Root/kernel/rcutree.c

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    .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&structname.fqslock), \
71    .n_force_qs = 0, \
72    .n_force_qs_ngp = 0, \
73    .name = #structname, \
74}
75
76struct rcu_state rcu_sched_state = RCU_STATE_INITIALIZER(rcu_sched_state);
77DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
78
79struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh_state);
80DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
81
82int rcu_scheduler_active __read_mostly;
83EXPORT_SYMBOL_GPL(rcu_scheduler_active);
84
85/*
86 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
87 * permit this function to be invoked without holding the root rcu_node
88 * structure's ->lock, but of course results can be subject to change.
89 */
90static int rcu_gp_in_progress(struct rcu_state *rsp)
91{
92    return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
93}
94
95/*
96 * Note a quiescent state. Because we do not need to know
97 * how many quiescent states passed, just if there was at least
98 * one since the start of the grace period, this just sets a flag.
99 */
100void rcu_sched_qs(int cpu)
101{
102    struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
103
104    rdp->passed_quiesc_completed = rdp->gpnum - 1;
105    barrier();
106    rdp->passed_quiesc = 1;
107}
108
109void rcu_bh_qs(int cpu)
110{
111    struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
112
113    rdp->passed_quiesc_completed = rdp->gpnum - 1;
114    barrier();
115    rdp->passed_quiesc = 1;
116}
117
118/*
119 * Note a context switch. This is a quiescent state for RCU-sched,
120 * and requires special handling for preemptible RCU.
121 */
122void rcu_note_context_switch(int cpu)
123{
124    rcu_sched_qs(cpu);
125    rcu_preempt_note_context_switch(cpu);
126}
127
128#ifdef CONFIG_NO_HZ
129DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
130    .dynticks_nesting = 1,
131    .dynticks = 1,
132};
133#endif /* #ifdef CONFIG_NO_HZ */
134
135static int blimit = 10; /* Maximum callbacks per softirq. */
136static int qhimark = 10000; /* If this many pending, ignore blimit. */
137static int qlowmark = 100; /* Once only this many pending, use blimit. */
138
139module_param(blimit, int, 0);
140module_param(qhimark, int, 0);
141module_param(qlowmark, int, 0);
142
143#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
144int rcu_cpu_stall_suppress __read_mostly = RCU_CPU_STALL_SUPPRESS_INIT;
145module_param(rcu_cpu_stall_suppress, int, 0644);
146#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
147
148static void force_quiescent_state(struct rcu_state *rsp, int relaxed);
149static int rcu_pending(int cpu);
150
151/*
152 * Return the number of RCU-sched batches processed thus far for debug & stats.
153 */
154long rcu_batches_completed_sched(void)
155{
156    return rcu_sched_state.completed;
157}
158EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
159
160/*
161 * Return the number of RCU BH batches processed thus far for debug & stats.
162 */
163long rcu_batches_completed_bh(void)
164{
165    return rcu_bh_state.completed;
166}
167EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
168
169/*
170 * Force a quiescent state for RCU BH.
171 */
172void rcu_bh_force_quiescent_state(void)
173{
174    force_quiescent_state(&rcu_bh_state, 0);
175}
176EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
177
178/*
179 * Force a quiescent state for RCU-sched.
180 */
181void rcu_sched_force_quiescent_state(void)
182{
183    force_quiescent_state(&rcu_sched_state, 0);
184}
185EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
186
187/*
188 * Does the CPU have callbacks ready to be invoked?
189 */
190static int
191cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
192{
193    return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
194}
195
196/*
197 * Does the current CPU require a yet-as-unscheduled grace period?
198 */
199static int
200cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
201{
202    return *rdp->nxttail[RCU_DONE_TAIL] && !rcu_gp_in_progress(rsp);
203}
204
205/*
206 * Return the root node of the specified rcu_state structure.
207 */
208static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
209{
210    return &rsp->node[0];
211}
212
213#ifdef CONFIG_SMP
214
215/*
216 * If the specified CPU is offline, tell the caller that it is in
217 * a quiescent state. Otherwise, whack it with a reschedule IPI.
218 * Grace periods can end up waiting on an offline CPU when that
219 * CPU is in the process of coming online -- it will be added to the
220 * rcu_node bitmasks before it actually makes it online. The same thing
221 * can happen while a CPU is in the process of coming online. Because this
222 * race is quite rare, we check for it after detecting that the grace
223 * period has been delayed rather than checking each and every CPU
224 * each and every time we start a new grace period.
225 */
226static int rcu_implicit_offline_qs(struct rcu_data *rdp)
227{
228    /*
229     * If the CPU is offline, it is in a quiescent state. We can
230     * trust its state not to change because interrupts are disabled.
231     */
232    if (cpu_is_offline(rdp->cpu)) {
233        rdp->offline_fqs++;
234        return 1;
235    }
236
237    /* If preemptable RCU, no point in sending reschedule IPI. */
238    if (rdp->preemptable)
239        return 0;
240
241    /* The CPU is online, so send it a reschedule IPI. */
242    if (rdp->cpu != smp_processor_id())
243        smp_send_reschedule(rdp->cpu);
244    else
245        set_need_resched();
246    rdp->resched_ipi++;
247    return 0;
248}
249
250#endif /* #ifdef CONFIG_SMP */
251
252#ifdef CONFIG_NO_HZ
253
254/**
255 * rcu_enter_nohz - inform RCU that current CPU is entering nohz
256 *
257 * Enter nohz mode, in other words, -leave- the mode in which RCU
258 * read-side critical sections can occur. (Though RCU read-side
259 * critical sections can occur in irq handlers in nohz mode, a possibility
260 * handled by rcu_irq_enter() and rcu_irq_exit()).
261 */
262void rcu_enter_nohz(void)
263{
264    unsigned long flags;
265    struct rcu_dynticks *rdtp;
266
267    smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
268    local_irq_save(flags);
269    rdtp = &__get_cpu_var(rcu_dynticks);
270    rdtp->dynticks++;
271    rdtp->dynticks_nesting--;
272    WARN_ON_ONCE(rdtp->dynticks & 0x1);
273    local_irq_restore(flags);
274}
275
276/*
277 * rcu_exit_nohz - inform RCU that current CPU is leaving nohz
278 *
279 * Exit nohz mode, in other words, -enter- the mode in which RCU
280 * read-side critical sections normally occur.
281 */
282void rcu_exit_nohz(void)
283{
284    unsigned long flags;
285    struct rcu_dynticks *rdtp;
286
287    local_irq_save(flags);
288    rdtp = &__get_cpu_var(rcu_dynticks);
289    rdtp->dynticks++;
290    rdtp->dynticks_nesting++;
291    WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
292    local_irq_restore(flags);
293    smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
294}
295
296/**
297 * rcu_nmi_enter - inform RCU of entry to NMI context
298 *
299 * If the CPU was idle with dynamic ticks active, and there is no
300 * irq handler running, this updates rdtp->dynticks_nmi to let the
301 * RCU grace-period handling know that the CPU is active.
302 */
303void rcu_nmi_enter(void)
304{
305    struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
306
307    if (rdtp->dynticks & 0x1)
308        return;
309    rdtp->dynticks_nmi++;
310    WARN_ON_ONCE(!(rdtp->dynticks_nmi & 0x1));
311    smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
312}
313
314/**
315 * rcu_nmi_exit - inform RCU of exit from NMI context
316 *
317 * If the CPU was idle with dynamic ticks active, and there is no
318 * irq handler running, this updates rdtp->dynticks_nmi to let the
319 * RCU grace-period handling know that the CPU is no longer active.
320 */
321void rcu_nmi_exit(void)
322{
323    struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
324
325    if (rdtp->dynticks & 0x1)
326        return;
327    smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
328    rdtp->dynticks_nmi++;
329    WARN_ON_ONCE(rdtp->dynticks_nmi & 0x1);
330}
331
332/**
333 * rcu_irq_enter - inform RCU of entry to hard irq context
334 *
335 * If the CPU was idle with dynamic ticks active, this updates the
336 * rdtp->dynticks to let the RCU handling know that the CPU is active.
