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 <asm/atomic.h>
39 #include <linux/bitops.h>
40 #include <linux/module.h>
41 #include <linux/completion.h>
42 #include <linux/moduleparam.h>
43 #include <linux/percpu.h>
44 #include <linux/notifier.h>
45 #include <linux/cpu.h>
46 #include <linux/mutex.h>
47 #include <linux/time.h>
49 #ifdef CONFIG_DEBUG_LOCK_ALLOC
50 static struct lock_class_key rcu_lock_key;
51 struct lockdep_map rcu_lock_map =
52 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
53 EXPORT_SYMBOL_GPL(rcu_lock_map);
56 /* Data structures. */
58 #define RCU_STATE_INITIALIZER(name) { \
59 .level = { &name.node[0] }, \
61 NUM_RCU_LVL_0, /* root of hierarchy. */ \
64 NUM_RCU_LVL_3, /* == MAX_RCU_LVLS */ \
66 .signaled = RCU_SIGNAL_INIT, \
69 .onofflock = __SPIN_LOCK_UNLOCKED(&name.onofflock), \
70 .fqslock = __SPIN_LOCK_UNLOCKED(&name.fqslock), \
72 .n_force_qs_ngp = 0, \
75 struct rcu_state rcu_state = RCU_STATE_INITIALIZER(rcu_state);
76 DEFINE_PER_CPU(struct rcu_data, rcu_data);
78 struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
79 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
82 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
83 .dynticks_nesting = 1,
86 #endif /* #ifdef CONFIG_NO_HZ */
88 static int blimit = 10; /* Maximum callbacks per softirq. */
89 static int qhimark = 10000; /* If this many pending, ignore blimit. */
90 static int qlowmark = 100; /* Once only this many pending, use blimit. */
92 static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
95 * Return the number of RCU batches processed thus far for debug & stats.
97 long rcu_batches_completed(void)
99 return rcu_state.completed;
101 EXPORT_SYMBOL_GPL(rcu_batches_completed);
104 * Return the number of RCU BH batches processed thus far for debug & stats.
106 long rcu_batches_completed_bh(void)
108 return rcu_bh_state.completed;
110 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
113 * Does the CPU have callbacks ready to be invoked?
116 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
118 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
122 * Does the current CPU require a yet-as-unscheduled grace period?
125 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
127 /* ACCESS_ONCE() because we are accessing outside of lock. */
128 return *rdp->nxttail[RCU_DONE_TAIL] &&
129 ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum);
133 * Return the root node of the specified rcu_state structure.
135 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
137 return &rsp->node[0];
143 * If the specified CPU is offline, tell the caller that it is in
144 * a quiescent state. Otherwise, whack it with a reschedule IPI.
145 * Grace periods can end up waiting on an offline CPU when that
146 * CPU is in the process of coming online -- it will be added to the
147 * rcu_node bitmasks before it actually makes it online. The same thing
148 * can happen while a CPU is in the process of coming online. Because this
149 * race is quite rare, we check for it after detecting that the grace
150 * period has been delayed rather than checking each and every CPU
151 * each and every time we start a new grace period.
153 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
156 * If the CPU is offline, it is in a quiescent state. We can
157 * trust its state not to change because interrupts are disabled.
159 if (cpu_is_offline(rdp->cpu)) {
164 /* The CPU is online, so send it a reschedule IPI. */
165 if (rdp->cpu != smp_processor_id())
166 smp_send_reschedule(rdp->cpu);
173 #endif /* #ifdef CONFIG_SMP */
176 static DEFINE_RATELIMIT_STATE(rcu_rs, 10 * HZ, 5);
179 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
181 * Enter nohz mode, in other words, -leave- the mode in which RCU
182 * read-side critical sections can occur. (Though RCU read-side
183 * critical sections can occur in irq handlers in nohz mode, a possibility
184 * handled by rcu_irq_enter() and rcu_irq_exit()).
186 void rcu_enter_nohz(void)
189 struct rcu_dynticks *rdtp;
191 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
192 local_irq_save(flags);
193 rdtp = &__get_cpu_var(rcu_dynticks);
195 rdtp->dynticks_nesting--;
196 WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);
197 local_irq_restore(flags);
201 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
203 * Exit nohz mode, in other words, -enter- the mode in which RCU
204 * read-side critical sections normally occur.
206 void rcu_exit_nohz(void)
209 struct rcu_dynticks *rdtp;
211 local_irq_save(flags);
212 rdtp = &__get_cpu_var(rcu_dynticks);
214 rdtp->dynticks_nesting++;
215 WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs);
216 local_irq_restore(flags);
217 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
221 * rcu_nmi_enter - inform RCU of entry to NMI context
223 * If the CPU was idle with dynamic ticks active, and there is no
224 * irq handler running, this updates rdtp->dynticks_nmi to let the
225 * RCU grace-period handling know that the CPU is active.
227 void rcu_nmi_enter(void)
229 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
231 if (rdtp->dynticks & 0x1)
233 rdtp->dynticks_nmi++;
234 WARN_ON_RATELIMIT(!(rdtp->dynticks_nmi & 0x1), &rcu_rs);
235 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
239 * rcu_nmi_exit - inform RCU of exit from NMI context
241 * If the CPU was idle with dynamic ticks active, and there is no
242 * irq handler running, this updates rdtp->dynticks_nmi to let the
243 * RCU grace-period handling know that the CPU is no longer active.
