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1/*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
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.
8 *
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.
13 *
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.
17 *
18 * Copyright IBM Corporation, 2008
19 *
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
23 *
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 *
27 * For detailed explanation of Read-Copy Update mechanism see -
28 *	Documentation/RCU
29 */
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>
50
51#include "rcutree.h"
52
53/* Data structures. */
54
55static struct lock_class_key rcu_node_class[NUM_RCU_LVLS];
56
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	.orphan_cbs_list = NULL, \
71	.orphan_cbs_tail = &structname.orphan_cbs_list, \
72	.orphan_qlen = 0, \
73	.fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \
74	.n_force_qs = 0, \
75	.n_force_qs_ngp = 0, \
76	.name = #structname, \
77}
78
79struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
80DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
81
82struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
83DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
84
85int rcu_scheduler_active __read_mostly;
86EXPORT_SYMBOL_GPL(rcu_scheduler_active);
87
88/*
89 * Return true if an RCU grace period is in progress.  The ACCESS_ONCE()s
90 * permit this function to be invoked without holding the root rcu_node
91 * structure's ->lock, but of course results can be subject to change.
92 */
93static int rcu_gp_in_progress(struct rcu_state *rsp)
94{
95	return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
96}
97
98/*
99 * Note a quiescent state.  Because we do not need to know
100 * how many quiescent states passed, just if there was at least
101 * one since the start of the grace period, this just sets a flag.
102 */
103void rcu_sched_qs(int cpu)
104{
105	struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
106
107	rdp->passed_quiesc_completed = rdp->gpnum - 1;
108	barrier();
109	rdp->passed_quiesc = 1;
110}
111
112void rcu_bh_qs(int cpu)
113{
114	struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
115
116	rdp->passed_quiesc_completed = rdp->gpnum - 1;
117	barrier();
118	rdp->passed_quiesc = 1;
119}
120
121/*
122 * Note a context switch.  This is a quiescent state for RCU-sched,
123 * and requires special handling for preemptible RCU.
124 */
125void rcu_note_context_switch(int cpu)
126{
127	rcu_sched_qs(cpu);
128	rcu_preempt_note_context_switch(cpu);
129}
130
131#ifdef CONFIG_NO_HZ
132DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
133	.dynticks_nesting = 1,
134	.dynticks = 1,
135};
136#endif /* #ifdef CONFIG_NO_HZ */
137
138static int blimit = 10;		/* Maximum callbacks per softirq. */
139static int qhimark = 10000;	/* If this many pending, ignore blimit. */
140static int qlowmark = 100;	/* Once only this many pending, use blimit. */
141
142module_param(blimit, int, 0);
143module_param(qhimark, int, 0);
144module_param(qlowmark, int, 0);
145
146static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
147static int rcu_pending(int cpu);
148
149/*
150 * Return the number of RCU-sched batches processed thus far for debug & stats.
151 */
152long rcu_batches_completed_sched(void)
153{
154	return rcu_sched_state.completed;
155}
156EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
157
158/*
159 * Return the number of RCU BH batches processed thus far for debug & stats.
160 */
161long rcu_batches_completed_bh(void)
162{
163	return rcu_bh_state.completed;
164}
165EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
166
167/*
168 * Force a quiescent state for RCU BH.
169 */
170void rcu_bh_force_quiescent_state(void)
171{
172	force_quiescent_state(&rcu_bh_state, 0);
173}
174EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
175
176/*
177 * Force a quiescent state for RCU-sched.
178 */
179void rcu_sched_force_quiescent_state(void)
180{
181	force_quiescent_state(&rcu_sched_state, 0);
182}
183EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
184
185/*
186 * Does the CPU have callbacks ready to be invoked?
187 */
188static int
189cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
190{
191	return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
192}
193
194/*
195 * Does the current CPU require a yet-as-unscheduled grace period?
196 */
197static int
198cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
199{
200	return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
201}
202
203/*
204 * Return the root node of the specified rcu_state structure.
205 */
206static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
207{
208	return &rsp->node[0];
209}
210
211#ifdef CONFIG_SMP
212
213/*
214 * If the specified CPU is offline, tell the caller that it is in
215 * a quiescent state.  Otherwise, whack it with a reschedule IPI.
216 * Grace periods can end up waiting on an offline CPU when that
217 * CPU is in the process of coming online -- it will be added to the
218 * rcu_node bitmasks before it actually makes it online.  The same thing
219 * can happen while a CPU is in the process of coming online.  Because this
220 * race is quite rare, we check for it after detecting that the grace
221 * period has been delayed rather than checking each and every CPU
222 * each and every time we start a new grace period.
223 */
224static int rcu_implicit_offline_qs(struct rcu_data *rdp)
225{
226	/*
227	 * If the CPU is offline, it is in a quiescent state.  We can
228	 * trust its state not to change because interrupts are disabled.
229	 */
230	if (cpu_is_offline(rdp->cpu)) {
231		rdp->offline_fqs++;
232		return 1;
233	}
234
235	/* If preemptable RCU, no point in sending reschedule IPI. */
236	if (rdp->preemptable)
237		return 0;
238
239	/* The CPU is online, so send it a reschedule IPI. */
240	if (rdp->cpu != smp_processor_id())
241		smp_send_reschedule(rdp->cpu);
242	else
243		set_need_resched();
244	rdp->resched_ipi++;
245	return 0;
246}
247
248#endif /* #ifdef CONFIG_SMP */
249
250#ifdef CONFIG_NO_HZ
251
252/**
253 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
254 *
255 * Enter nohz mode, in other words, -leave- the mode in which RCU
256 * read-side critical sections can occur.  (Though RCU read-side
257 * critical sections can occur in irq handlers in nohz mode, a possibility
258 * handled by rcu_irq_enter() and rcu_irq_exit()).
259 */
260void rcu_enter_nohz(void)
261{
262	unsigned long flags;
263	struct rcu_dynticks *rdtp;
264
265	smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
266	local_irq_save(flags);
267	rdtp = &__get_cpu_var(rcu_dynticks);
268	rdtp->dynticks++;
269	rdtp->dynticks_nesting--;
270	WARN_ON_ONCE(rdtp->dynticks & 0x1);
271	local_irq_restore(flags);
272}
273
274/*
275 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
276 *
277 * Exit nohz mode, in other words, -enter- the mode in which RCU
278 * read-side critical sections normally occur.
279 */
280void rcu_exit_nohz(void)
281{
282	unsigned long flags;
283	struct rcu_dynticks *rdtp;
284
285	local_irq_save(flags);
286	rdtp = &__get_cpu_var(rcu_dynticks);
287	rdtp->dynticks++;
288	rdtp->dynticks_nesting++;
289	WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
290	local_irq_restore(flags);
291	smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
292}
293
294/**
295 * rcu_nmi_enter - inform RCU of entry to NMI context
296 *
297 * If the CPU was idle with dynamic ticks active, and there is no
298 * irq handler running, this updates rdtp->dynticks_nmi to let the
299 * RCU grace-period handling know that the CPU is active.
300 */
301void rcu_nmi_enter(void)
302{
303	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
304
305	if (rdtp->dynticks & 0x1)
306		return;
307	rdtp->dynticks_nmi++;
308	WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
309	smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
310}
311
312/**
313 * rcu_nmi_exit - inform RCU of exit from NMI context
314 *
315 * If the CPU was idle with dynamic ticks active, and there is no
316 * irq handler running, this updates rdtp->dynticks_nmi to let the
317 * RCU grace-period handling know that the CPU is no longer active.
318 */
319void rcu_nmi_exit(void)
320{
321	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
322
323	if (rdtp->dynticks & 0x1)
324		return;
325	smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
326	rdtp->dynticks_nmi++;
327	WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
328}
329
330/**
331 * rcu_irq_enter - inform RCU of entry to hard irq context
332 *
333 * If the CPU was idle with dynamic ticks active, this updates the
334 * rdtp->dynticks to let the RCU handling know that the CPU is active.