337 */
338void rcu_irq_enter(void)
339{
340    struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
341
342    if (rdtp->dynticks_nesting++)
343        return;
344    rdtp->dynticks++;
345    WARN_ON_ONCE(!(rdtp->dynticks & 0x1));
346    smp_mb(); /* CPUs seeing ++ must see later RCU read-side crit sects */
347}
348
349/**
350 * rcu_irq_exit - inform RCU of exit from hard irq context
351 *
352 * If the CPU was idle with dynamic ticks active, update the rdp->dynticks
353 * to put let the RCU handling be aware that the CPU is going back to idle
354 * with no ticks.
355 */
356void rcu_irq_exit(void)
357{
358    struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
359
360    if (--rdtp->dynticks_nesting)
361        return;
362    smp_mb(); /* CPUs seeing ++ must see prior RCU read-side crit sects */
363    rdtp->dynticks++;
364    WARN_ON_ONCE(rdtp->dynticks & 0x1);
365
366    /* If the interrupt queued a callback, get out of dyntick mode. */
367    if (__this_cpu_read(rcu_sched_data.nxtlist) ||
368        __this_cpu_read(rcu_bh_data.nxtlist))
369        set_need_resched();
370}
371
372#ifdef CONFIG_SMP
373
374/*
375 * Snapshot the specified CPU's dynticks counter so that we can later
376 * credit them with an implicit quiescent state. Return 1 if this CPU
377 * is in dynticks idle mode, which is an extended quiescent state.
378 */
379static int dyntick_save_progress_counter(struct rcu_data *rdp)
380{
381    int ret;
382    int snap;
383    int snap_nmi;
384
385    snap = rdp->dynticks->dynticks;
386    snap_nmi = rdp->dynticks->dynticks_nmi;
387    smp_mb(); /* Order sampling of snap with end of grace period. */
388    rdp->dynticks_snap = snap;
389    rdp->dynticks_nmi_snap = snap_nmi;
390    ret = ((snap & 0x1) == 0) && ((snap_nmi & 0x1) == 0);
391    if (ret)
392        rdp->dynticks_fqs++;
393    return ret;
394}
395
396/*
397 * Return true if the specified CPU has passed through a quiescent
398 * state by virtue of being in or having passed through an dynticks
399 * idle state since the last call to dyntick_save_progress_counter()
400 * for this same CPU.
401 */
402static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
403{
404    long curr;
405    long curr_nmi;
406    long snap;
407    long snap_nmi;
408
409    curr = rdp->dynticks->dynticks;
410    snap = rdp->dynticks_snap;
411    curr_nmi = rdp->dynticks->dynticks_nmi;
412    snap_nmi = rdp->dynticks_nmi_snap;
413    smp_mb(); /* force ordering with cpu entering/leaving dynticks. */
414
415    /*
416     * If the CPU passed through or entered a dynticks idle phase with
417     * no active irq/NMI handlers, then we can safely pretend that the CPU
418     * already acknowledged the request to pass through a quiescent
419     * state. Either way, that CPU cannot possibly be in an RCU
420     * read-side critical section that started before the beginning
421     * of the current RCU grace period.
422     */
423    if ((curr != snap || (curr & 0x1) == 0) &&
424        (curr_nmi != snap_nmi || (curr_nmi & 0x1) == 0)) {
425        rdp->dynticks_fqs++;
426        return 1;
427    }
428
429    /* Go check for the CPU being offline. */
430    return rcu_implicit_offline_qs(rdp);
431}
432
433#endif /* #ifdef CONFIG_SMP */
434
435#else /* #ifdef CONFIG_NO_HZ */
436
437#ifdef CONFIG_SMP
438
439static int dyntick_save_progress_counter(struct rcu_data *rdp)
440{
441    return 0;
442}
443
444static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
445{
446    return rcu_implicit_offline_qs(rdp);
447}
448
449#endif /* #ifdef CONFIG_SMP */
450
451#endif /* #else #ifdef CONFIG_NO_HZ */
452
453#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
454
455int rcu_cpu_stall_suppress __read_mostly;
456
457static void record_gp_stall_check_time(struct rcu_state *rsp)
458{
459    rsp->gp_start = jiffies;
460    rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK;
461}
462
463static void print_other_cpu_stall(struct rcu_state *rsp)
464{
465    int cpu;
466    long delta;
467    unsigned long flags;
468    struct rcu_node *rnp = rcu_get_root(rsp);
469
470    /* Only let one CPU complain about others per time interval. */
471
472    raw_spin_lock_irqsave(&rnp->lock, flags);
473    delta = jiffies - rsp->jiffies_stall;
474    if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
475        raw_spin_unlock_irqrestore(&rnp->lock, flags);
476        return;
477    }
478    rsp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
479
480    /*
481     * Now rat on any tasks that got kicked up to the root rcu_node
482     * due to CPU offlining.
483     */
484    rcu_print_task_stall(rnp);
485    raw_spin_unlock_irqrestore(&rnp->lock, flags);
486
487    /*
488     * OK, time to rat on our buddy...
489     * See Documentation/RCU/stallwarn.txt for info on how to debug
490     * RCU CPU stall warnings.
491     */
492    printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks: {",
493           rsp->name);
494    rcu_for_each_leaf_node(rsp, rnp) {
495        raw_spin_lock_irqsave(&rnp->lock, flags);
496        rcu_print_task_stall(rnp);
497        raw_spin_unlock_irqrestore(&rnp->lock, flags);
498        if (rnp->qsmask == 0)
499            continue;
500        for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
501            if (rnp->qsmask & (1UL << cpu))
502                printk(" %d", rnp->grplo + cpu);
503    }
504    printk("} (detected by %d, t=%ld jiffies)\n",
505           smp_processor_id(), (long)(jiffies - rsp->gp_start));
506    trigger_all_cpu_backtrace();
507
508    /* If so configured, complain about tasks blocking the grace period. */
509
510    rcu_print_detail_task_stall(rsp);
511
512    force_quiescent_state(rsp, 0); /* Kick them all. */
513}
514
515static void print_cpu_stall(struct rcu_state *rsp)
516{
517    unsigned long flags;
518    struct rcu_node *rnp = rcu_get_root(rsp);
519
520    /*
521     * OK, time to rat on ourselves...
522     * See Documentation/RCU/stallwarn.txt for info on how to debug
523     * RCU CPU stall warnings.
524     */
525    printk(KERN_ERR "INFO: %s detected stall on CPU %d (t=%lu jiffies)\n",
526           rsp->name, smp_processor_id(), jiffies - rsp->gp_start);
527    trigger_all_cpu_backtrace();
528
529    raw_spin_lock_irqsave(&rnp->lock, flags);
530    if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
531        rsp->jiffies_stall =
532            jiffies + RCU_SECONDS_TILL_STALL_RECHECK;
533    raw_spin_unlock_irqrestore(&rnp->lock, flags);
534
535    set_need_resched(); /* kick ourselves to get things going. */
536}
537
538static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
539{
540    long delta;
541    struct rcu_node *rnp;
542
543    if (rcu_cpu_stall_suppress)
544        return;
545    delta = jiffies - ACCESS_ONCE(rsp->jiffies_stall);
546    rnp = rdp->mynode;
547    if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && delta >= 0) {
548
549        /* We haven't checked in, so go dump stack. */
550        print_cpu_stall(rsp);
551
552    } else if (rcu_gp_in_progress(rsp) && delta >= RCU_STALL_RAT_DELAY) {
553
554        /* They had two time units to dump stack, so complain. */
555        print_other_cpu_stall(rsp);
556    }
557}
558
559static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
560{
561    rcu_cpu_stall_suppress = 1;
562    return NOTIFY_DONE;
563}
564
565/**
566 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
567 *
568 * Set the stall-warning timeout way off into the future, thus preventing
569 * any RCU CPU stall-warning messages from appearing in the current set of
570 * RCU grace periods.
571 *
572 * The caller must disable hard irqs.
573 */
574void rcu_cpu_stall_reset(void)
575{
576    rcu_sched_state.jiffies_stall = jiffies + ULONG_MAX / 2;
577    rcu_bh_state.jiffies_stall = jiffies + ULONG_MAX / 2;
578    rcu_preempt_stall_reset();
579}
580
581static struct notifier_block rcu_panic_block = {
582    .notifier_call = rcu_panic,
583};
584
585static void __init check_cpu_stall_init(void)
586{
587    atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
588}
589
590#else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
591
592static void record_gp_stall_check_time(struct rcu_state *rsp)
593{
594}
595
596static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
597{
598}
599
600void rcu_cpu_stall_reset(void)
601{
602}
603
604static void __init check_cpu_stall_init(void)
605{
606}
607
608#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
609
610/*
611 * Update CPU-local rcu_data state to record the newly noticed grace period.
