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
) {
1772 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1773 if (!rcu_gp_in_progress(rsp
)) {
1774 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1777 if (rnp
->qsmask
== 0) {
1778 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
1783 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
1784 if ((rnp
->qsmask
& bit
) != 0 &&
1785 f(per_cpu_ptr(rsp
->rda
, cpu
)))
1790 /* rcu_report_qs_rnp() releases rnp->lock. */
1791 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
1794 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1796 rnp
= rcu_get_root(rsp
);
1797 if (rnp
->qsmask
== 0) {
1798 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1799 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
1804 * Force quiescent states on reluctant CPUs, and also detect which
1805 * CPUs are in dyntick-idle mode.
1807 static void force_quiescent_state(struct rcu_state
*rsp
)
1809 unsigned long flags
;
1810 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1812 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
)
1813 return; /* Someone beat us to it. */
1814 if (!raw_spin_trylock_irqsave(&rnp
->lock
, flags
)) {
1815 rsp
->n_force_qs_lh
++; /* Inexact, can lose counts. Tough! */
1818 rsp
->gp_flags
|= RCU_GP_FLAG_FQS
;
1819 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1820 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1824 * This does the RCU core processing work for the specified rcu_state
1825 * and rcu_data structures. This may be called only from the CPU to
1826 * whom the rdp belongs.
1829 __rcu_process_callbacks(struct rcu_state
*rsp
)
1831 unsigned long flags
;
1832 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1834 WARN_ON_ONCE(rdp
->beenonline
== 0);
1837 * Advance callbacks in response to end of earlier grace
1838 * period that some other CPU ended.
1840 rcu_process_gp_end(rsp
, rdp
);
1842 /* Update RCU state based on any recent quiescent states. */
1843 rcu_check_quiescent_state(rsp
, rdp
);
1845 /* Does this CPU require a not-yet-started grace period? */
1846 if (cpu_needs_another_gp(rsp
, rdp
)) {
1847 raw_spin_lock_irqsave(&rcu_get_root(rsp
)->lock
, flags
);
1848 rcu_start_gp(rsp
, flags
); /* releases above lock */
1851 /* If there are callbacks ready, invoke them. */
1852 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1853 invoke_rcu_callbacks(rsp
, rdp
);
1857 * Do RCU core processing for the current CPU.
1859 static void rcu_process_callbacks(struct softirq_action
*unused
)
1861 struct rcu_state
*rsp
;
1863 if (cpu_is_offline(smp_processor_id()))
1865 trace_rcu_utilization("Start RCU core");
1866 for_each_rcu_flavor(rsp
)
1867 __rcu_process_callbacks(rsp
);
1868 trace_rcu_utilization("End RCU core");
1872 * Schedule RCU callback invocation. If the specified type of RCU
1873 * does not support RCU priority boosting, just do a direct call,
1874 * otherwise wake up the per-CPU kernel kthread. Note that because we
1875 * are running on the current CPU with interrupts disabled, the
1876 * rcu_cpu_kthread_task cannot disappear out from under us.
1878 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1880 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
1882 if (likely(!rsp
->boost
)) {
1883 rcu_do_batch(rsp
, rdp
);
1886 invoke_rcu_callbacks_kthread();
1889 static void invoke_rcu_core(void)
1891 raise_softirq(RCU_SOFTIRQ
);
1895 * Handle any core-RCU processing required by a call_rcu() invocation.
1897 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
1898 struct rcu_head
*head
, unsigned long flags
)
1901 * If called from an extended quiescent state, invoke the RCU
1902 * core in order to force a re-evaluation of RCU's idleness.
1904 if (rcu_is_cpu_idle() && cpu_online(smp_processor_id()))
1907 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
1908 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
1912 * Force the grace period if too many callbacks or too long waiting.
1913 * Enforce hysteresis, and don't invoke force_quiescent_state()
1914 * if some other CPU has recently done so. Also, don't bother
1915 * invoking force_quiescent_state() if the newly enqueued callback
1916 * is the only one waiting for a grace period to complete.