335 */
336void rcu_irq_enter(void)
337{
338	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
339
340	if (rdtp->dynticks_nesting++)
341		return;
342	rdtp->dynticks++;
343	WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
344	smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
345}
346
347/**
348 * rcu_irq_exit - inform RCU of exit from hard irq context
349 *
350 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
351 * to put let the RCU handling be aware that the CPU is going back to idle
352 * with no ticks.
353 */
354void rcu_irq_exit(void)
355{
356	struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
357
358	if (--rdtp->dynticks_nesting)
359		return;
360	smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
361	rdtp->dynticks++;
362	WARN_ON_ONCE(rdtp->dynticks & 0x1);
363
364	/* If the interrupt queued a callback, get out of dyntick mode. */
365	if (__get_cpu_var(rcu_sched_data).nxtlist ||
366	    __get_cpu_var(rcu_bh_data).nxtlist)
367		set_need_resched();
368}
369
370#ifdef CONFIG_SMP
371
372/*
373 * Snapshot the specified CPU's dynticks counter so that we can later
374 * credit them with an implicit quiescent state.  Return 1 if this CPU
375 * is in dynticks idle mode, which is an extended quiescent state.
376 */
377static int dyntick_save_progress_counter(struct rcu_data *rdp)
378{
379	int ret;
380	int snap;
381	int snap_nmi;
382
383	snap = rdp->dynticks->dynticks;
384	snap_nmi = rdp->dynticks->dynticks_nmi;
385	smp_mb();	/* Order sampling of snap with end of grace period. */
386	rdp->dynticks_snap = snap;
387	rdp->dynticks_nmi_snap = snap_nmi;
388	ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
389	if (ret)
390		rdp->dynticks_fqs++;
391	return ret;
392}
393
394/*
395 * Return true if the specified CPU has passed through a quiescent
396 * state by virtue of being in or having passed through an dynticks
397 * idle state since the last call to dyntick_save_progress_counter()
398 * for this same CPU.
399 */
400static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
401{
402	long curr;
403	long curr_nmi;
404	long snap;
405	long snap_nmi;
406
407	curr = rdp->dynticks->dynticks;
408	snap = rdp->dynticks_snap;
409	curr_nmi = rdp->dynticks->dynticks_nmi;
410	snap_nmi = rdp->dynticks_nmi_snap;
411	smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
412
413	/*
414	 * If the CPU passed through or entered a dynticks idle phase with
415	 * no active irq/NMI handlers, then we can safely pretend that the CPU
416	 * already acknowledged the request to pass through a quiescent
417	 * state.  Either way, that CPU cannot possibly be in an RCU
418	 * read-side critical section that started before the beginning
419	 * of the current RCU grace period.
420	 */
421	if ((curr != snap || (curr & 0x1) == 0) &&
422	    (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
423		rdp->dynticks_fqs++;
424		return 1;
425	}
426
427	/* Go check for the CPU being offline. */
428	return rcu_implicit_offline_qs(rdp);
429}
430
431#endif /* #ifdef CONFIG_SMP */
432
433#else /* #ifdef CONFIG_NO_HZ */
434
435#ifdef CONFIG_SMP
436
437static int dyntick_save_progress_counter(struct rcu_data *rdp)
438{
439	return 0;
440}
441
442static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
443{
444	return rcu_implicit_offline_qs(rdp);
445}
446
447#endif /* #ifdef CONFIG_SMP */
448
449#endif /* #else #ifdef CONFIG_NO_HZ */
450
451#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
452
453int rcu_cpu_stall_panicking __read_mostly;
454
455static void record_gp_stall_check_time(struct rcu_state *rsp)
456{
457	rsp->gp_start = jiffies;
458	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
459}
460
461static void print_other_cpu_stall(struct rcu_state *rsp)
462{
463	int cpu;
464	long delta;
465	unsigned long flags;
466	struct rcu_node *rnp = rcu_get_root(rsp);
467
468	/* Only let one CPU complain about others per time interval. */
469
470	raw_spin_lock_irqsave(&rnp->lock, flags);
471	delta = jiffies - rsp->jiffies_stall;
472	if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
473		raw_spin_unlock_irqrestore(&rnp->lock, flags);
474		return;
475	}
476	rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
477
478	/*
479	 * Now rat on any tasks that got kicked up to the root rcu_node
480	 * due to CPU offlining.
481	 */
482	rcu_print_task_stall(rnp);
483	raw_spin_unlock_irqrestore(&rnp->lock, flags);
484
485	/* OK, time to rat on our buddy... */
486
487	printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
488	       rsp->name);
489	rcu_for_each_leaf_node(rsp, rnp) {
490		raw_spin_lock_irqsave(&rnp->lock, flags);
491		rcu_print_task_stall(rnp);
492		raw_spin_unlock_irqrestore(&rnp->lock, flags);
493		if (rnp->qsmask == 0)
494			continue;
495		for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
496			if (rnp->qsmask & (1UL << cpu))
497				printk(" %d", rnp->grplo + cpu);
498	}
499	printk("} (detected by %d, t=%ld jiffies)\n",
500	       smp_processor_id(), (long)(jiffies - rsp->gp_start));
501	trigger_all_cpu_backtrace();
502
503	/* If so configured, complain about tasks blocking the grace period. */
504
505	rcu_print_detail_task_stall(rsp);
506
507	force_quiescent_state(rsp, 0);  /* Kick them all. */
508}
509
510static void print_cpu_stall(struct rcu_state *rsp)
511{
512	unsigned long flags;
513	struct rcu_node *rnp = rcu_get_root(rsp);
514
515	printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
516	       rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
517	trigger_all_cpu_backtrace();
518
519	raw_spin_lock_irqsave(&rnp->lock, flags);
520	if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
521		rsp->jiffies_stall =
522			jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
523	raw_spin_unlock_irqrestore(&rnp->lock, flags);
524
525	set_need_resched();  /* kick ourselves to get things going. */
526}
527
528static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
529{
530	long delta;
531	struct rcu_node *rnp;
532
533	if (rcu_cpu_stall_panicking)
534		return;
535	delta = jiffies - rsp->jiffies_stall;
536	rnp = rdp->mynode;
537	if ((rnp->qsmask & rdp->grpmask) && delta >= 0) {
538
539		/* We haven't checked in, so go dump stack. */
540		print_cpu_stall(rsp);
541
542	} else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
543
544		/* They had two time units to dump stack, so complain. */
545		print_other_cpu_stall(rsp);
546	}
547}
548
549static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
550{
551	rcu_cpu_stall_panicking = 1;
552	return NOTIFY_DONE;
553}
554
555static struct notifier_block rcu_panic_block = {
556	.notifier_call = rcu_panic,
557};
558
559static void __init check_cpu_stall_init(void)
560{
561	atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
562}
563
564#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
565
566static void record_gp_stall_check_time(struct rcu_state *rsp)
567{
568}
569
570static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
571{
572}
573
574static void __init check_cpu_stall_init(void)
575{
576}
577
578#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
579
580/*
581 * Update CPU-local rcu_data state to record the newly noticed grace period.
582 * This is used both when we started the grace period and when we notice
583 * that someone else started the grace period.  The caller must hold the
584 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
585 *  and must have irqs disabled.
586 */
587static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
588{
589	if (rdp->gpnum != rnp->gpnum) {
590		rdp->qs_pending = 1;
591		rdp->passed_quiesc = 0;
592		rdp->gpnum = rnp->gpnum;
593	}
594}
595
596static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
597{
598	unsigned long flags;
599	struct rcu_node *rnp;
600
601	local_irq_save(flags);
602	rnp = rdp->mynode;
603	if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
604	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
605		local_irq_restore(flags);
606		return;
607	}
608	__note_new_gpnum(rsp, rnp, rdp);
609	raw_spin_unlock_irqrestore(&rnp->lock, flags);
610}
611
612/*
613 * Did someone else start a new RCU grace period start since we last
614 * checked?  Update local state appropriately if so.  Must be called
615 * on the CPU corresponding to rdp.