612 * This is used both when we started the grace period and when we notice
613 * that someone else started the grace period. The caller must hold the
614 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
615 * and must have irqs disabled.
616 */
617static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
618{
619    if (rdp->gpnum != rnp->gpnum) {
620        /*
621         * If the current grace period is waiting for this CPU,
622         * set up to detect a quiescent state, otherwise don't
623         * go looking for one.
624         */
625        rdp->gpnum = rnp->gpnum;
626        if (rnp->qsmask & rdp->grpmask) {
627            rdp->qs_pending = 1;
628            rdp->passed_quiesc = 0;
629        } else
630            rdp->qs_pending = 0;
631    }
632}
633
634static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
635{
636    unsigned long flags;
637    struct rcu_node *rnp;
638
639    local_irq_save(flags);
640    rnp = rdp->mynode;
641    if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
642        !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
643        local_irq_restore(flags);
644        return;
645    }
646    __note_new_gpnum(rsp, rnp, rdp);
647    raw_spin_unlock_irqrestore(&rnp->lock, flags);
648}
649
650/*
651 * Did someone else start a new RCU grace period start since we last
652 * checked? Update local state appropriately if so. Must be called
653 * on the CPU corresponding to rdp.
654 */
655static int
656check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
657{
658    unsigned long flags;
659    int ret = 0;
660
661    local_irq_save(flags);
662    if (rdp->gpnum != rsp->gpnum) {
663        note_new_gpnum(rsp, rdp);
664        ret = 1;
665    }
666    local_irq_restore(flags);
667    return ret;
668}
669
670/*
671 * Advance this CPU's callbacks, but only if the current grace period
672 * has ended. This may be called only from the CPU to whom the rdp
673 * belongs. In addition, the corresponding leaf rcu_node structure's
674 * ->lock must be held by the caller, with irqs disabled.
675 */
676static void
677__rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
678{
679    /* Did another grace period end? */
680    if (rdp->completed != rnp->completed) {
681
682        /* Advance callbacks. No harm if list empty. */
683        rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
684        rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
685        rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
686
687        /* Remember that we saw this grace-period completion. */
688        rdp->completed = rnp->completed;
689
690        /*
691         * If we were in an extended quiescent state, we may have
692         * missed some grace periods that others CPUs handled on
693         * our behalf. Catch up with this state to avoid noting
694         * spurious new grace periods. If another grace period
695         * has started, then rnp->gpnum will have advanced, so
696         * we will detect this later on.
697         */
698        if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
699            rdp->gpnum = rdp->completed;
700
701        /*
702         * If RCU does not need a quiescent state from this CPU,
703         * then make sure that this CPU doesn't go looking for one.
704         */
705        if ((rnp->qsmask & rdp->grpmask) == 0)
706            rdp->qs_pending = 0;
707    }
708}
709
710/*
711 * Advance this CPU's callbacks, but only if the current grace period
712 * has ended. This may be called only from the CPU to whom the rdp
713 * belongs.
714 */
715static void
716rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
717{
718    unsigned long flags;
719    struct rcu_node *rnp;
720
721    local_irq_save(flags);
722    rnp = rdp->mynode;
723    if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
724        !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
725        local_irq_restore(flags);
726        return;
727    }
728    __rcu_process_gp_end(rsp, rnp, rdp);
729    raw_spin_unlock_irqrestore(&rnp->lock, flags);
730}
731
732/*
733 * Do per-CPU grace-period initialization for running CPU. The caller
734 * must hold the lock of the leaf rcu_node structure corresponding to
735 * this CPU.
736 */
737static void
738rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
739{
740    /* Prior grace period ended, so advance callbacks for current CPU. */
741    __rcu_process_gp_end(rsp, rnp, rdp);
742
743    /*
744     * Because this CPU just now started the new grace period, we know
745     * that all of its callbacks will be covered by this upcoming grace
746     * period, even the ones that were registered arbitrarily recently.
747     * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
748     *
749     * Other CPUs cannot be sure exactly when the grace period started.
750     * Therefore, their recently registered callbacks must pass through
751     * an additional RCU_NEXT_READY stage, so that they will be handled
752     * by the next RCU grace period.
753     */
754    rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
755    rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
756
757    /* Set state so that this CPU will detect the next quiescent state. */
758    __note_new_gpnum(rsp, rnp, rdp);
759}
760
761/*
762 * Start a new RCU grace period if warranted, re-initializing the hierarchy
763 * in preparation for detecting the next grace period. The caller must hold
764 * the root node's ->lock, which is released before return. Hard irqs must
765 * be disabled.
766 */
767static void
768rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
769    __releases(rcu_get_root(rsp)->lock)
770{
771    struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
772    struct rcu_node *rnp = rcu_get_root(rsp);
773
774    if (!cpu_needs_another_gp(rsp, rdp) || rsp->fqs_active) {
775        if (cpu_needs_another_gp(rsp, rdp))
776            rsp->fqs_need_gp = 1;
777        if (rnp->completed == rsp->completed) {
778            raw_spin_unlock_irqrestore(&rnp->lock, flags);
779            return;
780        }
781        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
782
783        /*
784         * Propagate new ->completed value to rcu_node structures
785         * so that other CPUs don't have to wait until the start
786         * of the next grace period to process their callbacks.
787         */
788        rcu_for_each_node_breadth_first(rsp, rnp) {
789            raw_spin_lock(&rnp->lock); /* irqs already disabled. */
790            rnp->completed = rsp->completed;
791            raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
792        }
793        local_irq_restore(flags);
794        return;
795    }
796
797    /* Advance to a new grace period and initialize state. */
798    rsp->gpnum++;
799    WARN_ON_ONCE(rsp->signaled == RCU_GP_INIT);
800    rsp->signaled = RCU_GP_INIT; /* Hold off force_quiescent_state. */
801    rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
802    record_gp_stall_check_time(rsp);
803
804    /* Special-case the common single-level case. */
805    if (NUM_RCU_NODES == 1) {
806        rcu_preempt_check_blocked_tasks(rnp);
807        rnp->qsmask = rnp->qsmaskinit;
808        rnp->gpnum = rsp->gpnum;
809        rnp->completed = rsp->completed;
810        rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state OK. */
811        rcu_start_gp_per_cpu(rsp, rnp, rdp);
812        raw_spin_unlock_irqrestore(&rnp->lock, flags);
813        return;
814    }
815
816    raw_spin_unlock(&rnp->lock); /* leave irqs disabled. */
817
818
819    /* Exclude any concurrent CPU-hotplug operations. */
820    raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
821
822    /*
823     * Set the quiescent-state-needed bits in all the rcu_node
824     * structures for all currently online CPUs in breadth-first
825     * order, starting from the root rcu_node structure. This
826     * operation relies on the layout of the hierarchy within the
827     * rsp->node[] array. Note that other CPUs will access only
828     * the leaves of the hierarchy, which still indicate that no
829     * grace period is in progress, at least until the corresponding
830     * leaf node has been initialized. In addition, we have excluded
831     * CPU-hotplug operations.
832     *
833     * Note that the grace period cannot complete until we finish
834     * the initialization process, as there will be at least one
835     * qsmask bit set in the root node until that time, namely the
836     * one corresponding to this CPU, due to the fact that we have
837     * irqs disabled.
838     */
839    rcu_for_each_node_breadth_first(rsp, rnp) {
840        raw_spin_lock(&rnp->lock); /* irqs already disabled. */
841        rcu_preempt_check_blocked_tasks(rnp);
842        rnp->qsmask = rnp->qsmaskinit;
843        rnp->gpnum = rsp->gpnum;
844        rnp->completed = rsp->completed;
845        if (rnp == rdp->mynode)
846            rcu_start_gp_per_cpu(rsp, rnp, rdp);
847        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
848    }
849
850    rnp = rcu_get_root(rsp);
851    raw_spin_lock(&rnp->lock); /* irqs already disabled. */
852    rsp->signaled = RCU_SIGNAL_INIT; /* force_quiescent_state now OK. */
853    raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
854    raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
855}
856
857/*
858 * Report a full set of quiescent states to the specified rcu_state
859 * data structure. This involves cleaning up after the prior grace
860 * period and letting rcu_start_gp() start up the next grace period
861 * if one is needed. Note that the caller must hold rnp->lock, as
862 * required by rcu_start_gp(), which will release it.
