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 -
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>
52 /* Data structures. */
54 #define RCU_STATE_INITIALIZER(name) { \
55 .level = { &name.node[0] }, \
57 NUM_RCU_LVL_0, /* root of hierarchy. */ \
60 NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \
62 .signaled = RCU_SIGNAL_INIT, \
65 .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
66 .fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \
68 .n_force_qs_ngp = 0, \
71 struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
72 DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
74 struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
75 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
79 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
80 * permit this function to be invoked without holding the root rcu_node
81 * structure's ->lock, but of course results can be subject to change.
83 static int rcu_gp_in_progress(struct rcu_state *rsp)
85 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
89 * Note a quiescent state. Because we do not need to know
90 * how many quiescent states passed, just if there was at least
91 * one since the start of the grace period, this just sets a flag.
93 void rcu_sched_qs(int cpu)
97 rdp = &per_cpu(rcu_sched_data, cpu);
98 rdp->passed_quiesc_completed = rdp->completed;
100 rdp->passed_quiesc = 1;
101 rcu_preempt_note_context_switch(cpu);
104 void rcu_bh_qs(int cpu)
106 struct rcu_data *rdp;
108 rdp = &per_cpu(rcu_bh_data, cpu);
109 rdp->passed_quiesc_completed = rdp->completed;
111 rdp->passed_quiesc = 1;
115 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
116 .dynticks_nesting = 1,
119 #endif /* #ifdef CONFIG_NO_HZ */
121 static int blimit = 10; /* Maximum callbacks per softirq. */
122 static int qhimark = 10000; /* If this many pending, ignore blimit. */
123 static int qlowmark = 100; /* Once only this many pending, use blimit. */
125 module_param(blimit, int, 0);
126 module_param(qhimark, int, 0);
127 module_param(qlowmark, int, 0);
129 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
130 static int rcu_pending(int cpu);
133 * Return the number of RCU-sched batches processed thus far for debug & stats.
135 long rcu_batches_completed_sched(void)
137 return rcu_sched_state.completed;
139 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
142 * Return the number of RCU BH batches processed thus far for debug & stats.
144 long rcu_batches_completed_bh(void)
146 return rcu_bh_state.completed;
148 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
151 * Does the CPU have callbacks ready to be invoked?
154 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
156 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
160 * Does the current CPU require a yet-as-unscheduled grace period?
163 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
165 return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
169 * Return the root node of the specified rcu_state structure.
171 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
173 return &rsp->node[0];
179 * If the specified CPU is offline, tell the caller that it is in
180 * a quiescent state. Otherwise, whack it with a reschedule IPI.
181 * Grace periods can end up waiting on an offline CPU when that
182 * CPU is in the process of coming online -- it will be added to the
183 * rcu_node bitmasks before it actually makes it online. The same thing
184 * can happen while a CPU is in the process of coming online. Because this
185 * race is quite rare, we check for it after detecting that the grace
186 * period has been delayed rather than checking each and every CPU
187 * each and every time we start a new grace period.
189 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
192 * If the CPU is offline, it is in a quiescent state. We can
193 * trust its state not to change because interrupts are disabled.
195 if (cpu_is_offline(rdp->cpu)) {
200 /* If preemptable RCU, no point in sending reschedule IPI. */
201 if (rdp->preemptable)
204 /* The CPU is online, so send it a reschedule IPI. */
205 if (rdp->cpu != smp_processor_id())
206 smp_send_reschedule(rdp->cpu);
213 #endif /* #ifdef CONFIG_SMP */
218 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
220 * Enter nohz mode, in other words, -leave- the mode in which RCU
221 * read-side critical sections can occur. (Though RCU read-side
222 * critical sections can occur in irq handlers in nohz mode, a possibility
223 * handled by rcu_irq_enter() and rcu_irq_exit()).
225 void rcu_enter_nohz(void)
228 struct rcu_dynticks *rdtp;
230 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
231 local_irq_save(flags);
232 rdtp = &__get_cpu_var(rcu_dynticks);
234 rdtp->dynticks_nesting--;
235 WARN_ON_ONCE(rdtp->dynticks & 0x1);
236 local_irq_restore(flags);
240 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
242 * Exit nohz mode, in other words, -enter- the mode in which RCU
243 * read-side critical sections normally occur.
245 void rcu_exit_nohz(void)
248 struct rcu_dynticks *rdtp;
250 local_irq_save(flags);
251 rdtp = &__get_cpu_var(rcu_dynticks);
253 rdtp->dynticks_nesting++;
254 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
255 local_irq_restore(flags);
256 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
260 * rcu_nmi_enter - inform RCU of entry to NMI context
262 * If the CPU was idle with dynamic ticks active, and there is no
263 * irq handler running, this updates rdtp->dynticks_nmi to let the
264 * RCU grace-period handling know that the CPU is active.
266 void rcu_nmi_enter(void)
268 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
270 if (rdtp->dynticks & 0x1)
272 rdtp->dynticks_nmi++;
273 WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
274 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
278 * rcu_nmi_exit - inform RCU of exit from NMI context
280 * If the CPU was idle with dynamic ticks active, and there is no
281 * irq handler running, this updates rdtp->dynticks_nmi to let the
282 * RCU grace-period handling know that the CPU is no longer active.
