_unqueue(list);
1146 list->func(list);
1147 list = next;
1148 if (++count >= rdp->blimit)
1149 break;
1152 local_irq_save(flags);
1154 /* Update count, and requeue any remaining callbacks. */
1155 rdp->qlen -= count;
1156 rdp->n_cbs_invoked += count;
1157 if (list != NULL) {
1158 *tail = rdp->nxtlist;
1159 rdp->nxtlist = list;
1160 for (count = 0; count < RCU_NEXT_SIZE; count++)
1161 if (&rdp->nxtlist == rdp->nxttail[count])
1162 rdp->nxttail[count] = tail;
1163 else
1164 break;
1167 /* Reinstate batch limit if we have worked down the excess. */
1168 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
1169 rdp->blimit = blimit;
1171 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1172 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
1173 rdp->qlen_last_fqs_check = 0;
1174 rdp->n_force_qs_snap = rsp->n_force_qs;
1175 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
1176 rdp->qlen_last_fqs_check = rdp->qlen;
1178 local_irq_restore(flags);
1180 /* Re-raise the RCU softirq if there are callbacks remaining. */
1181 if (cpu_has_callbacks_ready_to_invoke(rdp))
1182 raise_softirq(RCU_SOFTIRQ);
1186 * Check to see if this CPU is in a non-context-switch quiescent state
1187 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1188 * Also schedule the RCU softirq handler.
1190 * This function must be called with hardirqs disabled. It is normally
1191 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1192 * false, there is no point in invoking rcu_check_callbacks().
1194 void rcu_check_callbacks(int cpu, int user)
1196 if (user ||
1197 (idle_cpu(cpu) && rcu_scheduler_active &&
1198 !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1201 * Get here if this CPU took its interrupt from user
1202 * mode or from the idle loop, and if this is not a
1203 * nested interrupt. In this case, the CPU is in
1204 * a quiescent state, so note it.
1206 * No memory barrier is required here because both
1207 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1208 * variables that other CPUs neither access nor modify,
1209 * at least not while the corresponding CPU is online.
1212 rcu_sched_qs(cpu);
1213 rcu_bh_qs(cpu);
1215 } else if (!in_softirq()) {
1218 * Get here if this CPU did not take its interrupt from
1219 * softirq, in other words, if it is not interrupting
1220 * a rcu_bh read-side critical section. This is an _bh
1221 * critical section, so note it.
1224 rcu_bh_qs(cpu);
1226 rcu_preempt_check_callbacks(cpu);
1227 if (rcu_pending(cpu))
1228 raise_softirq(RCU_SOFTIRQ);
1231 #ifdef CONFIG_SMP
1234 * Scan the leaf rcu_node structures, processing dyntick state for any that
1235 * have not yet encountered a quiescent state, using the function specified.
1236 * The caller must have suppressed start of new grace periods.
1238 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1240 unsigned long bit;
1241 int cpu;
1242 unsigned long flags;
1243 unsigned long mask;
1244 struct rcu_node *rnp;
1246 rcu_for_each_leaf_node(rsp, rnp) {
1247 mask = 0;
1248 raw_spin_lock_irqsave(&rnp->lock, flags);
1249 if (!rcu_gp_in_progress(rsp)) {
1250 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1251 return;
1253 if (rnp->qsmask == 0) {
1254 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1255 continue;
1257 cpu = rnp->grplo;
1258 bit = 1;
1259 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1260 if ((rnp->qsmask & bit) != 0 &&
1261 f(per_cpu_ptr(rsp->rda, cpu)))
1262 mask |= bit;
1264 if (mask != 0) {
1266 /* rcu_report_qs_rnp() releases rnp->lock. */
1267 rcu_report_qs_rnp(mask, rsp, rnp, flags);
1268 continue;
1270 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1275 * Force quiescent states on reluctant CPUs, and also detect which
1276 * CPUs are in dyntick-idle mode.
