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), \
75 .fqslock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.fqslock), \
79 struct rcu_state rcu_sched_state
=
80 RCU_STATE_INITIALIZER(rcu_sched
, call_rcu_sched
);
81 DEFINE_PER_CPU(struct rcu_data
, rcu_sched_data
);
83 struct rcu_state rcu_bh_state
= RCU_STATE_INITIALIZER(rcu_bh
, call_rcu_bh
);
84 DEFINE_PER_CPU(struct rcu_data
, rcu_bh_data
);
86 static struct rcu_state
*rcu_state
;
87 LIST_HEAD(rcu_struct_flavors
);
89 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
90 static int rcu_fanout_leaf
= CONFIG_RCU_FANOUT_LEAF
;
91 module_param(rcu_fanout_leaf
, int, 0);
92 int rcu_num_lvls __read_mostly
= RCU_NUM_LVLS
;
93 static int num_rcu_lvl
[] = { /* Number of rcu_nodes at specified level. */
100 int rcu_num_nodes __read_mostly
= NUM_RCU_NODES
; /* Total # rcu_nodes in use. */
103 * The rcu_scheduler_active variable transitions from zero to one just
104 * before the first task is spawned. So when this variable is zero, RCU
105 * can assume that there is but one task, allowing RCU to (for example)
106 * optimized synchronize_sched() to a simple barrier(). When this variable
107 * is one, RCU must actually do all the hard work required to detect real
108 * grace periods. This variable is also used to suppress boot-time false
109 * positives from lockdep-RCU error checking.
111 int rcu_scheduler_active __read_mostly
;
112 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
115 * The rcu_scheduler_fully_active variable transitions from zero to one
116 * during the early_initcall() processing, which is after the scheduler
117 * is capable of creating new tasks. So RCU processing (for example,
118 * creating tasks for RCU priority boosting) must be delayed until after
119 * rcu_scheduler_fully_active transitions from zero to one. We also
120 * currently delay invocation of any RCU callbacks until after this point.
122 * It might later prove better for people registering RCU callbacks during
123 * early boot to take responsibility for these callbacks, but one step at
126 static int rcu_scheduler_fully_active __read_mostly
;
128 #ifdef CONFIG_RCU_BOOST
131 * Control variables for per-CPU and per-rcu_node kthreads. These
132 * handle all flavors of RCU.
134 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
135 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
136 DEFINE_PER_CPU(int, rcu_cpu_kthread_cpu
);
137 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
138 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
140 #endif /* #ifdef CONFIG_RCU_BOOST */
142 static void rcu_node_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
143 static void invoke_rcu_core(void);
144 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
147 * Track the rcutorture test sequence number and the update version
148 * number within a given test. The rcutorture_testseq is incremented
149 * on every rcutorture module load and unload, so has an odd value
150 * when a test is running. The rcutorture_vernum is set to zero
151 * when rcutorture starts and is incremented on each rcutorture update.
152 * These variables enable correlating rcutorture output with the
153 * RCU tracing information.
155 unsigned long rcutorture_testseq
;
156 unsigned long rcutorture_vernum
;
159 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
160 * permit this function to be invoked without holding the root rcu_node
161 * structure's ->lock, but of course results can be subject to change.
163 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
165 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
169 * Note a quiescent state. Because we do not need to know
170 * how many quiescent states passed, just if there was at least
171 * one since the start of the grace period, this just sets a flag.
172 * The caller must have disabled preemption.
174 void rcu_sched_qs(int cpu
)
176 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
178 rdp
->passed_quiesce_gpnum
= rdp
->gpnum
;
180 if (rdp
->passed_quiesce
== 0)
181 trace_rcu_grace_period("rcu_sched", rdp
->gpnum
, "cpuqs");
182 rdp
->passed_quiesce
= 1;
185 void rcu_bh_qs(int cpu
)
187 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
189 rdp
->passed_quiesce_gpnum
= rdp
->gpnum
;
191 if (rdp
->passed_quiesce
== 0)
192 trace_rcu_grace_period("rcu_bh", rdp
->gpnum
, "cpuqs");
193 rdp
->passed_quiesce
= 1;
197 * Note a context switch. This is a quiescent state for RCU-sched,
198 * and requires special handling for preemptible RCU.
199 * The caller must have disabled preemption.
201 void rcu_note_context_switch(int cpu
)
203 trace_rcu_utilization("Start context switch");
205 rcu_preempt_note_context_switch(cpu
);
206 trace_rcu_utilization("End context switch");
208 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
210 DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
211 .dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
,
212 .dynticks
= ATOMIC_INIT(1),
215 static int blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
216 static int qhimark
= 10000; /* If this many pending, ignore blimit. */
217 static int qlowmark
= 100; /* Once only this many pending, use blimit. */
219 module_param(blimit
, int, 0);
220 module_param(qhimark
, int, 0);
221 module_param(qlowmark
, int, 0);
223 int rcu_cpu_stall_suppress __read_mostly
; /* 1 = suppress stall warnings. */
224 int rcu_cpu_stall_timeout __read_mostly
= CONFIG_RCU_CPU_STALL_TIMEOUT
;
226 module_param(rcu_cpu_stall_suppress
, int, 0644);
227 module_param(rcu_cpu_stall_timeout
, int, 0644);
229 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
);
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
, 0);
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
, 0);
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 * rcu_idle_enter_common - inform RCU that current CPU is moving towards idle
324 * If the new value of the ->dynticks_nesting counter now is zero,
325 * we really have entered idle, and must do the appropriate accounting.
326 * The caller must have disabled interrupts.
328 static void rcu_idle_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
)
330 trace_rcu_dyntick("Start", oldval
, 0);
331 if (!is_idle_task(current
)) {
332 struct task_struct
*idle
= idle_task(smp_processor_id());
334 trace_rcu_dyntick("Error on entry: not idle task", oldval
, 0);
335 ftrace_dump(DUMP_ORIG
);
336 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
337 current
->pid
, current
->comm
,
338 idle
->pid
, idle
->comm
); /* must be idle task! */
340 rcu_prepare_for_idle(smp_processor_id());
341 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
342 smp_mb__before_atomic_inc(); /* See above. */
343 atomic_inc(&rdtp
->dynticks
);
344 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
345 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
348 * The idle task is not permitted to enter the idle loop while
349 * in an RCU read-side critical section.
351 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map
),
352 "Illegal idle entry in RCU read-side critical section.");
353 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
),
354 "Illegal idle entry in RCU-bh read-side critical section.");
355 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map
),
356 "Illegal idle entry in RCU-sched read-side critical section.");
360 * rcu_idle_enter - inform RCU that current CPU is entering idle
362 * Enter idle mode, in other words, -leave- the mode in which RCU
363 * read-side critical sections can occur. (Though RCU read-side
364 * critical sections can occur in irq handlers in idle, a possibility
365 * handled by irq_enter() and irq_exit().)
367 * We crowbar the ->dynticks_nesting field to zero to allow for
368 * the possibility of usermode upcalls having messed up our count
369 * of interrupt nesting level during the prior busy period.
371 void rcu_idle_enter(void)
375 struct rcu_dynticks
*rdtp
;
377 local_irq_save(flags
);
378 rdtp
= &__get_cpu_var(rcu_dynticks
);
379 oldval
= rdtp
->dynticks_nesting
;
380 WARN_ON_ONCE((oldval
& DYNTICK_TASK_NEST_MASK
) == 0);
381 if ((oldval
& DYNTICK_TASK_NEST_MASK
) == DYNTICK_TASK_NEST_VALUE
)
382 rdtp
->dynticks_nesting
= 0;
384 rdtp
->dynticks_nesting
-= DYNTICK_TASK_NEST_VALUE
;
385 rcu_idle_enter_common(rdtp
, oldval
);
386 local_irq_restore(flags
);
388 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
391 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
393 * Exit from an interrupt handler, which might possibly result in entering
394 * idle mode, in other words, leaving the mode in which read-side critical
395 * sections can occur.
397 * This code assumes that the idle loop never does anything that might
398 * result in unbalanced calls to irq_enter() and irq_exit(). If your
399 * architecture violates this assumption, RCU will give you what you
400 * deserve, good and hard. But very infrequently and irreproducibly.
402 * Use things like work queues to work around this limitation.
404 * You have been warned.
406 void rcu_irq_exit(void)
410 struct rcu_dynticks
*rdtp
;
412 local_irq_save(flags
);
413 rdtp
= &__get_cpu_var(rcu_dynticks
);
414 oldval
= rdtp
->dynticks_nesting
;
415 rdtp
->dynticks_nesting
--;
416 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
417 if (rdtp
->dynticks_nesting
)
418 trace_rcu_dyntick("--=", oldval
, rdtp
->dynticks_nesting
);
420 rcu_idle_enter_common(rdtp
, oldval
);
421 local_irq_restore(flags
);
425 * rcu_idle_exit_common - inform RCU that current CPU is moving away from idle
427 * If the new value of the ->dynticks_nesting counter was previously zero,
428 * we really have exited idle, and must do the appropriate accounting.
429 * The caller must have disabled interrupts.
431 static void rcu_idle_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
)
433 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
434 atomic_inc(&rdtp
->dynticks
);
435 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
436 smp_mb__after_atomic_inc(); /* See above. */
437 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
438 rcu_cleanup_after_idle(smp_processor_id());
439 trace_rcu_dyntick("End", oldval
, rdtp
->dynticks_nesting
);
440 if (!is_idle_task(current
)) {
441 struct task_struct
*idle
= idle_task(smp_processor_id());
443 trace_rcu_dyntick("Error on exit: not idle task",
444 oldval
, rdtp
->dynticks_nesting
);
445 ftrace_dump(DUMP_ORIG
);
446 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
447 current
->pid
, current
->comm
,
448 idle
->pid
, idle
->comm
); /* must be idle task! */
453 * rcu_idle_exit - inform RCU that current CPU is leaving idle
455 * Exit idle mode, in other words, -enter- the mode in which RCU
456 * read-side critical sections can occur.