863 */
864static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
865    __releases(rcu_get_root(rsp)->lock)
866{
867    WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
868    rsp->completed = rsp->gpnum;
869    rsp->signaled = RCU_GP_IDLE;
870    rcu_start_gp(rsp, flags); /* releases root node's rnp->lock. */
871}
872
873/*
874 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
875 * Allows quiescent states for a group of CPUs to be reported at one go
876 * to the specified rcu_node structure, though all the CPUs in the group
877 * must be represented by the same rcu_node structure (which need not be
878 * a leaf rcu_node structure, though it often will be). That structure's
879 * lock must be held upon entry, and it is released before return.
880 */
881static void
882rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
883          struct rcu_node *rnp, unsigned long flags)
884    __releases(rnp->lock)
885{
886    struct rcu_node *rnp_c;
887
888    /* Walk up the rcu_node hierarchy. */
889    for (;;) {
890        if (!(rnp->qsmask & mask)) {
891
892            /* Our bit has already been cleared, so done. */
893            raw_spin_unlock_irqrestore(&rnp->lock, flags);
894            return;
895        }
896        rnp->qsmask &= ~mask;
897        if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
898
899            /* Other bits still set at this level, so done. */
900            raw_spin_unlock_irqrestore(&rnp->lock, flags);
901            return;
902        }
903        mask = rnp->grpmask;
904        if (rnp->parent == NULL) {
905
906            /* No more levels. Exit loop holding root lock. */
907
908            break;
909        }
910        raw_spin_unlock_irqrestore(&rnp->lock, flags);
911        rnp_c = rnp;
912        rnp = rnp->parent;
913        raw_spin_lock_irqsave(&rnp->lock, flags);
914        WARN_ON_ONCE(rnp_c->qsmask);
915    }
916
917    /*
918     * Get here if we are the last CPU to pass through a quiescent
919     * state for this grace period. Invoke rcu_report_qs_rsp()
920     * to clean up and start the next grace period if one is needed.
921     */
922    rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
923}
924
925/*
926 * Record a quiescent state for the specified CPU to that CPU's rcu_data
927 * structure. This must be either called from the specified CPU, or
928 * called when the specified CPU is known to be offline (and when it is
929 * also known that no other CPU is concurrently trying to help the offline
930 * CPU). The lastcomp argument is used to make sure we are still in the
931 * grace period of interest. We don't want to end the current grace period
932 * based on quiescent states detected in an earlier grace period!
933 */
934static void
935rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastcomp)
936{
937    unsigned long flags;
938    unsigned long mask;
939    struct rcu_node *rnp;
940
941    rnp = rdp->mynode;
942    raw_spin_lock_irqsave(&rnp->lock, flags);
943    if (lastcomp != rnp->completed) {
944
945        /*
946         * Someone beat us to it for this grace period, so leave.
947         * The race with GP start is resolved by the fact that we
948         * hold the leaf rcu_node lock, so that the per-CPU bits
949         * cannot yet be initialized -- so we would simply find our
950         * CPU's bit already cleared in rcu_report_qs_rnp() if this
951         * race occurred.
952         */
953        rdp->passed_quiesc = 0; /* try again later! */
954        raw_spin_unlock_irqrestore(&rnp->lock, flags);
955        return;
956    }
957    mask = rdp->grpmask;
958    if ((rnp->qsmask & mask) == 0) {
959        raw_spin_unlock_irqrestore(&rnp->lock, flags);
960    } else {
961        rdp->qs_pending = 0;
962
963        /*
964         * This GP can't end until cpu checks in, so all of our
965         * callbacks can be processed during the next GP.
966         */
967        rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
968
969        rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
970    }
971}
972
973/*
974 * Check to see if there is a new grace period of which this CPU
975 * is not yet aware, and if so, set up local rcu_data state for it.
976 * Otherwise, see if this CPU has just passed through its first
977 * quiescent state for this grace period, and record that fact if so.
978 */
979static void
980rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
981{
982    /* If there is now a new grace period, record and return. */
983    if (check_for_new_grace_period(rsp, rdp))
984        return;
985
986    /*
987     * Does this CPU still need to do its part for current grace period?
988     * If no, return and let the other CPUs do their part as well.
989     */
990    if (!rdp->qs_pending)
991        return;
992
993    /*
994     * Was there a quiescent state since the beginning of the grace
995     * period? If no, then exit and wait for the next call.
996     */
997    if (!rdp->passed_quiesc)
998        return;
999
1000    /*
1001     * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1002     * judge of that).
1003     */
1004    rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesc_completed);
1005}
1006
1007#ifdef CONFIG_HOTPLUG_CPU
1008
1009/*
1010 * Move a dying CPU's RCU callbacks to online CPU's callback list.
1011 * Synchronization is not required because this function executes
1012 * in stop_machine() context.
1013 */
1014static void rcu_send_cbs_to_online(struct rcu_state *rsp)
1015{
1016    int i;
1017    /* current DYING CPU is cleared in the cpu_online_mask */
1018    int receive_cpu = cpumask_any(cpu_online_mask);
1019    struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1020    struct rcu_data *receive_rdp = per_cpu_ptr(rsp->rda, receive_cpu);
1021
1022    if (rdp->nxtlist == NULL)
1023        return; /* irqs disabled, so comparison is stable. */
1024
1025    *receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxtlist;
1026    receive_rdp->nxttail[RCU_NEXT_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
1027    receive_rdp->qlen += rdp->qlen;
1028    receive_rdp->n_cbs_adopted += rdp->qlen;
1029    rdp->n_cbs_orphaned += rdp->qlen;
1030
1031    rdp->nxtlist = NULL;
1032    for (i = 0; i < RCU_NEXT_SIZE; i++)
1033        rdp->nxttail[i] = &rdp->nxtlist;
1034    rdp->qlen = 0;
1035}
1036
1037/*
1038 * Remove the outgoing CPU from the bitmasks in the rcu_node hierarchy
1039 * and move all callbacks from the outgoing CPU to the current one.
1040 */
1041static void __rcu_offline_cpu(int cpu, struct rcu_state *rsp)
1042{
1043    unsigned long flags;
1044    unsigned long mask;
1045    int need_report = 0;
1046    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1047    struct rcu_node *rnp;
1048
1049    /* Exclude any attempts to start a new grace period. */
1050    raw_spin_lock_irqsave(&rsp->onofflock, flags);
1051
1052    /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1053    rnp = rdp->mynode; /* this is the outgoing CPU's rnp. */
1054    mask = rdp->grpmask; /* rnp->grplo is constant. */
1055    do {
1056        raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1057        rnp->qsmaskinit &= ~mask;
1058        if (rnp->qsmaskinit != 0) {
1059            if (rnp != rdp->mynode)
1060                raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1061            break;
1062        }
1063        if (rnp == rdp->mynode)
1064            need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
1065        else
1066            raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1067        mask = rnp->grpmask;
1068        rnp = rnp->parent;
1069    } while (rnp != NULL);
1070
1071    /*
1072     * We still hold the leaf rcu_node structure lock here, and
1073     * irqs are still disabled. The reason for this subterfuge is
1074     * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1075     * held leads to deadlock.
1076     */
1077    raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
1078    rnp = rdp->mynode;
1079    if (need_report & RCU_OFL_TASKS_NORM_GP)
1080        rcu_report_unblock_qs_rnp(rnp, flags);
1081    else
1082        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1083    if (need_report & RCU_OFL_TASKS_EXP_GP)
1084        rcu_report_exp_rnp(rsp, rnp);
1085}
1086
1087/*
1088 * Remove the specified CPU from the RCU hierarchy and move any pending
1089 * callbacks that it might have to the current CPU. This code assumes
1090 * that at least one CPU in the system will remain running at all times.