245 void rcu_nmi_exit(void)
247 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
249 if (rdtp->dynticks & 0x1)
251 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
252 rdtp->dynticks_nmi++;
253 WARN_ON_RATELIMIT(rdtp->dynticks_nmi & 0x1, &rcu_rs);
257 * rcu_irq_enter - inform RCU of entry to hard irq context
259 * If the CPU was idle with dynamic ticks active, this updates the
260 * rdtp->dynticks to let the RCU handling know that the CPU is active.
262 void rcu_irq_enter(void)
264 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
266 if (rdtp->dynticks_nesting++)
269 WARN_ON_RATELIMIT(!(rdtp->dynticks & 0x1), &rcu_rs);
270 smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
274 * rcu_irq_exit - inform RCU of exit from hard irq context
276 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
277 * to put let the RCU handling be aware that the CPU is going back to idle
280 void rcu_irq_exit(void)
282 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
284 if (--rdtp->dynticks_nesting)
286 smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
288 WARN_ON_RATELIMIT(rdtp->dynticks & 0x1, &rcu_rs);
290 /* If the interrupt queued a callback, get out of dyntick mode. */
291 if (__get_cpu_var(rcu_data).nxtlist ||
292 __get_cpu_var(rcu_bh_data).nxtlist)
297 * Record the specified "completed" value, which is later used to validate
298 * dynticks counter manipulations. Specify "rsp->completed - 1" to
299 * unconditionally invalidate any future dynticks manipulations (which is
300 * useful at the beginning of a grace period).
302 static void dyntick_record_completed(struct rcu_state *rsp, long comp)
304 rsp->dynticks_completed = comp;
310 * Recall the previously recorded value of the completion for dynticks.
312 static long dyntick_recall_completed(struct rcu_state *rsp)
314 return rsp->dynticks_completed;
318 * Snapshot the specified CPU's dynticks counter so that we can later
319 * credit them with an implicit quiescent state. Return 1 if this CPU
320 * is already in a quiescent state courtesy of dynticks idle mode.
322 static int dyntick_save_progress_counter(struct rcu_data *rdp)
328 snap = rdp->dynticks->dynticks;
329 snap_nmi = rdp->dynticks->dynticks_nmi;
330 smp_mb(); /* Order sampling of snap with end of grace period. */
331 rdp->dynticks_snap = snap;
332 rdp->dynticks_nmi_snap = snap_nmi;
333 ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
340 * Return true if the specified CPU has passed through a quiescent
341 * state by virtue of being in or having passed through an dynticks
342 * idle state since the last call to dyntick_save_progress_counter()
345 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
352 curr = rdp->dynticks->dynticks;
353 snap = rdp->dynticks_snap;
354 curr_nmi = rdp->dynticks->dynticks_nmi;
355 snap_nmi = rdp->dynticks_nmi_snap;
356 smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
359 * If the CPU passed through or entered a dynticks idle phase with
360 * no active irq/NMI handlers, then we can safely pretend that the CPU
361 * already acknowledged the request to pass through a quiescent
362 * state. Either way, that CPU cannot possibly be in an RCU
363 * read-side critical section that started before the beginning
364 * of the current RCU grace period.
366 if ((curr != snap || (curr & 0x1) == 0) &&
367 (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
372 /* Go check for the CPU being offline. */
373 return rcu_implicit_offline_qs(rdp);
376 #endif /* #ifdef CONFIG_SMP */
378 #else /* #ifdef CONFIG_NO_HZ */
380 static void dyntick_record_completed(struct rcu_state *rsp, long comp)
387 * If there are no dynticks, then the only way that a CPU can passively
388 * be in a quiescent state is to be offline. Unlike dynticks idle, which
389 * is a point in time during the prior (already finished) grace period,
390 * an offline CPU is always in a quiescent state, and thus can be
391 * unconditionally applied. So just return the current value of completed.