458 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
459 * allow for the possibility of usermode upcalls messing up our count
460 * of interrupt nesting level during the busy period that is just
463 void rcu_idle_exit(void)
466 struct rcu_dynticks
*rdtp
;
469 local_irq_save(flags
);
470 rdtp
= &__get_cpu_var(rcu_dynticks
);
471 oldval
= rdtp
->dynticks_nesting
;
472 WARN_ON_ONCE(oldval
< 0);
473 if (oldval
& DYNTICK_TASK_NEST_MASK
)
474 rdtp
->dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
476 rdtp
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
477 rcu_idle_exit_common(rdtp
, oldval
);
478 local_irq_restore(flags
);
480 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
483 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
485 * Enter an interrupt handler, which might possibly result in exiting
486 * idle mode, in other words, entering the mode in which read-side critical
487 * sections can occur.
489 * Note that the Linux kernel is fully capable of entering an interrupt
490 * handler that it never exits, for example when doing upcalls to
491 * user mode! This code assumes that the idle loop never does upcalls to
492 * user mode. If your architecture does do upcalls from the idle loop (or
493 * does anything else that results in unbalanced calls to the irq_enter()
494 * and irq_exit() functions), RCU will give you what you deserve, good
495 * and hard. But very infrequently and irreproducibly.
497 * Use things like work queues to work around this limitation.
499 * You have been warned.
501 void rcu_irq_enter(void)
504 struct rcu_dynticks
*rdtp
;
507 local_irq_save(flags
);
508 rdtp
= &__get_cpu_var(rcu_dynticks
);
509 oldval
= rdtp
->dynticks_nesting
;
510 rdtp
->dynticks_nesting
++;
511 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
513 trace_rcu_dyntick("++=", oldval
, rdtp
->dynticks_nesting
);
515 rcu_idle_exit_common(rdtp
, oldval
);
516 local_irq_restore(flags
);
520 * rcu_nmi_enter - inform RCU of entry to NMI context
522 * If the CPU was idle with dynamic ticks active, and there is no
523 * irq handler running, this updates rdtp->dynticks_nmi to let the
524 * RCU grace-period handling know that the CPU is active.
526 void rcu_nmi_enter(void)
528 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
530 if (rdtp
->dynticks_nmi_nesting
== 0 &&
531 (atomic_read(&rdtp
->dynticks
) & 0x1))
533 rdtp
->dynticks_nmi_nesting
++;
534 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
535 atomic_inc(&rdtp
->dynticks
);
536 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
537 smp_mb__after_atomic_inc(); /* See above. */
538 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
542 * rcu_nmi_exit - inform RCU of exit from NMI context
544 * If the CPU was idle with dynamic ticks active, and there is no
545 * irq handler running, this updates rdtp->dynticks_nmi to let the
546 * RCU grace-period handling know that the CPU is no longer active.
548 void rcu_nmi_exit(void)
550 struct rcu_dynticks
*rdtp
= &__get_cpu_var(rcu_dynticks
);
552 if (rdtp
->dynticks_nmi_nesting
== 0 ||
553 --rdtp
->dynticks_nmi_nesting
!= 0)
555 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
556 smp_mb__before_atomic_inc(); /* See above. */
557 atomic_inc(&rdtp
->dynticks
);
558 smp_mb__after_atomic_inc(); /* Force delay to next write. */
559 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
563 * rcu_is_cpu_idle - see if RCU thinks that the current CPU is idle
565 * If the current CPU is in its idle loop and is neither in an interrupt
566 * or NMI handler, return true.
568 int rcu_is_cpu_idle(void)
573 ret
= (atomic_read(&__get_cpu_var(rcu_dynticks
).dynticks
) & 0x1) == 0;
577 EXPORT_SYMBOL(rcu_is_cpu_idle
);
579 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
582 * Is the current CPU online? Disable preemption to avoid false positives
583 * that could otherwise happen due to the current CPU number being sampled,
584 * this task being preempted, its old CPU being taken offline, resuming
585 * on some other CPU, then determining that its old CPU is now offline.
586 * It is OK to use RCU on an offline processor during initial boot, hence
587 * the check for rcu_scheduler_fully_active. Note also that it is OK
588 * for a CPU coming online to use RCU for one jiffy prior to marking itself
589 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
590 * offline to continue to use RCU for one jiffy after marking itself
591 * offline in the cpu_online_mask. This leniency is necessary given the
592 * non-atomic nature of the online and offline processing, for example,
593 * the fact that a CPU enters the scheduler after completing the CPU_DYING
596 * This is also why RCU internally marks CPUs online during the
597 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
599 * Disable checking if in an NMI handler because we cannot safely report
600 * errors from NMI handlers anyway.
602 bool rcu_lockdep_current_cpu_online(void)
604 struct rcu_data
*rdp
;
605 struct rcu_node
*rnp
;
611 rdp
= &__get_cpu_var(rcu_sched_data
);
613 ret
= (rdp
->grpmask
& rnp
->qsmaskinit
) ||
614 !rcu_scheduler_fully_active
;
618 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online
);
620 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
623 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
625 * If the current CPU is idle or running at a first-level (not nested)
626 * interrupt from idle, return true. The caller must have at least
627 * disabled preemption.
629 int rcu_is_cpu_rrupt_from_idle(void)
631 return __get_cpu_var(rcu_dynticks
).dynticks_nesting
<= 1;
635 * Snapshot the specified CPU's dynticks counter so that we can later
636 * credit them with an implicit quiescent state. Return 1 if this CPU
637 * is in dynticks idle mode, which is an extended quiescent state.
639 static int dyntick_save_progress_counter(struct rcu_data
*rdp
)
641 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
642 return (rdp
->dynticks_snap
& 0x1) == 0;
646 * Return true if the specified CPU has passed through a quiescent
647 * state by virtue of being in or having passed through an dynticks
648 * idle state since the last call to dyntick_save_progress_counter()
649 * for this same CPU, or by virtue of having been offline.
651 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
)
656 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
657 snap
= (unsigned int)rdp
->dynticks_snap
;
660 * If the CPU passed through or entered a dynticks idle phase with
661 * no active irq/NMI handlers, then we can safely pretend that the CPU
662 * already acknowledged the request to pass through a quiescent
663 * state. Either way, that CPU cannot possibly be in an RCU
664 * read-side critical section that started before the beginning
665 * of the current RCU grace period.
667 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
668 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "dti");
674 * Check for the CPU being offline, but only if the grace period
675 * is old enough. We don't need to worry about the CPU changing
676 * state: If we see it offline even once, it has been through a
679 * The reason for insisting that the grace period be at least
680 * one jiffy old is that CPUs that are not quite online and that
681 * have just gone offline can still execute RCU read-side critical
684 if (ULONG_CMP_GE(rdp
->rsp
->gp_start
+ 2, jiffies
))
685 return 0; /* Grace period is not old enough. */
687 if (cpu_is_offline(rdp
->cpu
)) {
688 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, "ofl");
695 static int jiffies_till_stall_check(void)
697 int till_stall_check
= ACCESS_ONCE(rcu_cpu_stall_timeout
);
700 * Limit check must be consistent with the Kconfig limits
701 * for CONFIG_RCU_CPU_STALL_TIMEOUT.
703 if (till_stall_check
< 3) {
704 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 3;
705 till_stall_check
= 3;
706 } else if (till_stall_check
> 300) {
707 ACCESS_ONCE(rcu_cpu_stall_timeout
) = 300;
708 till_stall_check
= 300;
710 return till_stall_check
* HZ
+ RCU_STALL_DELAY_DELTA
;
713 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
715 rsp
->gp_start
= jiffies
;
716 rsp
->jiffies_stall
= jiffies
+ jiffies_till_stall_check();
719 static void print_other_cpu_stall(struct rcu_state
*rsp
)
725 struct rcu_node
*rnp
= rcu_get_root(rsp
);
727 /* Only let one CPU complain about others per time interval. */
729 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
730 delta
= jiffies
- rsp
->jiffies_stall
;
731 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
732 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
735 rsp
->jiffies_stall
= jiffies
+ 3 * jiffies_till_stall_check() + 3;
736 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
739 * OK, time to rat on our buddy...
740 * See Documentation/RCU/stallwarn.txt for info on how to debug
741 * RCU CPU stall warnings.
743 printk(KERN_ERR
"INFO: %s detected stalls on CPUs/tasks:",
745 print_cpu_stall_info_begin();
746 rcu_for_each_leaf_node(rsp
, rnp
) {
747 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
748 ndetected
+= rcu_print_task_stall(rnp
);
749 if (rnp
->qsmask
!= 0) {
750 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
751 if (rnp
->qsmask
& (1UL << cpu
)) {
752 print_cpu_stall_info(rsp
,
757 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
761 * Now rat on any tasks that got kicked up to the root rcu_node
762 * due to CPU offlining.
764 rnp
= rcu_get_root(rsp
);
765 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
766 ndetected
+= rcu_print_task_stall(rnp
);
767 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
769 print_cpu_stall_info_end();
770 printk(KERN_CONT
"(detected by %d, t=%ld jiffies)\n",
771 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
));
773 printk(KERN_ERR
"INFO: Stall ended before state dump start\n");
774 else if (!trigger_all_cpu_backtrace())
777 /* If so configured, complain about tasks blocking the grace period. */
779 rcu_print_detail_task_stall(rsp
);
781 force_quiescent_state(rsp
, 0); /* Kick them all. */
784 static void print_cpu_stall(struct rcu_state
*rsp
)
787 struct rcu_node
*rnp
= rcu_get_root(rsp
);
790 * OK, time to rat on ourselves...