1091 * Any attempt to offline -all- CPUs is likely to strand RCU callbacks.
1092 */
1093static void rcu_offline_cpu(int cpu)
1094{
1095    __rcu_offline_cpu(cpu, &rcu_sched_state);
1096    __rcu_offline_cpu(cpu, &rcu_bh_state);
1097    rcu_preempt_offline_cpu(cpu);
1098}
1099
1100#else /* #ifdef CONFIG_HOTPLUG_CPU */
1101
1102static void rcu_send_cbs_to_online(struct rcu_state *rsp)
1103{
1104}
1105
1106static void rcu_offline_cpu(int cpu)
1107{
1108}
1109
1110#endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1111
1112/*
1113 * Invoke any RCU callbacks that have made it to the end of their grace
1114 * period. Thottle as specified by rdp->blimit.
1115 */
1116static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1117{
1118    unsigned long flags;
1119    struct rcu_head *next, *list, **tail;
1120    int count;
1121
1122    /* If no callbacks are ready, just return.*/
1123    if (!cpu_has_callbacks_ready_to_invoke(rdp))
1124        return;
1125
1126    /*
1127     * Extract the list of ready callbacks, disabling to prevent
1128     * races with call_rcu() from interrupt handlers.
1129     */
1130    local_irq_save(flags);
1131    list = rdp->nxtlist;
1132    rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
1133    *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1134    tail = rdp->nxttail[RCU_DONE_TAIL];
1135    for (count = RCU_NEXT_SIZE - 1; count >= 0; count--)
1136        if (rdp->nxttail[count] == rdp->nxttail[RCU_DONE_TAIL])
1137            rdp->nxttail[count] = &rdp->nxtlist;
1138    local_irq_restore(flags);
1139
1140    /* Invoke callbacks. */
1141    count = 0;
1142    while (list) {
1143        next = list->next;
1144        prefetch(next);
1145        debug_rcu_head_unqueue(list);
1146        list->func(list);
1147        list = next;
1148        if (++count >= rdp->blimit)
1149            break;
1150    }
1151
1152    local_irq_save(flags);
1153
1154    /* Update count, and requeue any remaining callbacks. */
1155    rdp->qlen -= count;
1156    rdp->n_cbs_invoked += count;
1157    if (list != NULL) {
1158        *tail = rdp->nxtlist;
1159        rdp->nxtlist = list;
1160        for (count = 0; count < RCU_NEXT_SIZE; count++)
1161            if (&rdp->nxtlist == rdp->nxttail[count])
1162                rdp->nxttail[count] = tail;
1163            else
1164                break;
1165    }
1166
1167    /* Reinstate batch limit if we have worked down the excess. */
1168    if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
1169        rdp->blimit = blimit;
1170
1171    /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1172    if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
1173        rdp->qlen_last_fqs_check = 0;
1174        rdp->n_force_qs_snap = rsp->n_force_qs;
1175    } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
1176        rdp->qlen_last_fqs_check = rdp->qlen;
1177
1178    local_irq_restore(flags);
1179
1180    /* Re-raise the RCU softirq if there are callbacks remaining. */
1181    if (cpu_has_callbacks_ready_to_invoke(rdp))
1182        raise_softirq(RCU_SOFTIRQ);
1183}
1184
1185/*
1186 * Check to see if this CPU is in a non-context-switch quiescent state
1187 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1188 * Also schedule the RCU softirq handler.
1189 *
1190 * This function must be called with hardirqs disabled. It is normally
1191 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1192 * false, there is no point in invoking rcu_check_callbacks().
1193 */
1194void rcu_check_callbacks(int cpu, int user)
1195{
1196    if (user ||
1197        (idle_cpu(cpu) && rcu_scheduler_active &&
1198         !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
1199
1200        /*
1201         * Get here if this CPU took its interrupt from user
1202         * mode or from the idle loop, and if this is not a
1203         * nested interrupt. In this case, the CPU is in
1204         * a quiescent state, so note it.
1205         *
1206         * No memory barrier is required here because both
1207         * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1208         * variables that other CPUs neither access nor modify,
1209         * at least not while the corresponding CPU is online.
1210         */
1211
1212        rcu_sched_qs(cpu);
1213        rcu_bh_qs(cpu);
1214
1215    } else if (!in_softirq()) {
1216
1217        /*
1218         * Get here if this CPU did not take its interrupt from
1219         * softirq, in other words, if it is not interrupting
1220         * a rcu_bh read-side critical section. This is an _bh
1221         * critical section, so note it.
1222         */
1223
1224        rcu_bh_qs(cpu);
1225    }
1226    rcu_preempt_check_callbacks(cpu);
1227    if (rcu_pending(cpu))
1228        raise_softirq(RCU_SOFTIRQ);
1229}
1230
1231#ifdef CONFIG_SMP
1232
1233/*
1234 * Scan the leaf rcu_node structures, processing dyntick state for any that
1235 * have not yet encountered a quiescent state, using the function specified.
1236 * The caller must have suppressed start of new grace periods.
1237 */
1238static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1239{
1240    unsigned long bit;
1241    int cpu;
1242    unsigned long flags;
1243    unsigned long mask;
1244    struct rcu_node *rnp;
1245
1246    rcu_for_each_leaf_node(rsp, rnp) {
1247        mask = 0;
1248        raw_spin_lock_irqsave(&rnp->lock, flags);
1249        if (!rcu_gp_in_progress(rsp)) {
1250            raw_spin_unlock_irqrestore(&rnp->lock, flags);
1251            return;
1252        }
1253        if (rnp->qsmask == 0) {
1254            raw_spin_unlock_irqrestore(&rnp->lock, flags);
1255            continue;
1256        }
1257        cpu = rnp->grplo;
1258        bit = 1;
1259        for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1260            if ((rnp->qsmask & bit) != 0 &&
1261                f(per_cpu_ptr(rsp->rda, cpu)))
1262                mask |= bit;
1263        }
1264        if (mask != 0) {
1265
1266            /* rcu_report_qs_rnp() releases rnp->lock. */
1267            rcu_report_qs_rnp(mask, rsp, rnp, flags);
1268            continue;
1269        }
1270        raw_spin_unlock_irqrestore(&rnp->lock, flags);
1271    }
1272}
1273
1274/*
1275 * Force quiescent states on reluctant CPUs, and also detect which
1276 * CPUs are in dyntick-idle mode.
1277 */
1278static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1279{
1280    unsigned long flags;
1281    struct rcu_node *rnp = rcu_get_root(rsp);
1282
1283    if (!rcu_gp_in_progress(rsp))
1284        return; /* No grace period in progress, nothing to force. */
1285    if (!raw_spin_trylock_irqsave(&rsp->fqslock, flags)) {
1286        rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1287        return; /* Someone else is already on the job. */
1288    }
1289    if (relaxed && ULONG_CMP_GE(rsp->jiffies_force_qs, jiffies))
1290        goto unlock_fqs_ret; /* no emergency and done recently. */
1291    rsp->n_force_qs++;
1292    raw_spin_lock(&rnp->lock); /* irqs already disabled */
1293    rsp->jiffies_force_qs = jiffies + RCU_JIFFIES_TILL_FORCE_QS;
1294    if(!rcu_gp_in_progress(rsp)) {
1295        rsp->n_force_qs_ngp++;
1296        raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1297        goto unlock_fqs_ret; /* no GP in progress, time updated. */
1298    }
1299    rsp->fqs_active = 1;
1300    switch (rsp->signaled) {
1301    case RCU_GP_IDLE:
1302    case RCU_GP_INIT:
1303
1304        break; /* grace period idle or initializing, ignore. */
1305
1306    case RCU_SAVE_DYNTICK:
1307        if (RCU_SIGNAL_INIT != RCU_SAVE_DYNTICK)
1308            break; /* So gcc recognizes the dead code. */
1309
1310        raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1311
1312        /* Record dyntick-idle state. */
1313        force_qs_rnp(rsp, dyntick_save_progress_counter);
1314        raw_spin_lock(&rnp->lock); /* irqs already disabled */
1315        if (rcu_gp_in_progress(rsp))
1316            rsp->signaled = RCU_FORCE_QS;
1317        break;
1318
1319    case RCU_FORCE_QS:
1320
1321        /* Check dyntick-idle state, send IPI to laggarts. */
1322        raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1323        force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1324
1325        /* Leave state in case more forcing is required. */
1326
1327        raw_spin_lock(&rnp->lock); /* irqs already disabled */
1328        break;
1329    }
1330    rsp->fqs_active = 0;
1331    if (rsp->fqs_need_gp) {
1332        raw_spin_unlock(&rsp->fqslock); /* irqs remain disabled */
1333        rsp->fqs_need_gp = 0;
1334        rcu_start_gp(rsp, flags); /* releases rnp->lock */
1335        return;
1336    }
1337    raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
1338unlock_fqs_ret:
1339    raw_spin_unlock_irqrestore(&rsp->fqslock, flags);
1340}
1341
1342#else /* #ifdef CONFIG_SMP */
1343
1344static void force_quiescent_state(struct rcu_state *rsp, int relaxed)
1345{
1346    set_need_resched();
1347}
1348
1349#endif /* #else #ifdef CONFIG_SMP */
1350
1351/*
1352 * This does the RCU processing work from softirq context for the
1353 * specified rcu_state and rcu_data structures. This may be called
1354 * only from the CPU to whom the rdp belongs.
