2 * Read-Copy Update mechanism for mutual exclusion
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
18 * Copyright IBM Corporation, 2008
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 * Paul E. McKenney <paulmck@linux.vnet.ibm.com> Hierarchical version
24 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
25 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
27 * For detailed explanation of Read-Copy Update mechanism see -
30 #include <linux/types.h>
31 #include <linux/kernel.h>
32 #include <linux/init.h>
33 #include <linux/spinlock.h>
34 #include <linux/smp.h>
35 #include <linux/rcupdate.h>
36 #include <linux/interrupt.h>
37 #include <linux/sched.h>
38 #include <linux/nmi.h>
39 #include <linux/atomic.h>
40 #include <linux/bitops.h>
41 #include <linux/export.h>
42 #include <linux/completion.h>
43 #include <linux/moduleparam.h>
44 #include <linux/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>
61 #include <trace/events/rcu.h>
65 MODULE_ALIAS("rcutree");
66 #ifdef MODULE_PARAM_PREFIX
67 #undef MODULE_PARAM_PREFIX
69 #define MODULE_PARAM_PREFIX "rcutree."
71 /* Data structures. */
73 static struct lock_class_key rcu_node_class
[RCU_NUM_LVLS
];
74 static struct lock_class_key rcu_fqs_class
[RCU_NUM_LVLS
];
77 * In order to export the rcu_state name to the tracing tools, it
78 * needs to be added in the __tracepoint_string section.
79 * This requires defining a separate variable tp_<sname>_varname
80 * that points to the string being used, and this will allow
81 * the tracing userspace tools to be able to decipher the string
82 * address to the matching string.
84 #define RCU_STATE_INITIALIZER(sname, sabbr, cr) \
85 static char sname##_varname[] = #sname; \
86 static const char *tp_##sname##_varname __used __tracepoint_string = sname##_varname; \
87 struct rcu_state sname##_state = { \
88 .level = { &sname##_state.node[0] }, \
90 .fqs_state = RCU_GP_IDLE, \
91 .gpnum = 0UL - 300UL, \
92 .completed = 0UL - 300UL, \
93 .orphan_lock = __RAW_SPIN_LOCK_UNLOCKED(&sname##_state.orphan_lock), \
94 .orphan_nxttail = &sname##_state.orphan_nxtlist, \
95 .orphan_donetail = &sname##_state.orphan_donelist, \
96 .barrier_mutex = __MUTEX_INITIALIZER(sname##_state.barrier_mutex), \
97 .onoff_mutex = __MUTEX_INITIALIZER(sname##_state.onoff_mutex), \
98 .name = sname##_varname, \
101 DEFINE_PER_CPU(struct rcu_data, sname##_data)
103 RCU_STATE_INITIALIZER(rcu_sched
, 's', call_rcu_sched
);
104 RCU_STATE_INITIALIZER(rcu_bh
, 'b', call_rcu_bh
);
106 static struct rcu_state
*rcu_state
;
107 LIST_HEAD(rcu_struct_flavors
);
109 /* Increase (but not decrease) the CONFIG_RCU_FANOUT_LEAF at boot time. */
110 static int rcu_fanout_leaf
= CONFIG_RCU_FANOUT_LEAF
;
111 module_param(rcu_fanout_leaf
, int, 0444);
112 int rcu_num_lvls __read_mostly
= RCU_NUM_LVLS
;
113 static int num_rcu_lvl
[] = { /* Number of rcu_nodes at specified level. */
120 int rcu_num_nodes __read_mostly
= NUM_RCU_NODES
; /* Total # rcu_nodes in use. */
123 * The rcu_scheduler_active variable transitions from zero to one just
124 * before the first task is spawned. So when this variable is zero, RCU
125 * can assume that there is but one task, allowing RCU to (for example)
126 * optimize synchronize_sched() to a simple barrier(). When this variable
127 * is one, RCU must actually do all the hard work required to detect real
128 * grace periods. This variable is also used to suppress boot-time false
129 * positives from lockdep-RCU error checking.
131 int rcu_scheduler_active __read_mostly
;
132 EXPORT_SYMBOL_GPL(rcu_scheduler_active
);
135 * The rcu_scheduler_fully_active variable transitions from zero to one
136 * during the early_initcall() processing, which is after the scheduler
137 * is capable of creating new tasks. So RCU processing (for example,
138 * creating tasks for RCU priority boosting) must be delayed until after
139 * rcu_scheduler_fully_active transitions from zero to one. We also
140 * currently delay invocation of any RCU callbacks until after this point.
