2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2008
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
27 * For detailed explanation of Read-Copy Update mechanism see -
30 #include <linux/types.h>
31 #include <linux/kernel.h>
32 #include <linux/init.h>
33 #include <linux/spinlock.h>
34 #include <linux/smp.h>
35 #include <linux/rcupdate.h>
36 #include <linux/interrupt.h>
37 #include <linux/sched.h>
38 #include <linux/nmi.h>
39 #include <linux/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/export.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 #include <linux/wait.h>
51 #include <linux/kthread.h>
52 #include <linux/prefetch.h>
53 #include <linux/delay.h>
54 #include <linux/stop_machine.h>
57 #include <trace/events/rcu.h>
61 /* Data structures. */
63 static struct lock_class_key rcu_node_class[RCU_NUM_LVLS];
65 #define RCU_STATE_INITIALIZER(sname, cr) { \
66 .level = { &sname##_state.node[0] }, \
68 .fqs_state = RCU_GP_IDLE, \
71 .onofflock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.onofflock), \
72 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
73 .orphan_donetail = &sname##_state.orphan_donelist, \
74 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
78 struct rcu_state rcu_sched_state =
79 RCU_STATE_INITIALIZER(rcu_sched, call_rcu_sched);
80 DEFINE_PER_CPU(struct rcu_data, rcu_sched_data);
82 struct rcu_state rcu_bh_state = RCU_STATE_INITIALIZER(rcu_bh, call_rcu_bh);
83 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data);
85 static struct rcu_state *rcu_state;
86 LIST_HEAD(rcu_struct_flavors);
88 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
89 static int rcu_fanout_leaf = CONFIG_RCU_FANOUT_LEAF;
90 module_param(rcu_fanout_leaf, int, 0);
91 int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;
92 static int num_rcu_lvl[] = { /* Number of rcu_nodes at specified level. */
99 int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
102 * The rcu_scheduler_active variable transitions from zero to one just
103 * before the first task is spawned. So when this variable is zero, RCU
104 * can assume that there is but one task, allowing RCU to (for example)
105 * optimized synchronize_sched() to a simple barrier(). When this variable
106 * is one, RCU must actually do all the hard work required to detect real
107 * grace periods. This variable is also used to suppress boot-time false
108 * positives from lockdep-RCU error checking.
110 int rcu_scheduler_active __read_mostly;
111 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
114 * The rcu_scheduler_fully_active variable transitions from zero to one
115 * during the early_initcall() processing, which is after the scheduler
116 * is capable of creating new tasks. So RCU processing (for example,
117 * creating tasks for RCU priority boosting) must be delayed until after
118 * rcu_scheduler_fully_active transitions from zero to one. We also
119 * currently delay invocation of any RCU callbacks until after this point.
121 * It might later prove better for people registering RCU callbacks during
122 * early boot to take responsibility for these callbacks, but one step at
125 static int rcu_scheduler_fully_active __read_mostly;
127 #ifdef CONFIG_RCU_BOOST
130 * Control variables for per-CPU and per-rcu_node kthreads. These
131 * handle all flavors of RCU.
133 static DEFINE_PER_CPU(struct task_struct *, rcu_cpu_kthread_task);
134 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status);
135 DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu);
136 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops);
137 DEFINE_PER_CPU(char, rcu_cpu_has_work);
139 #endif /* #ifdef CONFIG_RCU_BOOST */
141 static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu);
142 static void invoke_rcu_core(void);
143 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp);
146 * Track the rcutorture test sequence number and the update version
147 * number within a given test. The rcutorture_testseq is incremented
148 * on every rcutorture module load and unload, so has an odd value
149 * when a test is running. The rcutorture_vernum is set to zero
150 * when rcutorture starts and is incremented on each rcutorture update.
151 * These variables enable correlating rcutorture output with the
152 * RCU tracing information.
154 unsigned long rcutorture_testseq;
155 unsigned long rcutorture_vernum;
158 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
159 * permit this function to be invoked without holding the root rcu_node
160 * structure's ->lock, but of course results can be subject to change.
162 static int rcu_gp_in_progress(struct rcu_state *rsp)
164 return ACCESS_ONCE(rsp->completed) != ACCESS_ONCE(rsp->gpnum);
168 * Note a quiescent state. Because we do not need to know
169 * how many quiescent states passed, just if there was at least
170 * one since the start of the grace period, this just sets a flag.
171 * The caller must have disabled preemption.
173 void rcu_sched_qs(int cpu)
175 struct rcu_data *rdp = &per_cpu(rcu_sched_data, cpu);
177 rdp->passed_quiesce_gpnum = rdp->gpnum;
179 if (rdp->passed_quiesce == 0)
180 trace_rcu_grace_period("rcu_sched", rdp->gpnum, "cpuqs");
181 rdp->passed_quiesce = 1;
184 void rcu_bh_qs(int cpu)
186 struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu);
188 rdp->passed_quiesce_gpnum = rdp->gpnum;
190 if (rdp->passed_quiesce == 0)
191 trace_rcu_grace_period("rcu_bh", rdp->gpnum, "cpuqs");
192 rdp->passed_quiesce = 1;
196 * Note a context switch. This is a quiescent state for RCU-sched,
197 * and requires special handling for preemptible RCU.
198 * The caller must have disabled preemption.
200 void rcu_note_context_switch(int cpu)
202 trace_rcu_utilization("Start context switch");
204 rcu_preempt_note_context_switch(cpu);
205 trace_rcu_utilization("End context switch");
207 EXPORT_SYMBOL_GPL(rcu_note_context_switch);
209 DEFINE_PER_CPU(struct rcu_dynticks, rcu_dynticks) = {
210 .dynticks_nesting = DYNTICK_TASK_EXIT_IDLE,
211 .dynticks = ATOMIC_INIT(1),
214 static int blimit = 10; /* Maximum callbacks per rcu_do_batch. */
215 static int qhimark = 10000; /* If this many pending, ignore blimit. */
216 static int qlowmark = 100; /* Once only this many pending, use blimit. */
218 module_param(blimit, int, 0);
219 module_param(qhimark, int, 0);
220 module_param(qlowmark, int, 0);
222 int rcu_cpu_stall_suppress __read_mostly; /* 1 = suppress stall warnings. */
223 int rcu_cpu_stall_timeout __read_mostly = CONFIG_RCU_CPU_STALL_TIMEOUT;
225 module_param(rcu_cpu_stall_suppress, int, 0644);
226 module_param(rcu_cpu_stall_timeout, int, 0644);
228 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *));
229 static void force_quiescent_state(struct rcu_state *rsp);
230 static int rcu_pending(int cpu);
233 * Return the number of RCU-sched batches processed thus far for debug & stats.
235 long rcu_batches_completed_sched(void)
237 return rcu_sched_state.completed;
239 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched);
242 * Return the number of RCU BH batches processed thus far for debug & stats.
244 long rcu_batches_completed_bh(void)
246 return rcu_bh_state.completed;
248 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
251 * Force a quiescent state for RCU BH.
253 void rcu_bh_force_quiescent_state(void)
255 force_quiescent_state(&rcu_bh_state);
257 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state);
260 * Record the number of times rcutorture tests have been initiated and
261 * terminated. This information allows the debugfs tracing stats to be
262 * correlated to the rcutorture messages, even when the rcutorture module
263 * is being repeatedly loaded and unloaded. In other words, we cannot
264 * store this state in rcutorture itself.
266 void rcutorture_record_test_transition(void)
268 rcutorture_testseq++;
269 rcutorture_vernum = 0;
271 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition);
274 * Record the number of writer passes through the current rcutorture test.
275 * This is also used to correlate debugfs tracing stats with the rcutorture
278 void rcutorture_record_progress(unsigned long vernum)
282 EXPORT_SYMBOL_GPL(rcutorture_record_progress);
285 * Force a quiescent state for RCU-sched.
287 void rcu_sched_force_quiescent_state(void)
289 force_quiescent_state(&rcu_sched_state);
291 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state);
294 * Does the CPU have callbacks ready to be invoked?
297 cpu_has_callbacks_ready_to_invoke(struct rcu_data *rdp)
299 return &rdp->nxtlist != rdp->nxttail[RCU_DONE_TAIL];
303 * Does the current CPU require a yet-as-unscheduled grace period?
306 cpu_needs_another_gp(struct rcu_state *rsp, struct rcu_data *rdp)
308 return *rdp->nxttail[RCU_DONE_TAIL +
309 ACCESS_ONCE(rsp->completed) != rdp->completed] &&
310 !rcu_gp_in_progress(rsp);
314 * Return the root node of the specified rcu_state structure.
316 static struct rcu_node *rcu_get_root(struct rcu_state *rsp)
318 return &rsp->node[0];
322 * If the specified CPU is offline, tell the caller that it is in
323 * a quiescent state. Otherwise, whack it with a reschedule IPI.
324 * Grace periods can end up waiting on an offline CPU when that
325 * CPU is in the process of coming online -- it will be added to the
326 * rcu_node bitmasks before it actually makes it online. The same thing
327 * can happen while a CPU is in the process of coming online. Because this
328 * race is quite rare, we check for it after detecting that the grace
329 * period has been delayed rather than checking each and every CPU
330 * each and every time we start a new grace period.
332 static int rcu_implicit_offline_qs(struct rcu_data *rdp)
335 * If the CPU is offline for more than a jiffy, it is in a quiescent
336 * state. We can trust its state not to change because interrupts
337 * are disabled. The reason for the jiffy's worth of slack is to
338 * handle CPUs initializing on the way up and finding their way
339 * to the idle loop on the way down.
341 if (cpu_is_offline(rdp->cpu) &&
342 ULONG_CMP_LT(rdp->rsp->gp_start + 2, jiffies)) {
343 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "ofl");
351 * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
353 * If the new value of the ->dynticks_nesting counter now is zero,
354 * we really have entered idle, and must do the appropriate accounting.
355 * The caller must have disabled interrupts.
357 static void rcu_idle_enter_common(struct rcu_dynticks *rdtp, long long oldval)
359 trace_rcu_dyntick("Start", oldval, 0);
360 if (!is_idle_task(current)) {
361 struct task_struct *idle = idle_task(smp_processor_id());
363 trace_rcu_dyntick("Error on entry: not idle task", oldval, 0);
364 ftrace_dump(DUMP_ORIG);
365 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
366 current->pid, current->comm,
367 idle->pid, idle->comm); /* must be idle task! */
369 rcu_prepare_for_idle(smp_processor_id());
370 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
371 smp_mb__before_atomic_inc(); /* See above. */
372 atomic_inc(&rdtp->dynticks);
373 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
374 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
377 * The idle task is not permitted to enter the idle loop while
378 * in an RCU read-side critical section.
380 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map),
381 "Illegal idle entry in RCU read-side critical section.");
382 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map),
383 "Illegal idle entry in RCU-bh read-side critical section.");
384 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map),
385 "Illegal idle entry in RCU-sched read-side critical section.");
389 * rcu_idle_enter - inform RCU that current CPU is entering idle
391 * Enter idle mode, in other words, -leave- the mode in which RCU
392 * read-side critical sections can occur. (Though RCU read-side
393 * critical sections can occur in irq handlers in idle, a possibility
394 * handled by irq_enter() and irq_exit().)
396 * We crowbar the ->dynticks_nesting field to zero to allow for
397 * the possibility of usermode upcalls having messed up our count
398 * of interrupt nesting level during the prior busy period.