1918 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
1920 /* Are we ignoring a completed grace period? */
1921 rcu_process_gp_end(rsp
, rdp
);
1922 check_for_new_grace_period(rsp
, rdp
);
1924 /* Start a new grace period if one not already started. */
1925 if (!rcu_gp_in_progress(rsp
)) {
1926 unsigned long nestflag
;
1927 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
1929 raw_spin_lock_irqsave(&rnp_root
->lock
, nestflag
);
1930 rcu_start_gp(rsp
, nestflag
); /* rlses rnp_root->lock */
1932 /* Give the grace period a kick. */
1933 rdp
->blimit
= LONG_MAX
;
1934 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
1935 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
1936 force_quiescent_state(rsp
);
1937 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
1938 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
1944 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
1945 struct rcu_state
*rsp
, bool lazy
)
1947 unsigned long flags
;
1948 struct rcu_data
*rdp
;
1950 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
1951 debug_rcu_head_queue(head
);
1955 smp_mb(); /* Ensure RCU update seen before callback registry. */
1958 * Opportunistically note grace-period endings and beginnings.
1959 * Note that we might see a beginning right after we see an
1960 * end, but never vice versa, since this CPU has to pass through
1961 * a quiescent state betweentimes.
1963 local_irq_save(flags
);
1964 rdp
= this_cpu_ptr(rsp
->rda
);
1966 /* Add the callback to our list. */
1967 ACCESS_ONCE(rdp
->qlen
)++;
1971 rcu_idle_count_callbacks_posted();
1972 smp_mb(); /* Count before adding callback for rcu_barrier(). */
1973 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
1974 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
1976 if (__is_kfree_rcu_offset((unsigned long)func
))
1977 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
1978 rdp
->qlen_lazy
, rdp
->qlen
);
1980 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
1982 /* Go handle any RCU core processing required. */
1983 __call_rcu_core(rsp
, rdp
, head
, flags
);
1984 local_irq_restore(flags
);
1988 * Queue an RCU-sched callback for invocation after a grace period.
1990 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
1992 __call_rcu(head
, func
, &rcu_sched_state
, 0);
1994 EXPORT_SYMBOL_GPL(call_rcu_sched
);
1997 * Queue an RCU callback for invocation after a quicker grace period.
1999 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2001 __call_rcu(head
, func
, &rcu_bh_state
, 0);
2003 EXPORT_SYMBOL_GPL(call_rcu_bh
);
2006 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2007 * any blocking grace-period wait automatically implies a grace period
2008 * if there is only one CPU online at any point time during execution
2009 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2010 * occasionally incorrectly indicate that there are multiple CPUs online
2011 * when there was in fact only one the whole time, as this just adds
2012 * some overhead: RCU still operates correctly.
2014 static inline int rcu_blocking_is_gp(void)
2018 might_sleep(); /* Check for RCU read-side critical section. */
2020 ret
= num_online_cpus() <= 1;
2026 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2028 * Control will return to the caller some time after a full rcu-sched
2029 * grace period has elapsed, in other words after all currently executing
2030 * rcu-sched read-side critical sections have completed. These read-side
2031 * critical sections are delimited by rcu_read_lock_sched() and
2032 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2033 * local_irq_disable(), and so on may be used in place of
2034 * rcu_read_lock_sched().
2036 * This means that all preempt_disable code sequences, including NMI and
2037 * hardware-interrupt handlers, in progress on entry will have completed
2038 * before this primitive returns. However, this does not guarantee that
2039 * softirq handlers will have completed, since in some kernels, these
2040 * handlers can run in process context, and can block.
2042 * This primitive provides the guarantees made by the (now removed)
2043 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2044 * guarantees that rcu_read_lock() sections will have completed.
2045 * In "classic RCU", these two guarantees happen to be one and
2046 * the same, but can differ in realtime RCU implementations.
