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, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
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/module.h>
45 #include <linux/percpu.h>
46 #include <linux/notifier.h>
47 #include <linux/cpu.h>
48 #include <linux/mutex.h>
49 #include <linux/time.h>
50 #include <linux/kernel_stat.h>
51 #include <linux/wait.h>
52 #include <linux/kthread.h>
53 #include <linux/prefetch.h>
54 #include <linux/delay.h>
55 #include <linux/stop_machine.h>
56 #include <linux/random.h>
57 #include <linux/ftrace_event.h>
58 #include <linux/suspend.h>
63 MODULE_ALIAS("rcutree");
64 #ifdef MODULE_PARAM_PREFIX
65 #undef MODULE_PARAM_PREFIX
67 #define MODULE_PARAM_PREFIX "rcutree."
69 /* Data structures. */
71 static struct lock_class_key rcu_node_class
[RCU_NUM_LVLS
];
72 static struct lock_class_key rcu_fqs_class
[RCU_NUM_LVLS
];
75 * In order to export the rcu_state name to the tracing tools, it
76 * needs to be added in the __tracepoint_string section.
77 * This requires defining a separate variable tp_<sname>_varname
78 * that points to the string being used, and this will allow
79 * the tracing userspace tools to be able to decipher the string
80 * address to the matching string.
82 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
83 static char sname##_varname[] = #sname; \
84 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
85 struct rcu_state sname##_state = { \
86 .level = { &sname##_state.node[0] }, \
88 .fqs_state = RCU_GP_IDLE, \
89 .gpnum = 0UL - 300UL, \
90 .completed = 0UL - 300UL, \
91 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
92 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
93 .orphan_donetail = &sname##_state.orphan_donelist, \
94 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
95 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
96 .name = sname##_varname, \
99 DEFINE_PER_CPU(struct rcu_data, sname##_data)
101 RCU_STATE_INITIALIZER(rcu_sched
, 's', call_rcu_sched
);
102 RCU_STATE_INITIALIZER(rcu_bh
, 'b', call_rcu_bh
);
104 static struct rcu_state
*rcu_state
;
105 LIST_HEAD(rcu_struct_flavors
);
107 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
108 static int rcu_fanout_leaf
= CONFIG_RCU_FANOUT_LEAF
;
109 module_param(rcu_fanout_leaf
, int, 0444);
110 int rcu_num_lvls __read_mostly
= RCU_NUM_LVLS
;
111 static int num_rcu_lvl
[] = { /* Number of rcu_nodes at specified level. */
118 int rcu_num_nodes __read_mostly
= NUM_RCU_NODES
; /* Total # rcu_nodes in use. */
121 * The rcu_scheduler_active variable transitions from zero to one just
122 * before the first task is spawned. So when this variable is zero, RCU
123 * can assume that there is but one task, allowing RCU to (for example)
124 * optimize synchronize_sched() to a simple barrier(). When this variable
125 * is one, RCU must actually do all the hard work required to detect real
126 * grace periods. This variable is also used to suppress boot-time false
127 * positives from lockdep-RCU error checking.
129 int rcu_scheduler_active __read_mostly
;
130 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
133 * The rcu_scheduler_fully_active variable transitions from zero to one
134 * during the early_initcall() processing, which is after the scheduler
135 * is capable of creating new tasks. So RCU processing (for example,
136 * creating tasks for RCU priority boosting) must be delayed until after
137 * rcu_scheduler_fully_active transitions from zero to one. We also
138 * currently delay invocation of any RCU callbacks until after this point.
140 * It might later prove better for people registering RCU callbacks during
141 * early boot to take responsibility for these callbacks, but one step at
144 static int rcu_scheduler_fully_active __read_mostly
;
146 #ifdef CONFIG_RCU_BOOST
149 * Control variables for per-CPU and per-rcu_node kthreads. These
150 * handle all flavors of RCU.
152 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
153 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
154 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
155 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
157 #endif /* #ifdef CONFIG_RCU_BOOST */
159 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
160 static void invoke_rcu_core(void);
161 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
164 * Track the rcutorture test sequence number and the update version
165 * number within a given test. The rcutorture_testseq is incremented
166 * on every rcutorture module load and unload, so has an odd value
167 * when a test is running. The rcutorture_vernum is set to zero
168 * when rcutorture starts and is incremented on each rcutorture update.
169 * These variables enable correlating rcutorture output with the
170 * RCU tracing information.
172 unsigned long rcutorture_testseq
;
173 unsigned long rcutorture_vernum
;
176 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
177 * permit this function to be invoked without holding the root rcu_node
178 * structure's ->lock, but of course results can be subject to change.
180 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
182 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
186 * Note a quiescent state. Because we do not need to know
187 * how many quiescent states passed, just if there was at least
188 * one since the start of the grace period, this just sets a flag.
189 * The caller must have disabled preemption.
191 void rcu_sched_qs(int cpu
)
193 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
195 if (rdp
->passed_quiesce
== 0)
196 trace_rcu_grace_period(TPS("rcu_sched"), rdp
->gpnum
, TPS("cpuqs"));
197 rdp
->passed_quiesce
= 1;
200 void rcu_bh_qs(int cpu
)
202 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
204 if (rdp
->passed_quiesce
== 0)
205 trace_rcu_grace_period(TPS("rcu_bh"), rdp
->gpnum
, TPS("cpuqs"));
206 rdp
->passed_quiesce
= 1;
210 * Note a context switch. This is a quiescent state for RCU-sched,
211 * and requires special handling for preemptible RCU.
212 * The caller must have disabled preemption.
214 void rcu_note_context_switch(int cpu
)
216 trace_rcu_utilization(TPS("Start context switch"));
218 rcu_preempt_note_context_switch(cpu
);
219 trace_rcu_utilization(TPS("End context switch"));
221 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
223 static DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
224 .dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
,
225 .dynticks
= ATOMIC_INIT(1),
226 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
227 .dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
,
228 .dynticks_idle
= ATOMIC_INIT(1),
229 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
232 static long blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
233 static long qhimark
= 10000; /* If this many pending, ignore blimit. */
234 static long qlowmark
= 100; /* Once only this many pending, use blimit. */
236 module_param(blimit
, long, 0444);
237 module_param(qhimark
, long, 0444);
238 module_param(qlowmark
, long, 0444);
240 static ulong jiffies_till_first_fqs
= ULONG_MAX
;
241 static ulong jiffies_till_next_fqs
= ULONG_MAX
;
243 module_param(jiffies_till_first_fqs
, ulong
, 0644);
244 module_param(jiffies_till_next_fqs
, ulong
, 0644);
246 static void rcu_start_gp_advanced(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
247 struct rcu_data
*rdp
);
248 static void force_qs_rnp(struct rcu_state
*rsp
,
249 int (*f
)(struct rcu_data
*rsp
, bool *isidle
,
250 unsigned long *maxj
),
251 bool *isidle
, unsigned long *maxj
);
252 static void force_quiescent_state(struct rcu_state
*rsp
);
253 static int rcu_pending(int cpu
);
256 * Return the number of RCU-sched batches processed thus far for debug & stats.
258 long rcu_batches_completed_sched(void)
260 return rcu_sched_state
.completed
;
262 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
265 * Return the number of RCU BH batches processed thus far for debug & stats.
267 long rcu_batches_completed_bh(void)
269 return rcu_bh_state
.completed
;
271 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
274 * Force a quiescent state for RCU BH.
276 void rcu_bh_force_quiescent_state(void)
278 force_quiescent_state(&rcu_bh_state
);
280 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
283 * Record the number of times rcutorture tests have been initiated and
284 * terminated. This information allows the debugfs tracing stats to be
285 * correlated to the rcutorture messages, even when the rcutorture module
286 * is being repeatedly loaded and unloaded. In other words, we cannot
287 * store this state in rcutorture itself.
289 void rcutorture_record_test_transition(void)
291 rcutorture_testseq
++;
292 rcutorture_vernum
= 0;
294 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition
);
297 * Record the number of writer passes through the current rcutorture test.
298 * This is also used to correlate debugfs tracing stats with the rcutorture
301 void rcutorture_record_progress(unsigned long vernum
)
305 EXPORT_SYMBOL_GPL(rcutorture_record_progress
);
308 * Force a quiescent state for RCU-sched.
310 void rcu_sched_force_quiescent_state(void)
312 force_quiescent_state(&rcu_sched_state
);
314 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
317 * Does the CPU have callbacks ready to be invoked?
320 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
322 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
] &&
323 rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
;
327 * Does the current CPU require a not-yet-started grace period?
328 * The caller must have disabled interrupts to prevent races with
329 * normal callback registry.
332 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
336 if (rcu_gp_in_progress(rsp
))
337 return 0; /* No, a grace period is already in progress. */
338 if (rcu_nocb_needs_gp(rsp
))
339 return 1; /* Yes, a no-CBs CPU needs one. */
340 if (!rdp
->nxttail
[RCU_NEXT_TAIL
])
341 return 0; /* No, this is a no-CBs (or offline) CPU. */
342 if (*rdp
->nxttail
[RCU_NEXT_READY_TAIL
])
343 return 1; /* Yes, this CPU has newly registered callbacks. */
344 for (i
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++)
345 if (rdp
->nxttail
[i
- 1] != rdp
->nxttail
[i
] &&
346 ULONG_CMP_LT(ACCESS_ONCE(rsp
->completed
),
347 rdp
->nxtcompleted
[i
]))
348 return 1; /* Yes, CBs for future grace period. */
349 return 0; /* No grace period needed. */
353 * Return the root node of the specified rcu_state structure.
355 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
357 return &rsp
->node
[0];
361 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
363 * If the new value of the ->dynticks_nesting counter now is zero,
364 * we really have entered idle, and must do the appropriate accounting.
365 * The caller must have disabled interrupts.
367 static void rcu_eqs_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
,
370 struct rcu_state
*rsp
;
371 struct rcu_data
*rdp
;
373 trace_rcu_dyntick(TPS("Start"), oldval
, rdtp
->dynticks_nesting
);
374 if (!user
&& !is_idle_task(current
)) {
375 struct task_struct
*idle __maybe_unused
=
376 idle_task(smp_processor_id());
378 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval
, 0);
379 ftrace_dump(DUMP_ORIG
);
380 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
381 current
->pid
, current
->comm
,
382 idle
->pid
, idle
->comm
); /* must be idle task! */
384 for_each_rcu_flavor(rsp
) {
385 rdp
= this_cpu_ptr(rsp
->rda
);
386 do_nocb_deferred_wakeup(rdp
);
388 rcu_prepare_for_idle(smp_processor_id());
389 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
390 smp_mb__before_atomic_inc(); /* See above. */
391 atomic_inc(&rdtp
->dynticks
);
392 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
393 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
396 * It is illegal to enter an extended quiescent state while
397 * in an RCU read-side critical section.
399 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map
),
400 "Illegal idle entry in RCU read-side critical section.");
401 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
),
402 "Illegal idle entry in RCU-bh read-side critical section.");
403 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map
),
404 "Illegal idle entry in RCU-sched read-side critical section.");
408 * Enter an RCU extended quiescent state, which can be either the
409 * idle loop or adaptive-tickless usermode execution.
411 static void rcu_eqs_enter(bool user
)
414 struct rcu_dynticks
*rdtp
;
416 rdtp
= this_cpu_ptr(&rcu_dynticks
);
417 oldval
= rdtp
->dynticks_nesting
;
418 WARN_ON_ONCE((oldval
& DYNTICK_TASK_NEST_MASK
) == 0);
419 if ((oldval
& DYNTICK_TASK_NEST_MASK
) == DYNTICK_TASK_NEST_VALUE
) {
420 rdtp
->dynticks_nesting
= 0;
421 rcu_eqs_enter_common(rdtp
, oldval
, user
);
423 rdtp
->dynticks_nesting
-= DYNTICK_TASK_NEST_VALUE
;
428 * rcu_idle_enter - inform RCU that current CPU is entering idle
430 * Enter idle mode, in other words, -leave- the mode in which RCU
431 * read-side critical sections can occur. (Though RCU read-side
432 * critical sections can occur in irq handlers in idle, a possibility
433 * handled by irq_enter() and irq_exit().)
435 * We crowbar the ->dynticks_nesting field to zero to allow for
436 * the possibility of usermode upcalls having messed up our count
437 * of interrupt nesting level during the prior busy period.
439 void rcu_idle_enter(void)
443 local_irq_save(flags
);
444 rcu_eqs_enter(false);
445 rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks
), 0);
446 local_irq_restore(flags
);
448 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
450 #ifdef CONFIG_RCU_USER_QS
452 * rcu_user_enter - inform RCU that we are resuming userspace.
454 * Enter RCU idle mode right before resuming userspace. No use of RCU
455 * is permitted between this call and rcu_user_exit(). This way the
456 * CPU doesn't need to maintain the tick for RCU maintenance purposes
457 * when the CPU runs in userspace.
459 void rcu_user_enter(void)
463 #endif /* CONFIG_RCU_USER_QS */
466 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
468 * Exit from an interrupt handler, which might possibly result in entering
469 * idle mode, in other words, leaving the mode in which read-side critical
470 * sections can occur.