393 static long dyntick_recall_completed(struct rcu_state *rsp)
395 return rsp->completed;
398 static int dyntick_save_progress_counter(struct rcu_data *rdp)
403 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
405 return rcu_implicit_offline_qs(rdp);
408 #endif /* #ifdef CONFIG_SMP */
410 #endif /* #else #ifdef CONFIG_NO_HZ */
412 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
414 static void record_gp_stall_check_time(struct rcu_state *rsp)
416 rsp->gp_start = jiffies;
417 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
420 static void print_other_cpu_stall(struct rcu_state *rsp)
425 struct rcu_node *rnp = rcu_get_root(rsp);
426 struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
427 struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];
429 /* Only let one CPU complain about others per time interval. */
431 spin_lock_irqsave(&rnp->lock, flags);
432 delta = jiffies - rsp->jiffies_stall;
433 if (delta < RCU_STALL_RAT_DELAY || rsp->gpnum == rsp->completed) {
434 spin_unlock_irqrestore(&rnp->lock, flags);
437 rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
438 spin_unlock_irqrestore(&rnp->lock, flags);
440 /* OK, time to rat on our buddy... */
442 printk(KERN_ERR "INFO: RCU detected CPU stalls:");
443 for (; rnp_cur < rnp_end; rnp_cur++) {
444 if (rnp_cur->qsmask == 0)
446 for (cpu = 0; cpu <= rnp_cur->grphi - rnp_cur->grplo; cpu++)
447 if (rnp_cur->qsmask & (1UL << cpu))
448 printk(" %d", rnp_cur->grplo + cpu);
450 printk(" (detected by %d, t=%ld jiffies)\n",
451 smp_processor_id(), (long)(jiffies - rsp->gp_start));
452 force_quiescent_state(rsp, 0); /* Kick them all. */
455 static void print_cpu_stall(struct rcu_state *rsp)
458 struct rcu_node *rnp = rcu_get_root(rsp);
460 printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu jiffies)\n",
461 smp_processor_id(), jiffies - rsp->gp_start);
463 spin_lock_irqsave(&rnp->lock, flags);
464 if ((long)(jiffies - rsp->jiffies_stall) >= 0)
466 jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
467 spin_unlock_irqrestore(&rnp->lock, flags);
468 set_need_resched(); /* kick ourselves to get things going. */
471 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
474 struct rcu_node *rnp;
476 delta = jiffies - rsp->jiffies_stall;
478 if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
480 /* We haven't checked in, so go dump stack. */
481 print_cpu_stall(rsp);
483 } else if (rsp->gpnum != rsp->completed &&
484 delta >= RCU_STALL_RAT_DELAY) {
486 /* They had two time units to dump stack, so complain. */
487 print_other_cpu_stall(rsp);
491 #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
493 static void record_gp_stall_check_time(struct rcu_state *rsp)
497 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
501 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
504 * Update CPU-local rcu_data state to record the newly noticed grace period.
505 * This is used both when we started the grace period and when we notice
506 * that someone else started the grace period.
508 static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
511 rdp->passed_quiesc = 0;
512 rdp->gpnum = rsp->gpnum;
513 rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
514 RCU_JIFFIES_TILL_FORCE_QS;
518 * Did someone else start a new RCU grace period start since we last
519 * checked? Update local state appropriately if so. Must be called
520 * on the CPU corresponding to rdp.
523 check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
528 local_irq_save(flags);
529 if (rdp->gpnum != rsp->gpnum) {
530 note_new_gpnum(rsp, rdp);
533 local_irq_restore(flags);
538 * Start a new RCU grace period if warranted, re-initializing the hierarchy
539 * in preparation for detecting the next grace period. The caller must hold
540 * the root node's ->lock, which is released before return. Hard irqs must
544 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
545 __releases(rcu_get_root(rsp)->lock)
547 struct rcu_data *rdp = rsp->rda[smp_processor_id()];
548 struct rcu_node *rnp = rcu_get_root(rsp);
549 struct rcu_node *rnp_cur;
550 struct rcu_node *rnp_end;
552 if (!cpu_needs_another_gp(rsp, rdp)) {
553 spin_unlock_irqrestore(&rnp->lock, flags);
557 /* Advance to a new grace period and initialize state. */
559 rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
560 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
561 rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
562 RCU_JIFFIES_TILL_FORCE_QS;
563 record_gp_stall_check_time(rsp);
564 dyntick_record_completed(rsp, rsp->completed - 1);
565 note_new_gpnum(rsp, rdp);
568 * Because we are first, we know that all our callbacks will
569 * be covered by this upcoming grace period, even the ones
570 * that were registered arbitrarily recently.
572 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
573 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
575 /* Special-case the common single-level case. */
576 if (NUM_RCU_NODES == 1) {
577 rnp->qsmask = rnp->qsmaskinit;
578 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
579 spin_unlock_irqrestore(&rnp->lock, flags);
583 spin_unlock(&rnp->lock); /* leave irqs disabled. */
586 /* Exclude any concurrent CPU-hotplug operations. */
587 spin_lock(&rsp->onofflock); /* irqs already disabled. */
590 * Set the quiescent-state-needed bits in all the non-leaf RCU
591 * nodes for all currently online CPUs. This operation relies
592 * on the layout of the hierarchy within the rsp->node[] array.
593 * Note that other CPUs will access only the leaves of the
594 * hierarchy, which still indicate that no grace period is in
595 * progress. In addition, we have excluded CPU-hotplug operations.
597 * We therefore do not need to hold any locks. Any required
598 * memory barriers will be supplied by the locks guarding the
599 * leaf rcu_nodes in the hierarchy.
602 rnp_end = rsp->level[NUM_RCU_LVLS - 1];
603 for (rnp_cur = &rsp->node[0]; rnp_cur < rnp_end; rnp_cur++)
604 rnp_cur->qsmask = rnp_cur->qsmaskinit;
607 * Now set up the leaf nodes. Here we must be careful. First,
608 * we need to hold the lock in order to exclude other CPUs, which
609 * might be contending for the leaf nodes' locks. Second, as
610 * soon as we initialize a given leaf node, its CPUs might run
611 * up the rest of the hierarchy. We must therefore acquire locks
612 * for each node that we touch during this stage. (But we still
613 * are excluding CPU-hotplug operations.)
615 * Note that the grace period cannot complete until we finish
616 * the initialization process, as there will be at least one
617 * qsmask bit set in the root node until that time, namely the
618 * one corresponding to this CPU.