2048 void synchronize_sched(void)
2050 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2051 !lock_is_held(&rcu_lock_map
) &&
2052 !lock_is_held(&rcu_sched_lock_map
),
2053 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2054 if (rcu_blocking_is_gp())
2056 wait_rcu_gp(call_rcu_sched
);
2058 EXPORT_SYMBOL_GPL(synchronize_sched
);
2061 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2063 * Control will return to the caller some time after a full rcu_bh grace
2064 * period has elapsed, in other words after all currently executing rcu_bh
2065 * read-side critical sections have completed. RCU read-side critical
2066 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2067 * and may be nested.
2069 void synchronize_rcu_bh(void)
2071 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2072 !lock_is_held(&rcu_lock_map
) &&
2073 !lock_is_held(&rcu_sched_lock_map
),
2074 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2075 if (rcu_blocking_is_gp())
2077 wait_rcu_gp(call_rcu_bh
);
2079 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2081 static atomic_t sync_sched_expedited_started
= ATOMIC_INIT(0);
2082 static atomic_t sync_sched_expedited_done
= ATOMIC_INIT(0);
2084 static int synchronize_sched_expedited_cpu_stop(void *data
)
2087 * There must be a full memory barrier on each affected CPU
2088 * between the time that try_stop_cpus() is called and the
2089 * time that it returns.
2091 * In the current initial implementation of cpu_stop, the
2092 * above condition is already met when the control reaches
2093 * this point and the following smp_mb() is not strictly
2094 * necessary. Do smp_mb() anyway for documentation and
2095 * robustness against future implementation changes.
2097 smp_mb(); /* See above comment block. */
2102 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2104 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2105 * approach to force the grace period to end quickly. This consumes
2106 * significant time on all CPUs and is unfriendly to real-time workloads,
2107 * so is thus not recommended for any sort of common-case code. In fact,
2108 * if you are using synchronize_sched_expedited() in a loop, please
2109 * restructure your code to batch your updates, and then use a single
2110 * synchronize_sched() instead.
2112 * Note that it is illegal to call this function while holding any lock
2113 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2114 * to call this function from a CPU-hotplug notifier. Failing to observe
2115 * these restriction will result in deadlock.
2117 * This implementation can be thought of as an application of ticket
2118 * locking to RCU, with sync_sched_expedited_started and
2119 * sync_sched_expedited_done taking on the roles of the halves
2120 * of the ticket-lock word. Each task atomically increments
2121 * sync_sched_expedited_started upon entry, snapshotting the old value,
2122 * then attempts to stop all the CPUs. If this succeeds, then each
2123 * CPU will have executed a context switch, resulting in an RCU-sched
2124 * grace period. We are then done, so we use atomic_cmpxchg() to
2125 * update sync_sched_expedited_done to match our snapshot -- but
2126 * only if someone else has not already advanced past our snapshot.
2128 * On the other hand, if try_stop_cpus() fails, we check the value
2129 * of sync_sched_expedited_done. If it has advanced past our
2130 * initial snapshot, then someone else must have forced a grace period
2131 * some time after we took our snapshot. In this case, our work is
2132 * done for us, and we can simply return. Otherwise, we try again,
2133 * but keep our initial snapshot for purposes of checking for someone
2134 * doing our work for us.
2136 * If we fail too many times in a row, we fall back to synchronize_sched().
2138 void synchronize_sched_expedited(void)
2140 int firstsnap
, s
, snap
, trycount
= 0;
2142 /* Note that atomic_inc_return() implies full memory barrier. */
2143 firstsnap
= snap
= atomic_inc_return(&sync_sched_expedited_started
);
2145 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2148 * Each pass through the following loop attempts to force a
2149 * context switch on each CPU.