472 * This code assumes that the idle loop never does anything that might
473 * result in unbalanced calls to irq_enter() and irq_exit(). If your
474 * architecture violates this assumption, RCU will give you what you
475 * deserve, good and hard. But very infrequently and irreproducibly.
477 * Use things like work queues to work around this limitation.
479 * You have been warned.
481 void rcu_irq_exit(void)
485 struct rcu_dynticks
*rdtp
;
487 local_irq_save(flags
);
488 rdtp
= this_cpu_ptr(&rcu_dynticks
);
489 oldval
= rdtp
->dynticks_nesting
;
490 rdtp
->dynticks_nesting
--;
491 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
492 if (rdtp
->dynticks_nesting
)
493 trace_rcu_dyntick(TPS("--="), oldval
, rdtp
->dynticks_nesting
);
495 rcu_eqs_enter_common(rdtp
, oldval
, true);
496 rcu_sysidle_enter(rdtp
, 1);
497 local_irq_restore(flags
);
501 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
503 * If the new value of the ->dynticks_nesting counter was previously zero,
504 * we really have exited idle, and must do the appropriate accounting.
505 * The caller must have disabled interrupts.
507 static void rcu_eqs_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
,
510 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
511 atomic_inc(&rdtp
->dynticks
);
512 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
513 smp_mb__after_atomic_inc(); /* See above. */
514 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
515 rcu_cleanup_after_idle(smp_processor_id());
516 trace_rcu_dyntick(TPS("End"), oldval
, rdtp
->dynticks_nesting
);
517 if (!user
&& !is_idle_task(current
)) {
518 struct task_struct
*idle __maybe_unused
=
519 idle_task(smp_processor_id());
521 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
522 oldval
, rdtp
->dynticks_nesting
);
523 ftrace_dump(DUMP_ORIG
);
524 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
525 current
->pid
, current
->comm
,
526 idle
->pid
, idle
->comm
); /* must be idle task! */
531 * Exit an RCU extended quiescent state, which can be either the
532 * idle loop or adaptive-tickless usermode execution.
534 static void rcu_eqs_exit(bool user
)
536 struct rcu_dynticks
*rdtp
;
539 rdtp
= this_cpu_ptr(&rcu_dynticks
);
540 oldval
= rdtp
->dynticks_nesting
;
541 WARN_ON_ONCE(oldval
< 0);
542 if (oldval
& DYNTICK_TASK_NEST_MASK
) {
543 rdtp
->dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
545 rdtp
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
546 rcu_eqs_exit_common(rdtp
, oldval
, user
);
551 * rcu_idle_exit - inform RCU that current CPU is leaving idle
553 * Exit idle mode, in other words, -enter- the mode in which RCU
554 * read-side critical sections can occur.
556 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
557 * allow for the possibility of usermode upcalls messing up our count
558 * of interrupt nesting level during the busy period that is just
561 void rcu_idle_exit(void)
565 local_irq_save(flags
);
567 rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks
), 0);
568 local_irq_restore(flags
);
570 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
572 #ifdef CONFIG_RCU_USER_QS
574 * rcu_user_exit - inform RCU that we are exiting userspace.
576 * Exit RCU idle mode while entering the kernel because it can
577 * run a RCU read side critical section anytime.
579 void rcu_user_exit(void)
583 #endif /* CONFIG_RCU_USER_QS */
586 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
588 * Enter an interrupt handler, which might possibly result in exiting
589 * idle mode, in other words, entering the mode in which read-side critical
590 * sections can occur.
592 * Note that the Linux kernel is fully capable of entering an interrupt
593 * handler that it never exits, for example when doing upcalls to
594 * user mode! This code assumes that the idle loop never does upcalls to
595 * user mode. If your architecture does do upcalls from the idle loop (or
596 * does anything else that results in unbalanced calls to the irq_enter()
597 * and irq_exit() functions), RCU will give you what you deserve, good
598 * and hard. But very infrequently and irreproducibly.
600 * Use things like work queues to work around this limitation.
602 * You have been warned.
604 void rcu_irq_enter(void)
607 struct rcu_dynticks
*rdtp
;
610 local_irq_save(flags
);
611 rdtp
= this_cpu_ptr(&rcu_dynticks
);
612 oldval
= rdtp
->dynticks_nesting
;
613 rdtp
->dynticks_nesting
++;
614 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
616 trace_rcu_dyntick(TPS("++="), oldval
, rdtp
->dynticks_nesting
);
618 rcu_eqs_exit_common(rdtp
, oldval
, true);
619 rcu_sysidle_exit(rdtp
, 1);
620 local_irq_restore(flags
);
624 * rcu_nmi_enter - inform RCU of entry to NMI context
626 * If the CPU was idle with dynamic ticks active, and there is no
627 * irq handler running, this updates rdtp->dynticks_nmi to let the
628 * RCU grace-period handling know that the CPU is active.
630 void rcu_nmi_enter(void)
632 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
634 if (rdtp
->dynticks_nmi_nesting
== 0 &&
635 (atomic_read(&rdtp
->dynticks
) & 0x1))
637 rdtp
->dynticks_nmi_nesting
++;
638 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
639 atomic_inc(&rdtp
->dynticks
);
640 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
641 smp_mb__after_atomic_inc(); /* See above. */
642 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
646 * rcu_nmi_exit - inform RCU of exit from NMI context
648 * If the CPU was idle with dynamic ticks active, and there is no
649 * irq handler running, this updates rdtp->dynticks_nmi to let the
650 * RCU grace-period handling know that the CPU is no longer active.
652 void rcu_nmi_exit(void)
654 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
656 if (rdtp
->dynticks_nmi_nesting
== 0 ||
657 --rdtp
->dynticks_nmi_nesting
!= 0)
659 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
660 smp_mb__before_atomic_inc(); /* See above. */
661 atomic_inc(&rdtp
->dynticks
);
662 smp_mb__after_atomic_inc(); /* Force delay to next write. */
663 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
667 * __rcu_is_watching - are RCU read-side critical sections safe?
669 * Return true if RCU is watching the running CPU, which means that
670 * this CPU can safely enter RCU read-side critical sections. Unlike
671 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
672 * least disabled preemption.
674 bool notrace
__rcu_is_watching(void)
676 return atomic_read(this_cpu_ptr(&rcu_dynticks
.dynticks
)) & 0x1;
680 * rcu_is_watching - see if RCU thinks that the current CPU is idle
682 * If the current CPU is in its idle loop and is neither in an interrupt
683 * or NMI handler, return true.
685 bool notrace
rcu_is_watching(void)
690 ret
= __rcu_is_watching();
694 EXPORT_SYMBOL_GPL(rcu_is_watching
);
696 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
699 * Is the current CPU online? Disable preemption to avoid false positives
700 * that could otherwise happen due to the current CPU number being sampled,
701 * this task being preempted, its old CPU being taken offline, resuming
702 * on some other CPU, then determining that its old CPU is now offline.
703 * It is OK to use RCU on an offline processor during initial boot, hence
704 * the check for rcu_scheduler_fully_active. Note also that it is OK
705 * for a CPU coming online to use RCU for one jiffy prior to marking itself
706 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
707 * offline to continue to use RCU for one jiffy after marking itself
708 * offline in the cpu_online_mask. This leniency is necessary given the
709 * non-atomic nature of the online and offline processing, for example,
710 * the fact that a CPU enters the scheduler after completing the CPU_DYING
713 * This is also why RCU internally marks CPUs online during the
714 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
716 * Disable checking if in an NMI handler because we cannot safely report
717 * errors from NMI handlers anyway.
719 bool rcu_lockdep_current_cpu_online(void)
721 struct rcu_data
*rdp
;
722 struct rcu_node
*rnp
;
728 rdp
= this_cpu_ptr(&rcu_sched_data
);
730 ret
= (rdp
->grpmask
& rnp
->qsmaskinit
) ||
731 !rcu_scheduler_fully_active
;
735 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online
);
737 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
740 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
742 * If the current CPU is idle or running at a first-level (not nested)
743 * interrupt from idle, return true. The caller must have at least
744 * disabled preemption.
746 static int rcu_is_cpu_rrupt_from_idle(void)
748 return __this_cpu_read(rcu_dynticks
.dynticks_nesting
) <= 1;
752 * Snapshot the specified CPU's dynticks counter so that we can later
753 * credit them with an implicit quiescent state. Return 1 if this CPU
754 * is in dynticks idle mode, which is an extended quiescent state.
756 static int dyntick_save_progress_counter(struct rcu_data
*rdp
,
757 bool *isidle
, unsigned long *maxj
)
759 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
760 rcu_sysidle_check_cpu(rdp
, isidle
, maxj
);
761 return (rdp
->dynticks_snap
& 0x1) == 0;
765 * This function really isn't for public consumption, but RCU is special in
766 * that context switches can allow the state machine to make progress.
768 extern void resched_cpu(int cpu
);
771 * Return true if the specified CPU has passed through a quiescent
772 * state by virtue of being in or having passed through an dynticks
773 * idle state since the last call to dyntick_save_progress_counter()
774 * for this same CPU, or by virtue of having been offline.
776 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
,
777 bool *isidle
, unsigned long *maxj
)
782 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
783 snap
= (unsigned int)rdp
->dynticks_snap
;
786 * If the CPU passed through or entered a dynticks idle phase with
787 * no active irq/NMI handlers, then we can safely pretend that the CPU
788 * already acknowledged the request to pass through a quiescent
789 * state. Either way, that CPU cannot possibly be in an RCU
790 * read-side critical section that started before the beginning
791 * of the current RCU grace period.
793 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
794 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("dti"));
800 * Check for the CPU being offline, but only if the grace period
801 * is old enough. We don't need to worry about the CPU changing
802 * state: If we see it offline even once, it has been through a
805 * The reason for insisting that the grace period be at least
806 * one jiffy old is that CPUs that are not quite online and that
807 * have just gone offline can still execute RCU read-side critical
810 if (ULONG_CMP_GE(rdp
->rsp
->gp_start
+ 2, jiffies
))
811 return 0; /* Grace period is not old enough. */
813 if (cpu_is_offline(rdp
->cpu
)) {
814 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("ofl"));
820 * There is a possibility that a CPU in adaptive-ticks state
821 * might run in the kernel with the scheduling-clock tick disabled
822 * for an extended time period. Invoke rcu_kick_nohz_cpu() to
823 * force the CPU to restart the scheduling-clock tick in this
824 * CPU is in this state.
826 rcu_kick_nohz_cpu(rdp
->cpu
);
829 * Alternatively, the CPU might be running in the kernel
830 * for an extended period of time without a quiescent state.
831 * Attempt to force the CPU through the scheduler to gain the
832 * needed quiescent state, but only if the grace period has gone
833 * on for an uncommonly long time. If there are many stuck CPUs,
834 * we will beat on the first one until it gets unstuck, then move
835 * to the next. Only do this for the primary flavor of RCU.
837 if (rdp
->rsp
== rcu_state
&&
838 ULONG_CMP_GE(jiffies
, rdp
->rsp
->jiffies_resched
)) {
839 rdp
->rsp
->jiffies_resched
+= 5;
840 resched_cpu(rdp
->cpu
);
846 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
848 unsigned long j
= jiffies
;
852 smp_wmb(); /* Record start time before stall time. */
853 j1
= rcu_jiffies_till_stall_check();
854 rsp
->jiffies_stall
= j
+ j1
;
855 rsp
->jiffies_resched
= j
+ j1
/ 2;
859 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
860 * for architectures that do not implement trigger_all_cpu_backtrace().
861 * The NMI-triggered stack traces are more accurate because they are
862 * printed by the target CPU.
864 static void rcu_dump_cpu_stacks(struct rcu_state
*rsp
)
868 struct rcu_node
*rnp
;
870 rcu_for_each_leaf_node(rsp
, rnp
) {
871 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
872 if (rnp
->qsmask
!= 0) {
873 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
874 if (rnp
->qsmask
& (1UL << cpu
))
875 dump_cpu_task(rnp
->grplo
+ cpu
);
877 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
881 static void print_other_cpu_stall(struct rcu_state
*rsp
)
887 struct rcu_node
*rnp
= rcu_get_root(rsp
);
890 /* Only let one CPU complain about others per time interval. */
892 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
893 delta
= jiffies
- rsp
->jiffies_stall
;
894 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
895 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
898 rsp
->jiffies_stall
= jiffies
+ 3 * rcu_jiffies_till_stall_check() + 3;
899 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
902 * OK, time to rat on our buddy...
903 * See Documentation/RCU/stallwarn.txt for info on how to debug
904 * RCU CPU stall warnings.
906 pr_err("INFO: %s detected stalls on CPUs/tasks:",
908 print_cpu_stall_info_begin();
909 rcu_for_each_leaf_node(rsp
, rnp
) {
910 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
911 ndetected
+= rcu_print_task_stall(rnp
);
912 if (rnp
->qsmask
!= 0) {
913 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
914 if (rnp
->qsmask
& (1UL << cpu
)) {
915 print_cpu_stall_info(rsp
,
920 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
924 * Now rat on any tasks that got kicked up to the root rcu_node
925 * due to CPU offlining.