1278 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1280 unsigned long flags;
1281 struct rcu_node *rnp = rcu_get_root(rsp);
1283 if (!rcu_gp_in_progress(rsp))
1284 return; /* No grace period in progress, nothing to force. */
1285 if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
1286 rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1287 return; /* Someone else is already on the job. */
1289 if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
1290 goto unlock_fqs_ret; /* no emergency and done recently. */
1291 rsp->n_force_qs++;
1292 raw_spin_lock(&rnp->lock); /* irqs already disabled */
1293 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1294 if(!rcu_gp_in_progress(rsp)) {
1295 rsp->n_force_qs_ngp++;
1296 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1297 goto unlock_fqs_ret; /* no GP in progress, time updated. */
1299 rsp->fqs_active = 1;
1300 switch (rsp->signaled) {
1301 case RCU_GP_IDLE:
1302 case RCU_GP_INIT:
1304 break; /* grace period idle or initializing, ignore. */
1306 case RCU_SAVE_DYNTICK:
1307 if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1308 break; /* So gcc recognizes the dead code. */
1310 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1312 /* Record dyntick-idle state. */
1313 force_qs_rnp(rsp, dyntick_save_progress_counter);
1314 raw_spin_lock(&rnp->lock); /* irqs already disabled */
1315 if (rcu_gp_in_progress(rsp))
1316 rsp->signaled = RCU_FORCE_QS;
1317 break;
1319 case RCU_FORCE_QS:
1321 /* Check dyntick-idle state, send IPI to laggarts. */
1322 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1323 force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1325 /* Leave state in case more forcing is required. */
1327 raw_spin_lock(&rnp->lock); /* irqs already disabled */
1328 break;
1330 rsp->fqs_active = 0;
1331 if (rsp->fqs_need_gp) {
1332 raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
1333 rsp->fqs_need_gp = 0;
1334 rcu_start_gp(rsp, flags); /* releases rnp->lock */
1335 return;
1337 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1338 unlock_fqs_ret:
1339 raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
1342 #else /* #ifdef CONFIG_SMP */
1344 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1346 set_need_resched();
1349 #endif /* #else #ifdef CONFIG_SMP */
1352 * This does the RCU processing work from softirq context for the
1353 * specified rcu_state and rcu_data structures. This may be called
1354 * only from the CPU to whom the rdp belongs.
1356 static void
1357 __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1359 unsigned long flags;
1361 WARN_ON_ONCE(rdp->beenonline == 0);
1364 * If an RCU GP has gone long enough, go check for dyntick
1365 * idle CPUs and, if needed, send resched IPIs.
1367 if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1368 force_quiescent_state(rsp, 1);
1371 * Advance callbacks in response to end of earlier grace
1372 * period that some other CPU ended.
1374 rcu_process_gp_end(rsp, rdp);
1376 /* Update RCU state based on any recent quiescent states. */
1377 rcu_check_quiescent_state(rsp, rdp);
1379 /* Does this CPU require a not-yet-started grace period? */
1380 if (cpu_needs_another_gp(rsp, rdp)) {
1381 raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1382 rcu_start_gp(rsp, flags); /* releases above lock */
1385 /* If there are callbacks ready, invoke them. */
1386 rcu_do_batch(rsp, rdp);
1390 * Do softirq processing for the current CPU.
1392 static void rcu_process_callbacks(struct softirq_action *unused)
1395 * Memory references from any prior RCU read-side critical sections
1396 * executed by the interrupted code must be seen before any RCU
1397 * grace-period manipulations below.
1399 smp_mb(); /* See above block comment. */
1401 __rcu_process_callbacks(&rcu_sched_state,
1402 &__get_cpu_var(rcu_sched_data));
1403 __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1404 rcu_preempt_process_callbacks();
1407 * Memory references from any later RCU read-side critical sections
1408 * executed by the interrupted code must be seen after any RCU
1409 * grace-period manipulations above.
1411 smp_mb(); /* See above block comment. */
1413 /* If we are last CPU on way to dyntick-idle mode, accelerate it. */
1414 rcu_needs_cpu_flush();
1417 static void
1418 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1419 struct rcu_state *rsp)
1421 unsigned long flags;
1422 struct rcu_data *rdp;
1424 debug_rcu_head_queue(head);
1425 head->func = func;
1426 head->next = NULL;
1428 smp_mb(); /* Ensure RCU update seen before callback registry. */
1431 * Opportunistically note grace-period endings and beginnings.
1432 * Note that we might see a beginning right after we see an
1433 * end, but never vice versa, since this CPU has to pass through
1434 * a quiescent state betweentimes.