142 * It might later prove better for people registering RCU callbacks during
143 * early boot to take responsibility for these callbacks, but one step at
146 static int rcu_scheduler_fully_active __read_mostly
;
148 #ifdef CONFIG_RCU_BOOST
151 * Control variables for per-CPU and per-rcu_node kthreads. These
152 * handle all flavors of RCU.
154 static DEFINE_PER_CPU(struct task_struct
*, rcu_cpu_kthread_task
);
155 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_status
);
156 DEFINE_PER_CPU(unsigned int, rcu_cpu_kthread_loops
);
157 DEFINE_PER_CPU(char, rcu_cpu_has_work
);
159 #endif /* #ifdef CONFIG_RCU_BOOST */
161 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
);
162 static void invoke_rcu_core(void);
163 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
);
166 * Track the rcutorture test sequence number and the update version
167 * number within a given test. The rcutorture_testseq is incremented
168 * on every rcutorture module load and unload, so has an odd value
169 * when a test is running. The rcutorture_vernum is set to zero
170 * when rcutorture starts and is incremented on each rcutorture update.
171 * These variables enable correlating rcutorture output with the
172 * RCU tracing information.
174 unsigned long rcutorture_testseq
;
175 unsigned long rcutorture_vernum
;
178 * Return true if an RCU grace period is in progress. The ACCESS_ONCE()s
179 * permit this function to be invoked without holding the root rcu_node
180 * structure's ->lock, but of course results can be subject to change.
182 static int rcu_gp_in_progress(struct rcu_state
*rsp
)
184 return ACCESS_ONCE(rsp
->completed
) != ACCESS_ONCE(rsp
->gpnum
);
188 * Note a quiescent state. Because we do not need to know
189 * how many quiescent states passed, just if there was at least
190 * one since the start of the grace period, this just sets a flag.
191 * The caller must have disabled preemption.
193 void rcu_sched_qs(int cpu
)
195 struct rcu_data
*rdp
= &per_cpu(rcu_sched_data
, cpu
);
197 if (rdp
->passed_quiesce
== 0)
198 trace_rcu_grace_period(TPS("rcu_sched"), rdp
->gpnum
, TPS("cpuqs"));
199 rdp
->passed_quiesce
= 1;
202 void rcu_bh_qs(int cpu
)
204 struct rcu_data
*rdp
= &per_cpu(rcu_bh_data
, cpu
);
206 if (rdp
->passed_quiesce
== 0)
207 trace_rcu_grace_period(TPS("rcu_bh"), rdp
->gpnum
, TPS("cpuqs"));
208 rdp
->passed_quiesce
= 1;
212 * Note a context switch. This is a quiescent state for RCU-sched,
213 * and requires special handling for preemptible RCU.
214 * The caller must have disabled preemption.
216 void rcu_note_context_switch(int cpu
)
218 trace_rcu_utilization(TPS("Start context switch"));
220 rcu_preempt_note_context_switch(cpu
);
221 trace_rcu_utilization(TPS("End context switch"));
223 EXPORT_SYMBOL_GPL(rcu_note_context_switch
);
225 static DEFINE_PER_CPU(struct rcu_dynticks
, rcu_dynticks
) = {
226 .dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
,
227 .dynticks
= ATOMIC_INIT(1),
228 #ifdef CONFIG_NO_HZ_FULL_SYSIDLE
229 .dynticks_idle_nesting
= DYNTICK_TASK_NEST_VALUE
,
230 .dynticks_idle
= ATOMIC_INIT(1),
231 #endif /* #ifdef CONFIG_NO_HZ_FULL_SYSIDLE */
234 static long blimit
= 10; /* Maximum callbacks per rcu_do_batch. */
235 static long qhimark
= 10000; /* If this many pending, ignore blimit. */
236 static long qlowmark
= 100; /* Once only this many pending, use blimit. */
238 module_param(blimit
, long, 0444);
239 module_param(qhimark
, long, 0444);
240 module_param(qlowmark
, long, 0444);
242 static ulong jiffies_till_first_fqs
= ULONG_MAX
;
243 static ulong jiffies_till_next_fqs
= ULONG_MAX
;
245 module_param(jiffies_till_first_fqs
, ulong
, 0644);
246 module_param(jiffies_till_next_fqs
, ulong
, 0644);
248 static void rcu_start_gp_advanced(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
249 struct rcu_data
*rdp
);
250 static void force_qs_rnp(struct rcu_state
*rsp
,
251 int (*f
)(struct rcu_data
*rsp
, bool *isidle
,
252 unsigned long *maxj
),
253 bool *isidle
, unsigned long *maxj
);
254 static void force_quiescent_state(struct rcu_state
*rsp
);
255 static int rcu_pending(int cpu
);
258 * Return the number of RCU-sched batches processed thus far for debug & stats.