927 rnp
= rcu_get_root(rsp
);
928 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
929 ndetected
+= rcu_print_task_stall(rnp
);
930 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
932 print_cpu_stall_info_end();
933 for_each_possible_cpu(cpu
)
934 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
935 pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu, q=%lu)\n",
936 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
),
937 rsp
->gpnum
, rsp
->completed
, totqlen
);
939 pr_err("INFO: Stall ended before state dump start\n");
940 else if (!trigger_all_cpu_backtrace())
941 rcu_dump_cpu_stacks(rsp
);
943 /* Complain about tasks blocking the grace period. */
945 rcu_print_detail_task_stall(rsp
);
947 force_quiescent_state(rsp
); /* Kick them all. */
951 * This function really isn't for public consumption, but RCU is special in
952 * that context switches can allow the state machine to make progress.
954 extern void resched_cpu(int cpu
);
956 static void print_cpu_stall(struct rcu_state
*rsp
)
960 struct rcu_node
*rnp
= rcu_get_root(rsp
);
964 * OK, time to rat on ourselves...
965 * See Documentation/RCU/stallwarn.txt for info on how to debug
966 * RCU CPU stall warnings.
968 pr_err("INFO: %s self-detected stall on CPU", rsp
->name
);
969 print_cpu_stall_info_begin();
970 print_cpu_stall_info(rsp
, smp_processor_id());
971 print_cpu_stall_info_end();
972 for_each_possible_cpu(cpu
)
973 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
974 pr_cont(" (t=%lu jiffies g=%lu c=%lu q=%lu)\n",
975 jiffies
- rsp
->gp_start
, rsp
->gpnum
, rsp
->completed
, totqlen
);
976 if (!trigger_all_cpu_backtrace())
979 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
980 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
981 rsp
->jiffies_stall
= jiffies
+
982 3 * rcu_jiffies_till_stall_check() + 3;
983 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
986 * Attempt to revive the RCU machinery by forcing a context switch.
988 * A context switch would normally allow the RCU state machine to make
989 * progress and it could be we're stuck in kernel space without context
990 * switches for an entirely unreasonable amount of time.
992 resched_cpu(smp_processor_id());
995 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
997 unsigned long completed
;
1002 struct rcu_node
*rnp
;
1004 if (rcu_cpu_stall_suppress
|| !rcu_gp_in_progress(rsp
))
1009 * Lots of memory barriers to reject false positives.
1011 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1012 * then rsp->gp_start, and finally rsp->completed. These values
1013 * are updated in the opposite order with memory barriers (or
1014 * equivalent) during grace-period initialization and cleanup.
1015 * Now, a false positive can occur if we get an new value of
1016 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1017 * the memory barriers, the only way that this can happen is if one
1018 * grace period ends and another starts between these two fetches.
1019 * Detect this by comparing rsp->completed with the previous fetch
1022 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1023 * and rsp->gp_start suffice to forestall false positives.
1025 gpnum
= ACCESS_ONCE(rsp
->gpnum
);
1026 smp_rmb(); /* Pick up ->gpnum first... */
1027 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
1028 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1029 gps
= ACCESS_ONCE(rsp
->gp_start
);
1030 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1031 completed
= ACCESS_ONCE(rsp
->completed
);
1032 if (ULONG_CMP_GE(completed
, gpnum
) ||
1033 ULONG_CMP_LT(j
, js
) ||
1034 ULONG_CMP_GE(gps
, js
))
1035 return; /* No stall or GP completed since entering function. */
1037 if (rcu_gp_in_progress(rsp
) &&
1038 (ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
)) {
1040 /* We haven't checked in, so go dump stack. */
1041 print_cpu_stall(rsp
);
1043 } else if (rcu_gp_in_progress(rsp
) &&
1044 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
1046 /* They had a few time units to dump stack, so complain. */
1047 print_other_cpu_stall(rsp
);
1052 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1054 * Set the stall-warning timeout way off into the future, thus preventing
1055 * any RCU CPU stall-warning messages from appearing in the current set of
1056 * RCU grace periods.
1058 * The caller must disable hard irqs.
1060 void rcu_cpu_stall_reset(void)
1062 struct rcu_state
*rsp
;
1064 for_each_rcu_flavor(rsp
)
1065 rsp
->jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
1069 * Initialize the specified rcu_data structure's callback list to empty.
1071 static void init_callback_list(struct rcu_data
*rdp
)
1075 if (init_nocb_callback_list(rdp
))
1077 rdp
->nxtlist
= NULL
;
1078 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1079 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1083 * Determine the value that ->completed will have at the end of the
1084 * next subsequent grace period. This is used to tag callbacks so that
1085 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1086 * been dyntick-idle for an extended period with callbacks under the
1087 * influence of RCU_FAST_NO_HZ.
1089 * The caller must hold rnp->lock with interrupts disabled.
1091 static unsigned long rcu_cbs_completed(struct rcu_state
*rsp
,
1092 struct rcu_node
*rnp
)
1095 * If RCU is idle, we just wait for the next grace period.
1096 * But we can only be sure that RCU is idle if we are looking
1097 * at the root rcu_node structure -- otherwise, a new grace
1098 * period might have started, but just not yet gotten around
1099 * to initializing the current non-root rcu_node structure.
1101 if (rcu_get_root(rsp
) == rnp
&& rnp
->gpnum
== rnp
->completed
)
1102 return rnp
->completed
+ 1;
1105 * Otherwise, wait for a possible partial grace period and
1106 * then the subsequent full grace period.
1108 return rnp
->completed
+ 2;
1112 * Trace-event helper function for rcu_start_future_gp() and
1113 * rcu_nocb_wait_gp().
1115 static void trace_rcu_future_gp(struct rcu_node
*rnp
, struct rcu_data
*rdp
,
1116 unsigned long c
, const char *s
)
1118 trace_rcu_future_grace_period(rdp
->rsp
->name
, rnp
->gpnum
,
1119 rnp
->completed
, c
, rnp
->level
,
1120 rnp
->grplo
, rnp
->grphi
, s
);
1124 * Start some future grace period, as needed to handle newly arrived
1125 * callbacks. The required future grace periods are recorded in each
1126 * rcu_node structure's ->need_future_gp field.
1128 * The caller must hold the specified rcu_node structure's ->lock.
1130 static unsigned long __maybe_unused
1131 rcu_start_future_gp(struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1135 struct rcu_node
*rnp_root
= rcu_get_root(rdp
->rsp
);
1138 * Pick up grace-period number for new callbacks. If this
1139 * grace period is already marked as needed, return to the caller.
1141 c
= rcu_cbs_completed(rdp
->rsp
, rnp
);
1142 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startleaf"));
1143 if (rnp
->need_future_gp
[c
& 0x1]) {
1144 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Prestartleaf"));
1149 * If either this rcu_node structure or the root rcu_node structure
1150 * believe that a grace period is in progress, then we must wait
1151 * for the one following, which is in "c". Because our request
1152 * will be noticed at the end of the current grace period, we don't
1153 * need to explicitly start one.
1155 if (rnp
->gpnum
!= rnp
->completed
||
1156 ACCESS_ONCE(rnp
->gpnum
) != ACCESS_ONCE(rnp
->completed
)) {
1157 rnp
->need_future_gp
[c
& 0x1]++;
1158 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedleaf"));
1163 * There might be no grace period in progress. If we don't already
1164 * hold it, acquire the root rcu_node structure's lock in order to
1165 * start one (if needed).
1167 if (rnp
!= rnp_root
) {
1168 raw_spin_lock(&rnp_root
->lock
);
1169 smp_mb__after_unlock_lock();
1173 * Get a new grace-period number. If there really is no grace
1174 * period in progress, it will be smaller than the one we obtained
1175 * earlier. Adjust callbacks as needed. Note that even no-CBs
1176 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1178 c
= rcu_cbs_completed(rdp
->rsp
, rnp_root
);
1179 for (i
= RCU_DONE_TAIL
; i
< RCU_NEXT_TAIL
; i
++)
1180 if (ULONG_CMP_LT(c
, rdp
->nxtcompleted
[i
]))
1181 rdp
->nxtcompleted
[i
] = c
;
1184 * If the needed for the required grace period is already
1185 * recorded, trace and leave.
1187 if (rnp_root
->need_future_gp
[c
& 0x1]) {
1188 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Prestartedroot"));
1192 /* Record the need for the future grace period. */
1193 rnp_root
->need_future_gp
[c
& 0x1]++;
1195 /* If a grace period is not already in progress, start one. */
1196 if (rnp_root
->gpnum
!= rnp_root
->completed
) {
1197 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedleafroot"));
1199 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedroot"));
1200 rcu_start_gp_advanced(rdp
->rsp
, rnp_root
, rdp
);
1203 if (rnp
!= rnp_root
)
1204 raw_spin_unlock(&rnp_root
->lock
);
1209 * Clean up any old requests for the just-ended grace period. Also return
1210 * whether any additional grace periods have been requested. Also invoke
1211 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1212 * waiting for this grace period to complete.
1214 static int rcu_future_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
1216 int c
= rnp
->completed
;
1218 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1220 rcu_nocb_gp_cleanup(rsp
, rnp
);
1221 rnp
->need_future_gp
[c
& 0x1] = 0;
1222 needmore
= rnp
->need_future_gp
[(c
+ 1) & 0x1];
1223 trace_rcu_future_gp(rnp
, rdp
, c
,
1224 needmore
? TPS("CleanupMore") : TPS("Cleanup"));
1229 * If there is room, assign a ->completed number to any callbacks on
1230 * this CPU that have not already been assigned. Also accelerate any
1231 * callbacks that were previously assigned a ->completed number that has
1232 * since proven to be too conservative, which can happen if callbacks get
1233 * assigned a ->completed number while RCU is idle, but with reference to
1234 * a non-root rcu_node structure. This function is idempotent, so it does
1235 * not hurt to call it repeatedly.
1237 * The caller must hold rnp->lock with interrupts disabled.
1239 static void rcu_accelerate_cbs(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1240 struct rcu_data
*rdp
)
1245 /* If the CPU has no callbacks, nothing to do. */
1246 if (!rdp
->nxttail
[RCU_NEXT_TAIL
] || !*rdp
->nxttail
[RCU_DONE_TAIL
])
1250 * Starting from the sublist containing the callbacks most
1251 * recently assigned a ->completed number and working down, find the
1252 * first sublist that is not assignable to an upcoming grace period.
1253 * Such a sublist has something in it (first two tests) and has
1254 * a ->completed number assigned that will complete sooner than
1255 * the ->completed number for newly arrived callbacks (last test).
1257 * The key point is that any later sublist can be assigned the
1258 * same ->completed number as the newly arrived callbacks, which
1259 * means that the callbacks in any of these later sublist can be
1260 * grouped into a single sublist, whether or not they have already
1261 * been assigned a ->completed number.
1263 c
= rcu_cbs_completed(rsp
, rnp
);
1264 for (i
= RCU_NEXT_TAIL
- 1; i
> RCU_DONE_TAIL
; i
--)
1265 if (rdp
->nxttail
[i
] != rdp
->nxttail
[i
- 1] &&
1266 !ULONG_CMP_GE(rdp
->nxtcompleted
[i
], c
))
1270 * If there are no sublist for unassigned callbacks, leave.
1271 * At the same time, advance "i" one sublist, so that "i" will
1272 * index into the sublist where all the remaining callbacks should
1275 if (++i
>= RCU_NEXT_TAIL
)
1279 * Assign all subsequent callbacks' ->completed number to the next
1280 * full grace period and group them all in the sublist initially
1283 for (; i
<= RCU_NEXT_TAIL
; i
++) {
1284 rdp
->nxttail
[i
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1285 rdp
->nxtcompleted
[i
] = c
;
1287 /* Record any needed additional grace periods. */
1288 rcu_start_future_gp(rnp
, rdp
);
1290 /* Trace depending on how much we were able to accelerate. */
1291 if (!*rdp
->nxttail
[RCU_WAIT_TAIL
])
1292 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("AccWaitCB"));
1294 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("AccReadyCB"));
1298 * Move any callbacks whose grace period has completed to the
1299 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1300 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1301 * sublist. This function is idempotent, so it does not hurt to
1302 * invoke it repeatedly. As long as it is not invoked -too- often...
1304 * The caller must hold rnp->lock with interrupts disabled.
1306 static void rcu_advance_cbs(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1307 struct rcu_data
*rdp
)
1311 /* If the CPU has no callbacks, nothing to do. */
1312 if (!rdp
->nxttail
[RCU_NEXT_TAIL
] || !*rdp
->nxttail
[RCU_DONE_TAIL
])
1316 * Find all callbacks whose ->completed numbers indicate that they
1317 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1319 for (i
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++) {
1320 if (ULONG_CMP_LT(rnp
->completed
, rdp
->nxtcompleted
[i
]))
1322 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[i
];
1324 /* Clean up any sublist tail pointers that were misordered above. */
1325 for (j
= RCU_WAIT_TAIL
; j
< i
; j
++)
1326 rdp
->nxttail
[j
] = rdp
->nxttail
[RCU_DONE_TAIL
];
1328 /* Copy down callbacks to fill in empty sublists. */
1329 for (j
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++, j
++) {
1330 if (rdp
->nxttail
[j
] == rdp
->nxttail
[RCU_NEXT_TAIL
])
1332 rdp
->nxttail
[j
] = rdp
->nxttail
[i
];
1333 rdp
->nxtcompleted
[j
] = rdp
->nxtcompleted
[i
];
1336 /* Classify any remaining callbacks. */
1337 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1341 * Update CPU-local rcu_data state to record the beginnings and ends of
1342 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1343 * structure corresponding to the current CPU, and must have irqs disabled.