1436 local_irq_save(flags);
1437 rdp = this_cpu_ptr(rsp->rda);
1439 /* Add the callback to our list. */
1440 *rdp->nxttail[RCU_NEXT_TAIL] = head;
1441 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1444 * Force the grace period if too many callbacks or too long waiting.
1445 * Enforce hysteresis, and don't invoke force_quiescent_state()
1446 * if some other CPU has recently done so. Also, don't bother
1447 * invoking force_quiescent_state() if the newly enqueued callback
1448 * is the only one waiting for a grace period to complete.
1450 if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1452 /* Are we ignoring a completed grace period? */
1453 rcu_process_gp_end(rsp, rdp);
1454 check_for_new_grace_period(rsp, rdp);
1456 /* Start a new grace period if one not already started. */
1457 if (!rcu_gp_in_progress(rsp)) {
1458 unsigned long nestflag;
1459 struct rcu_node *rnp_root = rcu_get_root(rsp);
1461 raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
1462 rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */
1463 } else {
1464 /* Give the grace period a kick. */
1465 rdp->blimit = LONG_MAX;
1466 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
1467 *rdp->nxttail[RCU_DONE_TAIL] != head)
1468 force_quiescent_state(rsp, 0);
1469 rdp->n_force_qs_snap = rsp->n_force_qs;
1470 rdp->qlen_last_fqs_check = rdp->qlen;
1472 } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1473 force_quiescent_state(rsp, 1);
1474 local_irq_restore(flags);
1478 * Queue an RCU-sched callback for invocation after a grace period.
1480 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1482 __call_rcu(head, func, &rcu_sched_state);
1484 EXPORT_SYMBOL_GPL(call_rcu_sched);
1487 * Queue an RCU for invocation after a quicker grace period.
1489 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1491 __call_rcu(head, func, &rcu_bh_state);
1493 EXPORT_SYMBOL_GPL(call_rcu_bh);
1496 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1498 * Control will return to the caller some time after a full rcu-sched
1499 * grace period has elapsed, in other words after all currently executing
1500 * rcu-sched read-side critical sections have completed. These read-side
1501 * critical sections are delimited by rcu_read_lock_sched() and
1502 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1503 * local_irq_disable(), and so on may be used in place of
1504 * rcu_read_lock_sched().
1506 * This means that all preempt_disable code sequences, including NMI and
1507 * hardware-interrupt handlers, in progress on entry will have completed
1508 * before this primitive returns. However, this does not guarantee that
1509 * softirq handlers will have completed, since in some kernels, these
1510 * handlers can run in process context, and can block.
1512 * This primitive provides the guarantees made by the (now removed)
1513 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1514 * guarantees that rcu_read_lock() sections will have completed.
1515 * In "classic RCU", these two guarantees happen to be one and
1516 * the same, but can differ in realtime RCU implementations.
1518 void synchronize_sched(void)
1520 struct rcu_synchronize rcu;
1522 if (rcu_blocking_is_gp())
1523 return;
1525 init_rcu_head_on_stack(&rcu.head);
1526 init_completion(&rcu.completion);
1527 /* Will wake me after RCU finished. */
1528 call_rcu_sched(&rcu.head, wakeme_after_rcu);
1529 /* Wait for it. */
1530 wait_for_completion(&rcu.completion);
1531 destroy_rcu_head_on_stack(&rcu.head);
1533 EXPORT_SYMBOL_GPL(synchronize_sched);
1536 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1538 * Control will return to the caller some time after a full rcu_bh grace
1539 * period has elapsed, in other words after all currently executing rcu_bh
1540 * read-side critical sections have completed. RCU read-side critical
1541 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1542 * and may be nested.
1544 void synchronize_rcu_bh(void)
1546 struct rcu_synchronize rcu;
1548 if (rcu_blocking_is_gp())
1549 return;
1551 init_rcu_head_on_stack(&rcu.head);
1552 init_completion(&rcu.completion);
1553 /* Will wake me after RCU finished. */
1554 call_rcu_bh(&rcu.head, wakeme_after_rcu);
1555 /* Wait for it. */
1556 wait_for_completion(&rcu.completion);
1557 destroy_rcu_head_on_stack(&rcu.head);
1559 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
1562 * Check to see if there is any immediate RCU-related work to be done
1563 * by the current CPU, for the specified type of RCU, returning 1 if so.