400 void rcu_idle_enter(void)
404 struct rcu_dynticks *rdtp;
406 local_irq_save(flags);
407 rdtp = &__get_cpu_var(rcu_dynticks);
408 oldval = rdtp->dynticks_nesting;
409 WARN_ON_ONCE((oldval & DYNTICK_TASK_NEST_MASK) == 0);
410 if ((oldval & DYNTICK_TASK_NEST_MASK) == DYNTICK_TASK_NEST_VALUE)
411 rdtp->dynticks_nesting = 0;
413 rdtp->dynticks_nesting -= DYNTICK_TASK_NEST_VALUE;
414 rcu_idle_enter_common(rdtp, oldval);
415 local_irq_restore(flags);
417 EXPORT_SYMBOL_GPL(rcu_idle_enter);
420 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
422 * Exit from an interrupt handler, which might possibly result in entering
423 * idle mode, in other words, leaving the mode in which read-side critical
424 * sections can occur.
426 * This code assumes that the idle loop never does anything that might
427 * result in unbalanced calls to irq_enter() and irq_exit(). If your
428 * architecture violates this assumption, RCU will give you what you
429 * deserve, good and hard. But very infrequently and irreproducibly.
431 * Use things like work queues to work around this limitation.
433 * You have been warned.
435 void rcu_irq_exit(void)
439 struct rcu_dynticks *rdtp;
441 local_irq_save(flags);
442 rdtp = &__get_cpu_var(rcu_dynticks);
443 oldval = rdtp->dynticks_nesting;
444 rdtp->dynticks_nesting--;
445 WARN_ON_ONCE(rdtp->dynticks_nesting < 0);
446 if (rdtp->dynticks_nesting)
447 trace_rcu_dyntick("--=", oldval, rdtp->dynticks_nesting);
449 rcu_idle_enter_common(rdtp, oldval);
450 local_irq_restore(flags);
454 * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
456 * If the new value of the ->dynticks_nesting counter was previously zero,
457 * we really have exited idle, and must do the appropriate accounting.
458 * The caller must have disabled interrupts.
460 static void rcu_idle_exit_common(struct rcu_dynticks *rdtp, long long oldval)
462 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
463 atomic_inc(&rdtp->dynticks);
464 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
465 smp_mb__after_atomic_inc(); /* See above. */
466 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
467 rcu_cleanup_after_idle(smp_processor_id());
468 trace_rcu_dyntick("End", oldval, rdtp->dynticks_nesting);
469 if (!is_idle_task(current)) {
470 struct task_struct *idle = idle_task(smp_processor_id());
472 trace_rcu_dyntick("Error on exit: not idle task",
473 oldval, rdtp->dynticks_nesting);
474 ftrace_dump(DUMP_ORIG);
475 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
476 current->pid, current->comm,
477 idle->pid, idle->comm); /* must be idle task! */
482 * rcu_idle_exit - inform RCU that current CPU is leaving idle
484 * Exit idle mode, in other words, -enter- the mode in which RCU
485 * read-side critical sections can occur.
487 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
488 * allow for the possibility of usermode upcalls messing up our count
489 * of interrupt nesting level during the busy period that is just
492 void rcu_idle_exit(void)
495 struct rcu_dynticks *rdtp;
498 local_irq_save(flags);
499 rdtp = &__get_cpu_var(rcu_dynticks);
500 oldval = rdtp->dynticks_nesting;
501 WARN_ON_ONCE(oldval < 0);
502 if (oldval & DYNTICK_TASK_NEST_MASK)
503 rdtp->dynticks_nesting += DYNTICK_TASK_NEST_VALUE;
505 rdtp->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
506 rcu_idle_exit_common(rdtp, oldval);
507 local_irq_restore(flags);
509 EXPORT_SYMBOL_GPL(rcu_idle_exit);
512 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
514 * Enter an interrupt handler, which might possibly result in exiting
515 * idle mode, in other words, entering the mode in which read-side critical
516 * sections can occur.
518 * Note that the Linux kernel is fully capable of entering an interrupt
519 * handler that it never exits, for example when doing upcalls to
520 * user mode! This code assumes that the idle loop never does upcalls to
521 * user mode. If your architecture does do upcalls from the idle loop (or
522 * does anything else that results in unbalanced calls to the irq_enter()
523 * and irq_exit() functions), RCU will give you what you deserve, good
524 * and hard. But very infrequently and irreproducibly.
526 * Use things like work queues to work around this limitation.
528 * You have been warned.
530 void rcu_irq_enter(void)
533 struct rcu_dynticks *rdtp;
536 local_irq_save(flags);
537 rdtp = &__get_cpu_var(rcu_dynticks);
538 oldval = rdtp->dynticks_nesting;
539 rdtp->dynticks_nesting++;
540 WARN_ON_ONCE(rdtp->dynticks_nesting == 0);
542 trace_rcu_dyntick("++=", oldval, rdtp->dynticks_nesting);
544 rcu_idle_exit_common(rdtp, oldval);
545 local_irq_restore(flags);
549 * rcu_nmi_enter - inform RCU of entry to NMI context
551 * If the CPU was idle with dynamic ticks active, and there is no
552 * irq handler running, this updates rdtp->dynticks_nmi to let the
553 * RCU grace-period handling know that the CPU is active.
555 void rcu_nmi_enter(void)
557 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
559 if (rdtp->dynticks_nmi_nesting == 0 &&
560 (atomic_read(&rdtp->dynticks) & 0x1))
562 rdtp->dynticks_nmi_nesting++;
563 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
564 atomic_inc(&rdtp->dynticks);
565 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
566 smp_mb__after_atomic_inc(); /* See above. */
567 WARN_ON_ONCE(!(atomic_read(&rdtp->dynticks) & 0x1));
571 * rcu_nmi_exit - inform RCU of exit from NMI context
573 * If the CPU was idle with dynamic ticks active, and there is no
574 * irq handler running, this updates rdtp->dynticks_nmi to let the
575 * RCU grace-period handling know that the CPU is no longer active.
577 void rcu_nmi_exit(void)
579 struct rcu_dynticks *rdtp = &__get_cpu_var(rcu_dynticks);
581 if (rdtp->dynticks_nmi_nesting == 0 ||
582 --rdtp->dynticks_nmi_nesting != 0)
584 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
585 smp_mb__before_atomic_inc(); /* See above. */
586 atomic_inc(&rdtp->dynticks);
587 smp_mb__after_atomic_inc(); /* Force delay to next write. */
588 WARN_ON_ONCE(atomic_read(&rdtp->dynticks) & 0x1);
592 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
594 * If the current CPU is in its idle loop and is neither in an interrupt
595 * or NMI handler, return true.
597 int rcu_is_cpu_idle(void)
602 ret = (atomic_read(&__get_cpu_var(rcu_dynticks).dynticks) & 0x1) == 0;
606 EXPORT_SYMBOL(rcu_is_cpu_idle);
608 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
611 * Is the current CPU online? Disable preemption to avoid false positives
612 * that could otherwise happen due to the current CPU number being sampled,
613 * this task being preempted, its old CPU being taken offline, resuming
614 * on some other CPU, then determining that its old CPU is now offline.
615 * It is OK to use RCU on an offline processor during initial boot, hence
616 * the check for rcu_scheduler_fully_active. Note also that it is OK
617 * for a CPU coming online to use RCU for one jiffy prior to marking itself
618 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
619 * offline to continue to use RCU for one jiffy after marking itself
620 * offline in the cpu_online_mask. This leniency is necessary given the
621 * non-atomic nature of the online and offline processing, for example,
622 * the fact that a CPU enters the scheduler after completing the CPU_DYING
625 * This is also why RCU internally marks CPUs online during the
626 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
628 * Disable checking if in an NMI handler because we cannot safely report
629 * errors from NMI handlers anyway.
631 bool rcu_lockdep_current_cpu_online(void)
633 struct rcu_data *rdp;
634 struct rcu_node *rnp;
640 rdp = &__get_cpu_var(rcu_sched_data);
642 ret = (rdp->grpmask & rnp->qsmaskinit) ||
643 !rcu_scheduler_fully_active;
647 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
649 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
652 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
654 * If the current CPU is idle or running at a first-level (not nested)
655 * interrupt from idle, return true. The caller must have at least
656 * disabled preemption.
658 int rcu_is_cpu_rrupt_from_idle(void)
660 return __get_cpu_var(rcu_dynticks).dynticks_nesting <= 1;
664 * Snapshot the specified CPU's dynticks counter so that we can later
665 * credit them with an implicit quiescent state. Return 1 if this CPU
666 * is in dynticks idle mode, which is an extended quiescent state.
668 static int dyntick_save_progress_counter(struct rcu_data *rdp)
670 rdp->dynticks_snap = atomic_add_return(0, &rdp->dynticks->dynticks);
671 return (rdp->dynticks_snap & 0x1) == 0;
675 * Return true if the specified CPU has passed through a quiescent
676 * state by virtue of being in or having passed through an dynticks
677 * idle state since the last call to dyntick_save_progress_counter()
680 static int rcu_implicit_dynticks_qs(struct rcu_data *rdp)
685 curr = (unsigned int)atomic_add_return(0, &rdp->dynticks->dynticks);
686 snap = (unsigned int)rdp->dynticks_snap;
689 * If the CPU passed through or entered a dynticks idle phase with
690 * no active irq/NMI handlers, then we can safely pretend that the CPU
691 * already acknowledged the request to pass through a quiescent
692 * state. Either way, that CPU cannot possibly be in an RCU
693 * read-side critical section that started before the beginning
694 * of the current RCU grace period.
696 if ((curr & 0x1) == 0 || UINT_CMP_GE(curr, snap + 2)) {
697 trace_rcu_fqs(rdp->rsp->name, rdp->gpnum, rdp->cpu, "dti");
702 /* Go check for the CPU being offline. */
703 return rcu_implicit_offline_qs(rdp);
706 static int jiffies_till_stall_check(void)
708 int till_stall_check = ACCESS_ONCE(rcu_cpu_stall_timeout);
711 * Limit check must be consistent with the Kconfig limits
712 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
714 if (till_stall_check < 3) {
715 ACCESS_ONCE(rcu_cpu_stall_timeout) = 3;
716 till_stall_check = 3;
717 } else if (till_stall_check > 300) {
718 ACCESS_ONCE(rcu_cpu_stall_timeout) = 300;
719 till_stall_check = 300;
721 return till_stall_check * HZ + RCU_STALL_DELAY_DELTA;
724 static void record_gp_stall_check_time(struct rcu_state *rsp)
726 rsp->gp_start = jiffies;
727 rsp->jiffies_stall = jiffies + jiffies_till_stall_check();
730 static void print_other_cpu_stall(struct rcu_state *rsp)
736 struct rcu_node *rnp = rcu_get_root(rsp);
738 /* Only let one CPU complain about others per time interval. */
740 raw_spin_lock_irqsave(&rnp->lock, flags);
741 delta = jiffies - rsp->jiffies_stall;
742 if (delta < RCU_STALL_RAT_DELAY || !rcu_gp_in_progress(rsp)) {
743 raw_spin_unlock_irqrestore(&rnp->lock, flags);
746 rsp->jiffies_stall = jiffies + 3 * jiffies_till_stall_check() + 3;
747 raw_spin_unlock_irqrestore(&rnp->lock, flags);
750 * OK, time to rat on our buddy...
751 * See Documentation/RCU/stallwarn.txt for info on how to debug
752 * RCU CPU stall warnings.