284 void rcu_nmi_exit(void)
286 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
288 if (rdtp->dynticks & 0x1)
290 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
291 rdtp->dynticks_nmi++;
292 WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
296 * rcu_irq_enter - inform RCU of entry to hard irq context
298 * If the CPU was idle with dynamic ticks active, this updates the
299 * rdtp->dynticks to let the RCU handling know that the CPU is active.
301 void rcu_irq_enter(void)
303 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
305 if (rdtp->dynticks_nesting++)
308 WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
309 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
313 * rcu_irq_exit - inform RCU of exit from hard irq context
315 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
316 * to put let the RCU handling be aware that the CPU is going back to idle
319 void rcu_irq_exit(void)
321 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
323 if (--rdtp->dynticks_nesting)
325 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
327 WARN_ON_ONCE(rdtp->dynticks & 0x1);
329 /* If the interrupt queued a callback, get out of dyntick mode. */
330 if (__get_cpu_var(rcu_sched_data).nxtlist ||
331 __get_cpu_var(rcu_bh_data).nxtlist)
336 * Record the specified "completed" value, which is later used to validate
337 * dynticks counter manipulations. Specify "rsp->completed - 1" to
338 * unconditionally invalidate any future dynticks manipulations (which is
339 * useful at the beginning of a grace period).
341 static void dyntick_record_completed(struct rcu_state *rsp, long comp)
343 rsp->dynticks_completed = comp;
349 * Recall the previously recorded value of the completion for dynticks.
351 static long dyntick_recall_completed(struct rcu_state *rsp)
353 return rsp->dynticks_completed;
357 * Snapshot the specified CPU's dynticks counter so that we can later
358 * credit them with an implicit quiescent state. Return 1 if this CPU
359 * is in dynticks idle mode, which is an extended quiescent state.
361 static int dyntick_save_progress_counter(struct rcu_data *rdp)
367 snap = rdp->dynticks->dynticks;
368 snap_nmi = rdp->dynticks->dynticks_nmi;
369 smp_mb(); /* Order sampling of snap with end of grace period. */
370 rdp->dynticks_snap = snap;
371 rdp->dynticks_nmi_snap = snap_nmi;
372 ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
379 * Return true if the specified CPU has passed through a quiescent
380 * state by virtue of being in or having passed through an dynticks
381 * idle state since the last call to dyntick_save_progress_counter()
384 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
391 curr = rdp->dynticks->dynticks;
392 snap = rdp->dynticks_snap;
393 curr_nmi = rdp->dynticks->dynticks_nmi;
394 snap_nmi = rdp->dynticks_nmi_snap;
395 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
398 * If the CPU passed through or entered a dynticks idle phase with
399 * no active irq/NMI handlers, then we can safely pretend that the CPU
400 * already acknowledged the request to pass through a quiescent
401 * state. Either way, that CPU cannot possibly be in an RCU
402 * read-side critical section that started before the beginning
403 * of the current RCU grace period.
405 if ((curr != snap || (curr & 0x1) == 0) &&
406 (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
411 /* Go check for the CPU being offline. */
412 return rcu_implicit_offline_qs(rdp);
415 #endif /* #ifdef CONFIG_SMP */
417 #else /* #ifdef CONFIG_NO_HZ */
419 static void dyntick_record_completed(struct rcu_state *rsp, long comp)
426 * If there are no dynticks, then the only way that a CPU can passively
427 * be in a quiescent state is to be offline. Unlike dynticks idle, which
428 * is a point in time during the prior (already finished) grace period,
429 * an offline CPU is always in a quiescent state, and thus can be
430 * unconditionally applied. So just return the current value of completed.
432 static long dyntick_recall_completed(struct rcu_state *rsp)
434 return rsp->completed;
437 static int dyntick_save_progress_counter(struct rcu_data *rdp)
442 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
444 return rcu_implicit_offline_qs(rdp);
447 #endif /* #ifdef CONFIG_SMP */
449 #endif /* #else #ifdef CONFIG_NO_HZ */
451 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
453 static void record_gp_stall_check_time(struct rcu_state *rsp)
455 rsp->gp_start = jiffies;
456 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
459 static void print_other_cpu_stall(struct rcu_state *rsp)
464 struct rcu_node *rnp = rcu_get_root(rsp);
466 /* Only let one CPU complain about others per time interval. */
468 spin_lock_irqsave(&rnp->lock, flags);
469 delta = jiffies - rsp->jiffies_stall;
470 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
471 spin_unlock_irqrestore(&rnp->lock, flags);
474 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
477 * Now rat on any tasks that got kicked up to the root rcu_node
478 * due to CPU offlining.
480 rcu_print_task_stall(rnp);
481 spin_unlock_irqrestore(&rnp->lock, flags);
483 /* OK, time to rat on our buddy... */
485 printk(KERN_ERR "INFO: RCU detected CPU stalls:");
486 rcu_for_each_leaf_node(rsp, rnp) {
487 rcu_print_task_stall(rnp);
488 if (rnp->qsmask == 0)
490 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
491 if (rnp->qsmask & (1UL << cpu))
492 printk(" %d", rnp->grplo + cpu);
494 printk(" (detected by %d, t=%ld jiffies)\n",
495 smp_processor_id(), (long)(jiffies - rsp->gp_start));
496 trigger_all_cpu_backtrace();
498 force_quiescent_state(rsp, 0); /* Kick them all. */
501 static void print_cpu_stall(struct rcu_state *rsp)
504 struct rcu_node *rnp = rcu_get_root(rsp);
506 printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
507 smp_processor_id(), jiffies - rsp->gp_start);
508 trigger_all_cpu_backtrace();
510 spin_lock_irqsave(&rnp->lock, flags);
511 if ((long)(jiffies - rsp->jiffies_stall) >= 0)
513 jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
514 spin_unlock_irqrestore(&rnp->lock, flags);
516 set_need_resched(); /* kick ourselves to get things going. */
519 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
522 struct rcu_node *rnp;
524 delta = jiffies - rsp->jiffies_stall;
526 if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
528 /* We haven't checked in, so go dump stack. */
529 print_cpu_stall(rsp);
531 } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
533 /* They had two time units to dump stack, so complain. */
534 print_other_cpu_stall(rsp);
538 #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
540 static void record_gp_stall_check_time(struct rcu_state *rsp)
544 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
548 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
551 * Update CPU-local rcu_data state to record the newly noticed grace period.