1345 static void __note_gp_changes(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1347 /* Handle the ends of any preceding grace periods first. */
1348 if (rdp
->completed
== rnp
->completed
) {
1350 /* No grace period end, so just accelerate recent callbacks. */
1351 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1355 /* Advance callbacks. */
1356 rcu_advance_cbs(rsp
, rnp
, rdp
);
1358 /* Remember that we saw this grace-period completion. */
1359 rdp
->completed
= rnp
->completed
;
1360 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpuend"));
1363 if (rdp
->gpnum
!= rnp
->gpnum
) {
1365 * If the current grace period is waiting for this CPU,
1366 * set up to detect a quiescent state, otherwise don't
1367 * go looking for one.
1369 rdp
->gpnum
= rnp
->gpnum
;
1370 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpustart"));
1371 rdp
->passed_quiesce
= 0;
1372 rdp
->qs_pending
= !!(rnp
->qsmask
& rdp
->grpmask
);
1373 zero_cpu_stall_ticks(rdp
);
1377 static void note_gp_changes(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1379 unsigned long flags
;
1380 struct rcu_node
*rnp
;
1382 local_irq_save(flags
);
1384 if ((rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) &&
1385 rdp
->completed
== ACCESS_ONCE(rnp
->completed
)) || /* w/out lock. */
1386 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1387 local_irq_restore(flags
);
1390 smp_mb__after_unlock_lock();
1391 __note_gp_changes(rsp
, rnp
, rdp
);
1392 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1396 * Initialize a new grace period. Return 0 if no grace period required.
1398 static int rcu_gp_init(struct rcu_state
*rsp
)
1400 struct rcu_data
*rdp
;
1401 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1403 rcu_bind_gp_kthread();
1404 raw_spin_lock_irq(&rnp
->lock
);
1405 smp_mb__after_unlock_lock();
1406 if (rsp
->gp_flags
== 0) {
1407 /* Spurious wakeup, tell caller to go back to sleep. */
1408 raw_spin_unlock_irq(&rnp
->lock
);
1411 rsp
->gp_flags
= 0; /* Clear all flags: New grace period. */
1413 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp
))) {
1415 * Grace period already in progress, don't start another.
1416 * Not supposed to be able to happen.
1418 raw_spin_unlock_irq(&rnp
->lock
);
1422 /* Advance to a new grace period and initialize state. */
1423 record_gp_stall_check_time(rsp
);
1424 /* Record GP times before starting GP, hence smp_store_release(). */
1425 smp_store_release(&rsp
->gpnum
, rsp
->gpnum
+ 1);
1426 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, TPS("start"));
1427 raw_spin_unlock_irq(&rnp
->lock
);
1429 /* Exclude any concurrent CPU-hotplug operations. */
1430 mutex_lock(&rsp
->onoff_mutex
);
1431 smp_mb__after_unlock_lock(); /* ->gpnum increment before GP! */
1434 * Set the quiescent-state-needed bits in all the rcu_node
1435 * structures for all currently online CPUs in breadth-first order,
1436 * starting from the root rcu_node structure, relying on the layout
1437 * of the tree within the rsp->node[] array. Note that other CPUs
1438 * will access only the leaves of the hierarchy, thus seeing that no
1439 * grace period is in progress, at least until the corresponding
1440 * leaf node has been initialized. In addition, we have excluded
1441 * CPU-hotplug operations.
1443 * The grace period cannot complete until the initialization
1444 * process finishes, because this kthread handles both.
1446 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1447 raw_spin_lock_irq(&rnp
->lock
);
1448 smp_mb__after_unlock_lock();
1449 rdp
= this_cpu_ptr(rsp
->rda
);
1450 rcu_preempt_check_blocked_tasks(rnp
);
1451 rnp
->qsmask
= rnp
->qsmaskinit
;
1452 ACCESS_ONCE(rnp
->gpnum
) = rsp
->gpnum
;
1453 WARN_ON_ONCE(rnp
->completed
!= rsp
->completed
);
1454 ACCESS_ONCE(rnp
->completed
) = rsp
->completed
;
1455 if (rnp
== rdp
->mynode
)
1456 __note_gp_changes(rsp
, rnp
, rdp
);
1457 rcu_preempt_boost_start_gp(rnp
);
1458 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1459 rnp
->level
, rnp
->grplo
,
1460 rnp
->grphi
, rnp
->qsmask
);
1461 raw_spin_unlock_irq(&rnp
->lock
);
1462 #ifdef CONFIG_PROVE_RCU_DELAY
1463 if ((prandom_u32() % (rcu_num_nodes
+ 1)) == 0 &&
1464 system_state
== SYSTEM_RUNNING
)
1466 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1470 mutex_unlock(&rsp
->onoff_mutex
);
1475 * Do one round of quiescent-state forcing.
1477 static int rcu_gp_fqs(struct rcu_state
*rsp
, int fqs_state_in
)
1479 int fqs_state
= fqs_state_in
;
1480 bool isidle
= false;
1482 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1485 if (fqs_state
== RCU_SAVE_DYNTICK
) {
1486 /* Collect dyntick-idle snapshots. */
1487 if (is_sysidle_rcu_state(rsp
)) {
1489 maxj
= jiffies
- ULONG_MAX
/ 4;
1491 force_qs_rnp(rsp
, dyntick_save_progress_counter
,
1493 rcu_sysidle_report_gp(rsp
, isidle
, maxj
);
1494 fqs_state
= RCU_FORCE_QS
;
1496 /* Handle dyntick-idle and offline CPUs. */
1498 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
, &isidle
, &maxj
);
1500 /* Clear flag to prevent immediate re-entry. */
1501 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
1502 raw_spin_lock_irq(&rnp
->lock
);
1503 smp_mb__after_unlock_lock();
1504 rsp
->gp_flags
&= ~RCU_GP_FLAG_FQS
;
1505 raw_spin_unlock_irq(&rnp
->lock
);
1511 * Clean up after the old grace period.
1513 static void rcu_gp_cleanup(struct rcu_state
*rsp
)
1515 unsigned long gp_duration
;
1517 struct rcu_data
*rdp
;
1518 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1520 raw_spin_lock_irq(&rnp
->lock
);
1521 smp_mb__after_unlock_lock();
1522 gp_duration
= jiffies
- rsp
->gp_start
;
1523 if (gp_duration
> rsp
->gp_max
)
1524 rsp
->gp_max
= gp_duration
;
1527 * We know the grace period is complete, but to everyone else
1528 * it appears to still be ongoing. But it is also the case
1529 * that to everyone else it looks like there is nothing that
1530 * they can do to advance the grace period. It is therefore
1531 * safe for us to drop the lock in order to mark the grace
1532 * period as completed in all of the rcu_node structures.
1534 raw_spin_unlock_irq(&rnp
->lock
);
1537 * Propagate new ->completed value to rcu_node structures so
1538 * that other CPUs don't have to wait until the start of the next
1539 * grace period to process their callbacks. This also avoids
1540 * some nasty RCU grace-period initialization races by forcing
1541 * the end of the current grace period to be completely recorded in
1542 * all of the rcu_node structures before the beginning of the next
1543 * grace period is recorded in any of the rcu_node structures.
1545 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1546 raw_spin_lock_irq(&rnp
->lock
);
1547 smp_mb__after_unlock_lock();
1548 ACCESS_ONCE(rnp
->completed
) = rsp
->gpnum
;
1549 rdp
= this_cpu_ptr(rsp
->rda
);
1550 if (rnp
== rdp
->mynode
)
1551 __note_gp_changes(rsp
, rnp
, rdp
);
1552 /* smp_mb() provided by prior unlock-lock pair. */
1553 nocb
+= rcu_future_gp_cleanup(rsp
, rnp
);
1554 raw_spin_unlock_irq(&rnp
->lock
);
1557 rnp
= rcu_get_root(rsp
);
1558 raw_spin_lock_irq(&rnp
->lock
);
1559 smp_mb__after_unlock_lock(); /* Order GP before ->completed update. */
1560 rcu_nocb_gp_set(rnp
, nocb
);
1562 /* Declare grace period done. */
1563 ACCESS_ONCE(rsp
->completed
) = rsp
->gpnum
;
1564 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, TPS("end"));
1565 rsp
->fqs_state
= RCU_GP_IDLE
;
1566 rdp
= this_cpu_ptr(rsp
->rda
);
1567 rcu_advance_cbs(rsp
, rnp
, rdp
); /* Reduce false positives below. */
1568 if (cpu_needs_another_gp(rsp
, rdp
)) {
1569 rsp
->gp_flags
= RCU_GP_FLAG_INIT
;
1570 trace_rcu_grace_period(rsp
->name
,
1571 ACCESS_ONCE(rsp
->gpnum
),
1574 raw_spin_unlock_irq(&rnp
->lock
);
1578 * Body of kthread that handles grace periods.
1580 static int __noreturn
rcu_gp_kthread(void *arg
)
1586 struct rcu_state
*rsp
= arg
;
1587 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1591 /* Handle grace-period start. */
1593 trace_rcu_grace_period(rsp
->name
,
1594 ACCESS_ONCE(rsp
->gpnum
),
1596 wait_event_interruptible(rsp
->gp_wq
,
1597 ACCESS_ONCE(rsp
->gp_flags
) &
1599 /* Locking provides needed memory barrier. */
1600 if (rcu_gp_init(rsp
))
1603 flush_signals(current
);
1604 trace_rcu_grace_period(rsp
->name
,
1605 ACCESS_ONCE(rsp
->gpnum
),
1609 /* Handle quiescent-state forcing. */
1610 fqs_state
= RCU_SAVE_DYNTICK
;
1611 j
= jiffies_till_first_fqs
;
1614 jiffies_till_first_fqs
= HZ
;
1619 rsp
->jiffies_force_qs
= jiffies
+ j
;
1620 trace_rcu_grace_period(rsp
->name
,
1621 ACCESS_ONCE(rsp
->gpnum
),
1623 ret
= wait_event_interruptible_timeout(rsp
->gp_wq
,
1624 ((gf
= ACCESS_ONCE(rsp
->gp_flags
)) &
1626 (!ACCESS_ONCE(rnp
->qsmask
) &&
1627 !rcu_preempt_blocked_readers_cgp(rnp
)),
1629 /* Locking provides needed memory barriers. */
1630 /* If grace period done, leave loop. */
1631 if (!ACCESS_ONCE(rnp
->qsmask
) &&
1632 !rcu_preempt_blocked_readers_cgp(rnp
))
1634 /* If time for quiescent-state forcing, do it. */
1635 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_force_qs
) ||
1636 (gf
& RCU_GP_FLAG_FQS
)) {
1637 trace_rcu_grace_period(rsp
->name
,
1638 ACCESS_ONCE(rsp
->gpnum
),
1640 fqs_state
= rcu_gp_fqs(rsp
, fqs_state
);
1641 trace_rcu_grace_period(rsp
->name
,
1642 ACCESS_ONCE(rsp
->gpnum
),
1646 /* Deal with stray signal. */
1648 flush_signals(current
);
1649 trace_rcu_grace_period(rsp
->name
,
1650 ACCESS_ONCE(rsp
->gpnum
),
1653 j
= jiffies_till_next_fqs
;
1656 jiffies_till_next_fqs
= HZ
;
1659 jiffies_till_next_fqs
= 1;
1663 /* Handle grace-period end. */
1664 rcu_gp_cleanup(rsp
);
1668 static void rsp_wakeup(struct irq_work
*work
)
1670 struct rcu_state
*rsp
= container_of(work
, struct rcu_state
, wakeup_work
);
1672 /* Wake up rcu_gp_kthread() to start the grace period. */
1673 wake_up(&rsp
->gp_wq
);
1677 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1678 * in preparation for detecting the next grace period. The caller must hold
1679 * the root node's ->lock and hard irqs must be disabled.
1681 * Note that it is legal for a dying CPU (which is marked as offline) to
1682 * invoke this function. This can happen when the dying CPU reports its
1686 rcu_start_gp_advanced(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1687 struct rcu_data
*rdp
)
1689 if (!rsp
->gp_kthread
|| !cpu_needs_another_gp(rsp
, rdp
)) {
1691 * Either we have not yet spawned the grace-period
1692 * task, this CPU does not need another grace period,
1693 * or a grace period is already in progress.
1694 * Either way, don't start a new grace period.
1698 rsp
->gp_flags
= RCU_GP_FLAG_INIT
;
1699 trace_rcu_grace_period(rsp
->name
, ACCESS_ONCE(rsp
->gpnum
),
1703 * We can't do wakeups while holding the rnp->lock, as that
1704 * could cause possible deadlocks with the rq->lock. Defer
1705 * the wakeup to interrupt context. And don't bother waking
1706 * up the running kthread.