754 printk(KERN_ERR "INFO: %s detected stalls on CPUs/tasks:",
756 print_cpu_stall_info_begin();
757 rcu_for_each_leaf_node(rsp, rnp) {
758 raw_spin_lock_irqsave(&rnp->lock, flags);
759 ndetected += rcu_print_task_stall(rnp);
760 raw_spin_unlock_irqrestore(&rnp->lock, flags);
761 if (rnp->qsmask == 0)
763 for (cpu = 0; cpu <= rnp->grphi - rnp->grplo; cpu++)
764 if (rnp->qsmask & (1UL << cpu)) {
765 print_cpu_stall_info(rsp, rnp->grplo + cpu);
771 * Now rat on any tasks that got kicked up to the root rcu_node
772 * due to CPU offlining.
774 rnp = rcu_get_root(rsp);
775 raw_spin_lock_irqsave(&rnp->lock, flags);
776 ndetected += rcu_print_task_stall(rnp);
777 raw_spin_unlock_irqrestore(&rnp->lock, flags);
779 print_cpu_stall_info_end();
780 printk(KERN_CONT "(detected by %d, t=%ld jiffies)\n",
781 smp_processor_id(), (long)(jiffies - rsp->gp_start));
783 printk(KERN_ERR "INFO: Stall ended before state dump start\n");
784 else if (!trigger_all_cpu_backtrace())
787 /* Complain about tasks blocking the grace period. */
789 rcu_print_detail_task_stall(rsp);
791 force_quiescent_state(rsp); /* Kick them all. */
794 static void print_cpu_stall(struct rcu_state *rsp)
797 struct rcu_node *rnp = rcu_get_root(rsp);
800 * OK, time to rat on ourselves...
801 * See Documentation/RCU/stallwarn.txt for info on how to debug
802 * RCU CPU stall warnings.
804 printk(KERN_ERR "INFO: %s self-detected stall on CPU", rsp->name);
805 print_cpu_stall_info_begin();
806 print_cpu_stall_info(rsp, smp_processor_id());
807 print_cpu_stall_info_end();
808 printk(KERN_CONT " (t=%lu jiffies)\n", jiffies - rsp->gp_start);
809 if (!trigger_all_cpu_backtrace())
812 raw_spin_lock_irqsave(&rnp->lock, flags);
813 if (ULONG_CMP_GE(jiffies, rsp->jiffies_stall))
814 rsp->jiffies_stall = jiffies +
815 3 * jiffies_till_stall_check() + 3;
816 raw_spin_unlock_irqrestore(&rnp->lock, flags);
818 set_need_resched(); /* kick ourselves to get things going. */
821 static void check_cpu_stall(struct rcu_state *rsp, struct rcu_data *rdp)
825 struct rcu_node *rnp;
827 if (rcu_cpu_stall_suppress)
829 j = ACCESS_ONCE(jiffies);
830 js = ACCESS_ONCE(rsp->jiffies_stall);
832 if ((ACCESS_ONCE(rnp->qsmask) & rdp->grpmask) && ULONG_CMP_GE(j, js)) {
834 /* We haven't checked in, so go dump stack. */
835 print_cpu_stall(rsp);
837 } else if (rcu_gp_in_progress(rsp) &&
838 ULONG_CMP_GE(j, js + RCU_STALL_RAT_DELAY)) {
840 /* They had a few time units to dump stack, so complain. */
841 print_other_cpu_stall(rsp);
845 static int rcu_panic(struct notifier_block *this, unsigned long ev, void *ptr)
847 rcu_cpu_stall_suppress = 1;
852 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
854 * Set the stall-warning timeout way off into the future, thus preventing
855 * any RCU CPU stall-warning messages from appearing in the current set of
858 * The caller must disable hard irqs.
860 void rcu_cpu_stall_reset(void)
862 struct rcu_state *rsp;
864 for_each_rcu_flavor(rsp)
865 rsp->jiffies_stall = jiffies + ULONG_MAX / 2;
868 static struct notifier_block rcu_panic_block = {
869 .notifier_call = rcu_panic,
872 static void __init check_cpu_stall_init(void)
874 atomic_notifier_chain_register(&panic_notifier_list, &rcu_panic_block);
878 * Update CPU-local rcu_data state to record the newly noticed grace period.
879 * This is used both when we started the grace period and when we notice
880 * that someone else started the grace period. The caller must hold the
881 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
882 * and must have irqs disabled.
884 static void __note_new_gpnum(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
886 if (rdp->gpnum != rnp->gpnum) {
888 * If the current grace period is waiting for this CPU,
889 * set up to detect a quiescent state, otherwise don't
890 * go looking for one.
892 rdp->gpnum = rnp->gpnum;
893 trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpustart");
894 if (rnp->qsmask & rdp->grpmask) {
896 rdp->passed_quiesce = 0;
900 zero_cpu_stall_ticks(rdp);
904 static void note_new_gpnum(struct rcu_state *rsp, struct rcu_data *rdp)
907 struct rcu_node *rnp;
909 local_irq_save(flags);
911 if (rdp->gpnum == ACCESS_ONCE(rnp->gpnum) || /* outside lock. */
912 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
913 local_irq_restore(flags);
916 __note_new_gpnum(rsp, rnp, rdp);
917 raw_spin_unlock_irqrestore(&rnp->lock, flags);
921 * Did someone else start a new RCU grace period start since we last
922 * checked? Update local state appropriately if so. Must be called
923 * on the CPU corresponding to rdp.
926 check_for_new_grace_period(struct rcu_state *rsp, struct rcu_data *rdp)
931 local_irq_save(flags);
932 if (rdp->gpnum != rsp->gpnum) {
933 note_new_gpnum(rsp, rdp);
936 local_irq_restore(flags);
941 * Initialize the specified rcu_data structure's callback list to empty.
943 static void init_callback_list(struct rcu_data *rdp)
948 for (i = 0; i < RCU_NEXT_SIZE; i++)
949 rdp->nxttail[i] = &rdp->nxtlist;
953 * Advance this CPU's callbacks, but only if the current grace period
954 * has ended. This may be called only from the CPU to whom the rdp
955 * belongs. In addition, the corresponding leaf rcu_node structure's
956 * ->lock must be held by the caller, with irqs disabled.
959 __rcu_process_gp_end(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
961 /* Did another grace period end? */
962 if (rdp->completed != rnp->completed) {
964 /* Advance callbacks. No harm if list empty. */
965 rdp->nxttail[RCU_DONE_TAIL] = rdp->nxttail[RCU_WAIT_TAIL];
966 rdp->nxttail[RCU_WAIT_TAIL] = rdp->nxttail[RCU_NEXT_READY_TAIL];
967 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
969 /* Remember that we saw this grace-period completion. */
970 rdp->completed = rnp->completed;
971 trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuend");
974 * If we were in an extended quiescent state, we may have
975 * missed some grace periods that others CPUs handled on
976 * our behalf. Catch up with this state to avoid noting
977 * spurious new grace periods. If another grace period
978 * has started, then rnp->gpnum will have advanced, so
979 * we will detect this later on.
981 if (ULONG_CMP_LT(rdp->gpnum, rdp->completed))
982 rdp->gpnum = rdp->completed;
985 * If RCU does not need a quiescent state from this CPU,
986 * then make sure that this CPU doesn't go looking for one.
988 if ((rnp->qsmask & rdp->grpmask) == 0)
994 * Advance this CPU's callbacks, but only if the current grace period
995 * has ended. This may be called only from the CPU to whom the rdp
999 rcu_process_gp_end(struct rcu_state *rsp, struct rcu_data *rdp)
1001 unsigned long flags;
1002 struct rcu_node *rnp;
1004 local_irq_save(flags);
1006 if (rdp->completed == ACCESS_ONCE(rnp->completed) || /* outside lock. */
1007 !raw_spin_trylock(&rnp->lock)) { /* irqs already off, so later. */
1008 local_irq_restore(flags);
1011 __rcu_process_gp_end(rsp, rnp, rdp);
1012 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1016 * Do per-CPU grace-period initialization for running CPU. The caller
1017 * must hold the lock of the leaf rcu_node structure corresponding to
1021 rcu_start_gp_per_cpu(struct rcu_state *rsp, struct rcu_node *rnp, struct rcu_data *rdp)
1023 /* Prior grace period ended, so advance callbacks for current CPU. */
1024 __rcu_process_gp_end(rsp, rnp, rdp);
1026 /* Set state so that this CPU will detect the next quiescent state. */
1027 __note_new_gpnum(rsp, rnp, rdp);
1031 * Initialize a new grace period.
1033 static int rcu_gp_init(struct rcu_state *rsp)
1035 struct rcu_data *rdp;
1036 struct rcu_node *rnp = rcu_get_root(rsp);
1038 raw_spin_lock_irq(&rnp->lock);
1039 rsp->gp_flags = 0; /* Clear all flags: New grace period. */
1041 if (rcu_gp_in_progress(rsp)) {
1042 /* Grace period already in progress, don't start another. */
1043 raw_spin_unlock_irq(&rnp->lock);
1047 /* Advance to a new grace period and initialize state. */
1049 trace_rcu_grace_period(rsp->name, rsp->gpnum, "start");
1050 record_gp_stall_check_time(rsp);
1051 raw_spin_unlock_irq(&rnp->lock);
1053 /* Exclude any concurrent CPU-hotplug operations. */
1057 * Set the quiescent-state-needed bits in all the rcu_node
1058 * structures for all currently online CPUs in breadth-first order,
1059 * starting from the root rcu_node structure, relying on the layout
1060 * of the tree within the rsp->node[] array. Note that other CPUs
1061 * will access only the leaves of the hierarchy, thus seeing that no
1062 * grace period is in progress, at least until the corresponding
1063 * leaf node has been initialized. In addition, we have excluded
1064 * CPU-hotplug operations.
1066 * The grace period cannot complete until the initialization
1067 * process finishes, because this kthread handles both.
1069 rcu_for_each_node_breadth_first(rsp, rnp) {
1070 raw_spin_lock_irq(&rnp->lock);
1071 rdp = this_cpu_ptr(rsp->rda);
1072 rcu_preempt_check_blocked_tasks(rnp);
1073 rnp->qsmask = rnp->qsmaskinit;
1074 rnp->gpnum = rsp->gpnum;
1075 rnp->completed = rsp->completed;
1076 if (rnp == rdp->mynode)
1077 rcu_start_gp_per_cpu(rsp, rnp, rdp);
1078 rcu_preempt_boost_start_gp(rnp);
1079 trace_rcu_grace_period_init(rsp->name, rnp->gpnum,
1080 rnp->level, rnp->grplo,
1081 rnp->grphi, rnp->qsmask);
1082 raw_spin_unlock_irq(&rnp->lock);
1091 * Do one round of quiescent-state forcing.
1093 int rcu_gp_fqs(struct rcu_state *rsp, int fqs_state_in)
1095 int fqs_state = fqs_state_in;
1096 struct rcu_node *rnp = rcu_get_root(rsp);
1099 if (fqs_state == RCU_SAVE_DYNTICK) {
1100 /* Collect dyntick-idle snapshots. */
1101 force_qs_rnp(rsp, dyntick_save_progress_counter);
1102 fqs_state = RCU_FORCE_QS;
1104 /* Handle dyntick-idle and offline CPUs. */
1105 force_qs_rnp(rsp, rcu_implicit_dynticks_qs);
1107 /* Clear flag to prevent immediate re-entry. */
1108 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS) {
1109 raw_spin_lock_irq(&rnp->lock);
1110 rsp->gp_flags &= ~RCU_GP_FLAG_FQS;
1111 raw_spin_unlock_irq(&rnp->lock);
1117 * Clean up after the old grace period.