1355 */
1356static void
1357__rcu_process_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1358{
1359    unsigned long flags;
1360
1361    WARN_ON_ONCE(rdp->beenonline == 0);
1362
1363    /*
1364     * If an RCU GP has gone long enough, go check for dyntick
1365     * idle CPUs and, if needed, send resched IPIs.
1366     */
1367    if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1368        force_quiescent_state(rsp, 1);
1369
1370    /*
1371     * Advance callbacks in response to end of earlier grace
1372     * period that some other CPU ended.
1373     */
1374    rcu_process_gp_end(rsp, rdp);
1375
1376    /* Update RCU state based on any recent quiescent states. */
1377    rcu_check_quiescent_state(rsp, rdp);
1378
1379    /* Does this CPU require a not-yet-started grace period? */
1380    if (cpu_needs_another_gp(rsp, rdp)) {
1381        raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1382        rcu_start_gp(rsp, flags); /* releases above lock */
1383    }
1384
1385    /* If there are callbacks ready, invoke them. */
1386    rcu_do_batch(rsp, rdp);
1387}
1388
1389/*
1390 * Do softirq processing for the current CPU.
1391 */
1392static void rcu_process_callbacks(struct softirq_action *unused)
1393{
1394    /*
1395     * Memory references from any prior RCU read-side critical sections
1396     * executed by the interrupted code must be seen before any RCU
1397     * grace-period manipulations below.
1398     */
1399    smp_mb(); /* See above block comment. */
1400
1401    __rcu_process_callbacks(&rcu_sched_state,
1402                &__get_cpu_var(rcu_sched_data));
1403    __rcu_process_callbacks(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1404    rcu_preempt_process_callbacks();
1405
1406    /*
1407     * Memory references from any later RCU read-side critical sections
1408     * executed by the interrupted code must be seen after any RCU
1409     * grace-period manipulations above.
1410     */
1411    smp_mb(); /* See above block comment. */
1412
1413    /* If we are last CPU on way to dyntick-idle mode, accelerate it. */
1414    rcu_needs_cpu_flush();
1415}
1416
1417static void
1418__call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1419       struct rcu_state *rsp)
1420{
1421    unsigned long flags;
1422    struct rcu_data *rdp;
1423
1424    debug_rcu_head_queue(head);
1425    head->func = func;
1426    head->next = NULL;
1427
1428    smp_mb(); /* Ensure RCU update seen before callback registry. */
1429
1430    /*
1431     * Opportunistically note grace-period endings and beginnings.
1432     * Note that we might see a beginning right after we see an
1433     * end, but never vice versa, since this CPU has to pass through
1434     * a quiescent state betweentimes.
1435     */
1436    local_irq_save(flags);
1437    rdp = this_cpu_ptr(rsp->rda);
1438
1439    /* Add the callback to our list. */
1440    *rdp->nxttail[RCU_NEXT_TAIL] = head;
1441    rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1442
1443    /*
1444     * Force the grace period if too many callbacks or too long waiting.
1445     * Enforce hysteresis, and don't invoke force_quiescent_state()
1446     * if some other CPU has recently done so. Also, don't bother
1447     * invoking force_quiescent_state() if the newly enqueued callback
1448     * is the only one waiting for a grace period to complete.
1449     */
1450    if (unlikely(++rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1451
1452        /* Are we ignoring a completed grace period? */
1453        rcu_process_gp_end(rsp, rdp);
1454        check_for_new_grace_period(rsp, rdp);
1455
1456        /* Start a new grace period if one not already started. */
1457        if (!rcu_gp_in_progress(rsp)) {
1458            unsigned long nestflag;
1459            struct rcu_node *rnp_root = rcu_get_root(rsp);
1460
1461            raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
1462            rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */
1463        } else {
1464            /* Give the grace period a kick. */
1465            rdp->blimit = LONG_MAX;
1466            if (rsp->n_force_qs == rdp->n_force_qs_snap &&
1467                *rdp->nxttail[RCU_DONE_TAIL] != head)
1468                force_quiescent_state(rsp, 0);
1469            rdp->n_force_qs_snap = rsp->n_force_qs;
1470            rdp->qlen_last_fqs_check = rdp->qlen;
1471        }
1472    } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies))
1473        force_quiescent_state(rsp, 1);
1474    local_irq_restore(flags);
1475}
1476
1477/*
1478 * Queue an RCU-sched callback for invocation after a grace period.
1479 */
1480void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1481{
1482    __call_rcu(head, func, &rcu_sched_state);
1483}
1484EXPORT_SYMBOL_GPL(call_rcu_sched);
1485
1486/*
1487 * Queue an RCU for invocation after a quicker grace period.
1488 */
1489void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1490{
1491    __call_rcu(head, func, &rcu_bh_state);
1492}
1493EXPORT_SYMBOL_GPL(call_rcu_bh);
1494
1495/**
1496 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1497 *
1498 * Control will return to the caller some time after a full rcu-sched
1499 * grace period has elapsed, in other words after all currently executing
1500 * rcu-sched read-side critical sections have completed. These read-side
1501 * critical sections are delimited by rcu_read_lock_sched() and
1502 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
1503 * local_irq_disable(), and so on may be used in place of
1504 * rcu_read_lock_sched().
1505 *
1506 * This means that all preempt_disable code sequences, including NMI and
1507 * hardware-interrupt handlers, in progress on entry will have completed
1508 * before this primitive returns. However, this does not guarantee that
1509 * softirq handlers will have completed, since in some kernels, these
1510 * handlers can run in process context, and can block.
1511 *
1512 * This primitive provides the guarantees made by the (now removed)
1513 * synchronize_kernel() API. In contrast, synchronize_rcu() only
1514 * guarantees that rcu_read_lock() sections will have completed.
1515 * In "classic RCU", these two guarantees happen to be one and
1516 * the same, but can differ in realtime RCU implementations.
1517 */
1518void synchronize_sched(void)
1519{
1520    struct rcu_synchronize rcu;
1521
1522    if (rcu_blocking_is_gp())
1523        return;
1524
1525    init_rcu_head_on_stack(&rcu.head);
1526    init_completion(&rcu.completion);
1527    /* Will wake me after RCU finished. */
1528    call_rcu_sched(&rcu.head, wakeme_after_rcu);
1529    /* Wait for it. */
1530    wait_for_completion(&rcu.completion);
1531    destroy_rcu_head_on_stack(&rcu.head);
1532}
1533EXPORT_SYMBOL_GPL(synchronize_sched);
1534
1535/**
1536 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
1537 *
1538 * Control will return to the caller some time after a full rcu_bh grace
1539 * period has elapsed, in other words after all currently executing rcu_bh
1540 * read-side critical sections have completed. RCU read-side critical
1541 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
1542 * and may be nested.