616 */
617static int
618check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
619{
620	unsigned long flags;
621	int ret = 0;
622
623	local_irq_save(flags);
624	if (rdp->gpnum != rsp->gpnum) {
625		note_new_gpnum(rsp, rdp);
626		ret = 1;
627	}
628	local_irq_restore(flags);
629	return ret;
630}
631
632/*
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
635 * belongs.  In addition, the corresponding leaf rcu_node structure's
636 * ->lock must be held by the caller, with irqs disabled.
637 */
638static void
639__rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
640{
641	/* Did another grace period end? */
642	if (rdp->completed != rnp->completed) {
643
644		/* Advance callbacks.  No harm if list empty. */
645		rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
646		rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
647		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
648
649		/* Remember that we saw this grace-period completion. */
650		rdp->completed = rnp->completed;
651	}
652}
653
654/*
655 * Advance this CPU's callbacks, but only if the current grace period
656 * has ended.  This may be called only from the CPU to whom the rdp
657 * belongs.
658 */
659static void
660rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
661{
662	unsigned long flags;
663	struct rcu_node *rnp;
664
665	local_irq_save(flags);
666	rnp = rdp->mynode;
667	if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
668	    !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
669		local_irq_restore(flags);
670		return;
671	}
672	__rcu_process_gp_end(rsp, rnp, rdp);
673	raw_spin_unlock_irqrestore(&rnp->lock, flags);
674}
675
676/*
677 * Do per-CPU grace-period initialization for running CPU.  The caller
678 * must hold the lock of the leaf rcu_node structure corresponding to
679 * this CPU.
680 */
681static void
682rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
683{
684	/* Prior grace period ended, so advance callbacks for current CPU. */
685	__rcu_process_gp_end(rsp, rnp, rdp);
686
687	/*
688	 * Because this CPU just now started the new grace period, we know
689	 * that all of its callbacks will be covered by this upcoming grace
690	 * period, even the ones that were registered arbitrarily recently.
691	 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
692	 *
693	 * Other CPUs cannot be sure exactly when the grace period started.
694	 * Therefore, their recently registered callbacks must pass through
695	 * an additional RCU_NEXT_READY stage, so that they will be handled
696	 * by the next RCU grace period.
697	 */
698	rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
699	rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
700
701	/* Set state so that this CPU will detect the next quiescent state. */
702	__note_new_gpnum(rsp, rnp, rdp);
703}
704
705/*
706 * Start a new RCU grace period if warranted, re-initializing the hierarchy
707 * in preparation for detecting the next grace period.  The caller must hold
708 * the root node's ->lock, which is released before return.  Hard irqs must
709 * be disabled.
710 */
711static void
712rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
713	__releases(rcu_get_root(rsp)->lock)
714{
715	struct rcu_data *rdp = rsp->rda[smp_processor_id()];
716	struct rcu_node *rnp = rcu_get_root(rsp);
717
718	if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
719		if (cpu_needs_another_gp(rsp, rdp))
720			rsp->fqs_need_gp = 1;
721		if (rnp->completed == rsp->completed) {
722			raw_spin_unlock_irqrestore(&rnp->lock, flags);
723			return;
724		}
725		raw_spin_unlock(&rnp->lock);	 /* irqs remain disabled. */
726
727		/*
728		 * Propagate new ->completed value to rcu_node structures
729		 * so that other CPUs don't have to wait until the start
730		 * of the next grace period to process their callbacks.
731		 */
732		rcu_for_each_node_breadth_first(rsp, rnp) {
733			raw_spin_lock(&rnp->lock); /* irqs already disabled. */
734			rnp->completed = rsp->completed;
735			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
736		}
737		local_irq_restore(flags);
738		return;
739	}
740
741	/* Advance to a new grace period and initialize state. */
742	rsp->gpnum++;
743	WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
744	rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
745	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
746	record_gp_stall_check_time(rsp);
747
748	/* Special-case the common single-level case. */
749	if (NUM_RCU_NODES == 1) {
750		rcu_preempt_check_blocked_tasks(rnp);
751		rnp->qsmask = rnp->qsmaskinit;
752		rnp->gpnum = rsp->gpnum;
753		rnp->completed = rsp->completed;
754		rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
755		rcu_start_gp_per_cpu(rsp, rnp, rdp);
756		raw_spin_unlock_irqrestore(&rnp->lock, flags);
757		return;
758	}
759
760	raw_spin_unlock(&rnp->lock);  /* leave irqs disabled. */
761
762
763	/* Exclude any concurrent CPU-hotplug operations. */
764	raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
765
766	/*
767	 * Set the quiescent-state-needed bits in all the rcu_node
768	 * structures for all currently online CPUs in breadth-first
769	 * order, starting from the root rcu_node structure.  This
770	 * operation relies on the layout of the hierarchy within the
771	 * rsp->node[] array.  Note that other CPUs will access only
772	 * the leaves of the hierarchy, which still indicate that no
773	 * grace period is in progress, at least until the corresponding
774	 * leaf node has been initialized.  In addition, we have excluded
775	 * CPU-hotplug operations.
776	 *
777	 * Note that the grace period cannot complete until we finish
778	 * the initialization process, as there will be at least one
779	 * qsmask bit set in the root node until that time, namely the
780	 * one corresponding to this CPU, due to the fact that we have
781	 * irqs disabled.
782	 */
783	rcu_for_each_node_breadth_first(rsp, rnp) {
784		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
785		rcu_preempt_check_blocked_tasks(rnp);
786		rnp->qsmask = rnp->qsmaskinit;
787		rnp->gpnum = rsp->gpnum;
788		rnp->completed = rsp->completed;
789		if (rnp == rdp->mynode)
790			rcu_start_gp_per_cpu(rsp, rnp, rdp);
791		raw_spin_unlock(&rnp->lock);	/* irqs remain disabled. */
792	}
793
794	rnp = rcu_get_root(rsp);
795	raw_spin_lock(&rnp->lock);		/* irqs already disabled. */
796	rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
797	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
798	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
799}
800
801/*
802 * Report a full set of quiescent states to the specified rcu_state
803 * data structure.  This involves cleaning up after the prior grace
804 * period and letting rcu_start_gp() start up the next grace period
805 * if one is needed.  Note that the caller must hold rnp->lock, as
806 * required by rcu_start_gp(), which will release it.
807 */
808static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
809	__releases(rcu_get_root(rsp)->lock)
810{
811	WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
812	rsp->completed = rsp->gpnum;
813	rsp->signaled = RCU_GP_IDLE;
814	rcu_start_gp(rsp, flags);  /* releases root node's rnp->lock. */
815}
816
817/*
818 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
819 * Allows quiescent states for a group of CPUs to be reported at one go
820 * to the specified rcu_node structure, though all the CPUs in the group
821 * must be represented by the same rcu_node structure (which need not be
822 * a leaf rcu_node structure, though it often will be).  That structure's
823 * lock must be held upon entry, and it is released before return.
824 */
825static void
826rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
827		  struct rcu_node *rnp, unsigned long flags)
828	__releases(rnp->lock)
829{
830	struct rcu_node *rnp_c;
831
832	/* Walk up the rcu_node hierarchy. */
833	for (;;) {
834		if (!(rnp->qsmask & mask)) {
835
836			/* Our bit has already been cleared, so done. */
837			raw_spin_unlock_irqrestore(&rnp->lock, flags);
838			return;
839		}
840		rnp->qsmask &= ~mask;
841		if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
842
843			/* Other bits still set at this level, so done. */
844			raw_spin_unlock_irqrestore(&rnp->lock, flags);
845			return;
846		}
847		mask = rnp->grpmask;
848		if (rnp->parent == NULL) {
849
850			/* No more levels.  Exit loop holding root lock. */
851
852			break;
853		}
854		raw_spin_unlock_irqrestore(&rnp->lock, flags);
855		rnp_c = rnp;
856		rnp = rnp->parent;
857		raw_spin_lock_irqsave(&rnp->lock, flags);
858		WARN_ON_ONCE(rnp_c->qsmask);
859	}
860
861	/*
862	 * Get here if we are the last CPU to pass through a quiescent
863	 * state for this grace period.  Invoke rcu_report_qs_rsp()
864	 * to clean up and start the next grace period if one is needed.