791 * See Documentation/RCU/stallwarn.txt for info on how to debug
792 * RCU CPU stall warnings.
794 printk(KERN_ERR
"INFO: %s self-detected stall on CPU", rsp
->name
);
795 print_cpu_stall_info_begin();
796 print_cpu_stall_info(rsp
, smp_processor_id());
797 print_cpu_stall_info_end();
798 printk(KERN_CONT
" (t=%lu jiffies)\n", jiffies
- rsp
->gp_start
);
799 if (!trigger_all_cpu_backtrace())
802 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
803 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
804 rsp
->jiffies_stall
= jiffies
+
805 3 * jiffies_till_stall_check() + 3;
806 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
808 set_need_resched(); /* kick ourselves to get things going. */
811 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
815 struct rcu_node
*rnp
;
817 if (rcu_cpu_stall_suppress
)
819 j
= ACCESS_ONCE(jiffies
);
820 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
822 if (rcu_gp_in_progress(rsp
) &&
823 (ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
) && ULONG_CMP_GE(j
, js
)) {
825 /* We haven't checked in, so go dump stack. */
826 print_cpu_stall(rsp
);
828 } else if (rcu_gp_in_progress(rsp
) &&
829 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
831 /* They had a few time units to dump stack, so complain. */
832 print_other_cpu_stall(rsp
);
836 static int rcu_panic(struct notifier_block
*this, unsigned long ev
, void *ptr
)
838 rcu_cpu_stall_suppress
= 1;
843 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
845 * Set the stall-warning timeout way off into the future, thus preventing
846 * any RCU CPU stall-warning messages from appearing in the current set of
849 * The caller must disable hard irqs.
851 void rcu_cpu_stall_reset(void)
853 struct rcu_state
*rsp
;
855 for_each_rcu_flavor(rsp
)
856 rsp
->jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
859 static struct notifier_block rcu_panic_block
= {
860 .notifier_call
= rcu_panic
,
863 static void __init
check_cpu_stall_init(void)
865 atomic_notifier_chain_register(&panic_notifier_list
, &rcu_panic_block
);
869 * Update CPU-local rcu_data state to record the newly noticed grace period.
870 * This is used both when we started the grace period and when we notice
871 * that someone else started the grace period. The caller must hold the
872 * ->lock of the leaf rcu_node structure corresponding to the current CPU,
873 * and must have irqs disabled.
875 static void __note_new_gpnum(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
877 if (rdp
->gpnum
!= rnp
->gpnum
) {
879 * If the current grace period is waiting for this CPU,
880 * set up to detect a quiescent state, otherwise don't
881 * go looking for one.
883 rdp
->gpnum
= rnp
->gpnum
;
884 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpustart");
885 if (rnp
->qsmask
& rdp
->grpmask
) {
887 rdp
->passed_quiesce
= 0;
891 zero_cpu_stall_ticks(rdp
);
895 static void note_new_gpnum(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
898 struct rcu_node
*rnp
;
900 local_irq_save(flags
);
902 if (rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) || /* outside lock. */
903 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
904 local_irq_restore(flags
);
907 __note_new_gpnum(rsp
, rnp
, rdp
);
908 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
912 * Did someone else start a new RCU grace period start since we last
913 * checked? Update local state appropriately if so. Must be called
914 * on the CPU corresponding to rdp.
917 check_for_new_grace_period(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
922 local_irq_save(flags
);
923 if (rdp
->gpnum
!= rsp
->gpnum
) {
924 note_new_gpnum(rsp
, rdp
);
927 local_irq_restore(flags
);
932 * Initialize the specified rcu_data structure's callback list to empty.
934 static void init_callback_list(struct rcu_data
*rdp
)
939 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
940 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
944 * Advance this CPU's callbacks, but only if the current grace period
945 * has ended. This may be called only from the CPU to whom the rdp
946 * belongs. In addition, the corresponding leaf rcu_node structure's
947 * ->lock must be held by the caller, with irqs disabled.
950 __rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
952 /* Did another grace period end? */
953 if (rdp
->completed
!= rnp
->completed
) {
955 /* Advance callbacks. No harm if list empty. */
956 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[RCU_WAIT_TAIL
];
957 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_READY_TAIL
];
958 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
960 /* Remember that we saw this grace-period completion. */
961 rdp
->completed
= rnp
->completed
;
962 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuend");
965 * If we were in an extended quiescent state, we may have
966 * missed some grace periods that others CPUs handled on
967 * our behalf. Catch up with this state to avoid noting
968 * spurious new grace periods. If another grace period
969 * has started, then rnp->gpnum will have advanced, so
970 * we will detect this later on.
972 if (ULONG_CMP_LT(rdp
->gpnum
, rdp
->completed
))
973 rdp
->gpnum
= rdp
->completed
;
976 * If RCU does not need a quiescent state from this CPU,
977 * then make sure that this CPU doesn't go looking for one.
979 if ((rnp
->qsmask
& rdp
->grpmask
) == 0)
985 * Advance this CPU's callbacks, but only if the current grace period
986 * has ended. This may be called only from the CPU to whom the rdp
990 rcu_process_gp_end(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
993 struct rcu_node
*rnp
;
995 local_irq_save(flags
);
997 if (rdp
->completed
== ACCESS_ONCE(rnp
->completed
) || /* outside lock. */
998 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
999 local_irq_restore(flags
);
1002 __rcu_process_gp_end(rsp
, rnp
, rdp
);
1003 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1007 * Do per-CPU grace-period initialization for running CPU. The caller
1008 * must hold the lock of the leaf rcu_node structure corresponding to
1012 rcu_start_gp_per_cpu(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1014 /* Prior grace period ended, so advance callbacks for current CPU. */
1015 __rcu_process_gp_end(rsp
, rnp
, rdp
);
1018 * Because this CPU just now started the new grace period, we know
1019 * that all of its callbacks will be covered by this upcoming grace
1020 * period, even the ones that were registered arbitrarily recently.
1021 * Therefore, advance all outstanding callbacks to RCU_WAIT_TAIL.
1023 * Other CPUs cannot be sure exactly when the grace period started.
1024 * Therefore, their recently registered callbacks must pass through
1025 * an additional RCU_NEXT_READY stage, so that they will be handled
1026 * by the next RCU grace period.
1028 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1029 rdp
->nxttail
[RCU_WAIT_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1031 /* Set state so that this CPU will detect the next quiescent state. */
1032 __note_new_gpnum(rsp
, rnp
, rdp
);
1036 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1037 * in preparation for detecting the next grace period. The caller must hold
1038 * the root node's ->lock, which is released before return. Hard irqs must
1041 * Note that it is legal for a dying CPU (which is marked as offline) to
1042 * invoke this function. This can happen when the dying CPU reports its
1046 rcu_start_gp(struct rcu_state
*rsp
, unsigned long flags
)
1047 __releases(rcu_get_root(rsp
)->lock
)
1049 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1050 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1052 if (!rcu_scheduler_fully_active
||
1053 !cpu_needs_another_gp(rsp
, rdp
)) {
1055 * Either the scheduler hasn't yet spawned the first
1056 * non-idle task or this CPU does not need another
1057 * grace period. Either way, don't start a new grace
1060 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1064 if (rsp
->fqs_active
) {
1066 * This CPU needs a grace period, but force_quiescent_state()
1067 * is running. Tell it to start one on this CPU's behalf.
1069 rsp
->fqs_need_gp
= 1;
1070 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1074 /* Advance to a new grace period and initialize state. */
1076 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, "start");
1077 WARN_ON_ONCE(rsp
->fqs_state
== RCU_GP_INIT
);
1078 rsp
->fqs_state
= RCU_GP_INIT
; /* Hold off force_quiescent_state. */
1079 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
1080 record_gp_stall_check_time(rsp
);
1081 raw_spin_unlock(&rnp
->lock
); /* leave irqs disabled. */
1083 /* Exclude any concurrent CPU-hotplug operations. */
1084 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
1087 * Set the quiescent-state-needed bits in all the rcu_node
1088 * structures for all currently online CPUs in breadth-first
1089 * order, starting from the root rcu_node structure. This
1090 * operation relies on the layout of the hierarchy within the
1091 * rsp->node[] array. Note that other CPUs will access only
1092 * the leaves of the hierarchy, which still indicate that no
1093 * grace period is in progress, at least until the corresponding
1094 * leaf node has been initialized. In addition, we have excluded
1095 * CPU-hotplug operations.
1097 * Note that the grace period cannot complete until we finish
1098 * the initialization process, as there will be at least one
1099 * qsmask bit set in the root node until that time, namely the
1100 * one corresponding to this CPU, due to the fact that we have
1103 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1104 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1105 rcu_preempt_check_blocked_tasks(rnp
);
1106 rnp
->qsmask
= rnp
->qsmaskinit
;
1107 rnp
->gpnum
= rsp
->gpnum
;
1108 rnp
->completed
= rsp
->completed
;
1109 if (rnp
== rdp
->mynode
)
1110 rcu_start_gp_per_cpu(rsp
, rnp
, rdp
);
1111 rcu_preempt_boost_start_gp(rnp
);
1112 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1113 rnp
->level
, rnp
->grplo
,
1114 rnp
->grphi
, rnp
->qsmask
);
1115 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1118 rnp
= rcu_get_root(rsp
);
1119 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1120 rsp
->fqs_state
= RCU_SIGNAL_INIT
; /* force_quiescent_state now OK. */
1121 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1122 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
1126 * Report a full set of quiescent states to the specified rcu_state
1127 * data structure. This involves cleaning up after the prior grace
1128 * period and letting rcu_start_gp() start up the next grace period
1129 * if one is needed. Note that the caller must hold rnp->lock, as
1130 * required by rcu_start_gp(), which will release it.