620 rnp_end = &rsp->node[NUM_RCU_NODES];
621 rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
622 for (; rnp_cur < rnp_end; rnp_cur++) {
623 spin_lock(&rnp_cur->lock); /* irqs already disabled. */
624 rnp_cur->qsmask = rnp_cur->qsmaskinit;
625 spin_unlock(&rnp_cur->lock); /* irqs already disabled. */
628 rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
629 spin_unlock_irqrestore(&rsp->onofflock, flags);
633 * Advance this CPU's callbacks, but only if the current grace period
634 * has ended. This may be called only from the CPU to whom the rdp
638 rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
643 local_irq_save(flags);
644 completed_snap = ACCESS_ONCE(rsp->completed); /* outside of lock. */
646 /* Did another grace period end? */
647 if (rdp->completed != completed_snap) {
649 /* Advance callbacks. No harm if list empty. */
650 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
651 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
652 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
654 /* Remember that we saw this grace-period completion. */
655 rdp->completed = completed_snap;
657 local_irq_restore(flags);
661 * Similar to cpu_quiet(), for which it is a helper function. Allows
662 * a group of CPUs to be quieted at one go, though all the CPUs in the
663 * group must be represented by the same leaf rcu_node structure.
664 * That structure's lock must be held upon entry, and it is released
668 cpu_quiet_msk(unsigned long mask, struct rcu_state *rsp, struct rcu_node *rnp,
670 __releases(rnp->lock)
672 /* Walk up the rcu_node hierarchy. */
674 if (!(rnp->qsmask & mask)) {
676 /* Our bit has already been cleared, so done. */
677 spin_unlock_irqrestore(&rnp->lock, flags);
680 rnp->qsmask &= ~mask;
681 if (rnp->qsmask != 0) {
683 /* Other bits still set at this level, so done. */
684 spin_unlock_irqrestore(&rnp->lock, flags);
688 if (rnp->parent == NULL) {
690 /* No more levels. Exit loop holding root lock. */
694 spin_unlock_irqrestore(&rnp->lock, flags);
696 spin_lock_irqsave(&rnp->lock, flags);
700 * Get here if we are the last CPU to pass through a quiescent
701 * state for this grace period. Clean up and let rcu_start_gp()
702 * start up the next grace period if one is needed. Note that
703 * we still hold rnp->lock, as required by rcu_start_gp(), which
706 rsp->completed = rsp->gpnum;
707 rcu_process_gp_end(rsp, rsp->rda[smp_processor_id()]);
708 rcu_start_gp(rsp, flags); /* releases rnp->lock. */
712 * Record a quiescent state for the specified CPU, which must either be
713 * the current CPU or an offline CPU. The lastcomp argument is used to
714 * make sure we are still in the grace period of interest. We don't want
715 * to end the current grace period based on quiescent states detected in
716 * an earlier grace period!
719 cpu_quiet(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
723 struct rcu_node *rnp;
726 spin_lock_irqsave(&rnp->lock, flags);
727 if (lastcomp != ACCESS_ONCE(rsp->completed)) {
730 * Someone beat us to it for this grace period, so leave.
731 * The race with GP start is resolved by the fact that we
732 * hold the leaf rcu_node lock, so that the per-CPU bits
733 * cannot yet be initialized -- so we would simply find our
734 * CPU's bit already cleared in cpu_quiet_msk() if this race
737 rdp->passed_quiesc = 0; /* try again later! */
738 spin_unlock_irqrestore(&rnp->lock, flags);
742 if ((rnp->qsmask & mask) == 0) {
743 spin_unlock_irqrestore(&rnp->lock, flags);
748 * This GP can't end until cpu checks in, so all of our
749 * callbacks can be processed during the next GP.
751 rdp = rsp->rda[smp_processor_id()];
752 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
754 cpu_quiet_msk(mask, rsp, rnp, flags); /* releases rnp->lock */
759 * Check to see if there is a new grace period of which this CPU
760 * is not yet aware, and if so, set up local rcu_data state for it.
761 * Otherwise, see if this CPU has just passed through its first
762 * quiescent state for this grace period, and record that fact if so.
765 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
767 /* If there is now a new grace period, record and return. */
768 if (check_for_new_grace_period(rsp, rdp))
772 * Does this CPU still need to do its part for current grace period?
773 * If no, return and let the other CPUs do their part as well.
775 if (!rdp->qs_pending)
779 * Was there a quiescent state since the beginning of the grace
780 * period? If no, then exit and wait for the next call.
782 if (!rdp->passed_quiesc)
785 /* Tell RCU we are done (but cpu_quiet() will be the judge of that). */
786 cpu_quiet(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
789 #ifdef CONFIG_HOTPLUG_CPU
792 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
793 * and move all callbacks from the outgoing CPU to the current one.
795 static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
801 struct rcu_data *rdp = rsp->rda[cpu];
802 struct rcu_data *rdp_me;
803 struct rcu_node *rnp;
805 /* Exclude any attempts to start a new grace period. */
806 spin_lock_irqsave(&rsp->onofflock, flags);
808 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
810 mask = rdp->grpmask; /* rnp->grplo is constant. */
812 spin_lock(&rnp->lock); /* irqs already disabled. */
813 rnp->qsmaskinit &= ~mask;
814 if (rnp->qsmaskinit != 0) {
815 spin_unlock(&rnp->lock); /* irqs already disabled. */
819 spin_unlock(&rnp->lock); /* irqs already disabled. */
821 } while (rnp != NULL);
822 lastcomp = rsp->completed;
824 spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
826 /* Being offline is a quiescent state, so go record it. */
827 cpu_quiet(cpu, rsp, rdp, lastcomp);
830 * Move callbacks from the outgoing CPU to the running CPU.