1708 if (current
!= rsp
->gp_kthread
)
1709 irq_work_queue(&rsp
->wakeup_work
);
1713 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
1714 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
1715 * is invoked indirectly from rcu_advance_cbs(), which would result in
1716 * endless recursion -- or would do so if it wasn't for the self-deadlock
1717 * that is encountered beforehand.
1720 rcu_start_gp(struct rcu_state
*rsp
)
1722 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1723 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1726 * If there is no grace period in progress right now, any
1727 * callbacks we have up to this point will be satisfied by the
1728 * next grace period. Also, advancing the callbacks reduces the
1729 * probability of false positives from cpu_needs_another_gp()
1730 * resulting in pointless grace periods. So, advance callbacks
1731 * then start the grace period!
1733 rcu_advance_cbs(rsp
, rnp
, rdp
);
1734 rcu_start_gp_advanced(rsp
, rnp
, rdp
);
1738 * Report a full set of quiescent states to the specified rcu_state
1739 * data structure. This involves cleaning up after the prior grace
1740 * period and letting rcu_start_gp() start up the next grace period
1741 * if one is needed. Note that the caller must hold rnp->lock, which
1742 * is released before return.
1744 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1745 __releases(rcu_get_root(rsp
)->lock
)
1747 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1748 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
1749 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1753 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1754 * Allows quiescent states for a group of CPUs to be reported at one go
1755 * to the specified rcu_node structure, though all the CPUs in the group
1756 * must be represented by the same rcu_node structure (which need not be
1757 * a leaf rcu_node structure, though it often will be). That structure's
1758 * lock must be held upon entry, and it is released before return.
1761 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1762 struct rcu_node
*rnp
, unsigned long flags
)
1763 __releases(rnp
->lock
)
1765 struct rcu_node
*rnp_c
;
1767 /* Walk up the rcu_node hierarchy. */
1769 if (!(rnp
->qsmask
& mask
)) {
1771 /* Our bit has already been cleared, so done. */
1772 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1775 rnp
->qsmask
&= ~mask
;
1776 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1777 mask
, rnp
->qsmask
, rnp
->level
,
1778 rnp
->grplo
, rnp
->grphi
,
1780 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1782 /* Other bits still set at this level, so done. */
1783 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1786 mask
= rnp
->grpmask
;
1787 if (rnp
->parent
== NULL
) {
1789 /* No more levels. Exit loop holding root lock. */
1793 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1796 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1797 smp_mb__after_unlock_lock();
1798 WARN_ON_ONCE(rnp_c
->qsmask
);
1802 * Get here if we are the last CPU to pass through a quiescent
1803 * state for this grace period. Invoke rcu_report_qs_rsp()
1804 * to clean up and start the next grace period if one is needed.
1806 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1810 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1811 * structure. This must be either called from the specified CPU, or
1812 * called when the specified CPU is known to be offline (and when it is
1813 * also known that no other CPU is concurrently trying to help the offline
1814 * CPU). The lastcomp argument is used to make sure we are still in the
1815 * grace period of interest. We don't want to end the current grace period
1816 * based on quiescent states detected in an earlier grace period!
1819 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1821 unsigned long flags
;
1823 struct rcu_node
*rnp
;
1826 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1827 smp_mb__after_unlock_lock();
1828 if (rdp
->passed_quiesce
== 0 || rdp
->gpnum
!= rnp
->gpnum
||
1829 rnp
->completed
== rnp
->gpnum
) {
1832 * The grace period in which this quiescent state was
1833 * recorded has ended, so don't report it upwards.
1834 * We will instead need a new quiescent state that lies
1835 * within the current grace period.
1837 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1838 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1841 mask
= rdp
->grpmask
;
1842 if ((rnp
->qsmask
& mask
) == 0) {
1843 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1845 rdp
->qs_pending
= 0;
1848 * This GP can't end until cpu checks in, so all of our
1849 * callbacks can be processed during the next GP.
1851 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1853 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1858 * Check to see if there is a new grace period of which this CPU
1859 * is not yet aware, and if so, set up local rcu_data state for it.
1860 * Otherwise, see if this CPU has just passed through its first
1861 * quiescent state for this grace period, and record that fact if so.
1864 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1866 /* Check for grace-period ends and beginnings. */
1867 note_gp_changes(rsp
, rdp
);
1870 * Does this CPU still need to do its part for current grace period?
1871 * If no, return and let the other CPUs do their part as well.
1873 if (!rdp
->qs_pending
)
1877 * Was there a quiescent state since the beginning of the grace
1878 * period? If no, then exit and wait for the next call.
1880 if (!rdp
->passed_quiesce
)
1884 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1887 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
);
1890 #ifdef CONFIG_HOTPLUG_CPU
1893 * Send the specified CPU's RCU callbacks to the orphanage. The
1894 * specified CPU must be offline, and the caller must hold the
1898 rcu_send_cbs_to_orphanage(int cpu
, struct rcu_state
*rsp
,
1899 struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1901 /* No-CBs CPUs do not have orphanable callbacks. */
1902 if (rcu_is_nocb_cpu(rdp
->cpu
))
1906 * Orphan the callbacks. First adjust the counts. This is safe
1907 * because _rcu_barrier() excludes CPU-hotplug operations, so it
1908 * cannot be running now. Thus no memory barrier is required.
1910 if (rdp
->nxtlist
!= NULL
) {
1911 rsp
->qlen_lazy
+= rdp
->qlen_lazy
;
1912 rsp
->qlen
+= rdp
->qlen
;
1913 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1915 ACCESS_ONCE(rdp
->qlen
) = 0;
1919 * Next, move those callbacks still needing a grace period to
1920 * the orphanage, where some other CPU will pick them up.
1921 * Some of the callbacks might have gone partway through a grace
1922 * period, but that is too bad. They get to start over because we
1923 * cannot assume that grace periods are synchronized across CPUs.
1924 * We don't bother updating the ->nxttail[] array yet, instead
1925 * we just reset the whole thing later on.
1927 if (*rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
) {
1928 *rsp
->orphan_nxttail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1929 rsp
->orphan_nxttail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
1930 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1934 * Then move the ready-to-invoke callbacks to the orphanage,
1935 * where some other CPU will pick them up. These will not be
1936 * required to pass though another grace period: They are done.
1938 if (rdp
->nxtlist
!= NULL
) {
1939 *rsp
->orphan_donetail
= rdp
->nxtlist
;
1940 rsp
->orphan_donetail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1943 /* Finally, initialize the rcu_data structure's list to empty. */
1944 init_callback_list(rdp
);
1948 * Adopt the RCU callbacks from the specified rcu_state structure's
1949 * orphanage. The caller must hold the ->orphan_lock.
1951 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
, unsigned long flags
)
1954 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1956 /* No-CBs CPUs are handled specially. */
1957 if (rcu_nocb_adopt_orphan_cbs(rsp
, rdp
, flags
))
1960 /* Do the accounting first. */
1961 rdp
->qlen_lazy
+= rsp
->qlen_lazy
;
1962 rdp
->qlen
+= rsp
->qlen
;
1963 rdp
->n_cbs_adopted
+= rsp
->qlen
;
1964 if (rsp
->qlen_lazy
!= rsp
->qlen
)
1965 rcu_idle_count_callbacks_posted();
1970 * We do not need a memory barrier here because the only way we
1971 * can get here if there is an rcu_barrier() in flight is if
1972 * we are the task doing the rcu_barrier().
1975 /* First adopt the ready-to-invoke callbacks. */
1976 if (rsp
->orphan_donelist
!= NULL
) {
1977 *rsp
->orphan_donetail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1978 *rdp
->nxttail
[RCU_DONE_TAIL
] = rsp
->orphan_donelist
;
1979 for (i
= RCU_NEXT_SIZE
- 1; i
>= RCU_DONE_TAIL
; i
--)
1980 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1981 rdp
->nxttail
[i
] = rsp
->orphan_donetail
;
1982 rsp
->orphan_donelist
= NULL
;
1983 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
1986 /* And then adopt the callbacks that still need a grace period. */
1987 if (rsp
->orphan_nxtlist
!= NULL
) {
1988 *rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxtlist
;
1989 rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxttail
;
1990 rsp
->orphan_nxtlist
= NULL
;
1991 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
1996 * Trace the fact that this CPU is going offline.
1998 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
2000 RCU_TRACE(unsigned long mask
);
2001 RCU_TRACE(struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
));
2002 RCU_TRACE(struct rcu_node
*rnp
= rdp
->mynode
);
2004 RCU_TRACE(mask
= rdp
->grpmask
);
2005 trace_rcu_grace_period(rsp
->name
,
2006 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
2011 * The CPU has been completely removed, and some other CPU is reporting
2012 * this fact from process context. Do the remainder of the cleanup,
2013 * including orphaning the outgoing CPU's RCU callbacks, and also
2014 * adopting them. There can only be one CPU hotplug operation at a time,
2015 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
2017 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
2019 unsigned long flags
;
2021 int need_report
= 0;
2022 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2023 struct rcu_node
*rnp
= rdp
->mynode
; /* Outgoing CPU's rdp & rnp. */
2025 /* Adjust any no-longer-needed kthreads. */
2026 rcu_boost_kthread_setaffinity(rnp
, -1);
2028 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
2030 /* Exclude any attempts to start a new grace period. */
2031 mutex_lock(&rsp
->onoff_mutex
);
2032 raw_spin_lock_irqsave(&rsp
->orphan_lock
, flags
);
2034 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2035 rcu_send_cbs_to_orphanage(cpu
, rsp
, rnp
, rdp
);
2036 rcu_adopt_orphan_cbs(rsp
, flags
);
2038 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
2039 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
2041 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2042 smp_mb__after_unlock_lock();
2043 rnp
->qsmaskinit
&= ~mask
;
2044 if (rnp
->qsmaskinit
!= 0) {
2045 if (rnp
!= rdp
->mynode
)
2046 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2049 if (rnp
== rdp
->mynode
)
2050 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
2052 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2053 mask
= rnp
->grpmask
;
2055 } while (rnp
!= NULL
);
2058 * We still hold the leaf rcu_node structure lock here, and
2059 * irqs are still disabled. The reason for this subterfuge is
2060 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2061 * held leads to deadlock.
2063 raw_spin_unlock(&rsp
->orphan_lock
); /* irqs remain disabled. */
2065 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
2066 rcu_report_unblock_qs_rnp(rnp
, flags
);
2068 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2069 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
2070 rcu_report_exp_rnp(rsp
, rnp
, true);
2071 WARN_ONCE(rdp
->qlen
!= 0 || rdp
->nxtlist
!= NULL
,
2072 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2073 cpu
, rdp
->qlen
, rdp
->nxtlist
);
2074 init_callback_list(rdp
);
2075 /* Disallow further callbacks on this CPU. */
2076 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2077 mutex_unlock(&rsp
->onoff_mutex
);
2080 #else /* #ifdef CONFIG_HOTPLUG_CPU */
2082 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
2086 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
2090 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
2093 * Invoke any RCU callbacks that have made it to the end of their grace
2094 * period. Thottle as specified by rdp->blimit.
2096 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2098 unsigned long flags
;
2099 struct rcu_head
*next
, *list
, **tail
;
2100 long bl
, count
, count_lazy
;
2103 /* If no callbacks are ready, just return. */
2104 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
2105 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
2106 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
2107 need_resched(), is_idle_task(current
),
2108 rcu_is_callbacks_kthread());
2113 * Extract the list of ready callbacks, disabling to prevent
2114 * races with call_rcu() from interrupt handlers.
2116 local_irq_save(flags
);
2117 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2119 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
2120 list
= rdp
->nxtlist
;
2121 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
2122 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
2123 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
2124 for (i
= RCU_NEXT_SIZE
- 1; i
>= 0; i
--)
2125 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
2126 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
2127 local_irq_restore(flags
);
2129 /* Invoke callbacks. */
2130 count
= count_lazy
= 0;
2134 debug_rcu_head_unqueue(list
);
2135 if (__rcu_reclaim(rsp
->name
, list
))
2138 /* Stop only if limit reached and CPU has something to do. */
2139 if (++count
>= bl
&&
2141 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
2145 local_irq_save(flags
);
2146 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
2147 is_idle_task(current
),
2148 rcu_is_callbacks_kthread());
2150 /* Update count, and requeue any remaining callbacks. */
2152 *tail
= rdp
->nxtlist
;
2153 rdp
->nxtlist
= list
;
2154 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
2155 if (&rdp
->nxtlist
== rdp
->nxttail
[i
])
2156 rdp
->nxttail
[i
] = tail
;
2160 smp_mb(); /* List handling before counting for rcu_barrier(). */
2161 rdp
->qlen_lazy
-= count_lazy
;
2162 ACCESS_ONCE(rdp
->qlen
) -= count
;
2163 rdp
->n_cbs_invoked
+= count
;
2165 /* Reinstate batch limit if we have worked down the excess. */
2166 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
2167 rdp
->blimit
= blimit
;
2169 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2170 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
2171 rdp
->qlen_last_fqs_check
= 0;
2172 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2173 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
2174 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2175 WARN_ON_ONCE((rdp
->nxtlist
== NULL
) != (rdp
->qlen
== 0));
2177 local_irq_restore(flags
);
2179 /* Re-invoke RCU core processing if there are callbacks remaining. */
2180 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2185 * Check to see if this CPU is in a non-context-switch quiescent state
2186 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2187 * Also schedule RCU core processing.