1119 static void rcu_gp_cleanup(struct rcu_state *rsp)
1121 unsigned long gp_duration;
1122 struct rcu_data *rdp;
1123 struct rcu_node *rnp = rcu_get_root(rsp);
1125 raw_spin_lock_irq(&rnp->lock);
1126 gp_duration = jiffies - rsp->gp_start;
1127 if (gp_duration > rsp->gp_max)
1128 rsp->gp_max = gp_duration;
1131 * We know the grace period is complete, but to everyone else
1132 * it appears to still be ongoing. But it is also the case
1133 * that to everyone else it looks like there is nothing that
1134 * they can do to advance the grace period. It is therefore
1135 * safe for us to drop the lock in order to mark the grace
1136 * period as completed in all of the rcu_node structures.
1138 * But if this CPU needs another grace period, it will take
1139 * care of this while initializing the next grace period.
1140 * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
1141 * because the callbacks have not yet been advanced: Those
1142 * callbacks are waiting on the grace period that just now
1145 rdp = this_cpu_ptr(rsp->rda);
1146 if (*rdp->nxttail[RCU_WAIT_TAIL] == NULL) {
1147 raw_spin_unlock_irq(&rnp->lock);
1150 * Propagate new ->completed value to rcu_node
1151 * structures so that other CPUs don't have to
1152 * wait until the start of the next grace period
1153 * to process their callbacks.
1155 rcu_for_each_node_breadth_first(rsp, rnp) {
1156 raw_spin_lock_irq(&rnp->lock);
1157 rnp->completed = rsp->gpnum;
1158 raw_spin_unlock_irq(&rnp->lock);
1161 rnp = rcu_get_root(rsp);
1162 raw_spin_lock_irq(&rnp->lock);
1165 rsp->completed = rsp->gpnum; /* Declare grace period done. */
1166 trace_rcu_grace_period(rsp->name, rsp->completed, "end");
1167 rsp->fqs_state = RCU_GP_IDLE;
1168 if (cpu_needs_another_gp(rsp, rdp))
1170 raw_spin_unlock_irq(&rnp->lock);
1174 * Body of kthread that handles grace periods.
1176 static int __noreturn rcu_gp_kthread(void *arg)
1180 struct rcu_state *rsp = arg;
1181 struct rcu_node *rnp = rcu_get_root(rsp);
1185 /* Handle grace-period start. */
1187 wait_event_interruptible(rsp->gp_wq,
1190 if ((rsp->gp_flags & RCU_GP_FLAG_INIT) &&
1194 flush_signals(current);
1197 /* Handle quiescent-state forcing. */
1198 fqs_state = RCU_SAVE_DYNTICK;
1200 rsp->jiffies_force_qs = jiffies +
1201 RCU_JIFFIES_TILL_FORCE_QS;
1202 ret = wait_event_interruptible_timeout(rsp->gp_wq,
1203 (rsp->gp_flags & RCU_GP_FLAG_FQS) ||
1204 (!ACCESS_ONCE(rnp->qsmask) &&
1205 !rcu_preempt_blocked_readers_cgp(rnp)),
1206 RCU_JIFFIES_TILL_FORCE_QS);
1207 /* If grace period done, leave loop. */
1208 if (!ACCESS_ONCE(rnp->qsmask) &&
1209 !rcu_preempt_blocked_readers_cgp(rnp))
1211 /* If time for quiescent-state forcing, do it. */
1212 if (ret == 0 || (rsp->gp_flags & RCU_GP_FLAG_FQS)) {
1213 fqs_state = rcu_gp_fqs(rsp, fqs_state);
1216 /* Deal with stray signal. */
1218 flush_signals(current);
1222 /* Handle grace-period end. */
1223 rcu_gp_cleanup(rsp);
1228 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1229 * in preparation for detecting the next grace period. The caller must hold
1230 * the root node's ->lock, which is released before return. Hard irqs must
1233 * Note that it is legal for a dying CPU (which is marked as offline) to
1234 * invoke this function. This can happen when the dying CPU reports its
1238 rcu_start_gp(struct rcu_state *rsp, unsigned long flags)
1239 __releases(rcu_get_root(rsp)->lock)
1241 struct rcu_data *rdp = this_cpu_ptr(rsp->rda);
1242 struct rcu_node *rnp = rcu_get_root(rsp);
1244 if (!rsp->gp_kthread ||
1245 !cpu_needs_another_gp(rsp, rdp)) {
1247 * Either we have not yet spawned the grace-period
1248 * task or this CPU does not need another grace period.
1249 * Either way, don't start a new grace period.
1251 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1255 rsp->gp_flags = RCU_GP_FLAG_INIT;
1256 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1257 wake_up(&rsp->gp_wq);
1261 * Report a full set of quiescent states to the specified rcu_state
1262 * data structure. This involves cleaning up after the prior grace
1263 * period and letting rcu_start_gp() start up the next grace period
1264 * if one is needed. Note that the caller must hold rnp->lock, as
1265 * required by rcu_start_gp(), which will release it.
1267 static void rcu_report_qs_rsp(struct rcu_state *rsp, unsigned long flags)
1268 __releases(rcu_get_root(rsp)->lock)
1270 WARN_ON_ONCE(!rcu_gp_in_progress(rsp));
1271 raw_spin_unlock_irqrestore(&rcu_get_root(rsp)->lock, flags);
1272 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
1276 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1277 * Allows quiescent states for a group of CPUs to be reported at one go
1278 * to the specified rcu_node structure, though all the CPUs in the group
1279 * must be represented by the same rcu_node structure (which need not be
1280 * a leaf rcu_node structure, though it often will be). That structure's
1281 * lock must be held upon entry, and it is released before return.
1284 rcu_report_qs_rnp(unsigned long mask, struct rcu_state *rsp,
1285 struct rcu_node *rnp, unsigned long flags)
1286 __releases(rnp->lock)
1288 struct rcu_node *rnp_c;
1290 /* Walk up the rcu_node hierarchy. */
1292 if (!(rnp->qsmask & mask)) {
1294 /* Our bit has already been cleared, so done. */
1295 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1298 rnp->qsmask &= ~mask;
1299 trace_rcu_quiescent_state_report(rsp->name, rnp->gpnum,
1300 mask, rnp->qsmask, rnp->level,
1301 rnp->grplo, rnp->grphi,
1303 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
1305 /* Other bits still set at this level, so done. */
1306 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1309 mask = rnp->grpmask;
1310 if (rnp->parent == NULL) {
1312 /* No more levels. Exit loop holding root lock. */
1316 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1319 raw_spin_lock_irqsave(&rnp->lock, flags);
1320 WARN_ON_ONCE(rnp_c->qsmask);
1324 * Get here if we are the last CPU to pass through a quiescent
1325 * state for this grace period. Invoke rcu_report_qs_rsp()
1326 * to clean up and start the next grace period if one is needed.
1328 rcu_report_qs_rsp(rsp, flags); /* releases rnp->lock. */
1332 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1333 * structure. This must be either called from the specified CPU, or
1334 * called when the specified CPU is known to be offline (and when it is
1335 * also known that no other CPU is concurrently trying to help the offline
1336 * CPU). The lastcomp argument is used to make sure we are still in the
1337 * grace period of interest. We don't want to end the current grace period
1338 * based on quiescent states detected in an earlier grace period!
1341 rcu_report_qs_rdp(int cpu, struct rcu_state *rsp, struct rcu_data *rdp, long lastgp)
1343 unsigned long flags;
1345 struct rcu_node *rnp;
1348 raw_spin_lock_irqsave(&rnp->lock, flags);
1349 if (lastgp != rnp->gpnum || rnp->completed == rnp->gpnum) {
1352 * The grace period in which this quiescent state was
1353 * recorded has ended, so don't report it upwards.
1354 * We will instead need a new quiescent state that lies
1355 * within the current grace period.
1357 rdp->passed_quiesce = 0; /* need qs for new gp. */
1358 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1361 mask = rdp->grpmask;
1362 if ((rnp->qsmask & mask) == 0) {
1363 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1365 rdp->qs_pending = 0;
1368 * This GP can't end until cpu checks in, so all of our
1369 * callbacks can be processed during the next GP.
1371 rdp->nxttail[RCU_NEXT_READY_TAIL] = rdp->nxttail[RCU_NEXT_TAIL];
1373 rcu_report_qs_rnp(mask, rsp, rnp, flags); /* rlses rnp->lock */
1378 * Check to see if there is a new grace period of which this CPU
1379 * is not yet aware, and if so, set up local rcu_data state for it.
1380 * Otherwise, see if this CPU has just passed through its first
1381 * quiescent state for this grace period, and record that fact if so.
1384 rcu_check_quiescent_state(struct rcu_state *rsp, struct rcu_data *rdp)
1386 /* If there is now a new grace period, record and return. */
1387 if (check_for_new_grace_period(rsp, rdp))
1391 * Does this CPU still need to do its part for current grace period?
1392 * If no, return and let the other CPUs do their part as well.
1394 if (!rdp->qs_pending)
1398 * Was there a quiescent state since the beginning of the grace
1399 * period? If no, then exit and wait for the next call.
1401 if (!rdp->passed_quiesce)
1405 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1408 rcu_report_qs_rdp(rdp->cpu, rsp, rdp, rdp->passed_quiesce_gpnum);
1411 #ifdef CONFIG_HOTPLUG_CPU
1414 * Send the specified CPU's RCU callbacks to the orphanage. The
1415 * specified CPU must be offline, and the caller must hold the
1419 rcu_send_cbs_to_orphanage(int cpu, struct rcu_state *rsp,
1420 struct rcu_node *rnp, struct rcu_data *rdp)
1423 * Orphan the callbacks. First adjust the counts. This is safe
1424 * because ->onofflock excludes _rcu_barrier()'s adoption of
1425 * the callbacks, thus no memory barrier is required.
1427 if (rdp->nxtlist != NULL) {
1428 rsp->qlen_lazy += rdp->qlen_lazy;
1429 rsp->qlen += rdp->qlen;
1430 rdp->n_cbs_orphaned += rdp->qlen;
1432 ACCESS_ONCE(rdp->qlen) = 0;
1436 * Next, move those callbacks still needing a grace period to
1437 * the orphanage, where some other CPU will pick them up.
1438 * Some of the callbacks might have gone partway through a grace
1439 * period, but that is too bad. They get to start over because we
1440 * cannot assume that grace periods are synchronized across CPUs.
1441 * We don't bother updating the ->nxttail[] array yet, instead
1442 * we just reset the whole thing later on.
1444 if (*rdp->nxttail[RCU_DONE_TAIL] != NULL) {
1445 *rsp->orphan_nxttail = *rdp->nxttail[RCU_DONE_TAIL];
1446 rsp->orphan_nxttail = rdp->nxttail[RCU_NEXT_TAIL];
1447 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1451 * Then move the ready-to-invoke callbacks to the orphanage,
1452 * where some other CPU will pick them up. These will not be
1453 * required to pass though another grace period: They are done.
1455 if (rdp->nxtlist != NULL) {
1456 *rsp->orphan_donetail = rdp->nxtlist;
1457 rsp->orphan_donetail = rdp->nxttail[RCU_DONE_TAIL];
1460 /* Finally, initialize the rcu_data structure's list to empty. */
1461 init_callback_list(rdp);
1465 * Adopt the RCU callbacks from the specified rcu_state structure's
1466 * orphanage. The caller must hold the ->onofflock.