2151 while (try_stop_cpus(cpu_online_mask
,
2152 synchronize_sched_expedited_cpu_stop
,
2156 /* No joy, try again later. Or just synchronize_sched(). */
2157 if (trycount
++ < 10) {
2158 udelay(trycount
* num_online_cpus());
2160 synchronize_sched();
2164 /* Check to see if someone else did our work for us. */
2165 s
= atomic_read(&sync_sched_expedited_done
);
2166 if (UINT_CMP_GE((unsigned)s
, (unsigned)firstsnap
)) {
2167 smp_mb(); /* ensure test happens before caller kfree */
2172 * Refetching sync_sched_expedited_started allows later
2173 * callers to piggyback on our grace period. We subtract
2174 * 1 to get the same token that the last incrementer got.
2175 * We retry after they started, so our grace period works
2176 * for them, and they started after our first try, so their
2177 * grace period works for us.
2180 snap
= atomic_read(&sync_sched_expedited_started
);
2181 smp_mb(); /* ensure read is before try_stop_cpus(). */
2185 * Everyone up to our most recent fetch is covered by our grace
2186 * period. Update the counter, but only if our work is still
2187 * relevant -- which it won't be if someone who started later
2188 * than we did beat us to the punch.
2191 s
= atomic_read(&sync_sched_expedited_done
);
2192 if (UINT_CMP_GE((unsigned)s
, (unsigned)snap
)) {
2193 smp_mb(); /* ensure test happens before caller kfree */
2196 } while (atomic_cmpxchg(&sync_sched_expedited_done
, s
, snap
) != s
);
2200 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2203 * Check to see if there is any immediate RCU-related work to be done
2204 * by the current CPU, for the specified type of RCU, returning 1 if so.
2205 * The checks are in order of increasing expense: checks that can be
2206 * carried out against CPU-local state are performed first. However,
2207 * we must check for CPU stalls first, else we might not get a chance.
2209 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2211 struct rcu_node
*rnp
= rdp
->mynode
;
2213 rdp
->n_rcu_pending
++;
2215 /* Check for CPU stalls, if enabled. */
2216 check_cpu_stall(rsp
, rdp
);
2218 /* Is the RCU core waiting for a quiescent state from this CPU? */
2219 if (rcu_scheduler_fully_active
&&
2220 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2221 rdp
->n_rp_qs_pending
++;
2222 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2223 rdp
->n_rp_report_qs
++;
2227 /* Does this CPU have callbacks ready to invoke? */
2228 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2229 rdp
->n_rp_cb_ready
++;
2233 /* Has RCU gone idle with this CPU needing another grace period? */
2234 if (cpu_needs_another_gp(rsp
, rdp
)) {
2235 rdp
->n_rp_cpu_needs_gp
++;
2239 /* Has another RCU grace period completed? */
2240 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2241 rdp
->n_rp_gp_completed
++;
2245 /* Has a new RCU grace period started? */
2246 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2247 rdp
->n_rp_gp_started
++;
2252 rdp
->n_rp_need_nothing
++;
2257 * Check to see if there is any immediate RCU-related work to be done
2258 * by the current CPU, returning 1 if so. This function is part of the
2259 * RCU implementation; it is -not- an exported member of the RCU API.
2261 static int rcu_pending(int cpu
)
2263 struct rcu_state
*rsp
;
2265 for_each_rcu_flavor(rsp
)
2266 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
2272 * Check to see if any future RCU-related work will need to be done
2273 * by the current CPU, even if none need be done immediately, returning
2276 static int rcu_cpu_has_callbacks(int cpu
)
2278 struct rcu_state
*rsp
;
2280 /* RCU callbacks either ready or pending? */
2281 for_each_rcu_flavor(rsp
)
2282 if (per_cpu_ptr(rsp
->rda
, cpu
)->nxtlist
)
2288 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2289 * the compiler is expected to optimize this away.
2291 static void _rcu_barrier_trace(struct rcu_state
*rsp
, char *s
,
2292 int cpu
, unsigned long done
)
2294 trace_rcu_barrier(rsp
->name
, s
, cpu
,
2295 atomic_read(&rsp
->barrier_cpu_count
), done
);
2299 * RCU callback function for _rcu_barrier(). If we are last, wake
2300 * up the task executing _rcu_barrier().