1132 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1133 __releases(rcu_get_root(rsp
)->lock
)
1135 unsigned long gp_duration
;
1136 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1137 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1139 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1142 * Ensure that all grace-period and pre-grace-period activity
1143 * is seen before the assignment to rsp->completed.
1145 smp_mb(); /* See above block comment. */
1146 gp_duration
= jiffies
- rsp
->gp_start
;
1147 if (gp_duration
> rsp
->gp_max
)
1148 rsp
->gp_max
= gp_duration
;
1151 * We know the grace period is complete, but to everyone else
1152 * it appears to still be ongoing. But it is also the case
1153 * that to everyone else it looks like there is nothing that
1154 * they can do to advance the grace period. It is therefore
1155 * safe for us to drop the lock in order to mark the grace
1156 * period as completed in all of the rcu_node structures.
1158 * But if this CPU needs another grace period, it will take
1159 * care of this while initializing the next grace period.
1160 * We use RCU_WAIT_TAIL instead of the usual RCU_DONE_TAIL
1161 * because the callbacks have not yet been advanced: Those
1162 * callbacks are waiting on the grace period that just now
1165 if (*rdp
->nxttail
[RCU_WAIT_TAIL
] == NULL
) {
1166 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1169 * Propagate new ->completed value to rcu_node structures
1170 * so that other CPUs don't have to wait until the start
1171 * of the next grace period to process their callbacks.
1173 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1174 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1175 rnp
->completed
= rsp
->gpnum
;
1176 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1178 rnp
= rcu_get_root(rsp
);
1179 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1182 rsp
->completed
= rsp
->gpnum
; /* Declare the grace period complete. */
1183 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, "end");
1184 rsp
->fqs_state
= RCU_GP_IDLE
;
1185 rcu_start_gp(rsp
, flags
); /* releases root node's rnp->lock. */
1189 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1190 * Allows quiescent states for a group of CPUs to be reported at one go
1191 * to the specified rcu_node structure, though all the CPUs in the group
1192 * must be represented by the same rcu_node structure (which need not be
1193 * a leaf rcu_node structure, though it often will be). That structure's
1194 * lock must be held upon entry, and it is released before return.
1197 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1198 struct rcu_node
*rnp
, unsigned long flags
)
1199 __releases(rnp
->lock
)
1201 struct rcu_node
*rnp_c
;
1203 /* Walk up the rcu_node hierarchy. */
1205 if (!(rnp
->qsmask
& mask
)) {
1207 /* Our bit has already been cleared, so done. */
1208 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1211 rnp
->qsmask
&= ~mask
;
1212 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1213 mask
, rnp
->qsmask
, rnp
->level
,
1214 rnp
->grplo
, rnp
->grphi
,
1216 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1218 /* Other bits still set at this level, so done. */
1219 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1222 mask
= rnp
->grpmask
;
1223 if (rnp
->parent
== NULL
) {
1225 /* No more levels. Exit loop holding root lock. */
1229 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1232 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1233 WARN_ON_ONCE(rnp_c
->qsmask
);
1237 * Get here if we are the last CPU to pass through a quiescent
1238 * state for this grace period. Invoke rcu_report_qs_rsp()
1239 * to clean up and start the next grace period if one is needed.
1241 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1245 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1246 * structure. This must be either called from the specified CPU, or
1247 * called when the specified CPU is known to be offline (and when it is
1248 * also known that no other CPU is concurrently trying to help the offline
1249 * CPU). The lastcomp argument is used to make sure we are still in the
1250 * grace period of interest. We don't want to end the current grace period
1251 * based on quiescent states detected in an earlier grace period!
1254 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
, long lastgp
)
1256 unsigned long flags
;
1258 struct rcu_node
*rnp
;
1261 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1262 if (lastgp
!= rnp
->gpnum
|| rnp
->completed
== rnp
->gpnum
) {
1265 * The grace period in which this quiescent state was
1266 * recorded has ended, so don't report it upwards.
1267 * We will instead need a new quiescent state that lies
1268 * within the current grace period.
1270 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1271 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1274 mask
= rdp
->grpmask
;
1275 if ((rnp
->qsmask
& mask
) == 0) {
1276 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1278 rdp
->qs_pending
= 0;
1281 * This GP can't end until cpu checks in, so all of our
1282 * callbacks can be processed during the next GP.
1284 rdp
->nxttail
[RCU_NEXT_READY_TAIL
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1286 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1291 * Check to see if there is a new grace period of which this CPU
1292 * is not yet aware, and if so, set up local rcu_data state for it.
1293 * Otherwise, see if this CPU has just passed through its first
1294 * quiescent state for this grace period, and record that fact if so.
1297 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1299 /* If there is now a new grace period, record and return. */
1300 if (check_for_new_grace_period(rsp
, rdp
))
1304 * Does this CPU still need to do its part for current grace period?
1305 * If no, return and let the other CPUs do their part as well.
1307 if (!rdp
->qs_pending
)
1311 * Was there a quiescent state since the beginning of the grace
1312 * period? If no, then exit and wait for the next call.
1314 if (!rdp
->passed_quiesce
)
1318 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1321 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
, rdp
->passed_quiesce_gpnum
);
1324 #ifdef CONFIG_HOTPLUG_CPU
1327 * Send the specified CPU's RCU callbacks to the orphanage. The
1328 * specified CPU must be offline, and the caller must hold the
1332 rcu_send_cbs_to_orphanage(int cpu
, struct rcu_state
*rsp
,
1333 struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1336 * Orphan the callbacks. First adjust the counts. This is safe
1337 * because ->onofflock excludes _rcu_barrier()'s adoption of
1338 * the callbacks, thus no memory barrier is required.
1340 if (rdp
->nxtlist
!= NULL
) {
1341 rsp
->qlen_lazy
+= rdp
->qlen_lazy
;
1342 rsp
->qlen
+= rdp
->qlen
;
1343 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1345 ACCESS_ONCE(rdp
->qlen
) = 0;
1349 * Next, move those callbacks still needing a grace period to
1350 * the orphanage, where some other CPU will pick them up.
1351 * Some of the callbacks might have gone partway through a grace
1352 * period, but that is too bad. They get to start over because we
1353 * cannot assume that grace periods are synchronized across CPUs.
1354 * We don't bother updating the ->nxttail[] array yet, instead
1355 * we just reset the whole thing later on.
1357 if (*rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
) {
1358 *rsp
->orphan_nxttail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1359 rsp
->orphan_nxttail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
1360 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1364 * Then move the ready-to-invoke callbacks to the orphanage,
1365 * where some other CPU will pick them up. These will not be
1366 * required to pass though another grace period: They are done.
1368 if (rdp
->nxtlist
!= NULL
) {
1369 *rsp
->orphan_donetail
= rdp
->nxtlist
;
1370 rsp
->orphan_donetail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1373 /* Finally, initialize the rcu_data structure's list to empty. */
1374 init_callback_list(rdp
);
1378 * Adopt the RCU callbacks from the specified rcu_state structure's
1379 * orphanage. The caller must hold the ->onofflock.
1381 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
)
1384 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1387 * If there is an rcu_barrier() operation in progress, then
1388 * only the task doing that operation is permitted to adopt
1389 * callbacks. To do otherwise breaks rcu_barrier() and friends
1390 * by causing them to fail to wait for the callbacks in the
1393 if (rsp
->rcu_barrier_in_progress
&&
1394 rsp
->rcu_barrier_in_progress
!= current
)
1397 /* Do the accounting first. */
1398 rdp
->qlen_lazy
+= rsp
->qlen_lazy
;
1399 rdp
->qlen
+= rsp
->qlen
;
1400 rdp
->n_cbs_adopted
+= rsp
->qlen
;
1401 if (rsp
->qlen_lazy
!= rsp
->qlen
)
1402 rcu_idle_count_callbacks_posted();
1407 * We do not need a memory barrier here because the only way we
1408 * can get here if there is an rcu_barrier() in flight is if
1409 * we are the task doing the rcu_barrier().
1412 /* First adopt the ready-to-invoke callbacks. */
1413 if (rsp
->orphan_donelist
!= NULL
) {
1414 *rsp
->orphan_donetail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1415 *rdp
->nxttail
[RCU_DONE_TAIL
] = rsp
->orphan_donelist
;
1416 for (i
= RCU_NEXT_SIZE
- 1; i
>= RCU_DONE_TAIL
; i
--)
1417 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1418 rdp
->nxttail
[i
] = rsp
->orphan_donetail
;
1419 rsp
->orphan_donelist
= NULL
;
1420 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
1423 /* And then adopt the callbacks that still need a grace period. */
1424 if (rsp
->orphan_nxtlist
!= NULL
) {
1425 *rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxtlist
;
1426 rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxttail
;
1427 rsp
->orphan_nxtlist
= NULL
;
1428 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
1433 * Trace the fact that this CPU is going offline.
1435 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1437 RCU_TRACE(unsigned long mask
);
1438 RCU_TRACE(struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
));
1439 RCU_TRACE(struct rcu_node
*rnp
= rdp
->mynode
);
1441 RCU_TRACE(mask
= rdp
->grpmask
);
1442 trace_rcu_grace_period(rsp
->name
,
1443 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
1448 * The CPU has been completely removed, and some other CPU is reporting
1449 * this fact from process context. Do the remainder of the cleanup,
1450 * including orphaning the outgoing CPU's RCU callbacks, and also
1451 * adopting them, if there is no _rcu_barrier() instance running.