831 * Note that the outgoing CPU is now quiscent, so it is now
832 * (uncharacteristically) safe to access it rcu_data structure.
833 * Note also that we must carefully retain the order of the
834 * outgoing CPU's callbacks in order for rcu_barrier() to work
835 * correctly. Finally, note that we start all the callbacks
836 * afresh, even those that have passed through a grace period
837 * and are therefore ready to invoke. The theory is that hotplug
838 * events are rare, and that if they are frequent enough to
839 * indefinitely delay callbacks, you have far worse things to
842 rdp_me = rsp->rda[smp_processor_id()];
843 if (rdp->nxtlist != NULL) {
844 *rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
845 rdp_me->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
847 for (i = 0; i < RCU_NEXT_SIZE; i++)
848 rdp->nxttail[i] = &rdp->nxtlist;
849 rdp_me->qlen += rdp->qlen;
852 local_irq_restore(flags);
856 * Remove the specified CPU from the RCU hierarchy and move any pending
857 * callbacks that it might have to the current CPU. This code assumes
858 * that at least one CPU in the system will remain running at all times.
859 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
861 static void rcu_offline_cpu(int cpu)
863 __rcu_offline_cpu(cpu, &rcu_state);
864 __rcu_offline_cpu(cpu, &rcu_bh_state);
867 #else /* #ifdef CONFIG_HOTPLUG_CPU */
869 static void rcu_offline_cpu(int cpu)
873 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
876 * Invoke any RCU callbacks that have made it to the end of their grace
877 * period. Thottle as specified by rdp->blimit.
879 static void rcu_do_batch(struct rcu_data *rdp)
882 struct rcu_head *next, *list, **tail;
885 /* If no callbacks are ready, just return.*/
886 if (!cpu_has_callbacks_ready_to_invoke(rdp))
890 * Extract the list of ready callbacks, disabling to prevent
891 * races with call_rcu() from interrupt handlers.
893 local_irq_save(flags);
895 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
896 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
897 tail = rdp->nxttail[RCU_DONE_TAIL];
898 for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
899 if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
900 rdp->nxttail[count] = &rdp->nxtlist;
901 local_irq_restore(flags);
903 /* Invoke callbacks. */
910 if (++count >= rdp->blimit)
914 local_irq_save(flags);
916 /* Update count, and requeue any remaining callbacks. */
919 *tail = rdp->nxtlist;
921 for (count = 0; count < RCU_NEXT_SIZE; count++)
922 if (&rdp->nxtlist == rdp->nxttail[count])
923 rdp->nxttail[count] = tail;
928 /* Reinstate batch limit if we have worked down the excess. */
929 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
930 rdp->blimit = blimit;
932 local_irq_restore(flags);
934 /* Re-raise the RCU softirq if there are callbacks remaining. */
935 if (cpu_has_callbacks_ready_to_invoke(rdp))
936 raise_softirq(RCU_SOFTIRQ);
940 * Check to see if this CPU is in a non-context-switch quiescent state
941 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
942 * Also schedule the RCU softirq handler.
944 * This function must be called with hardirqs disabled. It is normally
945 * invoked from the scheduling-clock interrupt. If rcu_pending returns
946 * false, there is no point in invoking rcu_check_callbacks().
948 void rcu_check_callbacks(int cpu, int user)
951 (idle_cpu(cpu) && rcu_scheduler_active &&
952 !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
955 * Get here if this CPU took its interrupt from user
956 * mode or from the idle loop, and if this is not a
957 * nested interrupt. In this case, the CPU is in
958 * a quiescent state, so count it.
960 * No memory barrier is required here because both
961 * rcu_qsctr_inc() and rcu_bh_qsctr_inc() reference
962 * only CPU-local variables that other CPUs neither
963 * access nor modify, at least not while the corresponding
968 rcu_bh_qsctr_inc(cpu);
970 } else if (!in_softirq()) {
973 * Get here if this CPU did not take its interrupt from
974 * softirq, in other words, if it is not interrupting
975 * a rcu_bh read-side critical section. This is an _bh
976 * critical section, so count it.
979 rcu_bh_qsctr_inc(cpu);
981 raise_softirq(RCU_SOFTIRQ);
987 * Scan the leaf rcu_node structures, processing dyntick state for any that
988 * have not yet encountered a quiescent state, using the function specified.
989 * Returns 1 if the current grace period ends while scanning (possibly
990 * because we made it end).