2302 static void rcu_barrier_callback(struct rcu_head
*rhp
)
2304 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
2305 struct rcu_state
*rsp
= rdp
->rsp
;
2307 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
2308 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
2309 complete(&rsp
->barrier_completion
);
2311 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
2316 * Called with preemption disabled, and from cross-cpu IRQ context.
2318 static void rcu_barrier_func(void *type
)
2320 struct rcu_state
*rsp
= type
;
2321 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2323 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
2324 atomic_inc(&rsp
->barrier_cpu_count
);
2325 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
2329 * Orchestrate the specified type of RCU barrier, waiting for all
2330 * RCU callbacks of the specified type to complete.
2332 static void _rcu_barrier(struct rcu_state
*rsp
)
2335 unsigned long flags
;
2336 struct rcu_data
*rdp
;
2338 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
2339 unsigned long snap_done
;
2341 init_rcu_head_on_stack(&rd
.barrier_head
);
2342 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
2344 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2345 mutex_lock(&rsp
->barrier_mutex
);
2348 * Ensure that all prior references, including to ->n_barrier_done,
2349 * are ordered before the _rcu_barrier() machinery.
2351 smp_mb(); /* See above block comment. */
2354 * Recheck ->n_barrier_done to see if others did our work for us.
2355 * This means checking ->n_barrier_done for an even-to-odd-to-even
2356 * transition. The "if" expression below therefore rounds the old
2357 * value up to the next even number and adds two before comparing.
2359 snap_done
= ACCESS_ONCE(rsp
->n_barrier_done
);
2360 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
2361 if (ULONG_CMP_GE(snap_done
, ((snap
+ 1) & ~0x1) + 2)) {
2362 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
2363 smp_mb(); /* caller's subsequent code after above check. */
2364 mutex_unlock(&rsp
->barrier_mutex
);
2369 * Increment ->n_barrier_done to avoid duplicate work. Use
2370 * ACCESS_ONCE() to prevent the compiler from speculating
2371 * the increment to precede the early-exit check.
2373 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2374 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
2375 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
2376 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2379 * Initialize the count to one rather than to zero in order to
2380 * avoid a too-soon return to zero in case of a short grace period
2381 * (or preemption of this task). Also flag this task as doing
2382 * an rcu_barrier(). This will prevent anyone else from adopting
2383 * orphaned callbacks, which could cause otherwise failure if a
2384 * CPU went offline and quickly came back online. To see this,
2385 * consider the following sequence of events:
2387 * 1. We cause CPU 0 to post an rcu_barrier_callback() callback.
2388 * 2. CPU 1 goes offline, orphaning its callbacks.
2389 * 3. CPU 0 adopts CPU 1's orphaned callbacks.
2390 * 4. CPU 1 comes back online.
2391 * 5. We cause CPU 1 to post an rcu_barrier_callback() callback.
2392 * 6. Both rcu_barrier_callback() callbacks are invoked, awakening
2393 * us -- but before CPU 1's orphaned callbacks are invoked!!!
2395 init_completion(&rsp
->barrier_completion
);
2396 atomic_set(&rsp
->barrier_cpu_count
, 1);
2397 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
2398 rsp
->rcu_barrier_in_progress
= current
;
2399 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2402 * Force every CPU with callbacks to register a new callback
2403 * that will tell us when all the preceding callbacks have
2404 * been invoked. If an offline CPU has callbacks, wait for
2405 * it to either come back online or to finish orphaning those
2408 for_each_possible_cpu(cpu
) {
2410 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2411 if (cpu_is_offline(cpu
)) {
2412 _rcu_barrier_trace(rsp
, "Offline", cpu
,
2413 rsp
->n_barrier_done
);
2415 while (cpu_is_offline(cpu
) && ACCESS_ONCE(rdp
->qlen
))
2416 schedule_timeout_interruptible(1);
2417 } else if (ACCESS_ONCE(rdp
->qlen
)) {
2418 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
2419 rsp
->n_barrier_done
);
2420 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
2423 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
2424 rsp
->n_barrier_done
);
2430 * Now that all online CPUs have rcu_barrier_callback() callbacks
2431 * posted, we can adopt all of the orphaned callbacks and place
2432 * an rcu_barrier_callback() callback after them. When that is done,
2433 * we are guaranteed to have an rcu_barrier_callback() callback
2434 * following every callback that could possibly have been
2435 * registered before _rcu_barrier() was called.