552 * This is used both when we started the grace period and when we notice
553 * that someone else started the grace period.
555 static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
558 rdp->passed_quiesc = 0;
559 rdp->gpnum = rsp->gpnum;
563 * Did someone else start a new RCU grace period start since we last
564 * checked? Update local state appropriately if so. Must be called
565 * on the CPU corresponding to rdp.
568 check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
573 local_irq_save(flags);
574 if (rdp->gpnum != rsp->gpnum) {
575 note_new_gpnum(rsp, rdp);
578 local_irq_restore(flags);
583 * Start a new RCU grace period if warranted, re-initializing the hierarchy
584 * in preparation for detecting the next grace period. The caller must hold
585 * the root node's ->lock, which is released before return. Hard irqs must
589 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
590 __releases(rcu_get_root(rsp)->lock)
592 struct rcu_data *rdp = rsp->rda[smp_processor_id()];
593 struct rcu_node *rnp = rcu_get_root(rsp);
595 if (!cpu_needs_another_gp(rsp, rdp)) {
596 spin_unlock_irqrestore(&rnp->lock, flags);
600 /* Advance to a new grace period and initialize state. */
602 WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
603 rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
604 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
605 record_gp_stall_check_time(rsp);
606 dyntick_record_completed(rsp, rsp->completed - 1);
607 note_new_gpnum(rsp, rdp);
610 * Because this CPU just now started the new grace period, we know
611 * that all of its callbacks will be covered by this upcoming grace
612 * period, even the ones that were registered arbitrarily recently.
613 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
615 * Other CPUs cannot be sure exactly when the grace period started.
616 * Therefore, their recently registered callbacks must pass through
617 * an additional RCU_NEXT_READY stage, so that they will be handled
618 * by the next RCU grace period.
620 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
621 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
623 /* Special-case the common single-level case. */
624 if (NUM_RCU_NODES == 1) {
625 rcu_preempt_check_blocked_tasks(rnp);
626 rnp->qsmask = rnp->qsmaskinit;
627 rnp->gpnum = rsp->gpnum;
628 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
629 spin_unlock_irqrestore(&rnp->lock, flags);
633 spin_unlock(&rnp->lock); /* leave irqs disabled. */
636 /* Exclude any concurrent CPU-hotplug operations. */
637 spin_lock(&rsp->onofflock); /* irqs already disabled. */
640 * Set the quiescent-state-needed bits in all the rcu_node
641 * structures for all currently online CPUs in breadth-first
642 * order, starting from the root rcu_node structure. This
643 * operation relies on the layout of the hierarchy within the
644 * rsp->node[] array. Note that other CPUs will access only
645 * the leaves of the hierarchy, which still indicate that no
646 * grace period is in progress, at least until the corresponding
647 * leaf node has been initialized. In addition, we have excluded
648 * CPU-hotplug operations.
650 * Note that the grace period cannot complete until we finish
651 * the initialization process, as there will be at least one
652 * qsmask bit set in the root node until that time, namely the
653 * one corresponding to this CPU, due to the fact that we have
656 rcu_for_each_node_breadth_first(rsp, rnp) {
657 spin_lock(&rnp->lock); /* irqs already disabled. */
658 rcu_preempt_check_blocked_tasks(rnp);
659 rnp->qsmask = rnp->qsmaskinit;
660 rnp->gpnum = rsp->gpnum;
661 spin_unlock(&rnp->lock); /* irqs already disabled. */
664 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
665 spin_unlock_irqrestore(&rsp->onofflock, flags);
669 * Advance this CPU's callbacks, but only if the current grace period
670 * has ended. This may be called only from the CPU to whom the rdp
674 rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
679 local_irq_save(flags);
680 completed_snap = ACCESS_ONCE(rsp->completed); /* outside of lock. */
682 /* Did another grace period end? */
683 if (rdp->completed != completed_snap) {
685 /* Advance callbacks. No harm if list empty. */
686 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
687 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
688 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
690 /* Remember that we saw this grace-period completion. */
691 rdp->completed = completed_snap;
693 local_irq_restore(flags);
697 * Clean up after the prior grace period and let rcu_start_gp() start up
698 * the next grace period if one is needed. Note that the caller must
699 * hold rnp->lock, as required by rcu_start_gp(), which will release it.
701 static void cpu_quiet_msk_finish(struct rcu_state *rsp, unsigned long flags)
702 __releases(rcu_get_root(rsp)->lock)
704 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
705 rsp->completed = rsp->gpnum;
706 rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]);
707 rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
711 * Similar to cpu_quiet(), for which it is a helper function. Allows
712 * a group of CPUs to be quieted at one go, though all the CPUs in the
713 * group must be represented by the same leaf rcu_node structure.