1452 * There can only be one CPU hotplug operation at a time, so no other
1453 * CPU can be attempting to update rcu_cpu_kthread_task.
1455 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1457 unsigned long flags
;
1459 int need_report
= 0;
1460 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1461 struct rcu_node
*rnp
= rdp
->mynode
; /* Outgoing CPU's rdp & rnp. */
1463 /* Adjust any no-longer-needed kthreads. */
1464 rcu_stop_cpu_kthread(cpu
);
1465 rcu_node_kthread_setaffinity(rnp
, -1);
1467 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
1469 /* Exclude any attempts to start a new grace period. */
1470 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
1472 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
1473 rcu_send_cbs_to_orphanage(cpu
, rsp
, rnp
, rdp
);
1474 rcu_adopt_orphan_cbs(rsp
);
1476 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
1477 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
1479 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1480 rnp
->qsmaskinit
&= ~mask
;
1481 if (rnp
->qsmaskinit
!= 0) {
1482 if (rnp
!= rdp
->mynode
)
1483 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1486 if (rnp
== rdp
->mynode
)
1487 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
1489 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1490 mask
= rnp
->grpmask
;
1492 } while (rnp
!= NULL
);
1495 * We still hold the leaf rcu_node structure lock here, and
1496 * irqs are still disabled. The reason for this subterfuge is
1497 * because invoking rcu_report_unblock_qs_rnp() with ->onofflock
1498 * held leads to deadlock.
1500 raw_spin_unlock(&rsp
->onofflock
); /* irqs remain disabled. */
1502 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
1503 rcu_report_unblock_qs_rnp(rnp
, flags
);
1505 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1506 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
1507 rcu_report_exp_rnp(rsp
, rnp
, true);
1508 WARN_ONCE(rdp
->qlen
!= 0 || rdp
->nxtlist
!= NULL
,
1509 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
1510 cpu
, rdp
->qlen
, rdp
->nxtlist
);
1513 #else /* #ifdef CONFIG_HOTPLUG_CPU */
1515 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
)
1519 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1523 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1527 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
1530 * Invoke any RCU callbacks that have made it to the end of their grace
1531 * period. Thottle as specified by rdp->blimit.
1533 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1535 unsigned long flags
;
1536 struct rcu_head
*next
, *list
, **tail
;
1537 int bl
, count
, count_lazy
, i
;
1539 /* If no callbacks are ready, just return.*/
1540 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
1541 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
1542 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
1543 need_resched(), is_idle_task(current
),
1544 rcu_is_callbacks_kthread());
1549 * Extract the list of ready callbacks, disabling to prevent
1550 * races with call_rcu() from interrupt handlers.
1552 local_irq_save(flags
);
1553 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
1555 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
1556 list
= rdp
->nxtlist
;
1557 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1558 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1559 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1560 for (i
= RCU_NEXT_SIZE
- 1; i
>= 0; i
--)
1561 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1562 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1563 local_irq_restore(flags
);
1565 /* Invoke callbacks. */
1566 count
= count_lazy
= 0;
1570 debug_rcu_head_unqueue(list
);
1571 if (__rcu_reclaim(rsp
->name
, list
))
1574 /* Stop only if limit reached and CPU has something to do. */
1575 if (++count
>= bl
&&
1577 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
1581 local_irq_save(flags
);
1582 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
1583 is_idle_task(current
),
1584 rcu_is_callbacks_kthread());
1586 /* Update count, and requeue any remaining callbacks. */
1588 *tail
= rdp
->nxtlist
;
1589 rdp
->nxtlist
= list
;
1590 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1591 if (&rdp
->nxtlist
== rdp
->nxttail
[i
])
1592 rdp
->nxttail
[i
] = tail
;
1596 smp_mb(); /* List handling before counting for rcu_barrier(). */
1597 rdp
->qlen_lazy
-= count_lazy
;
1598 ACCESS_ONCE(rdp
->qlen
) -= count
;
1599 rdp
->n_cbs_invoked
+= count
;
1601 /* Reinstate batch limit if we have worked down the excess. */
1602 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
1603 rdp
->blimit
= blimit
;
1605 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
1606 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
1607 rdp
->qlen_last_fqs_check
= 0;
1608 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1609 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
1610 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1611 WARN_ON_ONCE((rdp
->nxtlist
== NULL
) != (rdp
->qlen
== 0));
1613 local_irq_restore(flags
);
1615 /* Re-invoke RCU core processing if there are callbacks remaining. */
1616 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1621 * Check to see if this CPU is in a non-context-switch quiescent state
1622 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
1623 * Also schedule RCU core processing.
1625 * This function must be called from hardirq context. It is normally
1626 * invoked from the scheduling-clock interrupt. If rcu_pending returns
1627 * false, there is no point in invoking rcu_check_callbacks().
1629 void rcu_check_callbacks(int cpu
, int user
)
1631 trace_rcu_utilization("Start scheduler-tick");
1632 increment_cpu_stall_ticks();
1633 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
1636 * Get here if this CPU took its interrupt from user
1637 * mode or from the idle loop, and if this is not a
1638 * nested interrupt. In this case, the CPU is in
1639 * a quiescent state, so note it.
1641 * No memory barrier is required here because both
1642 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
1643 * variables that other CPUs neither access nor modify,
1644 * at least not while the corresponding CPU is online.
1650 } else if (!in_softirq()) {
1653 * Get here if this CPU did not take its interrupt from
1654 * softirq, in other words, if it is not interrupting
1655 * a rcu_bh read-side critical section. This is an _bh
1656 * critical section, so note it.
1661 rcu_preempt_check_callbacks(cpu
);
1662 if (rcu_pending(cpu
))
1664 trace_rcu_utilization("End scheduler-tick");
1668 * Scan the leaf rcu_node structures, processing dyntick state for any that
1669 * have not yet encountered a quiescent state, using the function specified.
1670 * Also initiate boosting for any threads blocked on the root rcu_node.
1672 * The caller must have suppressed start of new grace periods.
1674 static void force_qs_rnp(struct rcu_state
*rsp
, int (*f
)(struct rcu_data
*))
1678 unsigned long flags
;
1680 struct rcu_node
*rnp
;
1682 rcu_for_each_leaf_node(rsp
, rnp
) {
1684 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1685 if (!rcu_gp_in_progress(rsp
)) {
1686 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1689 if (rnp
->qsmask
== 0) {
1690 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
1695 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1696 if ((rnp
->qsmask
& bit
) != 0 &&
1697 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1702 /* rcu_report_qs_rnp() releases rnp->lock. */
1703 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1706 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1708 rnp
= rcu_get_root(rsp
);
1709 if (rnp
->qsmask
== 0) {
1710 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1711 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1716 * Force quiescent states on reluctant CPUs, and also detect which
1717 * CPUs are in dyntick-idle mode.
1719 static void force_quiescent_state(struct rcu_state
*rsp
, int relaxed
)
1721 unsigned long flags
;
1722 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1724 trace_rcu_utilization("Start fqs");
1725 if (!rcu_gp_in_progress(rsp
)) {
1726 trace_rcu_utilization("End fqs");
1727 return; /* No grace period in progress, nothing to force. */
1729 if (!raw_spin_trylock_irqsave(&rsp
->fqslock
, flags
)) {
1730 rsp
->n_force_qs_lh
++; /* Inexact, can lose counts. Tough! */
1731 trace_rcu_utilization("End fqs");
1732 return; /* Someone else is already on the job. */
1734 if (relaxed
&& ULONG_CMP_GE(rsp
->jiffies_force_qs
, jiffies
))
1735 goto unlock_fqs_ret
; /* no emergency and done recently. */
1737 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1738 rsp
->jiffies_force_qs
= jiffies
+ RCU_JIFFIES_TILL_FORCE_QS
;
1739 if(!rcu_gp_in_progress(rsp
)) {
1740 rsp
->n_force_qs_ngp
++;
1741 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1742 goto unlock_fqs_ret
; /* no GP in progress, time updated. */
1744 rsp
->fqs_active
= 1;
1745 switch (rsp
->fqs_state
) {
1749 break; /* grace period idle or initializing, ignore. */
1751 case RCU_SAVE_DYNTICK
:
1753 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1755 /* Record dyntick-idle state. */
1756 force_qs_rnp(rsp
, dyntick_save_progress_counter
);
1757 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1758 if (rcu_gp_in_progress(rsp
))
1759 rsp
->fqs_state
= RCU_FORCE_QS
;
1764 /* Check dyntick-idle state, send IPI to laggarts. */
1765 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1766 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
);
1768 /* Leave state in case more forcing is required. */
1770 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
1773 rsp
->fqs_active
= 0;
1774 if (rsp
->fqs_need_gp
) {
1775 raw_spin_unlock(&rsp
->fqslock
); /* irqs remain disabled */
1776 rsp
->fqs_need_gp
= 0;
1777 rcu_start_gp(rsp
, flags
); /* releases rnp->lock */
1778 trace_rcu_utilization("End fqs");
1781 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
1783 raw_spin_unlock_irqrestore(&rsp
->fqslock
, flags
);
1784 trace_rcu_utilization("End fqs");
1788 * This does the RCU core processing work for the specified rcu_state
1789 * and rcu_data structures. This may be called only from the CPU to
1790 * whom the rdp belongs.
1793 __rcu_process_callbacks(struct rcu_state
*rsp
)
1795 unsigned long flags
;
1796 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1798 WARN_ON_ONCE(rdp
->beenonline
== 0);
1801 * If an RCU GP has gone long enough, go check for dyntick
1802 * idle CPUs and, if needed, send resched IPIs.