1468 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
1471 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
1474 * If there is an rcu_barrier() operation in progress, then
1475 * only the task doing that operation is permitted to adopt
1476 * callbacks. To do otherwise breaks rcu_barrier() and friends
1477 * by causing them to fail to wait for the callbacks in the
1480 if (rsp->rcu_barrier_in_progress &&
1481 rsp->rcu_barrier_in_progress != current)
1484 /* Do the accounting first. */
1485 rdp->qlen_lazy += rsp->qlen_lazy;
1486 rdp->qlen += rsp->qlen;
1487 rdp->n_cbs_adopted += rsp->qlen;
1488 if (rsp->qlen_lazy != rsp->qlen)
1489 rcu_idle_count_callbacks_posted();
1494 * We do not need a memory barrier here because the only way we
1495 * can get here if there is an rcu_barrier() in flight is if
1496 * we are the task doing the rcu_barrier().
1499 /* First adopt the ready-to-invoke callbacks. */
1500 if (rsp->orphan_donelist != NULL) {
1501 *rsp->orphan_donetail = *rdp->nxttail[RCU_DONE_TAIL];
1502 *rdp->nxttail[RCU_DONE_TAIL] = rsp->orphan_donelist;
1503 for (i = RCU_NEXT_SIZE - 1; i >= RCU_DONE_TAIL; i--)
1504 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
1505 rdp->nxttail[i] = rsp->orphan_donetail;
1506 rsp->orphan_donelist = NULL;
1507 rsp->orphan_donetail = &rsp->orphan_donelist;
1510 /* And then adopt the callbacks that still need a grace period. */
1511 if (rsp->orphan_nxtlist != NULL) {
1512 *rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxtlist;
1513 rdp->nxttail[RCU_NEXT_TAIL] = rsp->orphan_nxttail;
1514 rsp->orphan_nxtlist = NULL;
1515 rsp->orphan_nxttail = &rsp->orphan_nxtlist;
1520 * Trace the fact that this CPU is going offline.
1522 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
1524 RCU_TRACE(unsigned long mask);
1525 RCU_TRACE(struct rcu_data *rdp = this_cpu_ptr(rsp->rda));
1526 RCU_TRACE(struct rcu_node *rnp = rdp->mynode);
1528 RCU_TRACE(mask = rdp->grpmask);
1529 trace_rcu_grace_period(rsp->name,
1530 rnp->gpnum + 1 - !!(rnp->qsmask & mask),
1535 * The CPU has been completely removed, and some other CPU is reporting
1536 * this fact from process context. Do the remainder of the cleanup,
1537 * including orphaning the outgoing CPU's RCU callbacks, and also
1538 * adopting them, if there is no _rcu_barrier() instance running.
1539 * There can only be one CPU hotplug operation at a time, so no other
1540 * CPU can be attempting to update rcu_cpu_kthread_task.
1542 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
1544 unsigned long flags;
1546 int need_report = 0;
1547 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
1548 struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
1550 /* Adjust any no-longer-needed kthreads. */
1551 rcu_stop_cpu_kthread(cpu);
1552 rcu_node_kthread_setaffinity(rnp, -1);
1554 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
1556 /* Exclude any attempts to start a new grace period. */
1557 raw_spin_lock_irqsave(&rsp->onofflock, flags);
1559 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
1560 rcu_send_cbs_to_orphanage(cpu, rsp, rnp, rdp);
1561 rcu_adopt_orphan_cbs(rsp);
1563 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1564 mask = rdp->grpmask; /* rnp->grplo is constant. */
1566 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
1567 rnp->qsmaskinit &= ~mask;
1568 if (rnp->qsmaskinit != 0) {
1569 if (rnp != rdp->mynode)
1570 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1573 if (rnp == rdp->mynode)
1574 need_report = rcu_preempt_offline_tasks(rsp, rnp, rdp);
1576 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
1577 mask = rnp->grpmask;
1579 } while (rnp != NULL);
1582 * We still hold the leaf rcu_node structure lock here, and
1583 * irqs are still disabled. The reason for this subterfuge is
1584 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1585 * held leads to deadlock.
1587 raw_spin_unlock(&rsp->onofflock); /* irqs remain disabled. */
1589 if (need_report & RCU_OFL_TASKS_NORM_GP)
1590 rcu_report_unblock_qs_rnp(rnp, flags);
1592 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1593 if (need_report & RCU_OFL_TASKS_EXP_GP)
1594 rcu_report_exp_rnp(rsp, rnp, true);
1595 WARN_ONCE(rdp->qlen != 0 || rdp->nxtlist != NULL,
1596 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
1597 cpu, rdp->qlen, rdp->nxtlist);
1600 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1602 static void rcu_adopt_orphan_cbs(struct rcu_state *rsp)
1606 static void rcu_cleanup_dying_cpu(struct rcu_state *rsp)
1610 static void rcu_cleanup_dead_cpu(int cpu, struct rcu_state *rsp)
1614 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1617 * Invoke any RCU callbacks that have made it to the end of their grace
1618 * period. Thottle as specified by rdp->blimit.
1620 static void rcu_do_batch(struct rcu_state *rsp, struct rcu_data *rdp)
1622 unsigned long flags;
1623 struct rcu_head *next, *list, **tail;
1624 int bl, count, count_lazy, i;
1626 /* If no callbacks are ready, just return.*/
1627 if (!cpu_has_callbacks_ready_to_invoke(rdp)) {
1628 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, 0);
1629 trace_rcu_batch_end(rsp->name, 0, !!ACCESS_ONCE(rdp->nxtlist),
1630 need_resched(), is_idle_task(current),
1631 rcu_is_callbacks_kthread());
1636 * Extract the list of ready callbacks, disabling to prevent
1637 * races with call_rcu() from interrupt handlers.
1639 local_irq_save(flags);
1640 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1642 trace_rcu_batch_start(rsp->name, rdp->qlen_lazy, rdp->qlen, bl);
1643 list = rdp->nxtlist;
1644 rdp->nxtlist = *rdp->nxttail[RCU_DONE_TAIL];
1645 *rdp->nxttail[RCU_DONE_TAIL] = NULL;
1646 tail = rdp->nxttail[RCU_DONE_TAIL];
1647 for (i = RCU_NEXT_SIZE - 1; i >= 0; i--)
1648 if (rdp->nxttail[i] == rdp->nxttail[RCU_DONE_TAIL])
1649 rdp->nxttail[i] = &rdp->nxtlist;
1650 local_irq_restore(flags);
1652 /* Invoke callbacks. */
1653 count = count_lazy = 0;
1657 debug_rcu_head_unqueue(list);
1658 if (__rcu_reclaim(rsp->name, list))
1661 /* Stop only if limit reached and CPU has something to do. */
1662 if (++count >= bl &&
1664 (!is_idle_task(current) && !rcu_is_callbacks_kthread())))
1668 local_irq_save(flags);
1669 trace_rcu_batch_end(rsp->name, count, !!list, need_resched(),
1670 is_idle_task(current),
1671 rcu_is_callbacks_kthread());
1673 /* Update count, and requeue any remaining callbacks. */
1675 *tail = rdp->nxtlist;
1676 rdp->nxtlist = list;
1677 for (i = 0; i < RCU_NEXT_SIZE; i++)
1678 if (&rdp->nxtlist == rdp->nxttail[i])
1679 rdp->nxttail[i] = tail;
1683 smp_mb(); /* List handling before counting for rcu_barrier(). */
1684 rdp->qlen_lazy -= count_lazy;
1685 ACCESS_ONCE(rdp->qlen) -= count;
1686 rdp->n_cbs_invoked += count;
1688 /* Reinstate batch limit if we have worked down the excess. */
1689 if (rdp->blimit == LONG_MAX && rdp->qlen <= qlowmark)
1690 rdp->blimit = blimit;
1692 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1693 if (rdp->qlen == 0 && rdp->qlen_last_fqs_check != 0) {
1694 rdp->qlen_last_fqs_check = 0;
1695 rdp->n_force_qs_snap = rsp->n_force_qs;
1696 } else if (rdp->qlen < rdp->qlen_last_fqs_check - qhimark)
1697 rdp->qlen_last_fqs_check = rdp->qlen;
1698 WARN_ON_ONCE((rdp->nxtlist == NULL) != (rdp->qlen == 0));
1700 local_irq_restore(flags);
1702 /* Re-invoke RCU core processing if there are callbacks remaining. */
1703 if (cpu_has_callbacks_ready_to_invoke(rdp))
1708 * Check to see if this CPU is in a non-context-switch quiescent state
1709 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1710 * Also schedule RCU core processing.
1712 * This function must be called from hardirq context. It is normally
1713 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1714 * false, there is no point in invoking rcu_check_callbacks().
1716 void rcu_check_callbacks(int cpu, int user)
1718 trace_rcu_utilization("Start scheduler-tick");
1719 increment_cpu_stall_ticks();
1720 if (user || rcu_is_cpu_rrupt_from_idle()) {
1723 * Get here if this CPU took its interrupt from user
1724 * mode or from the idle loop, and if this is not a
1725 * nested interrupt. In this case, the CPU is in
1726 * a quiescent state, so note it.
1728 * No memory barrier is required here because both
1729 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1730 * variables that other CPUs neither access nor modify,
1731 * at least not while the corresponding CPU is online.
1737 } else if (!in_softirq()) {
1740 * Get here if this CPU did not take its interrupt from
1741 * softirq, in other words, if it is not interrupting
1742 * a rcu_bh read-side critical section. This is an _bh
1743 * critical section, so note it.
1748 rcu_preempt_check_callbacks(cpu);
1749 if (rcu_pending(cpu))
1751 trace_rcu_utilization("End scheduler-tick");
1755 * Scan the leaf rcu_node structures, processing dyntick state for any that
1756 * have not yet encountered a quiescent state, using the function specified.
1757 * Also initiate boosting for any threads blocked on the root rcu_node.
1759 * The caller must have suppressed start of new grace periods.
1761 static void force_qs_rnp(struct rcu_state *rsp, int (*f)(struct rcu_data *))
1765 unsigned long flags;
1767 struct rcu_node *rnp;
1769 rcu_for_each_leaf_node(rsp, rnp) {
1771 raw_spin_lock_irqsave(&rnp->lock, flags);
1772 if (!rcu_gp_in_progress(rsp)) {
1773 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1776 if (rnp->qsmask == 0) {
1777 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
1782 for (; cpu <= rnp->grphi; cpu++, bit <<= 1) {
1783 if ((rnp->qsmask & bit) != 0 &&
1784 f(per_cpu_ptr(rsp->rda, cpu)))
1789 /* rcu_report_qs_rnp() releases rnp->lock. */
1790 rcu_report_qs_rnp(mask, rsp, rnp, flags);
1793 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1795 rnp = rcu_get_root(rsp);
1796 if (rnp->qsmask == 0) {
1797 raw_spin_lock_irqsave(&rnp->lock, flags);
1798 rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
1803 * Force quiescent states on reluctant CPUs, and also detect which
1804 * CPUs are in dyntick-idle mode.
1806 static void force_quiescent_state(struct rcu_state *rsp)
1808 unsigned long flags;
1809 struct rcu_node *rnp = rcu_get_root(rsp);
1811 if (ACCESS_ONCE(rsp->gp_flags) & RCU_GP_FLAG_FQS)
1812 return; /* Someone beat us to it. */
1813 if (!raw_spin_trylock_irqsave(&rnp->lock, flags)) {
1814 rsp->n_force_qs_lh++; /* Inexact, can lose counts. Tough! */
1817 rsp->gp_flags |= RCU_GP_FLAG_FQS;
1818 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1819 wake_up(&rsp->gp_wq); /* Memory barrier implied by wake_up() path. */
1823 * This does the RCU core processing work for the specified rcu_state
1824 * and rcu_data structures. This may be called only from the CPU to
1825 * whom the rdp belongs.