2189 * This function must be called from hardirq context. It is normally
2190 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2191 * false, there is no point in invoking rcu_check_callbacks().
2193 void rcu_check_callbacks(int cpu
, int user
)
2195 trace_rcu_utilization(TPS("Start scheduler-tick"));
2196 increment_cpu_stall_ticks();
2197 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
2200 * Get here if this CPU took its interrupt from user
2201 * mode or from the idle loop, and if this is not a
2202 * nested interrupt. In this case, the CPU is in
2203 * a quiescent state, so note it.
2205 * No memory barrier is required here because both
2206 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2207 * variables that other CPUs neither access nor modify,
2208 * at least not while the corresponding CPU is online.
2214 } else if (!in_softirq()) {
2217 * Get here if this CPU did not take its interrupt from
2218 * softirq, in other words, if it is not interrupting
2219 * a rcu_bh read-side critical section. This is an _bh
2220 * critical section, so note it.
2225 rcu_preempt_check_callbacks(cpu
);
2226 if (rcu_pending(cpu
))
2228 trace_rcu_utilization(TPS("End scheduler-tick"));
2232 * Scan the leaf rcu_node structures, processing dyntick state for any that
2233 * have not yet encountered a quiescent state, using the function specified.
2234 * Also initiate boosting for any threads blocked on the root rcu_node.
2236 * The caller must have suppressed start of new grace periods.
2238 static void force_qs_rnp(struct rcu_state
*rsp
,
2239 int (*f
)(struct rcu_data
*rsp
, bool *isidle
,
2240 unsigned long *maxj
),
2241 bool *isidle
, unsigned long *maxj
)
2245 unsigned long flags
;
2247 struct rcu_node
*rnp
;
2249 rcu_for_each_leaf_node(rsp
, rnp
) {
2252 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2253 smp_mb__after_unlock_lock();
2254 if (!rcu_gp_in_progress(rsp
)) {
2255 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2258 if (rnp
->qsmask
== 0) {
2259 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
2264 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
2265 if ((rnp
->qsmask
& bit
) != 0) {
2266 if ((rnp
->qsmaskinit
& bit
) != 0)
2268 if (f(per_cpu_ptr(rsp
->rda
, cpu
), isidle
, maxj
))
2274 /* rcu_report_qs_rnp() releases rnp->lock. */
2275 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
2278 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2280 rnp
= rcu_get_root(rsp
);
2281 if (rnp
->qsmask
== 0) {
2282 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2283 smp_mb__after_unlock_lock();
2284 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
2289 * Force quiescent states on reluctant CPUs, and also detect which
2290 * CPUs are in dyntick-idle mode.
2292 static void force_quiescent_state(struct rcu_state
*rsp
)
2294 unsigned long flags
;
2296 struct rcu_node
*rnp
;
2297 struct rcu_node
*rnp_old
= NULL
;
2299 /* Funnel through hierarchy to reduce memory contention. */
2300 rnp
= per_cpu_ptr(rsp
->rda
, raw_smp_processor_id())->mynode
;
2301 for (; rnp
!= NULL
; rnp
= rnp
->parent
) {
2302 ret
= (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) ||
2303 !raw_spin_trylock(&rnp
->fqslock
);
2304 if (rnp_old
!= NULL
)
2305 raw_spin_unlock(&rnp_old
->fqslock
);
2307 ACCESS_ONCE(rsp
->n_force_qs_lh
)++;
2312 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2314 /* Reached the root of the rcu_node tree, acquire lock. */
2315 raw_spin_lock_irqsave(&rnp_old
->lock
, flags
);
2316 smp_mb__after_unlock_lock();
2317 raw_spin_unlock(&rnp_old
->fqslock
);
2318 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
2319 ACCESS_ONCE(rsp
->n_force_qs_lh
)++;
2320 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2321 return; /* Someone beat us to it. */
2323 rsp
->gp_flags
|= RCU_GP_FLAG_FQS
;
2324 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2325 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
2329 * This does the RCU core processing work for the specified rcu_state
2330 * and rcu_data structures. This may be called only from the CPU to
2331 * whom the rdp belongs.
2334 __rcu_process_callbacks(struct rcu_state
*rsp
)
2336 unsigned long flags
;
2337 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2339 WARN_ON_ONCE(rdp
->beenonline
== 0);
2341 /* Update RCU state based on any recent quiescent states. */
2342 rcu_check_quiescent_state(rsp
, rdp
);
2344 /* Does this CPU require a not-yet-started grace period? */
2345 local_irq_save(flags
);
2346 if (cpu_needs_another_gp(rsp
, rdp
)) {
2347 raw_spin_lock(&rcu_get_root(rsp
)->lock
); /* irqs disabled. */
2349 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
2351 local_irq_restore(flags
);
2354 /* If there are callbacks ready, invoke them. */
2355 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2356 invoke_rcu_callbacks(rsp
, rdp
);
2358 /* Do any needed deferred wakeups of rcuo kthreads. */
2359 do_nocb_deferred_wakeup(rdp
);
2363 * Do RCU core processing for the current CPU.
2365 static void rcu_process_callbacks(struct softirq_action
*unused
)
2367 struct rcu_state
*rsp
;
2369 if (cpu_is_offline(smp_processor_id()))
2371 trace_rcu_utilization(TPS("Start RCU core"));
2372 for_each_rcu_flavor(rsp
)
2373 __rcu_process_callbacks(rsp
);
2374 trace_rcu_utilization(TPS("End RCU core"));
2378 * Schedule RCU callback invocation. If the specified type of RCU
2379 * does not support RCU priority boosting, just do a direct call,
2380 * otherwise wake up the per-CPU kernel kthread. Note that because we
2381 * are running on the current CPU with interrupts disabled, the
2382 * rcu_cpu_kthread_task cannot disappear out from under us.
2384 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2386 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
2388 if (likely(!rsp
->boost
)) {
2389 rcu_do_batch(rsp
, rdp
);
2392 invoke_rcu_callbacks_kthread();
2395 static void invoke_rcu_core(void)
2397 if (cpu_online(smp_processor_id()))
2398 raise_softirq(RCU_SOFTIRQ
);
2402 * Handle any core-RCU processing required by a call_rcu() invocation.
2404 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
2405 struct rcu_head
*head
, unsigned long flags
)
2408 * If called from an extended quiescent state, invoke the RCU
2409 * core in order to force a re-evaluation of RCU's idleness.
2411 if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2414 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2415 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
2419 * Force the grace period if too many callbacks or too long waiting.
2420 * Enforce hysteresis, and don't invoke force_quiescent_state()
2421 * if some other CPU has recently done so. Also, don't bother
2422 * invoking force_quiescent_state() if the newly enqueued callback
2423 * is the only one waiting for a grace period to complete.
2425 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
2427 /* Are we ignoring a completed grace period? */
2428 note_gp_changes(rsp
, rdp
);
2430 /* Start a new grace period if one not already started. */
2431 if (!rcu_gp_in_progress(rsp
)) {
2432 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
2434 raw_spin_lock(&rnp_root
->lock
);
2435 smp_mb__after_unlock_lock();
2437 raw_spin_unlock(&rnp_root
->lock
);
2439 /* Give the grace period a kick. */
2440 rdp
->blimit
= LONG_MAX
;
2441 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
2442 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
2443 force_quiescent_state(rsp
);
2444 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2445 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2451 * RCU callback function to leak a callback.
2453 static void rcu_leak_callback(struct rcu_head
*rhp
)
2458 * Helper function for call_rcu() and friends. The cpu argument will
2459 * normally be -1, indicating "currently running CPU". It may specify
2460 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2461 * is expected to specify a CPU.
2464 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
2465 struct rcu_state
*rsp
, int cpu
, bool lazy
)
2467 unsigned long flags
;
2468 struct rcu_data
*rdp
;
2470 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
2471 if (debug_rcu_head_queue(head
)) {
2472 /* Probable double call_rcu(), so leak the callback. */
2473 ACCESS_ONCE(head
->func
) = rcu_leak_callback
;
2474 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
2481 * Opportunistically note grace-period endings and beginnings.
2482 * Note that we might see a beginning right after we see an
2483 * end, but never vice versa, since this CPU has to pass through
2484 * a quiescent state betweentimes.
2486 local_irq_save(flags
);
2487 rdp
= this_cpu_ptr(rsp
->rda
);
2489 /* Add the callback to our list. */
2490 if (unlikely(rdp
->nxttail
[RCU_NEXT_TAIL
] == NULL
) || cpu
!= -1) {
2494 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2495 offline
= !__call_rcu_nocb(rdp
, head
, lazy
, flags
);
2496 WARN_ON_ONCE(offline
);
2497 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2498 local_irq_restore(flags
);
2501 ACCESS_ONCE(rdp
->qlen
)++;
2505 rcu_idle_count_callbacks_posted();
2506 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2507 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
2508 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
2510 if (__is_kfree_rcu_offset((unsigned long)func
))
2511 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
2512 rdp
->qlen_lazy
, rdp
->qlen
);
2514 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
2516 /* Go handle any RCU core processing required. */
2517 __call_rcu_core(rsp
, rdp
, head
, flags
);
2518 local_irq_restore(flags
);
2522 * Queue an RCU-sched callback for invocation after a grace period.
2524 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2526 __call_rcu(head
, func
, &rcu_sched_state
, -1, 0);
2528 EXPORT_SYMBOL_GPL(call_rcu_sched
);
2531 * Queue an RCU callback for invocation after a quicker grace period.
2533 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2535 __call_rcu(head
, func
, &rcu_bh_state
, -1, 0);
2537 EXPORT_SYMBOL_GPL(call_rcu_bh
);
2540 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2541 * any blocking grace-period wait automatically implies a grace period
2542 * if there is only one CPU online at any point time during execution
2543 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2544 * occasionally incorrectly indicate that there are multiple CPUs online
2545 * when there was in fact only one the whole time, as this just adds
2546 * some overhead: RCU still operates correctly.
2548 static inline int rcu_blocking_is_gp(void)
2552 might_sleep(); /* Check for RCU read-side critical section. */
2554 ret
= num_online_cpus() <= 1;
2560 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2562 * Control will return to the caller some time after a full rcu-sched
2563 * grace period has elapsed, in other words after all currently executing
2564 * rcu-sched read-side critical sections have completed. These read-side
2565 * critical sections are delimited by rcu_read_lock_sched() and
2566 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2567 * local_irq_disable(), and so on may be used in place of
2568 * rcu_read_lock_sched().
2570 * This means that all preempt_disable code sequences, including NMI and
2571 * non-threaded hardware-interrupt handlers, in progress on entry will
2572 * have completed before this primitive returns. However, this does not
2573 * guarantee that softirq handlers will have completed, since in some
2574 * kernels, these handlers can run in process context, and can block.
2576 * Note that this guarantee implies further memory-ordering guarantees.
2577 * On systems with more than one CPU, when synchronize_sched() returns,
2578 * each CPU is guaranteed to have executed a full memory barrier since the
2579 * end of its last RCU-sched read-side critical section whose beginning
2580 * preceded the call to synchronize_sched(). In addition, each CPU having
2581 * an RCU read-side critical section that extends beyond the return from
2582 * synchronize_sched() is guaranteed to have executed a full memory barrier
2583 * after the beginning of synchronize_sched() and before the beginning of
2584 * that RCU read-side critical section. Note that these guarantees include
2585 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2586 * that are executing in the kernel.
2588 * Furthermore, if CPU A invoked synchronize_sched(), which returned
2589 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2590 * to have executed a full memory barrier during the execution of
2591 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
2592 * again only if the system has more than one CPU).
2594 * This primitive provides the guarantees made by the (now removed)
2595 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2596 * guarantees that rcu_read_lock() sections will have completed.
2597 * In "classic RCU", these two guarantees happen to be one and
2598 * the same, but can differ in realtime RCU implementations.
2600 void synchronize_sched(void)
2602 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2603 !lock_is_held(&rcu_lock_map
) &&
2604 !lock_is_held(&rcu_sched_lock_map
),
2605 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2606 if (rcu_blocking_is_gp())
2609 synchronize_sched_expedited();
2611 wait_rcu_gp(call_rcu_sched
);
2613 EXPORT_SYMBOL_GPL(synchronize_sched
);
2616 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2618 * Control will return to the caller some time after a full rcu_bh grace
2619 * period has elapsed, in other words after all currently executing rcu_bh
2620 * read-side critical sections have completed. RCU read-side critical
2621 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2622 * and may be nested.
2624 * See the description of synchronize_sched() for more detailed information
2625 * on memory ordering guarantees.
2627 void synchronize_rcu_bh(void)
2629 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2630 !lock_is_held(&rcu_lock_map
) &&
2631 !lock_is_held(&rcu_sched_lock_map
),
2632 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2633 if (rcu_blocking_is_gp())
2636 synchronize_rcu_bh_expedited();
2638 wait_rcu_gp(call_rcu_bh
);
2640 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2643 * get_state_synchronize_rcu - Snapshot current RCU state
2645 * Returns a cookie that is used by a later call to cond_synchronize_rcu()
2646 * to determine whether or not a full grace period has elapsed in the
2649 unsigned long get_state_synchronize_rcu(void)
2652 * Any prior manipulation of RCU-protected data must happen
2653 * before the load from ->gpnum.