865	 */
866	rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
867}
868
869/*
870 * Record a quiescent state for the specified CPU to that CPU's rcu_data
871 * structure.  This must be either called from the specified CPU, or
872 * called when the specified CPU is known to be offline (and when it is
873 * also known that no other CPU is concurrently trying to help the offline
874 * CPU).  The lastcomp argument is used to make sure we are still in the
875 * grace period of interest.  We don't want to end the current grace period
876 * based on quiescent states detected in an earlier grace period!
877 */
878static void
879rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
880{
881	unsigned long flags;
882	unsigned long mask;
883	struct rcu_node *rnp;
884
885	rnp = rdp->mynode;
886	raw_spin_lock_irqsave(&rnp->lock, flags);
887	if (lastcomp != rnp->completed) {
888
889		/*
890		 * Someone beat us to it for this grace period, so leave.
891		 * The race with GP start is resolved by the fact that we
892		 * hold the leaf rcu_node lock, so that the per-CPU bits
893		 * cannot yet be initialized -- so we would simply find our
894		 * CPU's bit already cleared in rcu_report_qs_rnp() if this
895		 * race occurred.
896		 */
897		rdp->passed_quiesc = 0;	/* try again later! */
898		raw_spin_unlock_irqrestore(&rnp->lock, flags);
899		return;
900	}
901	mask = rdp->grpmask;
902	if ((rnp->qsmask & mask) == 0) {
903		raw_spin_unlock_irqrestore(&rnp->lock, flags);
904	} else {
905		rdp->qs_pending = 0;
906
907		/*
908		 * This GP can't end until cpu checks in, so all of our
909		 * callbacks can be processed during the next GP.
910		 */
911		rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
912
913		rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
914	}
915}
916
917/*
918 * Check to see if there is a new grace period of which this CPU
919 * is not yet aware, and if so, set up local rcu_data state for it.
920 * Otherwise, see if this CPU has just passed through its first
921 * quiescent state for this grace period, and record that fact if so.
922 */
923static void
924rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
925{
926	/* If there is now a new grace period, record and return. */
927	if (check_for_new_grace_period(rsp, rdp))
928		return;
929
930	/*
931	 * Does this CPU still need to do its part for current grace period?
932	 * If no, return and let the other CPUs do their part as well.
933	 */
934	if (!rdp->qs_pending)
935		return;
936
937	/*
938	 * Was there a quiescent state since the beginning of the grace
939	 * period? If no, then exit and wait for the next call.
940	 */
941	if (!rdp->passed_quiesc)
942		return;
943
944	/*
945	 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
946	 * judge of that).
947	 */
948	rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
949}
950
951#ifdef CONFIG_HOTPLUG_CPU
952
953/*
954 * Move a dying CPU's RCU callbacks to the ->orphan_cbs_list for the
955 * specified flavor of RCU.  The callbacks will be adopted by the next
956 * _rcu_barrier() invocation or by the CPU_DEAD notifier, whichever
957 * comes first.  Because this is invoked from the CPU_DYING notifier,
958 * irqs are already disabled.
959 */
960static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
961{
962	int i;
963	struct rcu_data *rdp = rsp->rda[smp_processor_id()];
964
965	if (rdp->nxtlist == NULL)
966		return;  /* irqs disabled, so comparison is stable. */
967	raw_spin_lock(&rsp->onofflock);  /* irqs already disabled. */
968	*rsp->orphan_cbs_tail = rdp->nxtlist;
969	rsp->orphan_cbs_tail = rdp->nxttail[RCU_NEXT_TAIL];
970	rdp->nxtlist = NULL;
971	for (i = 0; i < RCU_NEXT_SIZE; i++)
972		rdp->nxttail[i] = &rdp->nxtlist;
973	rsp->orphan_qlen += rdp->qlen;
974	rdp->qlen = 0;
975	raw_spin_unlock(&rsp->onofflock);  /* irqs remain disabled. */
976}
977
978/*
979 * Adopt previously orphaned RCU callbacks.
980 */
981static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
982{
983	unsigned long flags;
984	struct rcu_data *rdp;
985
986	raw_spin_lock_irqsave(&rsp->onofflock, flags);
987	rdp = rsp->rda[smp_processor_id()];
988	if (rsp->orphan_cbs_list == NULL) {
989		raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
990		return;
991	}
992	*rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_list;
993	rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_cbs_tail;
994	rdp->qlen += rsp->orphan_qlen;
995	rsp->orphan_cbs_list = NULL;
996	rsp->orphan_cbs_tail = &rsp->orphan_cbs_list;
997	rsp->orphan_qlen = 0;
998	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
999}
1000
1001/*
1002 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
1003 * and move all callbacks from the outgoing CPU to the current one.
1004 */
1005static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
1006{
1007	unsigned long flags;
1008	unsigned long mask;
1009	int need_report = 0;
1010	struct rcu_data *rdp = rsp->rda[cpu];
1011	struct rcu_node *rnp;
1012
1013	/* Exclude any attempts to start a new grace period. */
1014	raw_spin_lock_irqsave(&rsp->onofflock, flags);
1015
1016	/* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1017	rnp = rdp->mynode;	/* this is the outgoing CPU's rnp. */
1018	mask = rdp->grpmask;	/* rnp->grplo is constant. */
1019	do {
1020		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
1021		rnp->qsmaskinit &= ~mask;
1022		if (rnp->qsmaskinit != 0) {
1023			if (rnp != rdp->mynode)
1024				raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1025			break;
1026		}
1027		if (rnp == rdp->mynode)
1028			need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
1029		else
1030			raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1031		mask = rnp->grpmask;
1032		rnp = rnp->parent;
1033	} while (rnp != NULL);
1034
1035	/*
1036	 * We still hold the leaf rcu_node structure lock here, and
1037	 * irqs are still disabled.  The reason for this subterfuge is
1038	 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1039	 * held leads to deadlock.
1040	 */
1041	raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
1042	rnp = rdp->mynode;
1043	if (need_report & RCU_OFL_TASKS_NORM_GP)
1044		rcu_report_unblock_qs_rnp(rnp, flags);
1045	else
1046		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1047	if (need_report & RCU_OFL_TASKS_EXP_GP)
1048		rcu_report_exp_rnp(rsp, rnp);
1049
1050	rcu_adopt_orphan_cbs(rsp);
1051}
1052
1053/*
1054 * Remove the specified CPU from the RCU hierarchy and move any pending
1055 * callbacks that it might have to the current CPU.  This code assumes
1056 * that at least one CPU in the system will remain running at all times.
1057 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1058 */
1059static void rcu_offline_cpu(int cpu)
1060{
1061	__rcu_offline_cpu(cpu, &rcu_sched_state);
1062	__rcu_offline_cpu(cpu, &rcu_bh_state);
1063	rcu_preempt_offline_cpu(cpu);
1064}
1065
1066#else /* #ifdef CONFIG_HOTPLUG_CPU */
1067
1068static void rcu_send_cbs_to_orphanage(struct rcu_state *rsp)
1069{
1070}
1071
1072static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
1073{
1074}
1075
1076static void rcu_offline_cpu(int cpu)
1077{
1078}
1079
1080#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1081
1082/*
1083 * Invoke any RCU callbacks that have made it to the end of their grace
1084 * period.  Thottle as specified by rdp->blimit.