992 static int rcu_process_dyntick(struct rcu_state *rsp, long lastcomp,
993 int (*f)(struct rcu_data *))
999 struct rcu_node *rnp_cur = rsp->level[NUM_RCU_LVLS - 1];
1000 struct rcu_node *rnp_end = &rsp->node[NUM_RCU_NODES];
1002 for (; rnp_cur < rnp_end; rnp_cur++) {
1004 spin_lock_irqsave(&rnp_cur->lock, flags);
1005 if (rsp->completed != lastcomp) {
1006 spin_unlock_irqrestore(&rnp_cur->lock, flags);
1009 if (rnp_cur->qsmask == 0) {
1010 spin_unlock_irqrestore(&rnp_cur->lock, flags);
1013 cpu = rnp_cur->grplo;
1015 for (; cpu <= rnp_cur->grphi; cpu++, bit <<= 1) {
1016 if ((rnp_cur->qsmask & bit) != 0 && f(rsp->rda[cpu]))
1019 if (mask != 0 && rsp->completed == lastcomp) {
1021 /* cpu_quiet_msk() releases rnp_cur->lock. */
1022 cpu_quiet_msk(mask, rsp, rnp_cur, flags);
1025 spin_unlock_irqrestore(&rnp_cur->lock, flags);
1031 * Force quiescent states on reluctant CPUs, and also detect which
1032 * CPUs are in dyntick-idle mode.
1034 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1036 unsigned long flags;
1038 struct rcu_data *rdp = rsp->rda[smp_processor_id()];
1039 struct rcu_node *rnp = rcu_get_root(rsp);
1042 if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum))
1043 return; /* No grace period in progress, nothing to force. */
1044 if (!spin_trylock_irqsave(&rsp->fqslock, flags)) {
1045 rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1046 return; /* Someone else is already on the job. */
1049 (long)(rsp->jiffies_force_qs - jiffies) >= 0 &&
1050 (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) >= 0)
1051 goto unlock_ret; /* no emergency and done recently. */
1053 spin_lock(&rnp->lock);
1054 lastcomp = rsp->completed;
1055 signaled = rsp->signaled;
1056 rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1057 rdp->n_rcu_pending_force_qs = rdp->n_rcu_pending +
1058 RCU_JIFFIES_TILL_FORCE_QS;
1059 if (lastcomp == rsp->gpnum) {
1060 rsp->n_force_qs_ngp++;
1061 spin_unlock(&rnp->lock);
1062 goto unlock_ret; /* no GP in progress, time updated. */
1064 spin_unlock(&rnp->lock);
1068 break; /* grace period still initializing, ignore. */
1070 case RCU_SAVE_DYNTICK:
1072 if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1073 break; /* So gcc recognizes the dead code. */
1075 /* Record dyntick-idle state. */
1076 if (rcu_process_dyntick(rsp, lastcomp,
1077 dyntick_save_progress_counter))
1080 /* Update state, record completion counter. */
1081 spin_lock(&rnp->lock);
1082 if (lastcomp == rsp->completed) {
1083 rsp->signaled = RCU_FORCE_QS;
1084 dyntick_record_completed(rsp, lastcomp);
1086 spin_unlock(&rnp->lock);
1091 /* Check dyntick-idle state, send IPI to laggarts. */
1092 if (rcu_process_dyntick(rsp, dyntick_recall_completed(rsp),
1093 rcu_implicit_dynticks_qs))
1096 /* Leave state in case more forcing is required. */
1101 spin_unlock_irqrestore(&rsp->fqslock, flags);
1104 #else /* #ifdef CONFIG_SMP */
1106 static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1111 #endif /* #else #ifdef CONFIG_SMP */
1114 * This does the RCU processing work from softirq context for the
1115 * specified rcu_state and rcu_data structures. This may be called
1116 * only from the CPU to whom the rdp belongs.
1119 __rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1121 unsigned long flags;
1124 * If an RCU GP has gone long enough, go check for dyntick
1125 * idle CPUs and, if needed, send resched IPIs.
1127 if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0 ||
1128 (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) < 0)
1129 force_quiescent_state(rsp, 1);
1132 * Advance callbacks in response to end of earlier grace
1133 * period that some other CPU ended.
1135 rcu_process_gp_end(rsp, rdp);
1137 /* Update RCU state based on any recent quiescent states. */
1138 rcu_check_quiescent_state(rsp, rdp);
1140 /* Does this CPU require a not-yet-started grace period? */
1141 if (cpu_needs_another_gp(rsp, rdp)) {
1142 spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1143 rcu_start_gp(rsp, flags); /* releases above lock */
1146 /* If there are callbacks ready, invoke them. */
1151 * Do softirq processing for the current CPU.
1153 static void rcu_process_callbacks(struct softirq_action *unused)
1156 * Memory references from any prior RCU read-side critical sections
1157 * executed by the interrupted code must be seen before any RCU
1158 * grace-period manipulations below.
1160 smp_mb(); /* See above block comment. */
1162 __rcu_process_callbacks(&rcu_state, &__get_cpu_var(rcu_data));
1163 __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1166 * Memory references from any later RCU read-side critical sections
1167 * executed by the interrupted code must be seen after any RCU
1168 * grace-period manipulations above.
1170 smp_mb(); /* See above block comment. */
1174 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1175 struct rcu_state *rsp)
1177 unsigned long flags;
1178 struct rcu_data *rdp;
1183 smp_mb(); /* Ensure RCU update seen before callback registry. */
1186 * Opportunistically note grace-period endings and beginnings.
1187 * Note that we might see a beginning right after we see an
1188 * end, but never vice versa, since this CPU has to pass through
1189 * a quiescent state betweentimes.