1564 * The checks are in order of increasing expense: checks that can be
1565 * carried out against CPU-local state are performed first. However,
1566 * we must check for CPU stalls first, else we might not get a chance.
1568 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1570 struct rcu_node *rnp = rdp->mynode;
1572 rdp->n_rcu_pending++;
1574 /* Check for CPU stalls, if enabled. */
1575 check_cpu_stall(rsp, rdp);
1577 /* Is the RCU core waiting for a quiescent state from this CPU? */
1578 if (rdp->qs_pending && !rdp->passed_quiesc) {
1581 * If force_quiescent_state() coming soon and this CPU
1582 * needs a quiescent state, and this is either RCU-sched
1583 * or RCU-bh, force a local reschedule.
1585 rdp->n_rp_qs_pending++;
1586 if (!rdp->preemptable &&
1587 ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
1588 jiffies))
1589 set_need_resched();
1590 } else if (rdp->qs_pending && rdp->passed_quiesc) {
1591 rdp->n_rp_report_qs++;
1592 return 1;
1595 /* Does this CPU have callbacks ready to invoke? */
1596 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1597 rdp->n_rp_cb_ready++;
1598 return 1;
1601 /* Has RCU gone idle with this CPU needing another grace period? */
1602 if (cpu_needs_another_gp(rsp, rdp)) {
1603 rdp->n_rp_cpu_needs_gp++;
1604 return 1;
1607 /* Has another RCU grace period completed? */
1608 if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
1609 rdp->n_rp_gp_completed++;
1610 return 1;
1613 /* Has a new RCU grace period started? */
1614 if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
1615 rdp->n_rp_gp_started++;
1616 return 1;
1619 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1620 if (rcu_gp_in_progress(rsp) &&
1621 ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
1622 rdp->n_rp_need_fqs++;
1623 return 1;
1626 /* nothing to do */
1627 rdp->n_rp_need_nothing++;
1628 return 0;
1632 * Check to see if there is any immediate RCU-related work to be done
1633 * by the current CPU, returning 1 if so. This function is part of the
1634 * RCU implementation; it is -not- an exported member of the RCU API.
1636 static int rcu_pending(int cpu)
1638 return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1639 __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1640 rcu_preempt_pending(cpu);
1644 * Check to see if any future RCU-related work will need to be done
1645 * by the current CPU, even if none need be done immediately, returning
1646 * 1 if so.
1648 static int rcu_needs_cpu_quick_check(int cpu)
1650 /* RCU callbacks either ready or pending? */
1651 return per_cpu(rcu_sched_data, cpu).nxtlist ||
1652 per_cpu(rcu_bh_data, cpu).nxtlist ||
1653 rcu_preempt_needs_cpu(cpu);
1656 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
1657 static atomic_t rcu_barrier_cpu_count;
1658 static DEFINE_MUTEX(rcu_barrier_mutex);
1659 static struct completion rcu_barrier_completion;
1661 static void rcu_barrier_callback(struct rcu_head *notused)
1663 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1664 complete(&rcu_barrier_completion);
1668 * Called with preemption disabled, and from cross-cpu IRQ context.
1670 static void rcu_barrier_func(void *type)
1672 int cpu = smp_processor_id();
1673 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
1674 void (*call_rcu_func)(struct rcu_head *head,
1675 void (*func)(struct rcu_head *head));
1677 atomic_inc(&rcu_barrier_cpu_count);
1678 call_rcu_func = type;
1679 call_rcu_func(head, rcu_barrier_callback);
1683 * Orchestrate the specified type of RCU barrier, waiting for all
1684 * RCU callbacks of the specified type to complete.
1686 static void _rcu_barrier(struct rcu_state *rsp,
1687 void (*call_rcu_func)(struct rcu_head *head,
1688 void (*func)(struct rcu_head *head)))
1690 BUG_ON(in_interrupt());
1691 /* Take mutex to serialize concurrent rcu_barrier() requests. */
1692 mutex_lock(&rcu_barrier_mutex);
1693 init_completion(&rcu_barrier_completion);
1695 * Initialize rcu_barrier_cpu_count to 1, then invoke
1696 * rcu_barrier_func() on each CPU, so that each CPU also has
1697 * incremented rcu_barrier_cpu_count. Only then is it safe to
1698 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1699 * might complete its grace period before all of the other CPUs
1700 * did their increment, causing this function to return too
1701 * early. Note that on_each_cpu() disables irqs, which prevents
1702 * any CPUs from coming online or going offline until each online
1703 * CPU has queued its RCU-barrier callback.