714 * That structure's lock must be held upon entry, and it is released
718 cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp,
720 __releases(rnp->lock)
722 struct rcu_node *rnp_c;
724 /* Walk up the rcu_node hierarchy. */
726 if (!(rnp->qsmask & mask)) {
728 /* Our bit has already been cleared, so done. */
729 spin_unlock_irqrestore(&rnp->lock, flags);
732 rnp->qsmask &= ~mask;
733 if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
735 /* Other bits still set at this level, so done. */
736 spin_unlock_irqrestore(&rnp->lock, flags);
740 if (rnp->parent == NULL) {
742 /* No more levels. Exit loop holding root lock. */
746 spin_unlock_irqrestore(&rnp->lock, flags);
749 spin_lock_irqsave(&rnp->lock, flags);
750 WARN_ON_ONCE(rnp_c->qsmask);
754 * Get here if we are the last CPU to pass through a quiescent
755 * state for this grace period. Invoke cpu_quiet_msk_finish()
756 * to clean up and start the next grace period if one is needed.
758 cpu_quiet_msk_finish(rsp, flags); /* releases rnp->lock. */
762 * Record a quiescent state for the specified CPU, which must either be
763 * the current CPU. The lastcomp argument is used to make sure we are
764 * still in the grace period of interest. We don't want to end the current
765 * grace period based on quiescent states detected in an earlier grace
769 cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
773 struct rcu_node *rnp;
776 spin_lock_irqsave(&rnp->lock, flags);
777 if (lastcomp != ACCESS_ONCE(rsp->completed)) {
780 * Someone beat us to it for this grace period, so leave.
781 * The race with GP start is resolved by the fact that we
782 * hold the leaf rcu_node lock, so that the per-CPU bits
783 * cannot yet be initialized -- so we would simply find our
784 * CPU's bit already cleared in cpu_quiet_msk() if this race
787 rdp->passed_quiesc = 0; /* try again later! */
788 spin_unlock_irqrestore(&rnp->lock, flags);
792 if ((rnp->qsmask & mask) == 0) {
793 spin_unlock_irqrestore(&rnp->lock, flags);
798 * This GP can't end until cpu checks in, so all of our
799 * callbacks can be processed during the next GP.
801 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
803 cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */
808 * Check to see if there is a new grace period of which this CPU
809 * is not yet aware, and if so, set up local rcu_data state for it.
810 * Otherwise, see if this CPU has just passed through its first
811 * quiescent state for this grace period, and record that fact if so.
814 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
816 /* If there is now a new grace period, record and return. */
817 if (check_for_new_grace_period(rsp, rdp))
821 * Does this CPU still need to do its part for current grace period?
822 * If no, return and let the other CPUs do their part as well.
824 if (!rdp->qs_pending)
828 * Was there a quiescent state since the beginning of the grace
829 * period? If no, then exit and wait for the next call.
831 if (!rdp->passed_quiesc)
834 /* Tell RCU we are done (but cpu_quiet() will be the judge of that). */
835 cpu_quiet(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
838 #ifdef CONFIG_HOTPLUG_CPU
841 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
842 * and move all callbacks from the outgoing CPU to the current one.
844 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
850 struct rcu_data *rdp = rsp->rda[cpu];
851 struct rcu_data *rdp_me;
852 struct rcu_node *rnp;
854 /* Exclude any attempts to start a new grace period. */
855 spin_lock_irqsave(&rsp->onofflock, flags);
857 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
858 rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
859 mask = rdp->grpmask; /* rnp->grplo is constant. */
861 spin_lock(&rnp->lock); /* irqs already disabled. */
862 rnp->qsmaskinit &= ~mask;
863 if (rnp->qsmaskinit != 0) {
864 spin_unlock(&rnp->lock); /* irqs remain disabled. */
867 rcu_preempt_offline_tasks(rsp, rnp, rdp);
869 spin_unlock(&rnp->lock); /* irqs remain disabled. */
871 } while (rnp != NULL);
872 lastcomp = rsp->completed;
874 spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
877 * Move callbacks from the outgoing CPU to the running CPU.
878 * Note that the outgoing CPU is now quiescent, so it is now
879 * (uncharacteristically) safe to access its rcu_data structure.
880 * Note also that we must carefully retain the order of the
881 * outgoing CPU's callbacks in order for rcu_barrier() to work
882 * correctly. Finally, note that we start all the callbacks
883 * afresh, even those that have passed through a grace period
884 * and are therefore ready to invoke. The theory is that hotplug
885 * events are rare, and that if they are frequent enough to
886 * indefinitely delay callbacks, you have far worse things to
889 if (rdp->nxtlist != NULL) {
890 rdp_me = rsp->rda[smp_processor_id()];
891 *rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
892 rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
894 for (i = 0; i < RCU_NEXT_SIZE; i++)
895 rdp->nxttail[i] = &rdp->nxtlist;
896 rdp_me->qlen += rdp->qlen;
899 local_irq_restore(flags);
903 * Remove the specified CPU from the RCU hierarchy and move any pending
904 * callbacks that it might have to the current CPU. This code assumes
905 * that at least one CPU in the system will remain running at all times.