1191 local_irq_save(flags);
1192 rdp = rsp->rda[smp_processor_id()];
1193 rcu_process_gp_end(rsp, rdp);
1194 check_for_new_grace_period(rsp, rdp);
1196 /* Add the callback to our list. */
1197 *rdp->nxttail[RCU_NEXT_TAIL] = head;
1198 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1200 /* Start a new grace period if one not already started. */
1201 if (ACCESS_ONCE(rsp->completed) == ACCESS_ONCE(rsp->gpnum)) {
1202 unsigned long nestflag;
1203 struct rcu_node *rnp_root = rcu_get_root(rsp);
1205 spin_lock_irqsave(&rnp_root->lock, nestflag);
1206 rcu_start_gp(rsp, nestflag); /* releases rnp_root->lock. */
1209 /* Force the grace period if too many callbacks or too long waiting. */
1210 if (unlikely(++rdp->qlen > qhimark)) {
1211 rdp->blimit = LONG_MAX;
1212 force_quiescent_state(rsp, 0);
1213 } else if ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0 ||
1214 (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) < 0)
1215 force_quiescent_state(rsp, 1);
1216 local_irq_restore(flags);
1220 * Queue an RCU callback for invocation after a grace period.
1222 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1224 __call_rcu(head, func, &rcu_state);
1226 EXPORT_SYMBOL_GPL(call_rcu);
1229 * Queue an RCU for invocation after a quicker grace period.
1231 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1233 __call_rcu(head, func, &rcu_bh_state);
1235 EXPORT_SYMBOL_GPL(call_rcu_bh);
1238 * Check to see if there is any immediate RCU-related work to be done
1239 * by the current CPU, for the specified type of RCU, returning 1 if so.
1240 * The checks are in order of increasing expense: checks that can be
1241 * carried out against CPU-local state are performed first. However,
1242 * we must check for CPU stalls first, else we might not get a chance.
1244 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1246 rdp->n_rcu_pending++;
1248 /* Check for CPU stalls, if enabled. */
1249 check_cpu_stall(rsp, rdp);
1251 /* Is the RCU core waiting for a quiescent state from this CPU? */
1252 if (rdp->qs_pending)
1255 /* Does this CPU have callbacks ready to invoke? */
1256 if (cpu_has_callbacks_ready_to_invoke(rdp))
1259 /* Has RCU gone idle with this CPU needing another grace period? */
1260 if (cpu_needs_another_gp(rsp, rdp))
1263 /* Has another RCU grace period completed? */
1264 if (ACCESS_ONCE(rsp->completed) != rdp->completed) /* outside of lock */
1267 /* Has a new RCU grace period started? */
1268 if (ACCESS_ONCE(rsp->gpnum) != rdp->gpnum) /* outside of lock */
1271 /* Has an RCU GP gone long enough to send resched IPIs &c? */
1272 if (ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum) &&
1273 ((long)(ACCESS_ONCE(rsp->jiffies_force_qs) - jiffies) < 0 ||
1274 (rdp->n_rcu_pending_force_qs - rdp->n_rcu_pending) < 0))
1282 * Check to see if there is any immediate RCU-related work to be done
1283 * by the current CPU, returning 1 if so. This function is part of the
1284 * RCU implementation; it is -not- an exported member of the RCU API.
1286 int rcu_pending(int cpu)
1288 return __rcu_pending(&rcu_state, &per_cpu(rcu_data, cpu)) ||
1289 __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu));
1293 * Check to see if any future RCU-related work will need to be done
1294 * by the current CPU, even if none need be done immediately, returning
1295 * 1 if so. This function is part of the RCU implementation; it is -not-
1296 * an exported member of the RCU API.
1298 int rcu_needs_cpu(int cpu)
1300 /* RCU callbacks either ready or pending? */
1301 return per_cpu(rcu_data, cpu).nxtlist ||
1302 per_cpu(rcu_bh_data, cpu).nxtlist;
1306 * Initialize a CPU's per-CPU RCU data. We take this "scorched earth"
1307 * approach so that we don't have to worry about how long the CPU has
1308 * been gone, or whether it ever was online previously. We do trust the
1309 * ->mynode field, as it is constant for a given struct rcu_data and
1310 * initialized during early boot.
1312 * Note that only one online or offline event can be happening at a given
1313 * time. Note also that we can accept some slop in the rsp->completed
1314 * access due to the fact that this CPU cannot possibly have any RCU
1315 * callbacks in flight yet.
1317 static void __cpuinit
1318 rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
1320 unsigned long flags;
1324 struct rcu_data *rdp = rsp->rda[cpu];
1325 struct rcu_node *rnp = rcu_get_root(rsp);
1327 /* Set up local state, ensuring consistent view of global state. */
1328 spin_lock_irqsave(&rnp->lock, flags);
1329 lastcomp = rsp->completed;
1330 rdp->completed = lastcomp;
1331 rdp->gpnum = lastcomp;
1332 rdp->passed_quiesc = 0; /* We could be racing with new GP, */
1333 rdp->qs_pending = 1; /* so set up to respond to current GP. */
1334 rdp->beenonline = 1; /* We have now been online. */
1335 rdp->passed_quiesc_completed = lastcomp - 1;
1336 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1337 rdp->nxtlist = NULL;
1338 for (i = 0; i < RCU_NEXT_SIZE; i++)
1339 rdp->nxttail[i] = &rdp->nxtlist;
1341 rdp->blimit = blimit;
1343 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1344 #endif /* #ifdef CONFIG_NO_HZ */
1346 spin_unlock(&rnp->lock); /* irqs remain disabled. */
1349 * A new grace period might start here. If so, we won't be part
1350 * of it, but that is OK, as we are currently in a quiescent state.