1705 atomic_set(&rcu_barrier_cpu_count, 1);
1706 on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
1707 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1708 complete(&rcu_barrier_completion);
1709 wait_for_completion(&rcu_barrier_completion);
1710 mutex_unlock(&rcu_barrier_mutex);
1714 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1716 void rcu_barrier_bh(void)
1718 _rcu_barrier(&rcu_bh_state, call_rcu_bh);
1720 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
1723 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1725 void rcu_barrier_sched(void)
1727 _rcu_barrier(&rcu_sched_state, call_rcu_sched);
1729 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
1732 * Do boot-time initialization of a CPU's per-CPU RCU data.
1734 static void __init
1735 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1737 unsigned long flags;
1738 int i;
1739 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1740 struct rcu_node *rnp = rcu_get_root(rsp);
1742 /* Set up local state, ensuring consistent view of global state. */
1743 raw_spin_lock_irqsave(&rnp->lock, flags);
1744 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1745 rdp->nxtlist = NULL;
1746 for (i = 0; i < RCU_NEXT_SIZE; i++)
1747 rdp->nxttail[i] = &rdp->nxtlist;
1748 rdp->qlen = 0;
1749 #ifdef CONFIG_NO_HZ
1750 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1751 #endif /* #ifdef CONFIG_NO_HZ */
1752 rdp->cpu = cpu;
1753 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1757 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1758 * offline event can be happening at a given time. Note also that we
1759 * can accept some slop in the rsp->completed access due to the fact
1760 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1762 static void __cpuinit
1763 rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
1765 unsigned long flags;
1766 unsigned long mask;
1767 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1768 struct rcu_node *rnp = rcu_get_root(rsp);
1770 /* Set up local state, ensuring consistent view of global state. */
1771 raw_spin_lock_irqsave(&rnp->lock, flags);
1772 rdp->passed_quiesc = 0; /* We could be racing with new GP, */
1773 rdp->qs_pending = 1; /* so set up to respond to current GP. */
1774 rdp->beenonline = 1; /* We have now been online. */
1775 rdp->preemptable = preemptable;
1776 rdp->qlen_last_fqs_check = 0;
1777 rdp->n_force_qs_snap = rsp->n_force_qs;
1778 rdp->blimit = blimit;
1779 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1782 * A new grace period might start here. If so, we won't be part
1783 * of it, but that is OK, as we are currently in a quiescent state.
1786 /* Exclude any attempts to start a new GP on large systems. */
1787 raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
1789 /* Add CPU to rcu_node bitmasks. */
1790 rnp = rdp->mynode;
1791 mask = rdp->grpmask;
1792 do {
1793 /* Exclude any attempts to start a new GP on small systems. */
1794 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1795 rnp->qsmaskinit |= mask;
1796 mask = rnp->grpmask;
1797 if (rnp == rdp->mynode) {
1798 rdp->gpnum = rnp->completed; /* if GP in progress... */
1799 rdp->completed = rnp->completed;
1800 rdp->passed_quiesc_completed = rnp->completed - 1;
1802 raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
1803 rnp = rnp->parent;
1804 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1806 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
1809 static void __cpuinit rcu_online_cpu(int cpu)
1811 rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1812 rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1813 rcu_preempt_init_percpu_data(cpu);
1817 * Handle CPU online/offline notification events.
1819 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1820 unsigned long action, void *hcpu)
1822 long cpu = (long)hcpu;
1824 switch (action) {
1825 case CPU_UP_PREPARE:
1826 case CPU_UP_PREPARE_FROZEN:
1827 rcu_online_cpu(cpu);
1828 break;
1829 case CPU_DYING:
1830 case CPU_DYING_FROZEN:
1832 * The whole machine is "stopped" except this CPU, so we can
1833 * touch any data without introducing corruption. We send the
1834 * dying CPU's callbacks to an arbitrarily chosen online CPU.