2658 * Make sure this load happens before the purportedly
2659 * time-consuming work between get_state_synchronize_rcu()
2660 * and cond_synchronize_rcu().
2662 return smp_load_acquire(&rcu_state
->gpnum
);
2664 EXPORT_SYMBOL_GPL(get_state_synchronize_rcu
);
2667 * cond_synchronize_rcu - Conditionally wait for an RCU grace period
2669 * @oldstate: return value from earlier call to get_state_synchronize_rcu()
2671 * If a full RCU grace period has elapsed since the earlier call to
2672 * get_state_synchronize_rcu(), just return. Otherwise, invoke
2673 * synchronize_rcu() to wait for a full grace period.
2675 * Yes, this function does not take counter wrap into account. But
2676 * counter wrap is harmless. If the counter wraps, we have waited for
2677 * more than 2 billion grace periods (and way more on a 64-bit system!),
2678 * so waiting for one additional grace period should be just fine.
2680 void cond_synchronize_rcu(unsigned long oldstate
)
2682 unsigned long newstate
;
2685 * Ensure that this load happens before any RCU-destructive
2686 * actions the caller might carry out after we return.
2688 newstate
= smp_load_acquire(&rcu_state
->completed
);
2689 if (ULONG_CMP_GE(oldstate
, newstate
))
2692 EXPORT_SYMBOL_GPL(cond_synchronize_rcu
);
2694 static int synchronize_sched_expedited_cpu_stop(void *data
)
2697 * There must be a full memory barrier on each affected CPU
2698 * between the time that try_stop_cpus() is called and the
2699 * time that it returns.
2701 * In the current initial implementation of cpu_stop, the
2702 * above condition is already met when the control reaches
2703 * this point and the following smp_mb() is not strictly
2704 * necessary. Do smp_mb() anyway for documentation and
2705 * robustness against future implementation changes.
2707 smp_mb(); /* See above comment block. */
2712 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2714 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2715 * approach to force the grace period to end quickly. This consumes
2716 * significant time on all CPUs and is unfriendly to real-time workloads,
2717 * so is thus not recommended for any sort of common-case code. In fact,
2718 * if you are using synchronize_sched_expedited() in a loop, please
2719 * restructure your code to batch your updates, and then use a single
2720 * synchronize_sched() instead.
2722 * Note that it is illegal to call this function while holding any lock
2723 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2724 * to call this function from a CPU-hotplug notifier. Failing to observe
2725 * these restriction will result in deadlock.
2727 * This implementation can be thought of as an application of ticket
2728 * locking to RCU, with sync_sched_expedited_started and
2729 * sync_sched_expedited_done taking on the roles of the halves
2730 * of the ticket-lock word. Each task atomically increments
2731 * sync_sched_expedited_started upon entry, snapshotting the old value,
2732 * then attempts to stop all the CPUs. If this succeeds, then each
2733 * CPU will have executed a context switch, resulting in an RCU-sched
2734 * grace period. We are then done, so we use atomic_cmpxchg() to
2735 * update sync_sched_expedited_done to match our snapshot -- but
2736 * only if someone else has not already advanced past our snapshot.
2738 * On the other hand, if try_stop_cpus() fails, we check the value
2739 * of sync_sched_expedited_done. If it has advanced past our
2740 * initial snapshot, then someone else must have forced a grace period
2741 * some time after we took our snapshot. In this case, our work is
2742 * done for us, and we can simply return. Otherwise, we try again,
2743 * but keep our initial snapshot for purposes of checking for someone
2744 * doing our work for us.
2746 * If we fail too many times in a row, we fall back to synchronize_sched().
2748 void synchronize_sched_expedited(void)
2750 long firstsnap
, s
, snap
;
2752 struct rcu_state
*rsp
= &rcu_sched_state
;
2755 * If we are in danger of counter wrap, just do synchronize_sched().
2756 * By allowing sync_sched_expedited_started to advance no more than
2757 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
2758 * that more than 3.5 billion CPUs would be required to force a
2759 * counter wrap on a 32-bit system. Quite a few more CPUs would of
2760 * course be required on a 64-bit system.
2762 if (ULONG_CMP_GE((ulong
)atomic_long_read(&rsp
->expedited_start
),
2763 (ulong
)atomic_long_read(&rsp
->expedited_done
) +
2765 synchronize_sched();
2766 atomic_long_inc(&rsp
->expedited_wrap
);
2771 * Take a ticket. Note that atomic_inc_return() implies a
2772 * full memory barrier.
2774 snap
= atomic_long_inc_return(&rsp
->expedited_start
);
2777 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2780 * Each pass through the following loop attempts to force a
2781 * context switch on each CPU.
2783 while (try_stop_cpus(cpu_online_mask
,
2784 synchronize_sched_expedited_cpu_stop
,
2787 atomic_long_inc(&rsp
->expedited_tryfail
);
2789 /* Check to see if someone else did our work for us. */
2790 s
= atomic_long_read(&rsp
->expedited_done
);
2791 if (ULONG_CMP_GE((ulong
)s
, (ulong
)firstsnap
)) {
2792 /* ensure test happens before caller kfree */
2793 smp_mb__before_atomic_inc(); /* ^^^ */
2794 atomic_long_inc(&rsp
->expedited_workdone1
);
2798 /* No joy, try again later. Or just synchronize_sched(). */
2799 if (trycount
++ < 10) {
2800 udelay(trycount
* num_online_cpus());
2802 wait_rcu_gp(call_rcu_sched
);
2803 atomic_long_inc(&rsp
->expedited_normal
);
2807 /* Recheck to see if someone else did our work for us. */
2808 s
= atomic_long_read(&rsp
->expedited_done
);
2809 if (ULONG_CMP_GE((ulong
)s
, (ulong
)firstsnap
)) {
2810 /* ensure test happens before caller kfree */
2811 smp_mb__before_atomic_inc(); /* ^^^ */
2812 atomic_long_inc(&rsp
->expedited_workdone2
);
2817 * Refetching sync_sched_expedited_started allows later
2818 * callers to piggyback on our grace period. We retry
2819 * after they started, so our grace period works for them,
2820 * and they started after our first try, so their grace
2821 * period works for us.
2824 snap
= atomic_long_read(&rsp
->expedited_start
);
2825 smp_mb(); /* ensure read is before try_stop_cpus(). */
2827 atomic_long_inc(&rsp
->expedited_stoppedcpus
);
2830 * Everyone up to our most recent fetch is covered by our grace
2831 * period. Update the counter, but only if our work is still
2832 * relevant -- which it won't be if someone who started later
2833 * than we did already did their update.
2836 atomic_long_inc(&rsp
->expedited_done_tries
);
2837 s
= atomic_long_read(&rsp
->expedited_done
);
2838 if (ULONG_CMP_GE((ulong
)s
, (ulong
)snap
)) {
2839 /* ensure test happens before caller kfree */
2840 smp_mb__before_atomic_inc(); /* ^^^ */
2841 atomic_long_inc(&rsp
->expedited_done_lost
);
2844 } while (atomic_long_cmpxchg(&rsp
->expedited_done
, s
, snap
) != s
);
2845 atomic_long_inc(&rsp
->expedited_done_exit
);
2849 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2852 * Check to see if there is any immediate RCU-related work to be done
2853 * by the current CPU, for the specified type of RCU, returning 1 if so.
2854 * The checks are in order of increasing expense: checks that can be
2855 * carried out against CPU-local state are performed first. However,
2856 * we must check for CPU stalls first, else we might not get a chance.
2858 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2860 struct rcu_node
*rnp
= rdp
->mynode
;
2862 rdp
->n_rcu_pending
++;
2864 /* Check for CPU stalls, if enabled. */
2865 check_cpu_stall(rsp
, rdp
);
2867 /* Is this CPU a NO_HZ_FULL CPU that should ignore RCU? */
2868 if (rcu_nohz_full_cpu(rsp
))
2871 /* Is the RCU core waiting for a quiescent state from this CPU? */
2872 if (rcu_scheduler_fully_active
&&
2873 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2874 rdp
->n_rp_qs_pending
++;
2875 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2876 rdp
->n_rp_report_qs
++;
2880 /* Does this CPU have callbacks ready to invoke? */
2881 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2882 rdp
->n_rp_cb_ready
++;
2886 /* Has RCU gone idle with this CPU needing another grace period? */
2887 if (cpu_needs_another_gp(rsp
, rdp
)) {
2888 rdp
->n_rp_cpu_needs_gp
++;
2892 /* Has another RCU grace period completed? */
2893 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2894 rdp
->n_rp_gp_completed
++;
2898 /* Has a new RCU grace period started? */
2899 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2900 rdp
->n_rp_gp_started
++;
2904 /* Does this CPU need a deferred NOCB wakeup? */
2905 if (rcu_nocb_need_deferred_wakeup(rdp
)) {
2906 rdp
->n_rp_nocb_defer_wakeup
++;
2911 rdp
->n_rp_need_nothing
++;
2916 * Check to see if there is any immediate RCU-related work to be done
2917 * by the current CPU, returning 1 if so. This function is part of the
2918 * RCU implementation; it is -not- an exported member of the RCU API.
2920 static int rcu_pending(int cpu
)
2922 struct rcu_state
*rsp
;
2924 for_each_rcu_flavor(rsp
)
2925 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
2931 * Return true if the specified CPU has any callback. If all_lazy is
2932 * non-NULL, store an indication of whether all callbacks are lazy.
2933 * (If there are no callbacks, all of them are deemed to be lazy.)
2935 static int __maybe_unused
rcu_cpu_has_callbacks(int cpu
, bool *all_lazy
)
2939 struct rcu_data
*rdp
;
2940 struct rcu_state
*rsp
;
2942 for_each_rcu_flavor(rsp
) {
2943 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2947 if (rdp
->qlen
!= rdp
->qlen_lazy
|| !all_lazy
) {
2958 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2959 * the compiler is expected to optimize this away.
2961 static void _rcu_barrier_trace(struct rcu_state
*rsp
, const char *s
,
2962 int cpu
, unsigned long done
)
2964 trace_rcu_barrier(rsp
->name
, s
, cpu
,
2965 atomic_read(&rsp
->barrier_cpu_count
), done
);
2969 * RCU callback function for _rcu_barrier(). If we are last, wake
2970 * up the task executing _rcu_barrier().
2972 static void rcu_barrier_callback(struct rcu_head
*rhp
)
2974 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
2975 struct rcu_state
*rsp
= rdp
->rsp
;
2977 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
2978 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
2979 complete(&rsp
->barrier_completion
);
2981 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
2986 * Called with preemption disabled, and from cross-cpu IRQ context.
2988 static void rcu_barrier_func(void *type
)
2990 struct rcu_state
*rsp
= type
;
2991 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2993 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
2994 atomic_inc(&rsp
->barrier_cpu_count
);
2995 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
2999 * Orchestrate the specified type of RCU barrier, waiting for all
3000 * RCU callbacks of the specified type to complete.
3002 static void _rcu_barrier(struct rcu_state
*rsp
)
3005 struct rcu_data
*rdp
;
3006 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
3007 unsigned long snap_done
;
3009 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
3011 /* Take mutex to serialize concurrent rcu_barrier() requests. */
3012 mutex_lock(&rsp
->barrier_mutex
);
3015 * Ensure that all prior references, including to ->n_barrier_done,
3016 * are ordered before the _rcu_barrier() machinery.
3018 smp_mb(); /* See above block comment. */
3021 * Recheck ->n_barrier_done to see if others did our work for us.
3022 * This means checking ->n_barrier_done for an even-to-odd-to-even
3023 * transition. The "if" expression below therefore rounds the old
3024 * value up to the next even number and adds two before comparing.
3026 snap_done
= rsp
->n_barrier_done
;
3027 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
3030 * If the value in snap is odd, we needed to wait for the current
3031 * rcu_barrier() to complete, then wait for the next one, in other
3032 * words, we need the value of snap_done to be three larger than
3033 * the value of snap. On the other hand, if the value in snap is
3034 * even, we only had to wait for the next rcu_barrier() to complete,
3035 * in other words, we need the value of snap_done to be only two
3036 * greater than the value of snap. The "(snap + 3) & ~0x1" computes
3037 * this for us (thank you, Linus!).
3039 if (ULONG_CMP_GE(snap_done
, (snap
+ 3) & ~0x1)) {
3040 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
3041 smp_mb(); /* caller's subsequent code after above check. */
3042 mutex_unlock(&rsp
->barrier_mutex
);
3047 * Increment ->n_barrier_done to avoid duplicate work. Use
3048 * ACCESS_ONCE() to prevent the compiler from speculating
3049 * the increment to precede the early-exit check.
3051 ACCESS_ONCE(rsp
->n_barrier_done
)++;
3052 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
3053 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
3054 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
3057 * Initialize the count to one rather than to zero in order to
3058 * avoid a too-soon return to zero in case of a short grace period
3059 * (or preemption of this task). Exclude CPU-hotplug operations
3060 * to ensure that no offline CPU has callbacks queued.