1828 __rcu_process_callbacks(struct rcu_state *rsp)
1830 unsigned long flags;
1831 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
1833 WARN_ON_ONCE(rdp->beenonline == 0);
1836 * Advance callbacks in response to end of earlier grace
1837 * period that some other CPU ended.
1839 rcu_process_gp_end(rsp, rdp);
1841 /* Update RCU state based on any recent quiescent states. */
1842 rcu_check_quiescent_state(rsp, rdp);
1844 /* Does this CPU require a not-yet-started grace period? */
1845 if (cpu_needs_another_gp(rsp, rdp)) {
1846 raw_spin_lock_irqsave(&rcu_get_root(rsp)->lock, flags);
1847 rcu_start_gp(rsp, flags); /* releases above lock */
1850 /* If there are callbacks ready, invoke them. */
1851 if (cpu_has_callbacks_ready_to_invoke(rdp))
1852 invoke_rcu_callbacks(rsp, rdp);
1856 * Do RCU core processing for the current CPU.
1858 static void rcu_process_callbacks(struct softirq_action *unused)
1860 struct rcu_state *rsp;
1862 if (cpu_is_offline(smp_processor_id()))
1864 trace_rcu_utilization("Start RCU core");
1865 for_each_rcu_flavor(rsp)
1866 __rcu_process_callbacks(rsp);
1867 trace_rcu_utilization("End RCU core");
1871 * Schedule RCU callback invocation. If the specified type of RCU
1872 * does not support RCU priority boosting, just do a direct call,
1873 * otherwise wake up the per-CPU kernel kthread. Note that because we
1874 * are running on the current CPU with interrupts disabled, the
1875 * rcu_cpu_kthread_task cannot disappear out from under us.
1877 static void invoke_rcu_callbacks(struct rcu_state *rsp, struct rcu_data *rdp)
1879 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active)))
1881 if (likely(!rsp->boost)) {
1882 rcu_do_batch(rsp, rdp);
1885 invoke_rcu_callbacks_kthread();
1888 static void invoke_rcu_core(void)
1890 raise_softirq(RCU_SOFTIRQ);
1894 * Handle any core-RCU processing required by a call_rcu() invocation.
1896 static void __call_rcu_core(struct rcu_state *rsp, struct rcu_data *rdp,
1897 struct rcu_head *head, unsigned long flags)
1900 * If called from an extended quiescent state, invoke the RCU
1901 * core in order to force a re-evaluation of RCU's idleness.
1903 if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
1906 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
1907 if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id()))
1911 * Force the grace period if too many callbacks or too long waiting.
1912 * Enforce hysteresis, and don't invoke force_quiescent_state()
1913 * if some other CPU has recently done so. Also, don't bother
1914 * invoking force_quiescent_state() if the newly enqueued callback
1915 * is the only one waiting for a grace period to complete.
1917 if (unlikely(rdp->qlen > rdp->qlen_last_fqs_check + qhimark)) {
1919 /* Are we ignoring a completed grace period? */
1920 rcu_process_gp_end(rsp, rdp);
1921 check_for_new_grace_period(rsp, rdp);
1923 /* Start a new grace period if one not already started. */
1924 if (!rcu_gp_in_progress(rsp)) {
1925 unsigned long nestflag;
1926 struct rcu_node *rnp_root = rcu_get_root(rsp);
1928 raw_spin_lock_irqsave(&rnp_root->lock, nestflag);
1929 rcu_start_gp(rsp, nestflag); /* rlses rnp_root->lock */
1931 /* Give the grace period a kick. */
1932 rdp->blimit = LONG_MAX;
1933 if (rsp->n_force_qs == rdp->n_force_qs_snap &&
1934 *rdp->nxttail[RCU_DONE_TAIL] != head)
1935 force_quiescent_state(rsp);
1936 rdp->n_force_qs_snap = rsp->n_force_qs;
1937 rdp->qlen_last_fqs_check = rdp->qlen;
1943 __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu),
1944 struct rcu_state *rsp, bool lazy)
1946 unsigned long flags;
1947 struct rcu_data *rdp;
1949 WARN_ON_ONCE((unsigned long)head & 0x3); /* Misaligned rcu_head! */
1950 debug_rcu_head_queue(head);
1954 smp_mb(); /* Ensure RCU update seen before callback registry. */
1957 * Opportunistically note grace-period endings and beginnings.
1958 * Note that we might see a beginning right after we see an
1959 * end, but never vice versa, since this CPU has to pass through
1960 * a quiescent state betweentimes.
1962 local_irq_save(flags);
1963 rdp = this_cpu_ptr(rsp->rda);
1965 /* Add the callback to our list. */
1966 ACCESS_ONCE(rdp->qlen)++;
1970 rcu_idle_count_callbacks_posted();
1971 smp_mb(); /* Count before adding callback for rcu_barrier(). */
1972 *rdp->nxttail[RCU_NEXT_TAIL] = head;
1973 rdp->nxttail[RCU_NEXT_TAIL] = &head->next;
1975 if (__is_kfree_rcu_offset((unsigned long)func))
1976 trace_rcu_kfree_callback(rsp->name, head, (unsigned long)func,
1977 rdp->qlen_lazy, rdp->qlen);
1979 trace_rcu_callback(rsp->name, head, rdp->qlen_lazy, rdp->qlen);
1981 /* Go handle any RCU core processing required. */
1982 __call_rcu_core(rsp, rdp, head, flags);
1983 local_irq_restore(flags);
1987 * Queue an RCU-sched callback for invocation after a grace period.
1989 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
1991 __call_rcu(head, func, &rcu_sched_state, 0);
1993 EXPORT_SYMBOL_GPL(call_rcu_sched);
1996 * Queue an RCU callback for invocation after a quicker grace period.
1998 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
2000 __call_rcu(head, func, &rcu_bh_state, 0);
2002 EXPORT_SYMBOL_GPL(call_rcu_bh);
2005 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2006 * any blocking grace-period wait automatically implies a grace period
2007 * if there is only one CPU online at any point time during execution
2008 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2009 * occasionally incorrectly indicate that there are multiple CPUs online
2010 * when there was in fact only one the whole time, as this just adds
2011 * some overhead: RCU still operates correctly.
2013 static inline int rcu_blocking_is_gp(void)
2017 might_sleep(); /* Check for RCU read-side critical section. */
2019 ret = num_online_cpus() <= 1;
2025 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2027 * Control will return to the caller some time after a full rcu-sched
2028 * grace period has elapsed, in other words after all currently executing
2029 * rcu-sched read-side critical sections have completed. These read-side
2030 * critical sections are delimited by rcu_read_lock_sched() and
2031 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2032 * local_irq_disable(), and so on may be used in place of
2033 * rcu_read_lock_sched().
2035 * This means that all preempt_disable code sequences, including NMI and
2036 * hardware-interrupt handlers, in progress on entry will have completed
2037 * before this primitive returns. However, this does not guarantee that
2038 * softirq handlers will have completed, since in some kernels, these
2039 * handlers can run in process context, and can block.
2041 * This primitive provides the guarantees made by the (now removed)
2042 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2043 * guarantees that rcu_read_lock() sections will have completed.
2044 * In "classic RCU", these two guarantees happen to be one and
2045 * the same, but can differ in realtime RCU implementations.
2047 void synchronize_sched(void)
2049 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2050 !lock_is_held(&rcu_lock_map) &&
2051 !lock_is_held(&rcu_sched_lock_map),
2052 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2053 if (rcu_blocking_is_gp())
2055 wait_rcu_gp(call_rcu_sched);
2057 EXPORT_SYMBOL_GPL(synchronize_sched);
2060 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2062 * Control will return to the caller some time after a full rcu_bh grace
2063 * period has elapsed, in other words after all currently executing rcu_bh
2064 * read-side critical sections have completed. RCU read-side critical
2065 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2066 * and may be nested.
2068 void synchronize_rcu_bh(void)
2070 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
2071 !lock_is_held(&rcu_lock_map) &&
2072 !lock_is_held(&rcu_sched_lock_map),
2073 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2074 if (rcu_blocking_is_gp())
2076 wait_rcu_gp(call_rcu_bh);
2078 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
2080 static atomic_t sync_sched_expedited_started = ATOMIC_INIT(0);
2081 static atomic_t sync_sched_expedited_done = ATOMIC_INIT(0);
2083 static int synchronize_sched_expedited_cpu_stop(void *data)
2086 * There must be a full memory barrier on each affected CPU
2087 * between the time that try_stop_cpus() is called and the
2088 * time that it returns.
2090 * In the current initial implementation of cpu_stop, the
2091 * above condition is already met when the control reaches
2092 * this point and the following smp_mb() is not strictly
2093 * necessary. Do smp_mb() anyway for documentation and
2094 * robustness against future implementation changes.
2096 smp_mb(); /* See above comment block. */
2101 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2103 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2104 * approach to force the grace period to end quickly. This consumes
2105 * significant time on all CPUs and is unfriendly to real-time workloads,
2106 * so is thus not recommended for any sort of common-case code. In fact,
2107 * if you are using synchronize_sched_expedited() in a loop, please
2108 * restructure your code to batch your updates, and then use a single
2109 * synchronize_sched() instead.
2111 * Note that it is illegal to call this function while holding any lock
2112 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2113 * to call this function from a CPU-hotplug notifier. Failing to observe
2114 * these restriction will result in deadlock.
2116 * This implementation can be thought of as an application of ticket
2117 * locking to RCU, with sync_sched_expedited_started and
2118 * sync_sched_expedited_done taking on the roles of the halves
2119 * of the ticket-lock word. Each task atomically increments
2120 * sync_sched_expedited_started upon entry, snapshotting the old value,
2121 * then attempts to stop all the CPUs. If this succeeds, then each
2122 * CPU will have executed a context switch, resulting in an RCU-sched
2123 * grace period. We are then done, so we use atomic_cmpxchg() to
2124 * update sync_sched_expedited_done to match our snapshot -- but
2125 * only if someone else has not already advanced past our snapshot.
2127 * On the other hand, if try_stop_cpus() fails, we check the value
2128 * of sync_sched_expedited_done. If it has advanced past our
2129 * initial snapshot, then someone else must have forced a grace period
2130 * some time after we took our snapshot. In this case, our work is
2131 * done for us, and we can simply return. Otherwise, we try again,
2132 * but keep our initial snapshot for purposes of checking for someone
2133 * doing our work for us.
2135 * If we fail too many times in a row, we fall back to synchronize_sched().
2137 void synchronize_sched_expedited(void)
2139 int firstsnap, s, snap, trycount = 0;
2141 /* Note that atomic_inc_return() implies full memory barrier. */
2142 firstsnap = snap = atomic_inc_return(&sync_sched_expedited_started);
2144 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2147 * Each pass through the following loop attempts to force a
2148 * context switch on each CPU.
2150 while (try_stop_cpus(cpu_online_mask,
2151 synchronize_sched_expedited_cpu_stop,
2155 /* No joy, try again later. Or just synchronize_sched(). */
2156 if (trycount++ < 10) {
2157 udelay(trycount * num_online_cpus());
2159 synchronize_sched();
2163 /* Check to see if someone else did our work for us. */
2164 s = atomic_read(&sync_sched_expedited_done);
2165 if (UINT_CMP_GE((unsigned)s, (unsigned)firstsnap)) {
2166 smp_mb(); /* ensure test happens before caller kfree */
2171 * Refetching sync_sched_expedited_started allows later
2172 * callers to piggyback on our grace period. We subtract
2173 * 1 to get the same token that the last incrementer got.