1804 if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1805 force_quiescent_state(rsp
, 1);
1808 * Advance callbacks in response to end of earlier grace
1809 * period that some other CPU ended.
1811 rcu_process_gp_end(rsp
, rdp
);
1813 /* Update RCU state based on any recent quiescent states. */
1814 rcu_check_quiescent_state(rsp
, rdp
);
1816 /* Does this CPU require a not-yet-started grace period? */
1817 if (cpu_needs_another_gp(rsp
, rdp
)) {
1818 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
1819 rcu_start_gp(rsp
, flags
); /* releases above lock */
1822 /* If there are callbacks ready, invoke them. */
1823 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1824 invoke_rcu_callbacks(rsp
, rdp
);
1828 * Do RCU core processing for the current CPU.
1830 static void rcu_process_callbacks(struct softirq_action
*unused
)
1832 struct rcu_state
*rsp
;
1834 trace_rcu_utilization("Start RCU core");
1835 for_each_rcu_flavor(rsp
)
1836 __rcu_process_callbacks(rsp
);
1837 trace_rcu_utilization("End RCU core");
1841 * Schedule RCU callback invocation. If the specified type of RCU
1842 * does not support RCU priority boosting, just do a direct call,
1843 * otherwise wake up the per-CPU kernel kthread. Note that because we
1844 * are running on the current CPU with interrupts disabled, the
1845 * rcu_cpu_kthread_task cannot disappear out from under us.
1847 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1849 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
1851 if (likely(!rsp
->boost
)) {
1852 rcu_do_batch(rsp
, rdp
);
1855 invoke_rcu_callbacks_kthread();
1858 static void invoke_rcu_core(void)
1860 raise_softirq(RCU_SOFTIRQ
);
1864 * Handle any core-RCU processing required by a call_rcu() invocation.
1866 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
1867 struct rcu_head
*head
, unsigned long flags
)
1870 * If called from an extended quiescent state, invoke the RCU
1871 * core in order to force a re-evaluation of RCU's idleness.
1873 if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
1876 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
1877 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
1881 * Force the grace period if too many callbacks or too long waiting.
1882 * Enforce hysteresis, and don't invoke force_quiescent_state()
1883 * if some other CPU has recently done so. Also, don't bother
1884 * invoking force_quiescent_state() if the newly enqueued callback
1885 * is the only one waiting for a grace period to complete.
1887 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
1889 /* Are we ignoring a completed grace period? */
1890 rcu_process_gp_end(rsp
, rdp
);
1891 check_for_new_grace_period(rsp
, rdp
);
1893 /* Start a new grace period if one not already started. */
1894 if (!rcu_gp_in_progress(rsp
)) {
1895 unsigned long nestflag
;
1896 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
1898 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
1899 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
1901 /* Give the grace period a kick. */
1902 rdp
->blimit
= LONG_MAX
;
1903 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
1904 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
1905 force_quiescent_state(rsp
, 0);
1906 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1907 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1909 } else if (ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
))
1910 force_quiescent_state(rsp
, 1);
1914 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
1915 struct rcu_state
*rsp
, bool lazy
)
1917 unsigned long flags
;
1918 struct rcu_data
*rdp
;
1920 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
1921 debug_rcu_head_queue(head
);
1925 smp_mb(); /* Ensure RCU update seen before callback registry. */
1928 * Opportunistically note grace-period endings and beginnings.
1929 * Note that we might see a beginning right after we see an
1930 * end, but never vice versa, since this CPU has to pass through
1931 * a quiescent state betweentimes.
1933 local_irq_save(flags
);
1934 rdp
= this_cpu_ptr(rsp
->rda
);
1936 /* Add the callback to our list. */
1937 ACCESS_ONCE(rdp
->qlen
)++;
1941 rcu_idle_count_callbacks_posted();
1942 smp_mb(); /* Count before adding callback for rcu_barrier(). */
1943 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
1944 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
1946 if (__is_kfree_rcu_offset((unsigned long)func
))
1947 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
1948 rdp
->qlen_lazy
, rdp
->qlen
);
1950 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
1952 /* Go handle any RCU core processing required. */
1953 __call_rcu_core(rsp
, rdp
, head
, flags
);
1954 local_irq_restore(flags
);
1958 * Queue an RCU-sched callback for invocation after a grace period.
1960 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1962 __call_rcu(head
, func
, &rcu_sched_state
, 0);
1964 EXPORT_SYMBOL_GPL(call_rcu_sched
);
1967 * Queue an RCU callback for invocation after a quicker grace period.
1969 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1971 __call_rcu(head
, func
, &rcu_bh_state
, 0);
1973 EXPORT_SYMBOL_GPL(call_rcu_bh
);
1976 * Because a context switch is a grace period for RCU-sched and RCU-bh,
1977 * any blocking grace-period wait automatically implies a grace period
1978 * if there is only one CPU online at any point time during execution
1979 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
1980 * occasionally incorrectly indicate that there are multiple CPUs online
1981 * when there was in fact only one the whole time, as this just adds
1982 * some overhead: RCU still operates correctly.
1984 static inline int rcu_blocking_is_gp(void)
1988 might_sleep(); /* Check for RCU read-side critical section. */
1990 ret
= num_online_cpus() <= 1;
1996 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
1998 * Control will return to the caller some time after a full rcu-sched
1999 * grace period has elapsed, in other words after all currently executing
2000 * rcu-sched read-side critical sections have completed. These read-side
2001 * critical sections are delimited by rcu_read_lock_sched() and
2002 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2003 * local_irq_disable(), and so on may be used in place of
2004 * rcu_read_lock_sched().
2006 * This means that all preempt_disable code sequences, including NMI and
2007 * hardware-interrupt handlers, in progress on entry will have completed
2008 * before this primitive returns. However, this does not guarantee that
2009 * softirq handlers will have completed, since in some kernels, these
2010 * handlers can run in process context, and can block.
2012 * This primitive provides the guarantees made by the (now removed)
2013 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2014 * guarantees that rcu_read_lock() sections will have completed.
2015 * In "classic RCU", these two guarantees happen to be one and
2016 * the same, but can differ in realtime RCU implementations.
2018 void synchronize_sched(void)
2020 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2021 !lock_is_held(&rcu_lock_map
) &&
2022 !lock_is_held(&rcu_sched_lock_map
),
2023 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2024 if (rcu_blocking_is_gp())
2026 wait_rcu_gp(call_rcu_sched
);
2028 EXPORT_SYMBOL_GPL(synchronize_sched
);
2031 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2033 * Control will return to the caller some time after a full rcu_bh grace
2034 * period has elapsed, in other words after all currently executing rcu_bh
2035 * read-side critical sections have completed. RCU read-side critical
2036 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2037 * and may be nested.
2039 void synchronize_rcu_bh(void)
2041 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2042 !lock_is_held(&rcu_lock_map
) &&
2043 !lock_is_held(&rcu_sched_lock_map
),
2044 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2045 if (rcu_blocking_is_gp())
2047 wait_rcu_gp(call_rcu_bh
);
2049 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2051 static atomic_t sync_sched_expedited_started
= ATOMIC_INIT(0);
2052 static atomic_t sync_sched_expedited_done
= ATOMIC_INIT(0);
2054 static int synchronize_sched_expedited_cpu_stop(void *data
)
2057 * There must be a full memory barrier on each affected CPU
2058 * between the time that try_stop_cpus() is called and the
2059 * time that it returns.
2061 * In the current initial implementation of cpu_stop, the
2062 * above condition is already met when the control reaches
2063 * this point and the following smp_mb() is not strictly
2064 * necessary. Do smp_mb() anyway for documentation and
2065 * robustness against future implementation changes.
2067 smp_mb(); /* See above comment block. */
2072 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2074 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2075 * approach to force the grace period to end quickly. This consumes
2076 * significant time on all CPUs and is unfriendly to real-time workloads,
2077 * so is thus not recommended for any sort of common-case code. In fact,
2078 * if you are using synchronize_sched_expedited() in a loop, please
2079 * restructure your code to batch your updates, and then use a single
2080 * synchronize_sched() instead.
2082 * Note that it is illegal to call this function while holding any lock
2083 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2084 * to call this function from a CPU-hotplug notifier. Failing to observe
2085 * these restriction will result in deadlock.
2087 * This implementation can be thought of as an application of ticket
2088 * locking to RCU, with sync_sched_expedited_started and
2089 * sync_sched_expedited_done taking on the roles of the halves
2090 * of the ticket-lock word. Each task atomically increments
2091 * sync_sched_expedited_started upon entry, snapshotting the old value,
2092 * then attempts to stop all the CPUs. If this succeeds, then each
2093 * CPU will have executed a context switch, resulting in an RCU-sched
2094 * grace period. We are then done, so we use atomic_cmpxchg() to
2095 * update sync_sched_expedited_done to match our snapshot -- but
2096 * only if someone else has not already advanced past our snapshot.
2098 * On the other hand, if try_stop_cpus() fails, we check the value
2099 * of sync_sched_expedited_done. If it has advanced past our
2100 * initial snapshot, then someone else must have forced a grace period
2101 * some time after we took our snapshot. In this case, our work is
2102 * done for us, and we can simply return. Otherwise, we try again,
2103 * but keep our initial snapshot for purposes of checking for someone
2104 * doing our work for us.
2106 * If we fail too many times in a row, we fall back to synchronize_sched().