3062 init_completion(&rsp
->barrier_completion
);
3063 atomic_set(&rsp
->barrier_cpu_count
, 1);
3067 * Force each CPU with callbacks to register a new callback.
3068 * When that callback is invoked, we will know that all of the
3069 * corresponding CPU's preceding callbacks have been invoked.
3071 for_each_possible_cpu(cpu
) {
3072 if (!cpu_online(cpu
) && !rcu_is_nocb_cpu(cpu
))
3074 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3075 if (rcu_is_nocb_cpu(cpu
)) {
3076 _rcu_barrier_trace(rsp
, "OnlineNoCB", cpu
,
3077 rsp
->n_barrier_done
);
3078 atomic_inc(&rsp
->barrier_cpu_count
);
3079 __call_rcu(&rdp
->barrier_head
, rcu_barrier_callback
,
3081 } else if (ACCESS_ONCE(rdp
->qlen
)) {
3082 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
3083 rsp
->n_barrier_done
);
3084 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
3086 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
3087 rsp
->n_barrier_done
);
3093 * Now that we have an rcu_barrier_callback() callback on each
3094 * CPU, and thus each counted, remove the initial count.
3096 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
3097 complete(&rsp
->barrier_completion
);
3099 /* Increment ->n_barrier_done to prevent duplicate work. */
3100 smp_mb(); /* Keep increment after above mechanism. */
3101 ACCESS_ONCE(rsp
->n_barrier_done
)++;
3102 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
3103 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
3104 smp_mb(); /* Keep increment before caller's subsequent code. */
3106 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3107 wait_for_completion(&rsp
->barrier_completion
);
3109 /* Other rcu_barrier() invocations can now safely proceed. */
3110 mutex_unlock(&rsp
->barrier_mutex
);
3114 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3116 void rcu_barrier_bh(void)
3118 _rcu_barrier(&rcu_bh_state
);
3120 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
3123 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3125 void rcu_barrier_sched(void)
3127 _rcu_barrier(&rcu_sched_state
);
3129 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
3132 * Do boot-time initialization of a CPU's per-CPU RCU data.
3135 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
3137 unsigned long flags
;
3138 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3139 struct rcu_node
*rnp
= rcu_get_root(rsp
);
3141 /* Set up local state, ensuring consistent view of global state. */
3142 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3143 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
3144 init_callback_list(rdp
);
3146 ACCESS_ONCE(rdp
->qlen
) = 0;
3147 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
3148 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
3149 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
3152 rcu_boot_init_nocb_percpu_data(rdp
);
3153 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
3157 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3158 * offline event can be happening at a given time. Note also that we
3159 * can accept some slop in the rsp->completed access due to the fact
3160 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3163 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
3165 unsigned long flags
;
3167 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3168 struct rcu_node
*rnp
= rcu_get_root(rsp
);
3170 /* Exclude new grace periods. */
3171 mutex_lock(&rsp
->onoff_mutex
);
3173 /* Set up local state, ensuring consistent view of global state. */
3174 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3175 rdp
->beenonline
= 1; /* We have now been online. */
3176 rdp
->preemptible
= preemptible
;
3177 rdp
->qlen_last_fqs_check
= 0;
3178 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
3179 rdp
->blimit
= blimit
;
3180 init_callback_list(rdp
); /* Re-enable callbacks on this CPU. */
3181 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
3182 rcu_sysidle_init_percpu_data(rdp
->dynticks
);
3183 atomic_set(&rdp
->dynticks
->dynticks
,
3184 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
3185 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
3187 /* Add CPU to rcu_node bitmasks. */
3189 mask
= rdp
->grpmask
;
3191 /* Exclude any attempts to start a new GP on small systems. */
3192 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
3193 rnp
->qsmaskinit
|= mask
;
3194 mask
= rnp
->grpmask
;
3195 if (rnp
== rdp
->mynode
) {
3197 * If there is a grace period in progress, we will
3198 * set up to wait for it next time we run the
3201 rdp
->gpnum
= rnp
->completed
;
3202 rdp
->completed
= rnp
->completed
;
3203 rdp
->passed_quiesce
= 0;
3204 rdp
->qs_pending
= 0;
3205 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpuonl"));
3207 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
3209 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
3210 local_irq_restore(flags
);
3212 mutex_unlock(&rsp
->onoff_mutex
);
3215 static void rcu_prepare_cpu(int cpu
)
3217 struct rcu_state
*rsp
;
3219 for_each_rcu_flavor(rsp
)
3220 rcu_init_percpu_data(cpu
, rsp
,
3221 strcmp(rsp
->name
, "rcu_preempt") == 0);
3225 * Handle CPU online/offline notification events.
3227 static int rcu_cpu_notify(struct notifier_block
*self
,
3228 unsigned long action
, void *hcpu
)
3230 long cpu
= (long)hcpu
;
3231 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
3232 struct rcu_node
*rnp
= rdp
->mynode
;
3233 struct rcu_state
*rsp
;
3235 trace_rcu_utilization(TPS("Start CPU hotplug"));
3237 case CPU_UP_PREPARE
:
3238 case CPU_UP_PREPARE_FROZEN
:
3239 rcu_prepare_cpu(cpu
);
3240 rcu_prepare_kthreads(cpu
);
3243 case CPU_DOWN_FAILED
:
3244 rcu_boost_kthread_setaffinity(rnp
, -1);
3246 case CPU_DOWN_PREPARE
:
3247 rcu_boost_kthread_setaffinity(rnp
, cpu
);
3250 case CPU_DYING_FROZEN
:
3251 for_each_rcu_flavor(rsp
)
3252 rcu_cleanup_dying_cpu(rsp
);
3255 case CPU_DEAD_FROZEN
:
3256 case CPU_UP_CANCELED
:
3257 case CPU_UP_CANCELED_FROZEN
:
3258 for_each_rcu_flavor(rsp
)
3259 rcu_cleanup_dead_cpu(cpu
, rsp
);
3264 trace_rcu_utilization(TPS("End CPU hotplug"));
3268 static int rcu_pm_notify(struct notifier_block
*self
,
3269 unsigned long action
, void *hcpu
)
3272 case PM_HIBERNATION_PREPARE
:
3273 case PM_SUSPEND_PREPARE
:
3274 if (nr_cpu_ids
<= 256) /* Expediting bad for large systems. */
3277 case PM_POST_HIBERNATION
:
3278 case PM_POST_SUSPEND
:
3288 * Spawn the kthread that handles this RCU flavor's grace periods.
3290 static int __init
rcu_spawn_gp_kthread(void)
3292 unsigned long flags
;
3293 struct rcu_node
*rnp
;
3294 struct rcu_state
*rsp
;
3295 struct task_struct
*t
;
3297 for_each_rcu_flavor(rsp
) {
3298 t
= kthread_run(rcu_gp_kthread
, rsp
, "%s", rsp
->name
);
3300 rnp
= rcu_get_root(rsp
);
3301 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3302 rsp
->gp_kthread
= t
;
3303 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
3304 rcu_spawn_nocb_kthreads(rsp
);
3308 early_initcall(rcu_spawn_gp_kthread
);
3311 * This function is invoked towards the end of the scheduler's initialization
3312 * process. Before this is called, the idle task might contain
3313 * RCU read-side critical sections (during which time, this idle
3314 * task is booting the system). After this function is called, the
3315 * idle tasks are prohibited from containing RCU read-side critical
3316 * sections. This function also enables RCU lockdep checking.
3318 void rcu_scheduler_starting(void)
3320 WARN_ON(num_online_cpus() != 1);
3321 WARN_ON(nr_context_switches() > 0);
3322 rcu_scheduler_active
= 1;
3326 * Compute the per-level fanout, either using the exact fanout specified
3327 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
3329 #ifdef CONFIG_RCU_FANOUT_EXACT
3330 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
3334 rsp
->levelspread
[rcu_num_lvls
- 1] = rcu_fanout_leaf
;
3335 for (i
= rcu_num_lvls
- 2; i
>= 0; i
--)
3336 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
3338 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
3339 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
3346 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
3347 ccur
= rsp
->levelcnt
[i
];
3348 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
3352 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
3355 * Helper function for rcu_init() that initializes one rcu_state structure.
3357 static void __init
rcu_init_one(struct rcu_state
*rsp
,
3358 struct rcu_data __percpu
*rda
)
3360 static char *buf
[] = { "rcu_node_0",
3363 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
3364 static char *fqs
[] = { "rcu_node_fqs_0",
3367 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
3371 struct rcu_node
*rnp
;
3373 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
3375 /* Silence gcc 4.8 warning about array index out of range. */
3376 if (rcu_num_lvls
> RCU_NUM_LVLS
)
3377 panic("rcu_init_one: rcu_num_lvls overflow");
3379 /* Initialize the level-tracking arrays. */
3381 for (i
= 0; i
< rcu_num_lvls
; i
++)
3382 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
3383 for (i
= 1; i
< rcu_num_lvls
; i
++)
3384 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
3385 rcu_init_levelspread(rsp
);
3387 /* Initialize the elements themselves, starting from the leaves. */
3389 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
3390 cpustride
*= rsp
->levelspread
[i
];
3391 rnp
= rsp
->level
[i
];
3392 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
3393 raw_spin_lock_init(&rnp
->lock
);
3394 lockdep_set_class_and_name(&rnp
->lock
,
3395 &rcu_node_class
[i
], buf
[i
]);
3396 raw_spin_lock_init(&rnp
->fqslock
);
3397 lockdep_set_class_and_name(&rnp
->fqslock
,
3398 &rcu_fqs_class
[i
], fqs
[i
]);
3399 rnp
->gpnum
= rsp
->gpnum
;
3400 rnp
->completed
= rsp
->completed
;
3402 rnp
->qsmaskinit
= 0;
3403 rnp
->grplo
= j
* cpustride
;
3404 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
3405 if (rnp
->grphi
>= NR_CPUS
)
3406 rnp
->grphi
= NR_CPUS
- 1;
3412 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
3413 rnp
->grpmask
= 1UL << rnp
->grpnum
;
3414 rnp
->parent
= rsp
->level
[i
- 1] +
3415 j
/ rsp
->levelspread
[i
- 1];
3418 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
3419 rcu_init_one_nocb(rnp
);
3424 init_waitqueue_head(&rsp
->gp_wq
);
3425 init_irq_work(&rsp
->wakeup_work
, rsp_wakeup
);
3426 rnp
= rsp
->level
[rcu_num_lvls
- 1];
3427 for_each_possible_cpu(i
) {
3428 while (i
> rnp
->grphi
)
3430 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
3431 rcu_boot_init_percpu_data(i
, rsp
);
3433 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
3437 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3438 * replace the definitions in tree.h because those are needed to size
3439 * the ->node array in the rcu_state structure.
3441 static void __init
rcu_init_geometry(void)
3447 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
3450 * Initialize any unspecified boot parameters.
3451 * The default values of jiffies_till_first_fqs and
3452 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3453 * value, which is a function of HZ, then adding one for each
3454 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3456 d
= RCU_JIFFIES_TILL_FORCE_QS
+ nr_cpu_ids
/ RCU_JIFFIES_FQS_DIV
;
3457 if (jiffies_till_first_fqs
== ULONG_MAX
)
3458 jiffies_till_first_fqs
= d
;
3459 if (jiffies_till_next_fqs
== ULONG_MAX
)
3460 jiffies_till_next_fqs
= d
;
3462 /* If the compile-time values are accurate, just leave. */
3463 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
&&
3464 nr_cpu_ids
== NR_CPUS
)
3466 pr_info("RCU: Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%d\n",
3467 rcu_fanout_leaf
, nr_cpu_ids
);
3470 * Compute number of nodes that can be handled an rcu_node tree
3471 * with the given number of levels. Setting rcu_capacity[0] makes
3472 * some of the arithmetic easier.
3474 rcu_capacity
[0] = 1;
3475 rcu_capacity
[1] = rcu_fanout_leaf
;
3476 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
3477 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
3480 * The boot-time rcu_fanout_leaf parameter is only permitted
3481 * to increase the leaf-level fanout, not decrease it. Of course,
3482 * the leaf-level fanout cannot exceed the number of bits in
3483 * the rcu_node masks. Finally, the tree must be able to accommodate
3484 * the configured number of CPUs. Complain and fall back to the
3485 * compile-time values if these limits are exceeded.
3487 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
3488 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
3489 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
3494 /* Calculate the number of rcu_nodes at each level of the tree. */
3495 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
3496 if (n
<= rcu_capacity
[i
]) {
3497 for (j
= 0; j
<= i
; j
++)
3499 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
3501 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
3506 /* Calculate the total number of rcu_node structures. */
3508 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
3509 rcu_num_nodes
+= num_rcu_lvl
[i
];
3513 void __init
rcu_init(void)
3517 rcu_bootup_announce();
3518 rcu_init_geometry();
3519 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
3520 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
3521 __rcu_init_preempt();
3522 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
3525 * We don't need protection against CPU-hotplug here because
3526 * this is called early in boot, before either interrupts
3527 * or the scheduler are operational.
3529 cpu_notifier(rcu_cpu_notify
, 0);
3530 pm_notifier(rcu_pm_notify
, 0);
3531 for_each_online_cpu(cpu
)
3532 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
3535 #include "tree_plugin.h"