2174 * We retry after they started, so our grace period works
2175 * for them, and they started after our first try, so their
2176 * grace period works for us.
2179 snap = atomic_read(&sync_sched_expedited_started);
2180 smp_mb(); /* ensure read is before try_stop_cpus(). */
2184 * Everyone up to our most recent fetch is covered by our grace
2185 * period. Update the counter, but only if our work is still
2186 * relevant -- which it won't be if someone who started later
2187 * than we did beat us to the punch.
2190 s = atomic_read(&sync_sched_expedited_done);
2191 if (UINT_CMP_GE((unsigned)s, (unsigned)snap)) {
2192 smp_mb(); /* ensure test happens before caller kfree */
2195 } while (atomic_cmpxchg(&sync_sched_expedited_done, s, snap) != s);
2199 EXPORT_SYMBOL_GPL(synchronize_sched_expedited);
2202 * Check to see if there is any immediate RCU-related work to be done
2203 * by the current CPU, for the specified type of RCU, returning 1 if so.
2204 * The checks are in order of increasing expense: checks that can be
2205 * carried out against CPU-local state are performed first. However,
2206 * we must check for CPU stalls first, else we might not get a chance.
2208 static int __rcu_pending(struct rcu_state *rsp, struct rcu_data *rdp)
2210 struct rcu_node *rnp = rdp->mynode;
2212 rdp->n_rcu_pending++;
2214 /* Check for CPU stalls, if enabled. */
2215 check_cpu_stall(rsp, rdp);
2217 /* Is the RCU core waiting for a quiescent state from this CPU? */
2218 if (rcu_scheduler_fully_active &&
2219 rdp->qs_pending && !rdp->passed_quiesce) {
2220 rdp->n_rp_qs_pending++;
2221 } else if (rdp->qs_pending && rdp->passed_quiesce) {
2222 rdp->n_rp_report_qs++;
2226 /* Does this CPU have callbacks ready to invoke? */
2227 if (cpu_has_callbacks_ready_to_invoke(rdp)) {
2228 rdp->n_rp_cb_ready++;
2232 /* Has RCU gone idle with this CPU needing another grace period? */
2233 if (cpu_needs_another_gp(rsp, rdp)) {
2234 rdp->n_rp_cpu_needs_gp++;
2238 /* Has another RCU grace period completed? */
2239 if (ACCESS_ONCE(rnp->completed) != rdp->completed) { /* outside lock */
2240 rdp->n_rp_gp_completed++;
2244 /* Has a new RCU grace period started? */
2245 if (ACCESS_ONCE(rnp->gpnum) != rdp->gpnum) { /* outside lock */
2246 rdp->n_rp_gp_started++;
2251 rdp->n_rp_need_nothing++;
2256 * Check to see if there is any immediate RCU-related work to be done
2257 * by the current CPU, returning 1 if so. This function is part of the
2258 * RCU implementation; it is -not- an exported member of the RCU API.
2260 static int rcu_pending(int cpu)
2262 struct rcu_state *rsp;
2264 for_each_rcu_flavor(rsp)
2265 if (__rcu_pending(rsp, per_cpu_ptr(rsp->rda, cpu)))
2271 * Check to see if any future RCU-related work will need to be done
2272 * by the current CPU, even if none need be done immediately, returning
2275 static int rcu_cpu_has_callbacks(int cpu)
2277 struct rcu_state *rsp;
2279 /* RCU callbacks either ready or pending? */
2280 for_each_rcu_flavor(rsp)
2281 if (per_cpu_ptr(rsp->rda, cpu)->nxtlist)
2287 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2288 * the compiler is expected to optimize this away.
2290 static void _rcu_barrier_trace(struct rcu_state *rsp, char *s,
2291 int cpu, unsigned long done)
2293 trace_rcu_barrier(rsp->name, s, cpu,
2294 atomic_read(&rsp->barrier_cpu_count), done);
2298 * RCU callback function for _rcu_barrier(). If we are last, wake
2299 * up the task executing _rcu_barrier().
2301 static void rcu_barrier_callback(struct rcu_head *rhp)
2303 struct rcu_data *rdp = container_of(rhp, struct rcu_data, barrier_head);
2304 struct rcu_state *rsp = rdp->rsp;
2306 if (atomic_dec_and_test(&rsp->barrier_cpu_count)) {
2307 _rcu_barrier_trace(rsp, "LastCB", -1, rsp->n_barrier_done);
2308 complete(&rsp->barrier_completion);
2310 _rcu_barrier_trace(rsp, "CB", -1, rsp->n_barrier_done);
2315 * Called with preemption disabled, and from cross-cpu IRQ context.
2317 static void rcu_barrier_func(void *type)
2319 struct rcu_state *rsp = type;
2320 struct rcu_data *rdp = __this_cpu_ptr(rsp->rda);
2322 _rcu_barrier_trace(rsp, "IRQ", -1, rsp->n_barrier_done);
2323 atomic_inc(&rsp->barrier_cpu_count);
2324 rsp->call(&rdp->barrier_head, rcu_barrier_callback);
2328 * Orchestrate the specified type of RCU barrier, waiting for all
2329 * RCU callbacks of the specified type to complete.
2331 static void _rcu_barrier(struct rcu_state *rsp)
2334 unsigned long flags;
2335 struct rcu_data *rdp;
2337 unsigned long snap = ACCESS_ONCE(rsp->n_barrier_done);
2338 unsigned long snap_done;
2340 init_rcu_head_on_stack(&rd.barrier_head);
2341 _rcu_barrier_trace(rsp, "Begin", -1, snap);
2343 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2344 mutex_lock(&rsp->barrier_mutex);
2347 * Ensure that all prior references, including to ->n_barrier_done,
2348 * are ordered before the _rcu_barrier() machinery.
2350 smp_mb(); /* See above block comment. */
2353 * Recheck ->n_barrier_done to see if others did our work for us.
2354 * This means checking ->n_barrier_done for an even-to-odd-to-even
2355 * transition. The "if" expression below therefore rounds the old
2356 * value up to the next even number and adds two before comparing.
2358 snap_done = ACCESS_ONCE(rsp->n_barrier_done);
2359 _rcu_barrier_trace(rsp, "Check", -1, snap_done);
2360 if (ULONG_CMP_GE(snap_done, ((snap + 1) & ~0x1) + 2)) {
2361 _rcu_barrier_trace(rsp, "EarlyExit", -1, snap_done);
2362 smp_mb(); /* caller's subsequent code after above check. */
2363 mutex_unlock(&rsp->barrier_mutex);
2368 * Increment ->n_barrier_done to avoid duplicate work. Use
2369 * ACCESS_ONCE() to prevent the compiler from speculating
2370 * the increment to precede the early-exit check.
2372 ACCESS_ONCE(rsp->n_barrier_done)++;
2373 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 1);
2374 _rcu_barrier_trace(rsp, "Inc1", -1, rsp->n_barrier_done);
2375 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2378 * Initialize the count to one rather than to zero in order to
2379 * avoid a too-soon return to zero in case of a short grace period
2380 * (or preemption of this task). Also flag this task as doing
2381 * an rcu_barrier(). This will prevent anyone else from adopting
2382 * orphaned callbacks, which could cause otherwise failure if a
2383 * CPU went offline and quickly came back online. To see this,
2384 * consider the following sequence of events:
2386 * 1. We cause CPU 0 to post an rcu_barrier_callback() callback.
2387 * 2. CPU 1 goes offline, orphaning its callbacks.
2388 * 3. CPU 0 adopts CPU 1's orphaned callbacks.
2389 * 4. CPU 1 comes back online.
2390 * 5. We cause CPU 1 to post an rcu_barrier_callback() callback.
2391 * 6. Both rcu_barrier_callback() callbacks are invoked, awakening
2392 * us -- but before CPU 1's orphaned callbacks are invoked!!!
2394 init_completion(&rsp->barrier_completion);
2395 atomic_set(&rsp->barrier_cpu_count, 1);
2396 raw_spin_lock_irqsave(&rsp->onofflock, flags);
2397 rsp->rcu_barrier_in_progress = current;
2398 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
2401 * Force every CPU with callbacks to register a new callback
2402 * that will tell us when all the preceding callbacks have
2403 * been invoked. If an offline CPU has callbacks, wait for
2404 * it to either come back online or to finish orphaning those
2407 for_each_possible_cpu(cpu) {
2409 rdp = per_cpu_ptr(rsp->rda, cpu);
2410 if (cpu_is_offline(cpu)) {
2411 _rcu_barrier_trace(rsp, "Offline", cpu,
2412 rsp->n_barrier_done);
2414 while (cpu_is_offline(cpu) && ACCESS_ONCE(rdp->qlen))
2415 schedule_timeout_interruptible(1);
2416 } else if (ACCESS_ONCE(rdp->qlen)) {
2417 _rcu_barrier_trace(rsp, "OnlineQ", cpu,
2418 rsp->n_barrier_done);
2419 smp_call_function_single(cpu, rcu_barrier_func, rsp, 1);
2422 _rcu_barrier_trace(rsp, "OnlineNQ", cpu,
2423 rsp->n_barrier_done);
2429 * Now that all online CPUs have rcu_barrier_callback() callbacks
2430 * posted, we can adopt all of the orphaned callbacks and place
2431 * an rcu_barrier_callback() callback after them. When that is done,
2432 * we are guaranteed to have an rcu_barrier_callback() callback
2433 * following every callback that could possibly have been
2434 * registered before _rcu_barrier() was called.
2436 raw_spin_lock_irqsave(&rsp->onofflock, flags);
2437 rcu_adopt_orphan_cbs(rsp);
2438 rsp->rcu_barrier_in_progress = NULL;
2439 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
2440 atomic_inc(&rsp->barrier_cpu_count);
2441 smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */
2443 rsp->call(&rd.barrier_head, rcu_barrier_callback);
2446 * Now that we have an rcu_barrier_callback() callback on each
2447 * CPU, and thus each counted, remove the initial count.
2449 if (atomic_dec_and_test(&rsp->barrier_cpu_count))
2450 complete(&rsp->barrier_completion);
2452 /* Increment ->n_barrier_done to prevent duplicate work. */
2453 smp_mb(); /* Keep increment after above mechanism. */
2454 ACCESS_ONCE(rsp->n_barrier_done)++;
2455 WARN_ON_ONCE((rsp->n_barrier_done & 0x1) != 0);
2456 _rcu_barrier_trace(rsp, "Inc2", -1, rsp->n_barrier_done);
2457 smp_mb(); /* Keep increment before caller's subsequent code. */
2459 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2460 wait_for_completion(&rsp->barrier_completion);
2462 /* Other rcu_barrier() invocations can now safely proceed. */
2463 mutex_unlock(&rsp->barrier_mutex);
2465 destroy_rcu_head_on_stack(&rd.barrier_head);
2469 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2471 void rcu_barrier_bh(void)
2473 _rcu_barrier(&rcu_bh_state);
2475 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
2478 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2480 void rcu_barrier_sched(void)
2482 _rcu_barrier(&rcu_sched_state);
2484 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
2487 * Do boot-time initialization of a CPU's per-CPU RCU data.