906 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
908 static void rcu_offline_cpu(int cpu)
910 __rcu_offline_cpu(cpu, &rcu_sched_state);
911 __rcu_offline_cpu(cpu, &rcu_bh_state);
912 rcu_preempt_offline_cpu(cpu);
915 #else /* #ifdef CONFIG_HOTPLUG_CPU */
917 static void rcu_offline_cpu(int cpu)
921 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
924 * Invoke any RCU callbacks that have made it to the end of their grace
925 * period. Thottle as specified by rdp->blimit.
927 static void rcu_do_batch(struct rcu_data *rdp)
930 struct rcu_head *next, *list, **tail;
933 /* If no callbacks are ready, just return.*/
934 if (!cpu_has_callbacks_ready_to_invoke(rdp))
938 * Extract the list of ready callbacks, disabling to prevent
939 * races with call_rcu() from interrupt handlers.
941 local_irq_save(flags);
943 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
944 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
945 tail = rdp->nxttail[RCU_DONE_TAIL];
946 for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
947 if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
948 rdp->nxttail[count] = &rdp->nxtlist;
949 local_irq_restore(flags);
951 /* Invoke callbacks. */
958 if (++count >= rdp->blimit)
962 local_irq_save(flags);
964 /* Update count, and requeue any remaining callbacks. */
967 *tail = rdp->nxtlist;
969 for (count = 0; count < RCU_NEXT_SIZE; count++)
970 if (&rdp->nxtlist == rdp->nxttail[count])
971 rdp->nxttail[count] = tail;
976 /* Reinstate batch limit if we have worked down the excess. */
977 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
978 rdp->blimit = blimit;
980 local_irq_restore(flags);
982 /* Re-raise the RCU softirq if there are callbacks remaining. */
983 if (cpu_has_callbacks_ready_to_invoke(rdp))
984 raise_softirq(RCU_SOFTIRQ);
988 * Check to see if this CPU is in a non-context-switch quiescent state
989 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
990 * Also schedule the RCU softirq handler.
992 * This function must be called with hardirqs disabled. It is normally
993 * invoked from the scheduling-clock interrupt. If rcu_pending returns
994 * false, there is no point in invoking rcu_check_callbacks().
996 void rcu_check_callbacks(int cpu, int user)
998 if (!rcu_pending(cpu))
999 return; /* if nothing for RCU to do. */
1001 (idle_cpu(cpu) && rcu_scheduler_active &&
1002 !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1005 * Get here if this CPU took its interrupt from user
1006 * mode or from the idle loop, and if this is not a
1007 * nested interrupt. In this case, the CPU is in
1008 * a quiescent state, so note it.
1010 * No memory barrier is required here because both
1011 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1012 * variables that other CPUs neither access nor modify,
1013 * at least not while the corresponding CPU is online.
1019 } else if (!in_softirq()) {
1022 * Get here if this CPU did not take its interrupt from
1023 * softirq, in other words, if it is not interrupting
1024 * a rcu_bh read-side critical section. This is an _bh
1025 * critical section, so note it.
1030 rcu_preempt_check_callbacks(cpu);
1031 raise_softirq(RCU_SOFTIRQ);
1037 * Scan the leaf rcu_node structures, processing dyntick state for any that
1038 * have not yet encountered a quiescent state, using the function specified.
1039 * Returns 1 if the current grace period ends while scanning (possibly
1040 * because we made it end).
1042 static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
1043 int (*f)(struct rcu_data *))
1047 unsigned long flags;
1049 struct rcu_node *rnp;
1051 rcu_for_each_leaf_node(rsp, rnp) {
1053 spin_lock_irqsave(&rnp->lock, flags);
1054 if (rsp->completed != lastcomp) {
1055 spin_unlock_irqrestore(&rnp->lock, flags);
1058 if (rnp->qsmask == 0) {
1059 spin_unlock_irqrestore(&rnp->lock, flags);
1064 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1065 if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
1068 if (mask != 0 && rsp->completed == lastcomp) {
1070 /* cpu_quiet_msk() releases rnp->lock. */
1071 cpu_quiet_msk(mask, rsp, rnp, flags);
1074 spin_unlock_irqrestore(&rnp->lock, flags);
1080 * Force quiescent states on reluctant CPUs, and also detect which
1081 * CPUs are in dyntick-idle mode.
1083 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1085 unsigned long flags;
1087 struct rcu_node *rnp = rcu_get_root(rsp);
1090 if (!rcu_gp_in_progress(rsp))
1091 return; /* No grace period in progress, nothing to force. */
1092 if (!spin_trylock_irqsave(&rsp->fqslock, flags)) {
1093 rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1094 return; /* Someone else is already on the job. */
1097 (long)(rsp->jiffies_force_qs - jiffies) >= 0)
1098 goto unlock_ret; /* no emergency and done recently. */
1100 spin_lock(&rnp->lock);
1101 lastcomp = rsp->completed;
1102 signaled = rsp->signaled;
1103 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1104 if (lastcomp == rsp->gpnum) {
1105 rsp->n_force_qs_ngp++;
1106 spin_unlock(&rnp->lock);
1107 goto unlock_ret; /* no GP in progress, time updated. */
1109 spin_unlock(&rnp->lock);
1113 break; /* grace period still initializing, ignore. */
1115 case RCU_SAVE_DYNTICK:
1117 if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1118 break; /* So gcc recognizes the dead code. */
1120 /* Record dyntick-idle state. */
1121 if (rcu_process_dyntick(rsp, lastcomp,
1122 dyntick_save_progress_counter))
1125 /* Update state, record completion counter. */
1126 spin_lock(&rnp->lock);
1127 if (lastcomp == rsp->completed) {
1128 rsp->signaled = RCU_FORCE_QS;
1129 dyntick_record_completed(rsp, lastcomp);
1131 spin_unlock(&rnp->lock);
1136 /* Check dyntick-idle state, send IPI to laggarts. */
1137 if (rcu_process_dyntick(rsp, dyntick_recall_completed(rsp),
1138 rcu_implicit_dynticks_qs))
1141 /* Leave state in case more forcing is required. */
1146 spin_unlock_irqrestore(&rsp->fqslock, flags);
1149 #else /* #ifdef CONFIG_SMP */
1151 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1156 #endif /* #else #ifdef CONFIG_SMP */
1159 * This does the RCU processing work from softirq context for the
1160 * specified rcu_state and rcu_data structures. This may be called
1161 * only from the CPU to whom the rdp belongs.