1353 /* Exclude any attempts to start a new GP on large systems. */
1354 spin_lock(&rsp->onofflock); /* irqs already disabled. */
1356 /* Add CPU to rcu_node bitmasks. */
1358 mask = rdp->grpmask;
1360 /* Exclude any attempts to start a new GP on small systems. */
1361 spin_lock(&rnp->lock); /* irqs already disabled. */
1362 rnp->qsmaskinit |= mask;
1363 mask = rnp->grpmask;
1364 spin_unlock(&rnp->lock); /* irqs already disabled. */
1366 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1368 spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
1371 * A new grace period might start here. If so, we will be part of
1372 * it, and its gpnum will be greater than ours, so we will
1373 * participate. It is also possible for the gpnum to have been
1374 * incremented before this function was called, and the bitmasks
1375 * to not be filled out until now, in which case we will also
1376 * participate due to our gpnum being behind.
1379 /* Since it is coming online, the CPU is in a quiescent state. */
1380 cpu_quiet(cpu, rsp, rdp, lastcomp);
1381 local_irq_restore(flags);
1384 static void __cpuinit rcu_online_cpu(int cpu)
1386 rcu_init_percpu_data(cpu, &rcu_state);
1387 rcu_init_percpu_data(cpu, &rcu_bh_state);
1388 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1392 * Handle CPU online/offline notifcation events.
1394 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1395 unsigned long action, void *hcpu)
1397 long cpu = (long)hcpu;
1400 case CPU_UP_PREPARE:
1401 case CPU_UP_PREPARE_FROZEN:
1402 rcu_online_cpu(cpu);
1405 case CPU_DEAD_FROZEN:
1406 case CPU_UP_CANCELED:
1407 case CPU_UP_CANCELED_FROZEN:
1408 rcu_offline_cpu(cpu);
1417 * Compute the per-level fanout, either using the exact fanout specified
1418 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1420 #ifdef CONFIG_RCU_FANOUT_EXACT
1421 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1425 for (i = NUM_RCU_LVLS - 1; i >= 0; i--)
1426 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1428 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1429 static void __init rcu_init_levelspread(struct rcu_state *rsp)
1436 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1437 ccur = rsp->levelcnt[i];
1438 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1442 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1445 * Helper function for rcu_init() that initializes one rcu_state structure.
1447 static void __init rcu_init_one(struct rcu_state *rsp)
1452 struct rcu_node *rnp;
1454 /* Initialize the level-tracking arrays. */
1456 for (i = 1; i < NUM_RCU_LVLS; i++)
1457 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1458 rcu_init_levelspread(rsp);
1460 /* Initialize the elements themselves, starting from the leaves. */
1462 for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1463 cpustride *= rsp->levelspread[i];
1464 rnp = rsp->level[i];
1465 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1466 spin_lock_init(&rnp->lock);
1468 rnp->qsmaskinit = 0;
1469 rnp->grplo = j * cpustride;
1470 rnp->grphi = (j + 1) * cpustride - 1;
1471 if (rnp->grphi >= NR_CPUS)
1472 rnp->grphi = NR_CPUS - 1;
1478 rnp->grpnum = j % rsp->levelspread[i - 1];
1479 rnp->grpmask = 1UL << rnp->grpnum;
1480 rnp->parent = rsp->level[i - 1] +
1481 j / rsp->levelspread[i - 1];
1489 * Helper macro for __rcu_init(). To be used nowhere else!
1490 * Assigns leaf node pointers into each CPU's rcu_data structure.
1492 #define RCU_DATA_PTR_INIT(rsp, rcu_data) \
1494 rnp = (rsp)->level[NUM_RCU_LVLS - 1]; \
1496 for_each_possible_cpu(i) { \
1497 if (i > rnp[j].grphi) \
1499 per_cpu(rcu_data, i).mynode = &rnp[j]; \
1500 (rsp)->rda[i] = &per_cpu(rcu_data, i); \
1504 static struct notifier_block __cpuinitdata rcu_nb = {
1505 .notifier_call = rcu_cpu_notify,
1508 void __init __rcu_init(void)
1510 int i; /* All used by RCU_DATA_PTR_INIT(). */
1512 struct rcu_node *rnp;
1514 printk(KERN_WARNING "Experimental hierarchical RCU implementation.\n");
1515 #ifdef CONFIG_RCU_CPU_STALL_DETECTOR
1516 printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n");
1517 #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
1518 rcu_init_one(&rcu_state);
1519 RCU_DATA_PTR_INIT(&rcu_state, rcu_data);
1520 rcu_init_one(&rcu_bh_state);
1521 RCU_DATA_PTR_INIT(&rcu_bh_state, rcu_bh_data);
1523 for_each_online_cpu(i)
1524 rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)i);
1525 /* Register notifier for non-boot CPUs */
1526 register_cpu_notifier(&rcu_nb);
1527 printk(KERN_WARNING "Experimental hierarchical RCU init done.\n");
1530 module_param(blimit, int, 0);
1531 module_param(qhimark, int, 0);
1532 module_param(qlowmark, int, 0);