2437 raw_spin_lock_irqsave(&rsp
->onofflock
, flags
);
2438 rcu_adopt_orphan_cbs(rsp
);
2439 rsp
->rcu_barrier_in_progress
= NULL
;
2440 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2441 atomic_inc(&rsp
->barrier_cpu_count
);
2442 smp_mb__after_atomic_inc(); /* Ensure atomic_inc() before callback. */
2444 rsp
->call(&rd
.barrier_head
, rcu_barrier_callback
);
2447 * Now that we have an rcu_barrier_callback() callback on each
2448 * CPU, and thus each counted, remove the initial count.
2450 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
2451 complete(&rsp
->barrier_completion
);
2453 /* Increment ->n_barrier_done to prevent duplicate work. */
2454 smp_mb(); /* Keep increment after above mechanism. */
2455 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2456 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
2457 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
2458 smp_mb(); /* Keep increment before caller's subsequent code. */
2460 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
2461 wait_for_completion(&rsp
->barrier_completion
);
2463 /* Other rcu_barrier() invocations can now safely proceed. */
2464 mutex_unlock(&rsp
->barrier_mutex
);
2466 destroy_rcu_head_on_stack(&rd
.barrier_head
);
2470 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
2472 void rcu_barrier_bh(void)
2474 _rcu_barrier(&rcu_bh_state
);
2476 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
2479 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
2481 void rcu_barrier_sched(void)
2483 _rcu_barrier(&rcu_sched_state
);
2485 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
2488 * Do boot-time initialization of a CPU's per-CPU RCU data.
2491 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
2493 unsigned long flags
;
2494 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2495 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2497 /* Set up local state, ensuring consistent view of global state. */
2498 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2499 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
2500 init_callback_list(rdp
);
2502 ACCESS_ONCE(rdp
->qlen
) = 0;
2503 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
2504 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
2505 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
2508 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2512 * Initialize a CPU's per-CPU RCU data. Note that only one online or
2513 * offline event can be happening at a given time. Note also that we
2514 * can accept some slop in the rsp->completed access due to the fact
2515 * that this CPU cannot possibly have any RCU callbacks in flight yet.
2517 static void __cpuinit
2518 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
2520 unsigned long flags
;
2522 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2523 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2525 /* Set up local state, ensuring consistent view of global state. */
2526 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2527 rdp
->beenonline
= 1; /* We have now been online. */
2528 rdp
->preemptible
= preemptible
;
2529 rdp
->qlen_last_fqs_check
= 0;
2530 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2531 rdp
->blimit
= blimit
;
2532 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
2533 atomic_set(&rdp
->dynticks
->dynticks
,
2534 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
2535 rcu_prepare_for_idle_init(cpu
);
2536 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2539 * A new grace period might start here. If so, we won't be part
2540 * of it, but that is OK, as we are currently in a quiescent state.
2543 /* Exclude any attempts to start a new GP on large systems. */
2544 raw_spin_lock(&rsp
->onofflock
); /* irqs already disabled. */
2546 /* Add CPU to rcu_node bitmasks. */
2548 mask
= rdp
->grpmask
;
2550 /* Exclude any attempts to start a new GP on small systems. */
2551 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2552 rnp
->qsmaskinit
|= mask
;
2553 mask
= rnp
->grpmask
;
2554 if (rnp
== rdp
->mynode
) {
2556 * If there is a grace period in progress, we will
2557 * set up to wait for it next time we run the
2560 rdp
->gpnum
= rnp
->completed
;
2561 rdp
->completed
= rnp
->completed
;
2562 rdp
->passed_quiesce
= 0;
2563 rdp
->qs_pending
= 0;
2564 rdp
->passed_quiesce_gpnum
= rnp
->gpnum
- 1;
2565 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, "cpuonl");
2567 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
2569 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
2571 raw_spin_unlock_irqrestore(&rsp
->onofflock
, flags
);
2574 static void __cpuinit
rcu_prepare_cpu(int cpu
)
2576 struct rcu_state
*rsp
;
2578 for_each_rcu_flavor(rsp
)
2579 rcu_init_percpu_data(cpu
, rsp
,
2580 strcmp(rsp
->name
, "rcu_preempt") == 0);
2584 * Handle CPU online/offline notification events.