1164 __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1166 unsigned long flags;
1168 WARN_ON_ONCE(rdp->beenonline == 0);
1171 * If an RCU GP has gone long enough, go check for dyntick
1172 * idle CPUs and, if needed, send resched IPIs.
1174 if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
1175 force_quiescent_state(rsp, 1);
1178 * Advance callbacks in response to end of earlier grace
1179 * period that some other CPU ended.
1181 rcu_process_gp_end(rsp, rdp);
1183 /* Update RCU state based on any recent quiescent states. */
1184 rcu_check_quiescent_state(rsp, rdp);
1186 /* Does this CPU require a not-yet-started grace period? */
1187 if (cpu_needs_another_gp(rsp, rdp)) {
1188 spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1189 rcu_start_gp(rsp, flags); /* releases above lock */
1192 /* If there are callbacks ready, invoke them. */
1197 * Do softirq processing for the current CPU.
1199 static void rcu_process_callbacks(struct softirq_action *unused)
1202 * Memory references from any prior RCU read-side critical sections
1203 * executed by the interrupted code must be seen before any RCU
1204 * grace-period manipulations below.
1206 smp_mb(); /* See above block comment. */
1208 __rcu_process_callbacks(&rcu_sched_state,
1209 &__get_cpu_var(rcu_sched_data));
1210 __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1211 rcu_preempt_process_callbacks();
1214 * Memory references from any later RCU read-side critical sections
1215 * executed by the interrupted code must be seen after any RCU
1216 * grace-period manipulations above.
1218 smp_mb(); /* See above block comment. */
1222 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1223 struct rcu_state *rsp)
1225 unsigned long flags;
1226 struct rcu_data *rdp;
1231 smp_mb(); /* Ensure RCU update seen before callback registry. */
1234 * Opportunistically note grace-period endings and beginnings.
1235 * Note that we might see a beginning right after we see an
1236 * end, but never vice versa, since this CPU has to pass through
1237 * a quiescent state betweentimes.
1239 local_irq_save(flags);
1240 rdp = rsp->rda[smp_processor_id()];
1241 rcu_process_gp_end(rsp, rdp);
1242 check_for_new_grace_period(rsp, rdp);
1244 /* Add the callback to our list. */
1245 *rdp->nxttail[RCU_NEXT_TAIL] = head;
1246 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1248 /* Start a new grace period if one not already started. */
1249 if (!rcu_gp_in_progress(rsp)) {
1250 unsigned long nestflag;
1251 struct rcu_node *rnp_root = rcu_get_root(rsp);
1253 spin_lock_irqsave(&rnp_root->lock, nestflag);
1254 rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */
1257 /* Force the grace period if too many callbacks or too long waiting. */
1258 if (unlikely(++rdp->qlen > qhimark)) {
1259 rdp->blimit = LONG_MAX;
1260 force_quiescent_state(rsp, 0);
1261 } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)
1262 force_quiescent_state(rsp, 1);
1263 local_irq_restore(flags);
1267 * Queue an RCU-sched callback for invocation after a grace period.
1269 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1271 __call_rcu(head, func, &rcu_sched_state);
1273 EXPORT_SYMBOL_GPL(call_rcu_sched);
1276 * Queue an RCU for invocation after a quicker grace period.
1278 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1280 __call_rcu(head, func, &rcu_bh_state);
1282 EXPORT_SYMBOL_GPL(call_rcu_bh);
1285 * Check to see if there is any immediate RCU-related work to be done
1286 * by the current CPU, for the specified type of RCU, returning 1 if so.
1287 * The checks are in order of increasing expense: checks that can be
1288 * carried out against CPU-local state are performed first. However,
1289 * we must check for CPU stalls first, else we might not get a chance.
1291 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1293 rdp->n_rcu_pending++;
1295 /* Check for CPU stalls, if enabled. */
1296 check_cpu_stall(rsp, rdp);
1298 /* Is the RCU core waiting for a quiescent state from this CPU? */
1299 if (rdp->qs_pending) {
1300 rdp->n_rp_qs_pending++;
1304 /* Does this CPU have callbacks ready to invoke? */
1305 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1306 rdp->n_rp_cb_ready++;
1310 /* Has RCU gone idle with this CPU needing another grace period? */
1311 if (cpu_needs_another_gp(rsp, rdp)) {
1312 rdp->n_rp_cpu_needs_gp++;
1316 /* Has another RCU grace period completed? */
1317 if (ACCESS_ONCE(rsp->completed) != rdp->completed) { /* outside lock */
1318 rdp->n_rp_gp_completed++;
1322 /* Has a new RCU grace period started? */
1323 if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) { /* outside lock */
1324 rdp->n_rp_gp_started++;
1328 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1329 if (rcu_gp_in_progress(rsp) &&
1330 ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0)) {
1331 rdp->n_rp_need_fqs++;
1336 rdp->n_rp_need_nothing++;
1341 * Check to see if there is any immediate RCU-related work to be done
1342 * by the current CPU, returning 1 if so. This function is part of the
1343 * RCU implementation; it is -not- an exported member of the RCU API.