1543 */
1544void synchronize_rcu_bh(void)
1545{
1546    struct rcu_synchronize rcu;
1547
1548    if (rcu_blocking_is_gp())
1549        return;
1550
1551    init_rcu_head_on_stack(&rcu.head);
1552    init_completion(&rcu.completion);
1553    /* Will wake me after RCU finished. */
1554    call_rcu_bh(&rcu.head, wakeme_after_rcu);
1555    /* Wait for it. */
1556    wait_for_completion(&rcu.completion);
1557    destroy_rcu_head_on_stack(&rcu.head);
1558}
1559EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
1560
1561/*
1562 * Check to see if there is any immediate RCU-related work to be done
1563 * by the current CPU, for the specified type of RCU, returning 1 if so.
1564 * The checks are in order of increasing expense: checks that can be
1565 * carried out against CPU-local state are performed first. However,
1566 * we must check for CPU stalls first, else we might not get a chance.
1567 */
1568static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
1569{
1570    struct rcu_node *rnp = rdp->mynode;
1571
1572    rdp->n_rcu_pending++;
1573
1574    /* Check for CPU stalls, if enabled. */
1575    check_cpu_stall(rsp, rdp);
1576
1577    /* Is the RCU core waiting for a quiescent state from this CPU? */
1578    if (rdp->qs_pending && !rdp->passed_quiesc) {
1579
1580        /*
1581         * If force_quiescent_state() coming soon and this CPU
1582         * needs a quiescent state, and this is either RCU-sched
1583         * or RCU-bh, force a local reschedule.
1584         */
1585        rdp->n_rp_qs_pending++;
1586        if (!rdp->preemptable &&
1587            ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs) - 1,
1588                 jiffies))
1589            set_need_resched();
1590    } else if (rdp->qs_pending && rdp->passed_quiesc) {
1591        rdp->n_rp_report_qs++;
1592        return 1;
1593    }
1594
1595    /* Does this CPU have callbacks ready to invoke? */
1596    if (cpu_has_callbacks_ready_to_invoke(rdp)) {
1597        rdp->n_rp_cb_ready++;
1598        return 1;
1599    }
1600
1601    /* Has RCU gone idle with this CPU needing another grace period? */
1602    if (cpu_needs_another_gp(rsp, rdp)) {
1603        rdp->n_rp_cpu_needs_gp++;
1604        return 1;
1605    }
1606
1607    /* Has another RCU grace period completed? */
1608    if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
1609        rdp->n_rp_gp_completed++;
1610        return 1;
1611    }
1612
1613    /* Has a new RCU grace period started? */
1614    if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
1615        rdp->n_rp_gp_started++;
1616        return 1;
1617    }
1618
1619    /* Has an RCU GP gone long enough to send resched IPIs &c? */
1620    if (rcu_gp_in_progress(rsp) &&
1621        ULONG_CMP_LT(ACCESS_ONCE(rsp->jiffies_force_qs), jiffies)) {
1622        rdp->n_rp_need_fqs++;
1623        return 1;
1624    }
1625
1626    /* nothing to do */
1627    rdp->n_rp_need_nothing++;
1628    return 0;
1629}
1630
1631/*
1632 * Check to see if there is any immediate RCU-related work to be done
1633 * by the current CPU, returning 1 if so. This function is part of the
1634 * RCU implementation; it is -not- an exported member of the RCU API.
1635 */
1636static int rcu_pending(int cpu)
1637{
1638    return __rcu_pending(&rcu_sched_state, &per_cpu(rcu_sched_data, cpu)) ||
1639           __rcu_pending(&rcu_bh_state, &per_cpu(rcu_bh_data, cpu)) ||
1640           rcu_preempt_pending(cpu);
1641}
1642
1643/*
1644 * Check to see if any future RCU-related work will need to be done
1645 * by the current CPU, even if none need be done immediately, returning
1646 * 1 if so.
1647 */
1648static int rcu_needs_cpu_quick_check(int cpu)
1649{
1650    /* RCU callbacks either ready or pending? */
1651    return per_cpu(rcu_sched_data, cpu).nxtlist ||
1652           per_cpu(rcu_bh_data, cpu).nxtlist ||
1653           rcu_preempt_needs_cpu(cpu);
1654}
1655
1656static DEFINE_PER_CPU(struct rcu_head, rcu_barrier_head) = {NULL};
1657static atomic_t rcu_barrier_cpu_count;
1658static DEFINE_MUTEX(rcu_barrier_mutex);
1659static struct completion rcu_barrier_completion;
1660
1661static void rcu_barrier_callback(struct rcu_head *notused)
1662{
1663    if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1664        complete(&rcu_barrier_completion);
1665}
1666
1667/*
1668 * Called with preemption disabled, and from cross-cpu IRQ context.
1669 */
1670static void rcu_barrier_func(void *type)
1671{
1672    int cpu = smp_processor_id();
1673    struct rcu_head *head = &per_cpu(rcu_barrier_head, cpu);
1674    void (*call_rcu_func)(struct rcu_head *head,
1675                  void (*func)(struct rcu_head *head));
1676
1677    atomic_inc(&rcu_barrier_cpu_count);
1678    call_rcu_func = type;
1679    call_rcu_func(head, rcu_barrier_callback);
1680}
1681
1682/*
1683 * Orchestrate the specified type of RCU barrier, waiting for all
1684 * RCU callbacks of the specified type to complete.
1685 */
1686static void _rcu_barrier(struct rcu_state *rsp,
1687             void (*call_rcu_func)(struct rcu_head *head,
1688                           void (*func)(struct rcu_head *head)))
1689{
1690    BUG_ON(in_interrupt());
1691    /* Take mutex to serialize concurrent rcu_barrier() requests. */
1692    mutex_lock(&rcu_barrier_mutex);
1693    init_completion(&rcu_barrier_completion);
1694    /*
1695     * Initialize rcu_barrier_cpu_count to 1, then invoke
1696     * rcu_barrier_func() on each CPU, so that each CPU also has
1697     * incremented rcu_barrier_cpu_count. Only then is it safe to
1698     * decrement rcu_barrier_cpu_count -- otherwise the first CPU
1699     * might complete its grace period before all of the other CPUs
1700     * did their increment, causing this function to return too
1701     * early. Note that on_each_cpu() disables irqs, which prevents
1702     * any CPUs from coming online or going offline until each online
1703     * CPU has queued its RCU-barrier callback.
1704     */
1705    atomic_set(&rcu_barrier_cpu_count, 1);
1706    on_each_cpu(rcu_barrier_func, (void *)call_rcu_func, 1);
1707    if (atomic_dec_and_test(&rcu_barrier_cpu_count))
1708        complete(&rcu_barrier_completion);
1709    wait_for_completion(&rcu_barrier_completion);
1710    mutex_unlock(&rcu_barrier_mutex);
1711}
1712
1713/**
1714 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
1715 */
1716void rcu_barrier_bh(void)
1717{
1718    _rcu_barrier(&rcu_bh_state, call_rcu_bh);
1719}
1720EXPORT_SYMBOL_GPL(rcu_barrier_bh);
1721
1722/**
1723 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
1724 */
1725void rcu_barrier_sched(void)
1726{
1727    _rcu_barrier(&rcu_sched_state, call_rcu_sched);
1728}
1729EXPORT_SYMBOL_GPL(rcu_barrier_sched);
1730
1731/*
1732 * Do boot-time initialization of a CPU's per-CPU RCU data.
1733 */
1734static void __init
1735rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
1736{
1737    unsigned long flags;
1738    int i;
1739    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1740    struct rcu_node *rnp = rcu_get_root(rsp);
1741
1742    /* Set up local state, ensuring consistent view of global state. */
1743    raw_spin_lock_irqsave(&rnp->lock, flags);
1744    rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
1745    rdp->nxtlist = NULL;
1746    for (i = 0; i < RCU_NEXT_SIZE; i++)
1747        rdp->nxttail[i] = &rdp->nxtlist;
1748    rdp->qlen = 0;
1749#ifdef CONFIG_NO_HZ
1750    rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
1751#endif /* #ifdef CONFIG_NO_HZ */
1752    rdp->cpu = cpu;
1753    raw_spin_unlock_irqrestore(&rnp->lock, flags);
1754}
1755
1756/*
1757 * Initialize a CPU's per-CPU RCU data. Note that only one online or
1758 * offline event can be happening at a given time. Note also that we
1759 * can accept some slop in the rsp->completed access due to the fact
1760 * that this CPU cannot possibly have any RCU callbacks in flight yet.