2108 void synchronize_sched_expedited(void)
2110 int firstsnap
, s
, snap
, trycount
= 0;
2112 /* Note that atomic_inc_return() implies full memory barrier. */
2113 firstsnap
= snap
= atomic_inc_return(&sync_sched_expedited_started
);
2115 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2118 * Each pass through the following loop attempts to force a
2119 * context switch on each CPU.
2121 while (try_stop_cpus(cpu_online_mask
,
2122 synchronize_sched_expedited_cpu_stop
,
2126 /* No joy, try again later. Or just synchronize_sched(). */
2127 if (trycount
++ < 10) {
2128 udelay(trycount
* num_online_cpus());
2130 synchronize_sched();
2134 /* Check to see if someone else did our work for us. */
2135 s
= atomic_read(&sync_sched_expedited_done
);
2136 if (UINT_CMP_GE((unsigned)s
, (unsigned)firstsnap
)) {
2137 smp_mb(); /* ensure test happens before caller kfree */
2142 * Refetching sync_sched_expedited_started allows later
2143 * callers to piggyback on our grace period. We subtract
2144 * 1 to get the same token that the last incrementer got.
2145 * We retry after they started, so our grace period works
2146 * for them, and they started after our first try, so their
2147 * grace period works for us.
2150 snap
= atomic_read(&sync_sched_expedited_started
);
2151 smp_mb(); /* ensure read is before try_stop_cpus(). */
2155 * Everyone up to our most recent fetch is covered by our grace
2156 * period. Update the counter, but only if our work is still
2157 * relevant -- which it won't be if someone who started later
2158 * than we did beat us to the punch.
2161 s
= atomic_read(&sync_sched_expedited_done
);
2162 if (UINT_CMP_GE((unsigned)s
, (unsigned)snap
)) {
2163 smp_mb(); /* ensure test happens before caller kfree */
2166 } while (atomic_cmpxchg(&sync_sched_expedited_done
, s
, snap
) != s
);
2170 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2173 * Check to see if there is any immediate RCU-related work to be done
2174 * by the current CPU, for the specified type of RCU, returning 1 if so.
2175 * The checks are in order of increasing expense: checks that can be
2176 * carried out against CPU-local state are performed first. However,
2177 * we must check for CPU stalls first, else we might not get a chance.
2179 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2181 struct rcu_node
*rnp
= rdp
->mynode
;
2183 rdp
->n_rcu_pending
++;
2185 /* Check for CPU stalls, if enabled. */
2186 check_cpu_stall(rsp
, rdp
);
2188 /* Is the RCU core waiting for a quiescent state from this CPU? */
2189 if (rcu_scheduler_fully_active
&&
2190 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2193 * If force_quiescent_state() coming soon and this CPU
2194 * needs a quiescent state, and this is either RCU-sched
2195 * or RCU-bh, force a local reschedule.
2197 rdp
->n_rp_qs_pending
++;
2198 if (!rdp
->preemptible
&&
2199 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
) - 1,
2202 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2203 rdp
->n_rp_report_qs
++;
2207 /* Does this CPU have callbacks ready to invoke? */
2208 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2209 rdp
->n_rp_cb_ready
++;
2213 /* Has RCU gone idle with this CPU needing another grace period? */
2214 if (cpu_needs_another_gp(rsp
, rdp
)) {
2215 rdp
->n_rp_cpu_needs_gp
++;
2219 /* Has another RCU grace period completed? */
2220 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2221 rdp
->n_rp_gp_completed
++;
2225 /* Has a new RCU grace period started? */
2226 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2227 rdp
->n_rp_gp_started
++;
2231 /* Has an RCU GP gone long enough to send resched IPIs &c? */
2232 if (rcu_gp_in_progress(rsp
) &&
2233 ULONG_CMP_LT(ACCESS_ONCE(rsp
->jiffies_force_qs
), jiffies
)) {
2234 rdp
->n_rp_need_fqs
++;
2239 rdp
->n_rp_need_nothing
++;
2244 * Check to see if there is any immediate RCU-related work to be done
2245 * by the current CPU, returning 1 if so. This function is part of the
2246 * RCU implementation; it is -not- an exported member of the RCU API.
2248 static int rcu_pending(int cpu
)
2250 struct rcu_state
*rsp
;
2252 for_each_rcu_flavor(rsp
)
2253 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
2259 * Check to see if any future RCU-related work will need to be done
2260 * by the current CPU, even if none need be done immediately, returning
2263 static int rcu_cpu_has_callbacks(int cpu
)
2265 struct rcu_state
*rsp
;
2267 /* RCU callbacks either ready or pending? */
2268 for_each_rcu_flavor(rsp
)
2269 if (per_cpu_ptr(rsp
->rda
, cpu
)->nxtlist
)
2275 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2276 * the compiler is expected to optimize this away.
2278 static void _rcu_barrier_trace(struct rcu_state
*rsp
, char *s
,
2279 int cpu
, unsigned long done
)
2281 trace_rcu_barrier(rsp
->name
, s
, cpu
,
2282 atomic_read(&rsp
->barrier_cpu_count
), done
);
2286 * RCU callback function for _rcu_barrier(). If we are last, wake
2287 * up the task executing _rcu_barrier().
2289 static void rcu_barrier_callback(struct rcu_head
*rhp
)
2291 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
2292 struct rcu_state
*rsp
= rdp
->rsp
;
2294 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
2295 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
2296 complete(&rsp
->barrier_completion
);
2298 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
2303 * Called with preemption disabled, and from cross-cpu IRQ context.
2305 static void rcu_barrier_func(void *type
)
2307 struct rcu_state
*rsp
= type
;
2308 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2310 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
2311 atomic_inc(&rsp
->barrier_cpu_count
);
2312 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
2316 * Orchestrate the specified type of RCU barrier, waiting for all
2317 * RCU callbacks of the specified type to complete.
2319 static void _rcu_barrier(struct rcu_state
*rsp
)
2322 unsigned long flags
;
2323 struct rcu_data
*rdp
;
2325 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
2326 unsigned long snap_done
;
2328 init_rcu_head_on_stack(&rd
.barrier_head
);
2329 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
2331 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2332 mutex_lock(&rsp
->barrier_mutex
);
2335 * Ensure that all prior references, including to ->n_barrier_done,
2336 * are ordered before the _rcu_barrier() machinery.
2338 smp_mb(); /* See above block comment. */
2341 * Recheck ->n_barrier_done to see if others did our work for us.
2342 * This means checking ->n_barrier_done for an even-to-odd-to-even
2343 * transition. The "if" expression below therefore rounds the old
2344 * value up to the next even number and adds two before comparing.
2346 snap_done
= ACCESS_ONCE(rsp
->n_barrier_done
);
2347 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
2348 if (ULONG_CMP_GE(snap_done
, ((snap
+ 1) & ~0x1) + 2)) {
2349 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
2350 smp_mb(); /* caller's subsequent code after above check. */
2351 mutex_unlock(&rsp
->barrier_mutex
);
2356 * Increment ->n_barrier_done to avoid duplicate work. Use
2357 * ACCESS_ONCE() to prevent the compiler from speculating
2358 * the increment to precede the early-exit check.
2360 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2361 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
2362 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
2363 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2366 * Initialize the count to one rather than to zero in order to
2367 * avoid a too-soon return to zero in case of a short grace period
2368 * (or preemption of this task). Also flag this task as doing
2369 * an rcu_barrier(). This will prevent anyone else from adopting
2370 * orphaned callbacks, which could cause otherwise failure if a
2371 * CPU went offline and quickly came back online. To see this,
2372 * consider the following sequence of events:
2374 * 1. We cause CPU 0 to post an rcu_barrier_callback() callback.
2375 * 2. CPU 1 goes offline, orphaning its callbacks.
2376 * 3. CPU 0 adopts CPU 1's orphaned callbacks.
2377 * 4. CPU 1 comes back online.
2378 * 5. We cause CPU 1 to post an rcu_barrier_callback() callback.
2379 * 6. Both rcu_barrier_callback() callbacks are invoked, awakening
2380 * us -- but before CPU 1's orphaned callbacks are invoked!!!
2382 init_completion(&rsp
->barrier_completion
);
2383 atomic_set(&rsp
->barrier_cpu_count
, 1);
2384 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
2385 rsp
->rcu_barrier_in_progress
= current
;
2386 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2389 * Force every CPU with callbacks to register a new callback
2390 * that will tell us when all the preceding callbacks have
2391 * been invoked. If an offline CPU has callbacks, wait for
2392 * it to either come back online or to finish orphaning those
2395 for_each_possible_cpu(cpu
) {
2397 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2398 if (cpu_is_offline(cpu
)) {
2399 _rcu_barrier_trace(rsp
, "Offline", cpu
,
2400 rsp
->n_barrier_done
);
2402 while (cpu_is_offline(cpu
) && ACCESS_ONCE(rdp
->qlen
))
2403 schedule_timeout_interruptible(1);
2404 } else if (ACCESS_ONCE(rdp
->qlen
)) {
2405 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
2406 rsp
->n_barrier_done
);
2407 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
2410 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
2411 rsp
->n_barrier_done
);
2417 * Now that all online CPUs have rcu_barrier_callback() callbacks
2418 * posted, we can adopt all of the orphaned callbacks and place
2419 * an rcu_barrier_callback() callback after them. When that is done,
2420 * we are guaranteed to have an rcu_barrier_callback() callback
2421 * following every callback that could possibly have been
2422 * registered before _rcu_barrier() was called.
2424 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
2425 rcu_adopt_orphan_cbs(rsp
);
2426 rsp
->rcu_barrier_in_progress
= NULL
;
2427 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2428 atomic_inc(&rsp
->barrier_cpu_count
);
2429 smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */
2431 rsp
->call(&rd
.barrier_head
, rcu_barrier_callback
);
2434 * Now that we have an rcu_barrier_callback() callback on each
2435 * CPU, and thus each counted, remove the initial count.