1836 rcu_send_cbs_to_online(&rcu_bh_state);
1837 rcu_send_cbs_to_online(&rcu_sched_state);
1838 rcu_preempt_send_cbs_to_online();
1839 break;
1840 case CPU_DEAD:
1841 case CPU_DEAD_FROZEN:
1842 case CPU_UP_CANCELED:
1843 case CPU_UP_CANCELED_FROZEN:
1844 rcu_offline_cpu(cpu);
1845 break;
1846 default:
1847 break;
1849 return NOTIFY_OK;
1853 * This function is invoked towards the end of the scheduler's initialization
1854 * process. Before this is called, the idle task might contain
1855 * RCU read-side critical sections (during which time, this idle
1856 * task is booting the system). After this function is called, the
1857 * idle tasks are prohibited from containing RCU read-side critical
1858 * sections. This function also enables RCU lockdep checking.
1860 void rcu_scheduler_starting(void)
1862 WARN_ON(num_online_cpus() != 1);
1863 WARN_ON(nr_context_switches() > 0);
1864 rcu_scheduler_active = 1;
1868 * Compute the per-level fanout, either using the exact fanout specified
1869 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1871 #ifdef CONFIG_RCU_FANOUT_EXACT
1872 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1874 int i;
1876 for (i = NUM_RCU_LVLS - 1; i > 0; i--)
1877 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1878 rsp->levelspread[0] = RCU_FANOUT_LEAF;
1880 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1881 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1883 int ccur;
1884 int cprv;
1885 int i;
1887 cprv = NR_CPUS;
1888 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1889 ccur = rsp->levelcnt[i];
1890 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1891 cprv = ccur;
1894 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1897 * Helper function for rcu_init() that initializes one rcu_state structure.
1899 static void __init rcu_init_one(struct rcu_state *rsp,
1900 struct rcu_data __percpu *rda)
1902 static char *buf[] = { "rcu_node_level_0",
1903 "rcu_node_level_1",
1904 "rcu_node_level_2",
1905 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
1906 int cpustride = 1;
1907 int i;
1908 int j;
1909 struct rcu_node *rnp;
1911 BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
1913 /* Initialize the level-tracking arrays. */
1915 for (i = 1; i < NUM_RCU_LVLS; i++)
1916 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1917 rcu_init_levelspread(rsp);
1919 /* Initialize the elements themselves, starting from the leaves. */
1921 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1922 cpustride *= rsp->levelspread[i];
1923 rnp = rsp->level[i];
1924 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1925 raw_spin_lock_init(&rnp->lock);
1926 lockdep_set_class_and_name(&rnp->lock,
1927 &rcu_node_class[i], buf[i]);
1928 rnp->gpnum = 0;
1929 rnp->qsmask = 0;
1930 rnp->qsmaskinit = 0;
1931 rnp->grplo = j * cpustride;
1932 rnp->grphi = (j + 1) * cpustride - 1;
1933 if (rnp->grphi >= NR_CPUS)
1934 rnp->grphi = NR_CPUS - 1;
1935 if (i == 0) {
1936 rnp->grpnum = 0;
1937 rnp->grpmask = 0;
1938 rnp->parent = NULL;
1939 } else {
1940 rnp->grpnum = j % rsp->levelspread[i - 1];
1941 rnp->grpmask = 1UL << rnp->grpnum;
1942 rnp->parent = rsp->level[i - 1] +
1943 j / rsp->levelspread[i - 1];
1945 rnp->level = i;
1946 INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
1947 INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
1948 INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
1949 INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
1953 rsp->rda = rda;
1954 rnp = rsp->level[NUM_RCU_LVLS - 1];
1955 for_each_possible_cpu(i) {
1956 while (i > rnp->grphi)
1957 rnp++;
1958 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
1959 rcu_boot_init_percpu_data(i, rsp);
1963 void __init rcu_init(void)
1965 int cpu;
1967 rcu_bootup_announce();
1968 rcu_init_one(&rcu_sched_state, &rcu_sched_data);
1969 rcu_init_one(&rcu_bh_state, &rcu_bh_data);
1970 __rcu_init_preempt();
1971 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1974 * We don't need protection against CPU-hotplug here because
1975 * this is called early in boot, before either interrupts
1976 * or the scheduler are operational.
1978 cpu_notifier(rcu_cpu_notify, 0);
1979 for_each_online_cpu(cpu)
1980 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
1981 check_cpu_stall_init();
1984 #include "rcutree_plugin.h"