1085 */
1086static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1087{
1088	unsigned long flags;
1089	struct rcu_head *next, *list, **tail;
1090	int count;
1091
1092	/* If no callbacks are ready, just return.*/
1093	if (!cpu_has_callbacks_ready_to_invoke(rdp))
1094		return;
1095
1096	/*
1097	 * Extract the list of ready callbacks, disabling to prevent
1098	 * races with call_rcu() from interrupt handlers.
1099	 */
1100	local_irq_save(flags);
1101	list = rdp->nxtlist;
1102	rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
1103	*rdp->nxttail[RCU_DONE_TAIL] = NULL;
1104	tail = rdp->nxttail[RCU_DONE_TAIL];
1105	for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
1106		if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
1107			rdp->nxttail[count] = &rdp->nxtlist;
1108	local_irq_restore(flags);
1109
1110	/* Invoke callbacks. */
1111	count = 0;
1112	while (list) {
1113		next = list->next;
1114		prefetch(next);
1115		debug_rcu_head_unqueue(list);
1116		list->func(list);
1117		list = next;
1118		if (++count >= rdp->blimit)
1119			break;
1120	}
1121
1122	local_irq_save(flags);
1123
1124	/* Update count, and requeue any remaining callbacks. */
1125	rdp->qlen -= count;
1126	if (list != NULL) {
1127		*tail = rdp->nxtlist;
1128		rdp->nxtlist = list;
1129		for (count = 0; count < RCU_NEXT_SIZE; count++)
1130			if (&rdp->nxtlist == rdp->nxttail[count])
1131				rdp->nxttail[count] = tail;
1132			else
1133				break;
1134	}
1135
1136	/* Reinstate batch limit if we have worked down the excess. */
1137	if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
1138		rdp->blimit = blimit;
1139
1140	/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1141	if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
1142		rdp->qlen_last_fqs_check = 0;
1143		rdp->n_force_qs_snap = rsp->n_force_qs;
1144	} else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
1145		rdp->qlen_last_fqs_check = rdp->qlen;
1146
1147	local_irq_restore(flags);
1148
1149	/* Re-raise the RCU softirq if there are callbacks remaining. */
1150	if (cpu_has_callbacks_ready_to_invoke(rdp))
1151		raise_softirq(RCU_SOFTIRQ);
1152}
1153
1154/*
1155 * Check to see if this CPU is in a non-context-switch quiescent state
1156 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1157 * Also schedule the RCU softirq handler.
1158 *
1159 * This function must be called with hardirqs disabled.  It is normally
1160 * invoked from the scheduling-clock interrupt.  If rcu_pending returns
1161 * false, there is no point in invoking rcu_check_callbacks().
1162 */
1163void rcu_check_callbacks(int cpu, int user)
1164{
1165	if (user ||
1166	    (idle_cpu(cpu) && rcu_scheduler_active &&
1167	     !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1168
1169		/*
1170		 * Get here if this CPU took its interrupt from user
1171		 * mode or from the idle loop, and if this is not a
1172		 * nested interrupt.  In this case, the CPU is in
1173		 * a quiescent state, so note it.
1174		 *
1175		 * No memory barrier is required here because both
1176		 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1177		 * variables that other CPUs neither access nor modify,
1178		 * at least not while the corresponding CPU is online.
1179		 */
1180
1181		rcu_sched_qs(cpu);
1182		rcu_bh_qs(cpu);
1183
1184	} else if (!in_softirq()) {
1185
1186		/*
1187		 * Get here if this CPU did not take its interrupt from
1188		 * softirq, in other words, if it is not interrupting
1189		 * a rcu_bh read-side critical section.  This is an _bh
1190		 * critical section, so note it.
1191		 */
1192
1193		rcu_bh_qs(cpu);
1194	}
1195	rcu_preempt_check_callbacks(cpu);
1196	if (rcu_pending(cpu))
1197		raise_softirq(RCU_SOFTIRQ);
1198}
1199
1200#ifdef CONFIG_SMP
1201
1202/*
1203 * Scan the leaf rcu_node structures, processing dyntick state for any that
1204 * have not yet encountered a quiescent state, using the function specified.
1205 * The caller must have suppressed start of new grace periods.
1206 */
1207static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1208{
1209	unsigned long bit;
1210	int cpu;
1211	unsigned long flags;
1212	unsigned long mask;
1213	struct rcu_node *rnp;
1214
1215	rcu_for_each_leaf_node(rsp, rnp) {
1216		mask = 0;
1217		raw_spin_lock_irqsave(&rnp->lock, flags);
1218		if (!rcu_gp_in_progress(rsp)) {
1219			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1220			return;
1221		}
1222		if (rnp->qsmask == 0) {
1223			raw_spin_unlock_irqrestore(&rnp->lock, flags);
1224			continue;
1225		}
1226		cpu = rnp->grplo;
1227		bit = 1;
1228		for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1229			if ((rnp->qsmask & bit) != 0 && f(rsp->rda[cpu]))
1230				mask |= bit;
1231		}
1232		if (mask != 0) {
1233
1234			/* rcu_report_qs_rnp() releases rnp->lock. */
1235			rcu_report_qs_rnp(mask, rsp, rnp, flags);
1236			continue;
1237		}
1238		raw_spin_unlock_irqrestore(&rnp->lock, flags);
1239	}
1240}
1241
1242/*
1243 * Force quiescent states on reluctant CPUs, and also detect which
1244 * CPUs are in dyntick-idle mode.
1245 */
1246static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1247{
1248	unsigned long flags;
1249	struct rcu_node *rnp = rcu_get_root(rsp);
1250
1251	if (!rcu_gp_in_progress(rsp))
1252		return;  /* No grace period in progress, nothing to force. */
1253	if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
1254		rsp->n_force_qs_lh++; /* Inexact, can lose counts.  Tough! */
1255		return;	/* Someone else is already on the job. */
1256	}
1257	if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
1258		goto unlock_fqs_ret; /* no emergency and done recently. */
1259	rsp->n_force_qs++;
1260	raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1261	rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1262	if(!rcu_gp_in_progress(rsp)) {
1263		rsp->n_force_qs_ngp++;
1264		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1265		goto unlock_fqs_ret;  /* no GP in progress, time updated. */
1266	}
1267	rsp->fqs_active = 1;
1268	switch (rsp->signaled) {
1269	case RCU_GP_IDLE:
1270	case RCU_GP_INIT:
1271
1272		break; /* grace period idle or initializing, ignore. */
1273
1274	case RCU_SAVE_DYNTICK:
1275		if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1276			break; /* So gcc recognizes the dead code. */
1277
1278		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1279
1280		/* Record dyntick-idle state. */
1281		force_qs_rnp(rsp, dyntick_save_progress_counter);
1282		raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1283		if (rcu_gp_in_progress(rsp))
1284			rsp->signaled = RCU_FORCE_QS;
1285		break;
1286
1287	case RCU_FORCE_QS:
1288
1289		/* Check dyntick-idle state, send IPI to laggarts. */
1290		raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1291		force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1292
1293		/* Leave state in case more forcing is required. */
1294
1295		raw_spin_lock(&rnp->lock);  /* irqs already disabled */
1296		break;
1297	}
1298	rsp->fqs_active = 0;
1299	if (rsp->fqs_need_gp) {
1300		raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
1301		rsp->fqs_need_gp = 0;
1302		rcu_start_gp(rsp, flags); /* releases rnp->lock */
1303		return;
1304	}
1305	raw_spin_unlock(&rnp->lock);  /* irqs remain disabled */
1306unlock_fqs_ret:
1307	raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
1308}
1309
1310#else /* #ifdef CONFIG_SMP */
1311
1312static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1313{
1314	set_need_resched();
1315}
1316
1317#endif /* #else #ifdef CONFIG_SMP */
1318
1319/*
1320 * This does the RCU processing work from softirq context for the
1321 * specified rcu_state and rcu_data structures.  This may be called
1322 * only from the CPU to whom the rdp belongs.