2586 static int __cpuinit
rcu_cpu_notify(struct notifier_block
*self
,
2587 unsigned long action
, void *hcpu
)
2589 long cpu
= (long)hcpu
;
2590 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
2591 struct rcu_node
*rnp
= rdp
->mynode
;
2592 struct rcu_state
*rsp
;
2594 trace_rcu_utilization("Start CPU hotplug");
2596 case CPU_UP_PREPARE
:
2597 case CPU_UP_PREPARE_FROZEN
:
2598 rcu_prepare_cpu(cpu
);
2599 rcu_prepare_kthreads(cpu
);
2602 case CPU_DOWN_FAILED
:
2603 rcu_node_kthread_setaffinity(rnp
, -1);
2604 rcu_cpu_kthread_setrt(cpu
, 1);
2606 case CPU_DOWN_PREPARE
:
2607 rcu_node_kthread_setaffinity(rnp
, cpu
);
2608 rcu_cpu_kthread_setrt(cpu
, 0);
2611 case CPU_DYING_FROZEN
:
2613 * The whole machine is "stopped" except this CPU, so we can
2614 * touch any data without introducing corruption. We send the
2615 * dying CPU's callbacks to an arbitrarily chosen online CPU.
2617 for_each_rcu_flavor(rsp
)
2618 rcu_cleanup_dying_cpu(rsp
);
2619 rcu_cleanup_after_idle(cpu
);
2622 case CPU_DEAD_FROZEN
:
2623 case CPU_UP_CANCELED
:
2624 case CPU_UP_CANCELED_FROZEN
:
2625 for_each_rcu_flavor(rsp
)
2626 rcu_cleanup_dead_cpu(cpu
, rsp
);
2631 trace_rcu_utilization("End CPU hotplug");
2636 * Spawn the kthread that handles this RCU flavor's grace periods.
2638 static int __init
rcu_spawn_gp_kthread(void)
2640 unsigned long flags
;
2641 struct rcu_node
*rnp
;
2642 struct rcu_state
*rsp
;
2643 struct task_struct
*t
;
2645 for_each_rcu_flavor(rsp
) {
2646 t
= kthread_run(rcu_gp_kthread
, rsp
, rsp
->name
);
2648 rnp
= rcu_get_root(rsp
);
2649 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2650 rsp
->gp_kthread
= t
;
2651 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2655 early_initcall(rcu_spawn_gp_kthread
);
2658 * This function is invoked towards the end of the scheduler's initialization
2659 * process. Before this is called, the idle task might contain
2660 * RCU read-side critical sections (during which time, this idle
2661 * task is booting the system). After this function is called, the
2662 * idle tasks are prohibited from containing RCU read-side critical
2663 * sections. This function also enables RCU lockdep checking.
2665 void rcu_scheduler_starting(void)
2667 WARN_ON(num_online_cpus() != 1);
2668 WARN_ON(nr_context_switches() > 0);
2669 rcu_scheduler_active
= 1;
2673 * Compute the per-level fanout, either using the exact fanout specified
2674 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
2676 #ifdef CONFIG_RCU_FANOUT_EXACT
2677 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2681 for (i
= rcu_num_lvls
- 1; i
> 0; i
--)
2682 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
2683 rsp
->levelspread
[0] = rcu_fanout_leaf
;
2685 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
2686 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
2693 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2694 ccur
= rsp
->levelcnt
[i
];
2695 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
2699 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
2702 * Helper function for rcu_init() that initializes one rcu_state structure.