1345 static int rcu_pending(int cpu)
1347 return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1348 __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1349 rcu_preempt_pending(cpu);
1353 * Check to see if any future RCU-related work will need to be done
1354 * by the current CPU, even if none need be done immediately, returning
1355 * 1 if so. This function is part of the RCU implementation; it is -not-
1356 * an exported member of the RCU API.
1358 int rcu_needs_cpu(int cpu)
1360 /* RCU callbacks either ready or pending? */
1361 return per_cpu(rcu_sched_data, cpu).nxtlist ||
1362 per_cpu(rcu_bh_data, cpu).nxtlist ||
1363 rcu_preempt_needs_cpu(cpu);
1366 static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
1367 static atomic_t rcu_barrier_cpu_count;
1368 static DEFINE_MUTEX(rcu_barrier_mutex);
1369 static struct completion rcu_barrier_completion;
1370 static atomic_t rcu_migrate_type_count = ATOMIC_INIT(0);
1371 static struct rcu_head rcu_migrate_head[3];
1372 static DECLARE_WAIT_QUEUE_HEAD(rcu_migrate_wq);
1374 static void rcu_barrier_callback(struct rcu_head *notused)
1376 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1377 complete(&rcu_barrier_completion);
1381 * Called with preemption disabled, and from cross-cpu IRQ context.
1383 static void rcu_barrier_func(void *type)
1385 int cpu = smp_processor_id();
1386 struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
1387 void (*call_rcu_func)(struct rcu_head *head,
1388 void (*func)(struct rcu_head *head));
1390 atomic_inc(&rcu_barrier_cpu_count);
1391 call_rcu_func = type;
1392 call_rcu_func(head, rcu_barrier_callback);
1395 static inline void wait_migrated_callbacks(void)
1397 wait_event(rcu_migrate_wq, !atomic_read(&rcu_migrate_type_count));
1398 smp_mb(); /* In case we didn't sleep. */
1402 * Orchestrate the specified type of RCU barrier, waiting for all
1403 * RCU callbacks of the specified type to complete.
1405 static void _rcu_barrier(void (*call_rcu_func)(struct rcu_head *head,
1406 void (*func)(struct rcu_head *head)))
1408 BUG_ON(in_interrupt());
1409 /* Take cpucontrol mutex to protect against CPU hotplug */
1410 mutex_lock(&rcu_barrier_mutex);
1411 init_completion(&rcu_barrier_completion);
1413 * Initialize rcu_barrier_cpu_count to 1, then invoke
1414 * rcu_barrier_func() on each CPU, so that each CPU also has
1415 * incremented rcu_barrier_cpu_count. Only then is it safe to
1416 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1417 * might complete its grace period before all of the other CPUs
1418 * did their increment, causing this function to return too
1421 atomic_set(&rcu_barrier_cpu_count, 1);
1422 on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
1423 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1424 complete(&rcu_barrier_completion);
1425 wait_for_completion(&rcu_barrier_completion);
1426 mutex_unlock(&rcu_barrier_mutex);
1427 wait_migrated_callbacks();
1431 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
1433 void rcu_barrier(void)
1435 _rcu_barrier(call_rcu);
1437 EXPORT_SYMBOL_GPL(rcu_barrier);
1440 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1442 void rcu_barrier_bh(void)
1444 _rcu_barrier(call_rcu_bh);
1446 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
1449 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1451 void rcu_barrier_sched(void)
1453 _rcu_barrier(call_rcu_sched);
1455 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
1457 static void rcu_migrate_callback(struct rcu_head *notused)
1459 if (atomic_dec_and_test(&rcu_migrate_type_count))
1460 wake_up(&rcu_migrate_wq);
1464 * Do boot-time initialization of a CPU's per-CPU RCU data.
1467 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1469 unsigned long flags;
1471 struct rcu_data *rdp = rsp->rda[cpu];
1472 struct rcu_node *rnp = rcu_get_root(rsp);
1474 /* Set up local state, ensuring consistent view of global state. */
1475 spin_lock_irqsave(&rnp->lock, flags);
1476 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1477 rdp->nxtlist = NULL;
1478 for (i = 0; i < RCU_NEXT_SIZE; i++)
1479 rdp->nxttail[i] = &rdp->nxtlist;
1482 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1483 #endif /* #ifdef CONFIG_NO_HZ */
1485 spin_unlock_irqrestore(&rnp->lock, flags);
1489 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1490 * offline event can be happening at a given time. Note also that we
1491 * can accept some slop in the rsp->completed access due to the fact
1492 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1494 static void __cpuinit
1495 rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
1497 unsigned long flags;
1500 struct rcu_data *rdp = rsp->rda[cpu];
1501 struct rcu_node *rnp = rcu_get_root(rsp);
1503 /* Set up local state, ensuring consistent view of global state. */
1504 spin_lock_irqsave(&rnp->lock, flags);
1505 lastcomp = rsp->completed;
1506 rdp->completed = lastcomp;
1507 rdp->gpnum = lastcomp;
1508 rdp->passed_quiesc = 0; /* We could be racing with new GP, */
1509 rdp->qs_pending = 1; /* so set up to respond to current GP. */
1510 rdp->beenonline = 1; /* We have now been online. */
1511 rdp->preemptable = preemptable;
1512 rdp->passed_quiesc_completed = lastcomp - 1;
1513 rdp->blimit = blimit;
1514 spin_unlock(&rnp->lock); /* irqs remain disabled. */
1517 * A new grace period might start here. If so, we won't be part
1518 * of it, but that is OK, as we are currently in a quiescent state.