1323 */
1324static void
1325__rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1326{
1327	unsigned long flags;
1328
1329	WARN_ON_ONCE(rdp->beenonline == 0);
1330
1331	/*
1332	 * If an RCU GP has gone long enough, go check for dyntick
1333	 * idle CPUs and, if needed, send resched IPIs.
1334	 */
1335	if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1336		force_quiescent_state(rsp, 1);
1337
1338	/*
1339	 * Advance callbacks in response to end of earlier grace
1340	 * period that some other CPU ended.
1341	 */
1342	rcu_process_gp_end(rsp, rdp);
1343
1344	/* Update RCU state based on any recent quiescent states. */
1345	rcu_check_quiescent_state(rsp, rdp);
1346
1347	/* Does this CPU require a not-yet-started grace period? */
1348	if (cpu_needs_another_gp(rsp, rdp)) {
1349		raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1350		rcu_start_gp(rsp, flags);  /* releases above lock */
1351	}
1352
1353	/* If there are callbacks ready, invoke them. */
1354	rcu_do_batch(rsp, rdp);
1355}
1356
1357/*
1358 * Do softirq processing for the current CPU.
1359 */
1360static void rcu_process_callbacks(struct softirq_action *unused)
1361{
1362	/*
1363	 * Memory references from any prior RCU read-side critical sections
1364	 * executed by the interrupted code must be seen before any RCU
1365	 * grace-period manipulations below.
1366	 */
1367	smp_mb(); /* See above block comment. */
1368
1369	__rcu_process_callbacks(&rcu_sched_state,
1370				&__get_cpu_var(rcu_sched_data));
1371	__rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1372	rcu_preempt_process_callbacks();
1373
1374	/*
1375	 * Memory references from any later RCU read-side critical sections
1376	 * executed by the interrupted code must be seen after any RCU
1377	 * grace-period manipulations above.
1378	 */
1379	smp_mb(); /* See above block comment. */
1380
1381	/* If we are last CPU on way to dyntick-idle mode, accelerate it. */
1382	rcu_needs_cpu_flush();
1383}
1384
1385static void
1386__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1387	   struct rcu_state *rsp)
1388{
1389	unsigned long flags;
1390	struct rcu_data *rdp;
1391
1392	debug_rcu_head_queue(head);
1393	head->func = func;
1394	head->next = NULL;
1395
1396	smp_mb(); /* Ensure RCU update seen before callback registry. */
1397
1398	/*
1399	 * Opportunistically note grace-period endings and beginnings.
1400	 * Note that we might see a beginning right after we see an
1401	 * end, but never vice versa, since this CPU has to pass through
1402	 * a quiescent state betweentimes.
1403	 */
1404	local_irq_save(flags);
1405	rdp = rsp->rda[smp_processor_id()];
1406	rcu_process_gp_end(rsp, rdp);
1407	check_for_new_grace_period(rsp, rdp);
1408
1409	/* Add the callback to our list. */
1410	*rdp->nxttail[RCU_NEXT_TAIL] = head;
1411	rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1412
1413	/* Start a new grace period if one not already started. */
1414	if (!rcu_gp_in_progress(rsp)) {
1415		unsigned long nestflag;
1416		struct rcu_node *rnp_root = rcu_get_root(rsp);
1417
1418		raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
1419		rcu_start_gp(rsp, nestflag);  /* releases rnp_root->lock. */
1420	}
1421
1422	/*
1423	 * Force the grace period if too many callbacks or too long waiting.
1424	 * Enforce hysteresis, and don't invoke force_quiescent_state()
1425	 * if some other CPU has recently done so.  Also, don't bother
1426	 * invoking force_quiescent_state() if the newly enqueued callback
1427	 * is the only one waiting for a grace period to complete.
1428	 */
1429	if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1430		rdp->blimit = LONG_MAX;
1431		if (rsp->n_force_qs == rdp->n_force_qs_snap &&
1432		    *rdp->nxttail[RCU_DONE_TAIL] != head)
1433			force_quiescent_state(rsp, 0);
1434		rdp->n_force_qs_snap = rsp->n_force_qs;
1435		rdp->qlen_last_fqs_check = rdp->qlen;
1436	} else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1437		force_quiescent_state(rsp, 1);
1438	local_irq_restore(flags);
1439}
1440
1441/*
1442 * Queue an RCU-sched callback for invocation after a grace period.
1443 */
1444void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1445{
1446	__call_rcu(head, func, &rcu_sched_state);
1447}
1448EXPORT_SYMBOL_GPL(call_rcu_sched);
1449
1450/*
1451 * Queue an RCU for invocation after a quicker grace period.
1452 */
1453void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1454{
1455	__call_rcu(head, func, &rcu_bh_state);
1456}
1457EXPORT_SYMBOL_GPL(call_rcu_bh);
1458
1459/**
1460 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1461 *
1462 * Control will return to the caller some time after a full rcu-sched
1463 * grace period has elapsed, in other words after all currently executing
1464 * rcu-sched read-side critical sections have completed.   These read-side
1465 * critical sections are delimited by rcu_read_lock_sched() and
1466 * rcu_read_unlock_sched(), and may be nested.  Note that preempt_disable(),
1467 * local_irq_disable(), and so on may be used in place of
1468 * rcu_read_lock_sched().
1469 *
1470 * This means that all preempt_disable code sequences, including NMI and
1471 * hardware-interrupt handlers, in progress on entry will have completed
1472 * before this primitive returns.  However, this does not guarantee that
1473 * softirq handlers will have completed, since in some kernels, these
1474 * handlers can run in process context, and can block.
1475 *
1476 * This primitive provides the guarantees made by the (now removed)
1477 * synchronize_kernel() API.  In contrast, synchronize_rcu() only
1478 * guarantees that rcu_read_lock() sections will have completed.
1479 * In "classic RCU", these two guarantees happen to be one and
1480 * the same, but can differ in realtime RCU implementations.
1481 */
1482void synchronize_sched(void)
1483{
1484	struct rcu_synchronize rcu;
1485
1486	if (rcu_blocking_is_gp())
1487		return;
1488
1489	init_rcu_head_on_stack(&rcu.head);
1490	init_completion(&rcu.completion);
1491	/* Will wake me after RCU finished. */
1492	call_rcu_sched(&rcu.head, wakeme_after_rcu);
1493	/* Wait for it. */
1494	wait_for_completion(&rcu.completion);
1495	destroy_rcu_head_on_stack(&rcu.head);
1496}
1497EXPORT_SYMBOL_GPL(synchronize_sched);
1498
1499/**
1500 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1501 *
1502 * Control will return to the caller some time after a full rcu_bh grace
1503 * period has elapsed, in other words after all currently executing rcu_bh
1504 * read-side critical sections have completed.  RCU read-side critical
1505 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1506 * and may be nested.
1507 */
1508void synchronize_rcu_bh(void)
1509{
1510	struct rcu_synchronize rcu;
1511
1512	if (rcu_blocking_is_gp())
1513		return;
1514
1515	init_rcu_head_on_stack(&rcu.head);
1516	init_completion(&rcu.completion);
1517	/* Will wake me after RCU finished. */
1518	call_rcu_bh(&rcu.head, wakeme_after_rcu);
1519	/* Wait for it. */
1520	wait_for_completion(&rcu.completion);
1521	destroy_rcu_head_on_stack(&rcu.head);
1522}
1523EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
1524
1525/*
1526 * Check to see if there is any immediate RCU-related work to be done
1527 * by the current CPU, for the specified type of RCU, returning 1 if so.
1528 * The checks are in order of increasing expense: checks that can be
1529 * carried out against CPU-local state are performed first.  However,
1530 * we must check for CPU stalls first, else we might not get a chance.