2490 rcu_boot_init_percpu_data(int cpu, struct rcu_state *rsp)
2492 unsigned long flags;
2493 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2494 struct rcu_node *rnp = rcu_get_root(rsp);
2496 /* Set up local state, ensuring consistent view of global state. */
2497 raw_spin_lock_irqsave(&rnp->lock, flags);
2498 rdp->grpmask = 1UL << (cpu - rdp->mynode->grplo);
2499 init_callback_list(rdp);
2501 ACCESS_ONCE(rdp->qlen) = 0;
2502 rdp->dynticks = &per_cpu(rcu_dynticks, cpu);
2503 WARN_ON_ONCE(rdp->dynticks->dynticks_nesting != DYNTICK_TASK_EXIT_IDLE);
2504 WARN_ON_ONCE(atomic_read(&rdp->dynticks->dynticks) != 1);
2507 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2511 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2512 * offline event can be happening at a given time. Note also that we
2513 * can accept some slop in the rsp->completed access due to the fact
2514 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2516 static void __cpuinit
2517 rcu_init_percpu_data(int cpu, struct rcu_state *rsp, int preemptible)
2519 unsigned long flags;
2521 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2522 struct rcu_node *rnp = rcu_get_root(rsp);
2524 /* Set up local state, ensuring consistent view of global state. */
2525 raw_spin_lock_irqsave(&rnp->lock, flags);
2526 rdp->beenonline = 1; /* We have now been online. */
2527 rdp->preemptible = preemptible;
2528 rdp->qlen_last_fqs_check = 0;
2529 rdp->n_force_qs_snap = rsp->n_force_qs;
2530 rdp->blimit = blimit;
2531 rdp->dynticks->dynticks_nesting = DYNTICK_TASK_EXIT_IDLE;
2532 atomic_set(&rdp->dynticks->dynticks,
2533 (atomic_read(&rdp->dynticks->dynticks) & ~0x1) + 1);
2534 rcu_prepare_for_idle_init(cpu);
2535 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
2538 * A new grace period might start here. If so, we won't be part
2539 * of it, but that is OK, as we are currently in a quiescent state.
2542 /* Exclude any attempts to start a new GP on large systems. */
2543 raw_spin_lock(&rsp->onofflock); /* irqs already disabled. */
2545 /* Add CPU to rcu_node bitmasks. */
2547 mask = rdp->grpmask;
2549 /* Exclude any attempts to start a new GP on small systems. */
2550 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
2551 rnp->qsmaskinit |= mask;
2552 mask = rnp->grpmask;
2553 if (rnp == rdp->mynode) {
2555 * If there is a grace period in progress, we will
2556 * set up to wait for it next time we run the
2559 rdp->gpnum = rnp->completed;
2560 rdp->completed = rnp->completed;
2561 rdp->passed_quiesce = 0;
2562 rdp->qs_pending = 0;
2563 rdp->passed_quiesce_gpnum = rnp->gpnum - 1;
2564 trace_rcu_grace_period(rsp->name, rdp->gpnum, "cpuonl");
2566 raw_spin_unlock(&rnp->lock); /* irqs already disabled. */
2568 } while (rnp != NULL && !(rnp->qsmaskinit & mask));
2570 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
2573 static void __cpuinit rcu_prepare_cpu(int cpu)
2575 struct rcu_state *rsp;
2577 for_each_rcu_flavor(rsp)
2578 rcu_init_percpu_data(cpu, rsp,
2579 strcmp(rsp->name, "rcu_preempt") == 0);
2583 * Handle CPU online/offline notification events.
2585 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
2586 unsigned long action, void *hcpu)
2588 long cpu = (long)hcpu;
2589 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
2590 struct rcu_node *rnp = rdp->mynode;
2591 struct rcu_state *rsp;
2593 trace_rcu_utilization("Start CPU hotplug");
2595 case CPU_UP_PREPARE:
2596 case CPU_UP_PREPARE_FROZEN:
2597 rcu_prepare_cpu(cpu);
2598 rcu_prepare_kthreads(cpu);
2601 case CPU_DOWN_FAILED:
2602 rcu_node_kthread_setaffinity(rnp, -1);
2603 rcu_cpu_kthread_setrt(cpu, 1);
2605 case CPU_DOWN_PREPARE:
2606 rcu_node_kthread_setaffinity(rnp, cpu);
2607 rcu_cpu_kthread_setrt(cpu, 0);
2610 case CPU_DYING_FROZEN:
2612 * The whole machine is "stopped" except this CPU, so we can
2613 * touch any data without introducing corruption. We send the
2614 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2616 for_each_rcu_flavor(rsp)
2617 rcu_cleanup_dying_cpu(rsp);
2618 rcu_cleanup_after_idle(cpu);
2621 case CPU_DEAD_FROZEN:
2622 case CPU_UP_CANCELED:
2623 case CPU_UP_CANCELED_FROZEN:
2624 for_each_rcu_flavor(rsp)
2625 rcu_cleanup_dead_cpu(cpu, rsp);
2630 trace_rcu_utilization("End CPU hotplug");
2635 * Spawn the kthread that handles this RCU flavor's grace periods.
2637 static int __init rcu_spawn_gp_kthread(void)
2639 unsigned long flags;
2640 struct rcu_node *rnp;
2641 struct rcu_state *rsp;
2642 struct task_struct *t;
2644 for_each_rcu_flavor(rsp) {
2645 t = kthread_run(rcu_gp_kthread, rsp, rsp->name);
2647 rnp = rcu_get_root(rsp);
2648 raw_spin_lock_irqsave(&rnp->lock, flags);
2649 rsp->gp_kthread = t;
2650 raw_spin_unlock_irqrestore(&rnp->lock, flags);
2654 early_initcall(rcu_spawn_gp_kthread);
2657 * This function is invoked towards the end of the scheduler's initialization
2658 * process. Before this is called, the idle task might contain
2659 * RCU read-side critical sections (during which time, this idle
2660 * task is booting the system). After this function is called, the
2661 * idle tasks are prohibited from containing RCU read-side critical
2662 * sections. This function also enables RCU lockdep checking.
2664 void rcu_scheduler_starting(void)
2666 WARN_ON(num_online_cpus() != 1);
2667 WARN_ON(nr_context_switches() > 0);
2668 rcu_scheduler_active = 1;
2672 * Compute the per-level fanout, either using the exact fanout specified
2673 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2675 #ifdef CONFIG_RCU_FANOUT_EXACT
2676 static void __init rcu_init_levelspread(struct rcu_state *rsp)
2680 for (i = rcu_num_lvls - 1; i > 0; i--)
2681 rsp->levelspread[i] = CONFIG_RCU_FANOUT;
2682 rsp->levelspread[0] = rcu_fanout_leaf;
2684 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2685 static void __init rcu_init_levelspread(struct rcu_state *rsp)
2692 for (i = rcu_num_lvls - 1; i >= 0; i--) {
2693 ccur = rsp->levelcnt[i];
2694 rsp->levelspread[i] = (cprv + ccur - 1) / ccur;
2698 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2701 * Helper function for rcu_init() that initializes one rcu_state structure.
2703 static void __init rcu_init_one(struct rcu_state *rsp,
2704 struct rcu_data __percpu *rda)
2706 static char *buf[] = { "rcu_node_level_0",
2709 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
2713 struct rcu_node *rnp;
2715 BUILD_BUG_ON(MAX_RCU_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
2717 /* Initialize the level-tracking arrays. */
2719 for (i = 0; i < rcu_num_lvls; i++)
2720 rsp->levelcnt[i] = num_rcu_lvl[i];
2721 for (i = 1; i < rcu_num_lvls; i++)
2722 rsp->level[i] = rsp->level[i - 1] + rsp->levelcnt[i - 1];
2723 rcu_init_levelspread(rsp);
2725 /* Initialize the elements themselves, starting from the leaves. */
2727 for (i = rcu_num_lvls - 1; i >= 0; i--) {
2728 cpustride *= rsp->levelspread[i];
2729 rnp = rsp->level[i];
2730 for (j = 0; j < rsp->levelcnt[i]; j++, rnp++) {
2731 raw_spin_lock_init(&rnp->lock);
2732 lockdep_set_class_and_name(&rnp->lock,
2733 &rcu_node_class[i], buf[i]);
2736 rnp->qsmaskinit = 0;
2737 rnp->grplo = j * cpustride;
2738 rnp->grphi = (j + 1) * cpustride - 1;
2739 if (rnp->grphi >= NR_CPUS)
2740 rnp->grphi = NR_CPUS - 1;
2746 rnp->grpnum = j % rsp->levelspread[i - 1];
2747 rnp->grpmask = 1UL << rnp->grpnum;
2748 rnp->parent = rsp->level[i - 1] +
2749 j / rsp->levelspread[i - 1];
2752 INIT_LIST_HEAD(&rnp->blkd_tasks);
2757 init_waitqueue_head(&rsp->gp_wq);
2758 rnp = rsp->level[rcu_num_lvls - 1];
2759 for_each_possible_cpu(i) {
2760 while (i > rnp->grphi)
2762 per_cpu_ptr(rsp->rda, i)->mynode = rnp;
2763 rcu_boot_init_percpu_data(i, rsp);
2765 list_add(&rsp->flavors, &rcu_struct_flavors);
2769 * Compute the rcu_node tree geometry from kernel parameters. This cannot
2770 * replace the definitions in rcutree.h because those are needed to size
2771 * the ->node array in the rcu_state structure.
2773 static void __init rcu_init_geometry(void)
2778 int rcu_capacity[MAX_RCU_LVLS + 1];
2780 /* If the compile-time values are accurate, just leave. */
2781 if (rcu_fanout_leaf == CONFIG_RCU_FANOUT_LEAF)
2785 * Compute number of nodes that can be handled an rcu_node tree
2786 * with the given number of levels. Setting rcu_capacity[0] makes
2787 * some of the arithmetic easier.
2789 rcu_capacity[0] = 1;
2790 rcu_capacity[1] = rcu_fanout_leaf;
2791 for (i = 2; i <= MAX_RCU_LVLS; i++)
2792 rcu_capacity[i] = rcu_capacity[i - 1] * CONFIG_RCU_FANOUT;
2795 * The boot-time rcu_fanout_leaf parameter is only permitted
2796 * to increase the leaf-level fanout, not decrease it. Of course,
2797 * the leaf-level fanout cannot exceed the number of bits in
2798 * the rcu_node masks. Finally, the tree must be able to accommodate
2799 * the configured number of CPUs. Complain and fall back to the
2800 * compile-time values if these limits are exceeded.
2802 if (rcu_fanout_leaf < CONFIG_RCU_FANOUT_LEAF ||
2803 rcu_fanout_leaf > sizeof(unsigned long) * 8 ||
2804 n > rcu_capacity[MAX_RCU_LVLS]) {
2809 /* Calculate the number of rcu_nodes at each level of the tree. */
2810 for (i = 1; i <= MAX_RCU_LVLS; i++)
2811 if (n <= rcu_capacity[i]) {
2812 for (j = 0; j <= i; j++)
2814 DIV_ROUND_UP(n, rcu_capacity[i - j]);
2816 for (j = i + 1; j <= MAX_RCU_LVLS; j++)
2821 /* Calculate the total number of rcu_node structures. */
2823 for (i = 0; i <= MAX_RCU_LVLS; i++)
2824 rcu_num_nodes += num_rcu_lvl[i];
2828 void __init rcu_init(void)
2832 rcu_bootup_announce();
2833 rcu_init_geometry();
2834 rcu_init_one(&rcu_sched_state, &rcu_sched_data);
2835 rcu_init_one(&rcu_bh_state, &rcu_bh_data);
2836 __rcu_init_preempt();
2837 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
2840 * We don't need protection against CPU-hotplug here because
2841 * this is called early in boot, before either interrupts
2842 * or the scheduler are operational.
2844 cpu_notifier(rcu_cpu_notify, 0);
2845 for_each_online_cpu(cpu)
2846 rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
2847 check_cpu_stall_init();
2850 #include "rcutree_plugin.h"