2704 static void __init
rcu_init_one(struct rcu_state
*rsp
,
2705 struct rcu_data __percpu
*rda
)
2707 static char *buf
[] = { "rcu_node_level_0",
2710 "rcu_node_level_3" }; /* Match MAX_RCU_LVLS */
2714 struct rcu_node
*rnp
;
2716 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
2718 /* Initialize the level-tracking arrays. */
2720 for (i
= 0; i
< rcu_num_lvls
; i
++)
2721 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
2722 for (i
= 1; i
< rcu_num_lvls
; i
++)
2723 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
2724 rcu_init_levelspread(rsp
);
2726 /* Initialize the elements themselves, starting from the leaves. */
2728 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
2729 cpustride
*= rsp
->levelspread
[i
];
2730 rnp
= rsp
->level
[i
];
2731 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
2732 raw_spin_lock_init(&rnp
->lock
);
2733 lockdep_set_class_and_name(&rnp
->lock
,
2734 &rcu_node_class
[i
], buf
[i
]);
2737 rnp
->qsmaskinit
= 0;
2738 rnp
->grplo
= j
* cpustride
;
2739 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
2740 if (rnp
->grphi
>= NR_CPUS
)
2741 rnp
->grphi
= NR_CPUS
- 1;
2747 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
2748 rnp
->grpmask
= 1UL << rnp
->grpnum
;
2749 rnp
->parent
= rsp
->level
[i
- 1] +
2750 j
/ rsp
->levelspread
[i
- 1];
2753 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
2758 init_waitqueue_head(&rsp
->gp_wq
);
2759 rnp
= rsp
->level
[rcu_num_lvls
- 1];
2760 for_each_possible_cpu(i
) {
2761 while (i
> rnp
->grphi
)
2763 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
2764 rcu_boot_init_percpu_data(i
, rsp
);
2766 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
2770 * Compute the rcu_node tree geometry from kernel parameters. This cannot
2771 * replace the definitions in rcutree.h because those are needed to size
2772 * the ->node array in the rcu_state structure.
2774 static void __init
rcu_init_geometry(void)
2779 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
2781 /* If the compile-time values are accurate, just leave. */
2782 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
)
2786 * Compute number of nodes that can be handled an rcu_node tree
2787 * with the given number of levels. Setting rcu_capacity[0] makes
2788 * some of the arithmetic easier.
2790 rcu_capacity
[0] = 1;
2791 rcu_capacity
[1] = rcu_fanout_leaf
;
2792 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
2793 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
2796 * The boot-time rcu_fanout_leaf parameter is only permitted
2797 * to increase the leaf-level fanout, not decrease it. Of course,
2798 * the leaf-level fanout cannot exceed the number of bits in
2799 * the rcu_node masks. Finally, the tree must be able to accommodate
2800 * the configured number of CPUs. Complain and fall back to the
2801 * compile-time values if these limits are exceeded.
2803 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
2804 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
2805 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
2810 /* Calculate the number of rcu_nodes at each level of the tree. */
2811 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
2812 if (n
<= rcu_capacity
[i
]) {
2813 for (j
= 0; j
<= i
; j
++)
2815 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
2817 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
2822 /* Calculate the total number of rcu_node structures. */
2824 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
2825 rcu_num_nodes
+= num_rcu_lvl
[i
];
2829 void __init
rcu_init(void)
2833 rcu_bootup_announce();
2834 rcu_init_geometry();
2835 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
2836 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
2837 __rcu_init_preempt();
2838 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
2841 * We don't need protection against CPU-hotplug here because
2842 * this is called early in boot, before either interrupts
2843 * or the scheduler are operational.
2845 cpu_notifier(rcu_cpu_notify
, 0);
2846 for_each_online_cpu(cpu
)
2847 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
2848 check_cpu_stall_init();
2851 #include "rcutree_plugin.h"