1531 */
1532static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1533{
1534	struct rcu_node *rnp = rdp->mynode;
1535
1536	rdp->n_rcu_pending++;
1537
1538	/* Check for CPU stalls, if enabled. */
1539	check_cpu_stall(rsp, rdp);
1540
1541	/* Is the RCU core waiting for a quiescent state from this CPU? */
1542	if (rdp->qs_pending && !rdp->passed_quiesc) {
1543
1544		/*
1545		 * If force_quiescent_state() coming soon and this CPU
1546		 * needs a quiescent state, and this is either RCU-sched
1547		 * or RCU-bh, force a local reschedule.
1548		 */
1549		rdp->n_rp_qs_pending++;
1550		if (!rdp->preemptable &&
1551		    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
1552				 jiffies))
1553			set_need_resched();
1554	} else if (rdp->qs_pending && rdp->passed_quiesc) {
1555		rdp->n_rp_report_qs++;
1556		return 1;
1557	}
1558
1559	/* Does this CPU have callbacks ready to invoke? */
1560	if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1561		rdp->n_rp_cb_ready++;
1562		return 1;
1563	}
1564
1565	/* Has RCU gone idle with this CPU needing another grace period? */
1566	if (cpu_needs_another_gp(rsp, rdp)) {
1567		rdp->n_rp_cpu_needs_gp++;
1568		return 1;
1569	}
1570
1571	/* Has another RCU grace period completed?  */
1572	if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
1573		rdp->n_rp_gp_completed++;
1574		return 1;
1575	}
1576
1577	/* Has a new RCU grace period started? */
1578	if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
1579		rdp->n_rp_gp_started++;
1580		return 1;
1581	}
1582
1583	/* Has an RCU GP gone long enough to send resched IPIs &c? */
1584	if (rcu_gp_in_progress(rsp) &&
1585	    ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
1586		rdp->n_rp_need_fqs++;
1587		return 1;
1588	}
1589
1590	/* nothing to do */
1591	rdp->n_rp_need_nothing++;
1592	return 0;
1593}
1594
1595/*
1596 * Check to see if there is any immediate RCU-related work to be done
1597 * by the current CPU, returning 1 if so.  This function is part of the
1598 * RCU implementation; it is -not- an exported member of the RCU API.
1599 */
1600static int rcu_pending(int cpu)
1601{
1602	return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1603	       __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1604	       rcu_preempt_pending(cpu);
1605}
1606
1607/*
1608 * Check to see if any future RCU-related work will need to be done
1609 * by the current CPU, even if none need be done immediately, returning
1610 * 1 if so.
1611 */
1612static int rcu_needs_cpu_quick_check(int cpu)
1613{
1614	/* RCU callbacks either ready or pending? */
1615	return per_cpu(rcu_sched_data, cpu).nxtlist ||
1616	       per_cpu(rcu_bh_data, cpu).nxtlist ||
1617	       rcu_preempt_needs_cpu(cpu);
1618}
1619
1620static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
1621static atomic_t rcu_barrier_cpu_count;
1622static DEFINE_MUTEX(rcu_barrier_mutex);
1623static struct completion rcu_barrier_completion;
1624
1625static void rcu_barrier_callback(struct rcu_head *notused)
1626{
1627	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1628		complete(&rcu_barrier_completion);
1629}
1630
1631/*
1632 * Called with preemption disabled, and from cross-cpu IRQ context.
1633 */
1634static void rcu_barrier_func(void *type)
1635{
1636	int cpu = smp_processor_id();
1637	struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
1638	void (*call_rcu_func)(struct rcu_head *head,
1639			      void (*func)(struct rcu_head *head));
1640
1641	atomic_inc(&rcu_barrier_cpu_count);
1642	call_rcu_func = type;
1643	call_rcu_func(head, rcu_barrier_callback);
1644}
1645
1646/*
1647 * Orchestrate the specified type of RCU barrier, waiting for all
1648 * RCU callbacks of the specified type to complete.
1649 */
1650static void _rcu_barrier(struct rcu_state *rsp,
1651			 void (*call_rcu_func)(struct rcu_head *head,
1652					       void (*func)(struct rcu_head *head)))
1653{
1654	BUG_ON(in_interrupt());
1655	/* Take mutex to serialize concurrent rcu_barrier() requests. */
1656	mutex_lock(&rcu_barrier_mutex);
1657	init_completion(&rcu_barrier_completion);
1658	/*
1659	 * Initialize rcu_barrier_cpu_count to 1, then invoke
1660	 * rcu_barrier_func() on each CPU, so that each CPU also has
1661	 * incremented rcu_barrier_cpu_count.  Only then is it safe to
1662	 * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1663	 * might complete its grace period before all of the other CPUs
1664	 * did their increment, causing this function to return too
1665	 * early.
1666	 */
1667	atomic_set(&rcu_barrier_cpu_count, 1);
1668	preempt_disable(); /* stop CPU_DYING from filling orphan_cbs_list */
1669	rcu_adopt_orphan_cbs(rsp);
1670	on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
1671	preempt_enable(); /* CPU_DYING can again fill orphan_cbs_list */
1672	if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1673		complete(&rcu_barrier_completion);
1674	wait_for_completion(&rcu_barrier_completion);
1675	mutex_unlock(&rcu_barrier_mutex);
1676}
1677
1678/**
1679 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1680 */
1681void rcu_barrier_bh(void)
1682{
1683	_rcu_barrier(&rcu_bh_state, call_rcu_bh);
1684}
1685EXPORT_SYMBOL_GPL(rcu_barrier_bh);
1686
1687/**
1688 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1689 */
1690void rcu_barrier_sched(void)
1691{
1692	_rcu_barrier(&rcu_sched_state, call_rcu_sched);
1693}
1694EXPORT_SYMBOL_GPL(rcu_barrier_sched);
1695
1696/*
1697 * Do boot-time initialization of a CPU's per-CPU RCU data.
1698 */
1699static void __init
1700rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1701{
1702	unsigned long flags;
1703	int i;
1704	struct rcu_data *rdp = rsp->rda[cpu];
1705	struct rcu_node *rnp = rcu_get_root(rsp);
1706
1707	/* Set up local state, ensuring consistent view of global state. */
1708	raw_spin_lock_irqsave(&rnp->lock, flags);
1709	rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1710	rdp->nxtlist = NULL;
1711	for (i = 0; i < RCU_NEXT_SIZE; i++)
1712		rdp->nxttail[i] = &rdp->nxtlist;
1713	rdp->qlen = 0;
1714#ifdef CONFIG_NO_HZ
1715	rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1716#endif /* #ifdef CONFIG_NO_HZ */
1717	rdp->cpu = cpu;
1718	raw_spin_unlock_irqrestore(&rnp->lock, flags);
1719}
1720
1721/*
1722 * Initialize a CPU's per-CPU RCU data.  Note that only one online or
1723 * offline event can be happening at a given time.  Note also that we
1724 * can accept some slop in the rsp->completed access due to the fact
1725 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1726 */
1727static void __cpuinit
1728rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
1729{
1730	unsigned long flags;
1731	unsigned long mask;
1732	struct rcu_data *rdp = rsp->rda[cpu];
1733	struct rcu_node *rnp = rcu_get_root(rsp);
1734
1735	/* Set up local state, ensuring consistent view of global state. */
1736	raw_spin_lock_irqsave(&rnp->lock, flags);
1737	rdp->passed_quiesc = 0;  /* We could be racing with new GP, */
1738	rdp->qs_pending = 1;	 /*  so set up to respond to current GP. */
1739	rdp->beenonline = 1;	 /* We have now been online. */
1740	rdp->preemptable = preemptable;
1741	rdp->qlen_last_fqs_check = 0;
1742	rdp->n_force_qs_snap = rsp->n_force_qs;
1743	rdp->blimit = blimit;
1744	raw_spin_unlock(&rnp->lock);		/* irqs remain disabled. */
1745
1746	/*
1747	 * A new grace period might start here.  If so, we won't be part
1748	 * of it, but that is OK, as we are currently in a quiescent state.