1761 */
1762static void __cpuinit
1763rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptable)
1764{
1765    unsigned long flags;
1766    unsigned long mask;
1767    struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1768    struct rcu_node *rnp = rcu_get_root(rsp);
1769
1770    /* Set up local state, ensuring consistent view of global state. */
1771    raw_spin_lock_irqsave(&rnp->lock, flags);
1772    rdp->passed_quiesc = 0; /* We could be racing with new GP, */
1773    rdp->qs_pending = 1; /* so set up to respond to current GP. */
1774    rdp->beenonline = 1; /* We have now been online. */
1775    rdp->preemptable = preemptable;
1776    rdp->qlen_last_fqs_check = 0;
1777    rdp->n_force_qs_snap = rsp->n_force_qs;
1778    rdp->blimit = blimit;
1779    raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1780
1781    /*
1782     * A new grace period might start here. If so, we won't be part
1783     * of it, but that is OK, as we are currently in a quiescent state.
1784     */
1785
1786    /* Exclude any attempts to start a new GP on large systems. */
1787    raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
1788
1789    /* Add CPU to rcu_node bitmasks. */
1790    rnp = rdp->mynode;
1791    mask = rdp->grpmask;
1792    do {
1793        /* Exclude any attempts to start a new GP on small systems. */
1794        raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1795        rnp->qsmaskinit |= mask;
1796        mask = rnp->grpmask;
1797        if (rnp == rdp->mynode) {
1798            rdp->gpnum = rnp->completed; /* if GP in progress... */
1799            rdp->completed = rnp->completed;
1800            rdp->passed_quiesc_completed = rnp->completed - 1;
1801        }
1802        raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
1803        rnp = rnp->parent;
1804    } while (rnp != NULL && !(rnp->qsmaskinit & mask));
1805
1806    raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
1807}
1808
1809static void __cpuinit rcu_online_cpu(int cpu)
1810{
1811    rcu_init_percpu_data(cpu, &rcu_sched_state, 0);
1812    rcu_init_percpu_data(cpu, &rcu_bh_state, 0);
1813    rcu_preempt_init_percpu_data(cpu);
1814}
1815
1816/*
1817 * Handle CPU online/offline notification events.
1818 */
1819static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
1820                    unsigned long action, void *hcpu)
1821{
1822    long cpu = (long)hcpu;
1823
1824    switch (action) {
1825    case CPU_UP_PREPARE:
1826    case CPU_UP_PREPARE_FROZEN:
1827        rcu_online_cpu(cpu);
1828        break;
1829    case CPU_DYING:
1830    case CPU_DYING_FROZEN:
1831        /*
1832         * The whole machine is "stopped" except this CPU, so we can
1833         * touch any data without introducing corruption. We send the
1834         * dying CPU's callbacks to an arbitrarily chosen online CPU.
1835         */
1836        rcu_send_cbs_to_online(&rcu_bh_state);
1837        rcu_send_cbs_to_online(&rcu_sched_state);
1838        rcu_preempt_send_cbs_to_online();
1839        break;
1840    case CPU_DEAD:
1841    case CPU_DEAD_FROZEN:
1842    case CPU_UP_CANCELED:
1843    case CPU_UP_CANCELED_FROZEN:
1844        rcu_offline_cpu(cpu);
1845        break;
1846    default:
1847        break;
1848    }
1849    return NOTIFY_OK;
1850}
1851
1852/*
1853 * This function is invoked towards the end of the scheduler's initialization
1854 * process. Before this is called, the idle task might contain
1855 * RCU read-side critical sections (during which time, this idle
1856 * task is booting the system). After this function is called, the
1857 * idle tasks are prohibited from containing RCU read-side critical
1858 * sections. This function also enables RCU lockdep checking.
1859 */
1860void rcu_scheduler_starting(void)
1861{
1862    WARN_ON(num_online_cpus() != 1);
1863    WARN_ON(nr_context_switches() > 0);
1864    rcu_scheduler_active = 1;
1865}
1866
1867/*
1868 * Compute the per-level fanout, either using the exact fanout specified
1869 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
1870 */
1871#ifdef CONFIG_RCU_FANOUT_EXACT
1872static void __init rcu_init_levelspread(struct rcu_state *rsp)
1873{
1874    int i;
1875
1876    for (i = NUM_RCU_LVLS - 1; i > 0; i--)
1877        rsp->levelspread[i] = CONFIG_RCU_FANOUT;
1878    rsp->levelspread[0] = RCU_FANOUT_LEAF;
1879}
1880#else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
1881static void __init rcu_init_levelspread(struct rcu_state *rsp)
1882{
1883    int ccur;
1884    int cprv;
1885    int i;
1886
1887    cprv = NR_CPUS;
1888    for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1889        ccur = rsp->levelcnt[i];
1890        rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
1891        cprv = ccur;
1892    }
1893}
1894#endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
1895
1896/*
1897 * Helper function for rcu_init() that initializes one rcu_state structure.
1898 */
1899static void __init rcu_init_one(struct rcu_state *rsp,
1900        struct rcu_data __percpu *rda)
1901{
1902    static char *buf[] = { "rcu_node_level_0",
1903                   "rcu_node_level_1",
1904                   "rcu_node_level_2",
1905                   "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
1906    int cpustride = 1;
1907    int i;
1908    int j;
1909    struct rcu_node *rnp;
1910
1911    BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
1912
1913    /* Initialize the level-tracking arrays. */
1914
1915    for (i = 1; i < NUM_RCU_LVLS; i++)
1916        rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
1917    rcu_init_levelspread(rsp);
1918
1919    /* Initialize the elements themselves, starting from the leaves. */
1920
1921    for (i = NUM_RCU_LVLS - 1; i >= 0; i--) {
1922        cpustride *= rsp->levelspread[i];
1923        rnp = rsp->level[i];
1924        for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
1925            raw_spin_lock_init(&rnp->lock);
1926            lockdep_set_class_and_name(&rnp->lock,
1927                           &rcu_node_class[i], buf[i]);
1928            rnp->gpnum = 0;
1929            rnp->qsmask = 0;
1930            rnp->qsmaskinit = 0;
1931            rnp->grplo = j * cpustride;
1932            rnp->grphi = (j + 1) * cpustride - 1;
1933            if (rnp->grphi >= NR_CPUS)
1934                rnp->grphi = NR_CPUS - 1;
1935            if (i == 0) {
1936                rnp->grpnum = 0;
1937                rnp->grpmask = 0;
1938                rnp->parent = NULL;
1939            } else {
1940                rnp->grpnum = j % rsp->levelspread[i - 1];
1941                rnp->grpmask = 1UL << rnp->grpnum;
1942                rnp->parent = rsp->level[i - 1] +
1943                          j / rsp->levelspread[i - 1];
1944            }
1945            rnp->level = i;
1946            INIT_LIST_HEAD(&rnp->blocked_tasks[0]);
1947            INIT_LIST_HEAD(&rnp->blocked_tasks[1]);
1948            INIT_LIST_HEAD(&rnp->blocked_tasks[2]);
1949            INIT_LIST_HEAD(&rnp->blocked_tasks[3]);
1950        }
1951    }
1952
1953    rsp->rda = rda;
1954    rnp = rsp->level[NUM_RCU_LVLS - 1];
1955    for_each_possible_cpu(i) {
1956        while (i > rnp->grphi)
1957            rnp++;
1958        per_cpu_ptr(rsp->rda, i)->mynode = rnp;
1959        rcu_boot_init_percpu_data(i, rsp);
1960    }
1961}
1962
1963void __init rcu_init(void)
1964{
1965    int cpu;
1966
1967    rcu_bootup_announce();
1968    rcu_init_one(&rcu_sched_state, &rcu_sched_data);
1969    rcu_init_one(&rcu_bh_state, &rcu_bh_data);
1970    __rcu_init_preempt();
1971    open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
1972
1973    /*
1974     * We don't need protection against CPU-hotplug here because
1975     * this is called early in boot, before either interrupts
1976     * or the scheduler are operational.
1977     */
1978    cpu_notifier(rcu_cpu_notify, 0);
1979    for_each_online_cpu(cpu)
1980        rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
1981    check_cpu_stall_init();
1982}
1983
1984#include "rcutree_plugin.h"
1985

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