2437 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
2438 complete(&rsp
->barrier_completion
);
2440 /* Increment ->n_barrier_done to prevent duplicate work. */
2441 smp_mb(); /* Keep increment after above mechanism. */
2442 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2443 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
2444 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
2445 smp_mb(); /* Keep increment before caller's subsequent code. */
2447 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2448 wait_for_completion(&rsp
->barrier_completion
);
2450 /* Other rcu_barrier() invocations can now safely proceed. */
2451 mutex_unlock(&rsp
->barrier_mutex
);
2453 destroy_rcu_head_on_stack(&rd
.barrier_head
);
2457 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2459 void rcu_barrier_bh(void)
2461 _rcu_barrier(&rcu_bh_state
);
2463 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
2466 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2468 void rcu_barrier_sched(void)
2470 _rcu_barrier(&rcu_sched_state
);
2472 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
2475 * Do boot-time initialization of a CPU's per-CPU RCU data.
2478 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
2480 unsigned long flags
;
2481 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2482 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2484 /* Set up local state, ensuring consistent view of global state. */
2485 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2486 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
2487 init_callback_list(rdp
);
2489 ACCESS_ONCE(rdp
->qlen
) = 0;
2490 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
2491 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
2492 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
2495 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2499 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2500 * offline event can be happening at a given time. Note also that we
2501 * can accept some slop in the rsp->completed access due to the fact
2502 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2504 static void __cpuinit
2505 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
2507 unsigned long flags
;
2509 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2510 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2512 /* Set up local state, ensuring consistent view of global state. */
2513 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2514 rdp
->beenonline
= 1; /* We have now been online. */
2515 rdp
->preemptible
= preemptible
;
2516 rdp
->qlen_last_fqs_check
= 0;
2517 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2518 rdp
->blimit
= blimit
;
2519 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2520 atomic_set(&rdp
->dynticks
->dynticks
,
2521 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
2522 rcu_prepare_for_idle_init(cpu
);
2523 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2526 * A new grace period might start here. If so, we won't be part
2527 * of it, but that is OK, as we are currently in a quiescent state.
2530 /* Exclude any attempts to start a new GP on large systems. */
2531 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
2533 /* Add CPU to rcu_node bitmasks. */
2535 mask
= rdp
->grpmask
;
2537 /* Exclude any attempts to start a new GP on small systems. */
2538 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2539 rnp
->qsmaskinit
|= mask
;
2540 mask
= rnp
->grpmask
;
2541 if (rnp
== rdp
->mynode
) {
2543 * If there is a grace period in progress, we will
2544 * set up to wait for it next time we run the
2547 rdp
->gpnum
= rnp
->completed
;
2548 rdp
->completed
= rnp
->completed
;
2549 rdp
->passed_quiesce
= 0;
2550 rdp
->qs_pending
= 0;
2551 rdp
->passed_quiesce_gpnum
= rnp
->gpnum
- 1;
2552 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuonl");
2554 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
2556 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
2558 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2561 static void __cpuinit
rcu_prepare_cpu(int cpu
)
2563 struct rcu_state
*rsp
;
2565 for_each_rcu_flavor(rsp
)
2566 rcu_init_percpu_data(cpu
, rsp
,
2567 strcmp(rsp
->name
, "rcu_preempt") == 0);
2571 * Handle CPU online/offline notification events.
2573 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
2574 unsigned long action
, void *hcpu
)
2576 long cpu
= (long)hcpu
;
2577 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
2578 struct rcu_node
*rnp
= rdp
->mynode
;
2579 struct rcu_state
*rsp
;
2581 trace_rcu_utilization("Start CPU hotplug");
2583 case CPU_UP_PREPARE
:
2584 case CPU_UP_PREPARE_FROZEN
:
2585 rcu_prepare_cpu(cpu
);
2586 rcu_prepare_kthreads(cpu
);
2589 case CPU_DOWN_FAILED
:
2590 rcu_node_kthread_setaffinity(rnp
, -1);
2591 rcu_cpu_kthread_setrt(cpu
, 1);
2593 case CPU_DOWN_PREPARE
:
2594 rcu_node_kthread_setaffinity(rnp
, cpu
);
2595 rcu_cpu_kthread_setrt(cpu
, 0);
2598 case CPU_DYING_FROZEN
:
2600 * The whole machine is "stopped" except this CPU, so we can
2601 * touch any data without introducing corruption. We send the
2602 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2604 for_each_rcu_flavor(rsp
)
2605 rcu_cleanup_dying_cpu(rsp
);
2606 rcu_cleanup_after_idle(cpu
);
2609 case CPU_DEAD_FROZEN
:
2610 case CPU_UP_CANCELED
:
2611 case CPU_UP_CANCELED_FROZEN
:
2612 for_each_rcu_flavor(rsp
)
2613 rcu_cleanup_dead_cpu(cpu
, rsp
);
2618 trace_rcu_utilization("End CPU hotplug");
2623 * This function is invoked towards the end of the scheduler's initialization
2624 * process. Before this is called, the idle task might contain
2625 * RCU read-side critical sections (during which time, this idle
2626 * task is booting the system). After this function is called, the
2627 * idle tasks are prohibited from containing RCU read-side critical
2628 * sections. This function also enables RCU lockdep checking.
2630 void rcu_scheduler_starting(void)
2632 WARN_ON(num_online_cpus() != 1);
2633 WARN_ON(nr_context_switches() > 0);
2634 rcu_scheduler_active
= 1;
2638 * Compute the per-level fanout, either using the exact fanout specified
2639 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2641 #ifdef CONFIG_RCU_FANOUT_EXACT
2642 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2646 for (i
= rcu_num_lvls
- 1; i
> 0; i
--)
2647 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
2648 rsp
->levelspread
[0] = rcu_fanout_leaf
;
2650 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2651 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2658 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2659 ccur
= rsp
->levelcnt
[i
];
2660 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
2664 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2667 * Helper function for rcu_init() that initializes one rcu_state structure.
2669 static void __init
rcu_init_one(struct rcu_state
*rsp
,
2670 struct rcu_data __percpu
*rda
)
2672 static char *buf
[] = { "rcu_node_level_0",
2675 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
2679 struct rcu_node
*rnp
;
2681 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
2683 /* Initialize the level-tracking arrays. */
2685 for (i
= 0; i
< rcu_num_lvls
; i
++)
2686 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
2687 for (i
= 1; i
< rcu_num_lvls
; i
++)
2688 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
2689 rcu_init_levelspread(rsp
);
2691 /* Initialize the elements themselves, starting from the leaves. */
2693 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2694 cpustride
*= rsp
->levelspread
[i
];
2695 rnp
= rsp
->level
[i
];
2696 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
2697 raw_spin_lock_init(&rnp
->lock
);
2698 lockdep_set_class_and_name(&rnp
->lock
,
2699 &rcu_node_class
[i
], buf
[i
]);
2702 rnp
->qsmaskinit
= 0;
2703 rnp
->grplo
= j
* cpustride
;
2704 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
2705 if (rnp
->grphi
>= NR_CPUS
)
2706 rnp
->grphi
= NR_CPUS
- 1;
2712 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
2713 rnp
->grpmask
= 1UL << rnp
->grpnum
;
2714 rnp
->parent
= rsp
->level
[i
- 1] +
2715 j
/ rsp
->levelspread
[i
- 1];
2718 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
2723 rnp
= rsp
->level
[rcu_num_lvls
- 1];
2724 for_each_possible_cpu(i
) {
2725 while (i
> rnp
->grphi
)
2727 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
2728 rcu_boot_init_percpu_data(i
, rsp
);
2730 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
2734 * Compute the rcu_node tree geometry from kernel parameters. This cannot
2735 * replace the definitions in rcutree.h because those are needed to size
2736 * the ->node array in the rcu_state structure.
2738 static void __init
rcu_init_geometry(void)
2743 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
2745 /* If the compile-time values are accurate, just leave. */
2746 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
)
2750 * Compute number of nodes that can be handled an rcu_node tree
2751 * with the given number of levels. Setting rcu_capacity[0] makes
2752 * some of the arithmetic easier.
2754 rcu_capacity
[0] = 1;
2755 rcu_capacity
[1] = rcu_fanout_leaf
;
2756 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
2757 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
2760 * The boot-time rcu_fanout_leaf parameter is only permitted
2761 * to increase the leaf-level fanout, not decrease it. Of course,
2762 * the leaf-level fanout cannot exceed the number of bits in
2763 * the rcu_node masks. Finally, the tree must be able to accommodate
2764 * the configured number of CPUs. Complain and fall back to the
2765 * compile-time values if these limits are exceeded.
2767 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
2768 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
2769 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
2774 /* Calculate the number of rcu_nodes at each level of the tree. */
2775 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
2776 if (n
<= rcu_capacity
[i
]) {
2777 for (j
= 0; j
<= i
; j
++)
2779 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
2781 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
2786 /* Calculate the total number of rcu_node structures. */
2788 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
2789 rcu_num_nodes
+= num_rcu_lvl
[i
];
2793 void __init
rcu_init(void)
2797 rcu_bootup_announce();
2798 rcu_init_geometry();
2799 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
2800 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
2801 __rcu_init_preempt();
2802 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
2805 * We don't need protection against CPU-hotplug here because
2806 * this is called early in boot, before either interrupts
2807 * or the scheduler are operational.
2809 cpu_notifier(rcu_cpu_notify
, 0);
2810 for_each_online_cpu(cpu
)
2811 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
2812 check_cpu_stall_init();
2815 #include "rcutree_plugin.h"