1749	 */
1750
1751	/* Exclude any attempts to start a new GP on large systems. */
1752	raw_spin_lock(&rsp->onofflock);		/* irqs already disabled. */
1753
1754	/* Add CPU to rcu_node bitmasks. */
1755	rnp = rdp->mynode;
1756	mask = rdp->grpmask;
1757	do {
1758		/* Exclude any attempts to start a new GP on small systems. */
1759		raw_spin_lock(&rnp->lock);	/* irqs already disabled. */
1760		rnp->qsmaskinit |= mask;
1761		mask = rnp->grpmask;
1762		if (rnp == rdp->mynode) {
1763			rdp->gpnum = rnp->completed; /* if GP in progress... */
1764			rdp->completed = rnp->completed;
1765			rdp->passed_quiesc_completed = rnp->completed - 1;
1766		}
1767		raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
1768		rnp = rnp->parent;
1769	} while (rnp != NULL && !(rnp->qsmaskinit & mask));
1770
1771	raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
1772}
1773
1774static void __cpuinit rcu_online_cpu(int cpu)
1775{
1776	rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1777	rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1778	rcu_preempt_init_percpu_data(cpu);
1779}
1780
1781/*
1782 * Handle CPU online/offline notification events.
1783 */
1784static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1785				    unsigned long action, void *hcpu)
1786{
1787	long cpu = (long)hcpu;
1788
1789	switch (action) {
1790	case CPU_UP_PREPARE:
1791	case CPU_UP_PREPARE_FROZEN:
1792		rcu_online_cpu(cpu);
1793		break;
1794	case CPU_DYING:
1795	case CPU_DYING_FROZEN:
1796		/*
1797		 * preempt_disable() in _rcu_barrier() prevents stop_machine(),
1798		 * so when "on_each_cpu(rcu_barrier_func, (void *)type, 1);"
1799		 * returns, all online cpus have queued rcu_barrier_func().
1800		 * The dying CPU clears its cpu_online_mask bit and
1801		 * moves all of its RCU callbacks to ->orphan_cbs_list
1802		 * in the context of stop_machine(), so subsequent calls
1803		 * to _rcu_barrier() will adopt these callbacks and only
1804		 * then queue rcu_barrier_func() on all remaining CPUs.
1805		 */
1806		rcu_send_cbs_to_orphanage(&rcu_bh_state);
1807		rcu_send_cbs_to_orphanage(&rcu_sched_state);
1808		rcu_preempt_send_cbs_to_orphanage();
1809		break;
1810	case CPU_DEAD:
1811	case CPU_DEAD_FROZEN:
1812	case CPU_UP_CANCELED:
1813	case CPU_UP_CANCELED_FROZEN:
1814		rcu_offline_cpu(cpu);
1815		break;
1816	default:
1817		break;
1818	}
1819	return NOTIFY_OK;
1820}
1821
1822/*
1823 * This function is invoked towards the end of the scheduler's initialization
1824 * process.  Before this is called, the idle task might contain
1825 * RCU read-side critical sections (during which time, this idle
1826 * task is booting the system).  After this function is called, the
1827 * idle tasks are prohibited from containing RCU read-side critical
1828 * sections.  This function also enables RCU lockdep checking.
1829 */
1830void rcu_scheduler_starting(void)
1831{
1832	WARN_ON(num_online_cpus() != 1);
1833	WARN_ON(nr_context_switches() > 0);
1834	rcu_scheduler_active = 1;
1835}
1836
1837/*
1838 * Compute the per-level fanout, either using the exact fanout specified
1839 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1840 */
1841#ifdef CONFIG_RCU_FANOUT_EXACT
1842static void __init rcu_init_levelspread(struct rcu_state *rsp)
1843{
1844	int i;
1845
1846	for (i = NUM_RCU_LVLS - 1; i >= 0; i--)
1847		rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1848}
1849#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1850static void __init rcu_init_levelspread(struct rcu_state *rsp)
1851{
1852	int ccur;
1853	int cprv;
1854	int i;
1855
1856	cprv = NR_CPUS;
1857	for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1858		ccur = rsp->levelcnt[i];
1859		rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1860		cprv = ccur;
1861	}
1862}
1863#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1864
1865/*
1866 * Helper function for rcu_init() that initializes one rcu_state structure.
1867 */
1868static void __init rcu_init_one(struct rcu_state *rsp)
1869{
1870	static char *buf[] = { "rcu_node_level_0",
1871			       "rcu_node_level_1",
1872			       "rcu_node_level_2",
1873			       "rcu_node_level_3" };  /* Match MAX_RCU_LVLS */
1874	int cpustride = 1;
1875	int i;
1876	int j;
1877	struct rcu_node *rnp;
1878
1879	BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf));  /* Fix buf[] init! */
1880
1881	/* Initialize the level-tracking arrays. */
1882
1883	for (i = 1; i < NUM_RCU_LVLS; i++)
1884		rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1885	rcu_init_levelspread(rsp);
1886
1887	/* Initialize the elements themselves, starting from the leaves. */
1888
1889	for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1890		cpustride *= rsp->levelspread[i];
1891		rnp = rsp->level[i];
1892		for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1893			raw_spin_lock_init(&rnp->lock);
1894			lockdep_set_class_and_name(&rnp->lock,
1895						   &rcu_node_class[i], buf[i]);
1896			rnp->gpnum = 0;
1897			rnp->qsmask = 0;
1898			rnp->qsmaskinit = 0;
1899			rnp->grplo = j * cpustride;
1900			rnp->grphi = (j + 1) * cpustride - 1;
1901			if (rnp->grphi >= NR_CPUS)
1902				rnp->grphi = NR_CPUS - 1;
1903			if (i == 0) {
1904				rnp->grpnum = 0;
1905				rnp->grpmask = 0;
1906				rnp->parent = NULL;
1907			} else {
1908				rnp->grpnum = j % rsp->levelspread[i - 1];
1909				rnp->grpmask = 1UL << rnp->grpnum;
1910				rnp->parent = rsp->level[i - 1] +
1911					      j / rsp->levelspread[i - 1];
1912			}
1913			rnp->level = i;
1914			INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
1915			INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
1916			INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
1917			INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
1918		}
1919	}
1920
1921	rnp = rsp->level[NUM_RCU_LVLS - 1];
1922	for_each_possible_cpu(i) {
1923		while (i > rnp->grphi)
1924			rnp++;
1925		rsp->rda[i]->mynode = rnp;
1926		rcu_boot_init_percpu_data(i, rsp);
1927	}
1928}
1929
1930/*
1931 * Helper macro for __rcu_init() and __rcu_init_preempt().  To be used
1932 * nowhere else!  Assigns leaf node pointers into each CPU's rcu_data
1933 * structure.
1934 */
1935#define RCU_INIT_FLAVOR(rsp, rcu_data) \
1936do { \
1937	int i; \
1938	\
1939	for_each_possible_cpu(i) { \
1940		(rsp)->rda[i] = &per_cpu(rcu_data, i); \
1941	} \
1942	rcu_init_one(rsp); \
1943} while (0)
1944
1945void __init rcu_init(void)
1946{
1947	int cpu;
1948
1949	rcu_bootup_announce();
1950	RCU_INIT_FLAVOR(&rcu_sched_state, rcu_sched_data);
1951	RCU_INIT_FLAVOR(&rcu_bh_state, rcu_bh_data);
1952	__rcu_init_preempt();
1953	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1954
1955	/*
1956	 * We don't need protection against CPU-hotplug here because
1957	 * this is called early in boot, before either interrupts
1958	 * or the scheduler are operational.
1959	 */
1960	cpu_notifier(rcu_cpu_notify, 0);
1961	for_each_online_cpu(cpu)
1962		rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
1963	check_cpu_stall_init();
1964}
1965
1966#include "rcutree_plugin.h"
1967