1521 /* Exclude any attempts to start a new GP on large systems. */
1522 spin_lock(&rsp->onofflock); /* irqs already disabled. */
1524 /* Add CPU to rcu_node bitmasks. */
1526 mask = rdp->grpmask;
1528 /* Exclude any attempts to start a new GP on small systems. */
1529 spin_lock(&rnp->lock); /* irqs already disabled. */
1530 rnp->qsmaskinit |= mask;
1531 mask = rnp->grpmask;
1532 spin_unlock(&rnp->lock); /* irqs already disabled. */
1534 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1536 spin_unlock_irqrestore(&rsp->onofflock, flags);
1539 static void __cpuinit rcu_online_cpu(int cpu)
1541 rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1542 rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1543 rcu_preempt_init_percpu_data(cpu);
1547 * Handle CPU online/offline notification events.
1549 int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1550 unsigned long action, void *hcpu)
1552 long cpu = (long)hcpu;
1555 case CPU_UP_PREPARE:
1556 case CPU_UP_PREPARE_FROZEN:
1557 rcu_online_cpu(cpu);
1559 case CPU_DOWN_PREPARE:
1560 case CPU_DOWN_PREPARE_FROZEN:
1561 /* Don't need to wait until next removal operation. */
1562 /* rcu_migrate_head is protected by cpu_add_remove_lock */
1563 wait_migrated_callbacks();
1566 case CPU_DYING_FROZEN:
1568 * preempt_disable() in on_each_cpu() prevents stop_machine(),
1569 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
1570 * returns, all online cpus have queued rcu_barrier_func(),
1571 * and the dead cpu(if it exist) queues rcu_migrate_callback()s.
1573 * These callbacks ensure _rcu_barrier() waits for all
1574 * RCU callbacks of the specified type to complete.
1576 atomic_set(&rcu_migrate_type_count, 3);
1577 call_rcu_bh(rcu_migrate_head, rcu_migrate_callback);
1578 call_rcu_sched(rcu_migrate_head + 1, rcu_migrate_callback);
1579 call_rcu(rcu_migrate_head + 2, rcu_migrate_callback);
1582 case CPU_DEAD_FROZEN:
1583 case CPU_UP_CANCELED:
1584 case CPU_UP_CANCELED_FROZEN:
1585 rcu_offline_cpu(cpu);
1594 * Compute the per-level fanout, either using the exact fanout specified
1595 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1597 #ifdef CONFIG_RCU_FANOUT_EXACT
1598 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1602 for (i = NUM_RCU_LVLS - 1; i >= 0; i--)
1603 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1605 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1606 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1613 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1614 ccur = rsp->levelcnt[i];
1615 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1619 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1622 * Helper function for rcu_init() that initializes one rcu_state structure.
1624 static void __init rcu_init_one(struct rcu_state *rsp)
1629 struct rcu_node *rnp;
1631 /* Initialize the level-tracking arrays. */
1633 for (i = 1; i < NUM_RCU_LVLS; i++)
1634 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1635 rcu_init_levelspread(rsp);
1637 /* Initialize the elements themselves, starting from the leaves. */
1639 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1640 cpustride *= rsp->levelspread[i];
1641 rnp = rsp->level[i];
1642 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1643 spin_lock_init(&rnp->lock);
1646 rnp->qsmaskinit = 0;
1647 rnp->grplo = j * cpustride;
1648 rnp->grphi = (j + 1) * cpustride - 1;
1649 if (rnp->grphi >= NR_CPUS)
1650 rnp->grphi = NR_CPUS - 1;
1656 rnp->grpnum = j % rsp->levelspread[i - 1];
1657 rnp->grpmask = 1UL << rnp->grpnum;
1658 rnp->parent = rsp->level[i - 1] +
1659 j / rsp->levelspread[i - 1];
1662 INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
1663 INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
1669 * Helper macro for __rcu_init() and __rcu_init_preempt(). To be used
1670 * nowhere else! Assigns leaf node pointers into each CPU's rcu_data
1673 #define RCU_INIT_FLAVOR(rsp, rcu_data) \
1677 struct rcu_node *rnp; \
1679 rcu_init_one(rsp); \
1680 rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
1682 for_each_possible_cpu(i) { \
1683 if (i > rnp[j].grphi) \
1685 per_cpu(rcu_data, i).mynode = &rnp[j]; \
1686 (rsp)->rda[i] = &per_cpu(rcu_data, i); \
1687 rcu_boot_init_percpu_data(i, rsp); \
1691 void __init __rcu_init(void)
1693 rcu_bootup_announce();
1694 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
1695 printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
1696 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
1697 RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data);
1698 RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data);
1699 __rcu_init_preempt();
1700 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1703 #include "rcutree_plugin.h"