260 long rcu_batches_completed_sched(void)
262 return rcu_sched_state
.completed
;
264 EXPORT_SYMBOL_GPL(rcu_batches_completed_sched
);
267 * Return the number of RCU BH batches processed thus far for debug & stats.
269 long rcu_batches_completed_bh(void)
271 return rcu_bh_state
.completed
;
273 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh
);
276 * Force a quiescent state for RCU BH.
278 void rcu_bh_force_quiescent_state(void)
280 force_quiescent_state(&rcu_bh_state
);
282 EXPORT_SYMBOL_GPL(rcu_bh_force_quiescent_state
);
285 * Record the number of times rcutorture tests have been initiated and
286 * terminated. This information allows the debugfs tracing stats to be
287 * correlated to the rcutorture messages, even when the rcutorture module
288 * is being repeatedly loaded and unloaded. In other words, we cannot
289 * store this state in rcutorture itself.
291 void rcutorture_record_test_transition(void)
293 rcutorture_testseq
++;
294 rcutorture_vernum
= 0;
296 EXPORT_SYMBOL_GPL(rcutorture_record_test_transition
);
299 * Record the number of writer passes through the current rcutorture test.
300 * This is also used to correlate debugfs tracing stats with the rcutorture
303 void rcutorture_record_progress(unsigned long vernum
)
307 EXPORT_SYMBOL_GPL(rcutorture_record_progress
);
310 * Force a quiescent state for RCU-sched.
312 void rcu_sched_force_quiescent_state(void)
314 force_quiescent_state(&rcu_sched_state
);
316 EXPORT_SYMBOL_GPL(rcu_sched_force_quiescent_state
);
319 * Does the CPU have callbacks ready to be invoked?
322 cpu_has_callbacks_ready_to_invoke(struct rcu_data
*rdp
)
324 return &rdp
->nxtlist
!= rdp
->nxttail
[RCU_DONE_TAIL
] &&
325 rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
;
329 * Does the current CPU require a not-yet-started grace period?
330 * The caller must have disabled interrupts to prevent races with
331 * normal callback registry.
334 cpu_needs_another_gp(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
338 if (rcu_gp_in_progress(rsp
))
339 return 0; /* No, a grace period is already in progress. */
340 if (rcu_nocb_needs_gp(rsp
))
341 return 1; /* Yes, a no-CBs CPU needs one. */
342 if (!rdp
->nxttail
[RCU_NEXT_TAIL
])
343 return 0; /* No, this is a no-CBs (or offline) CPU. */
344 if (*rdp
->nxttail
[RCU_NEXT_READY_TAIL
])
345 return 1; /* Yes, this CPU has newly registered callbacks. */
346 for (i
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++)
347 if (rdp
->nxttail
[i
- 1] != rdp
->nxttail
[i
] &&
348 ULONG_CMP_LT(ACCESS_ONCE(rsp
->completed
),
349 rdp
->nxtcompleted
[i
]))
350 return 1; /* Yes, CBs for future grace period. */
351 return 0; /* No grace period needed. */
355 * Return the root node of the specified rcu_state structure.
357 static struct rcu_node
*rcu_get_root(struct rcu_state
*rsp
)
359 return &rsp
->node
[0];
363 * rcu_eqs_enter_common - current CPU is moving towards extended quiescent state
365 * If the new value of the ->dynticks_nesting counter now is zero,
366 * we really have entered idle, and must do the appropriate accounting.
367 * The caller must have disabled interrupts.
369 static void rcu_eqs_enter_common(struct rcu_dynticks
*rdtp
, long long oldval
,
372 trace_rcu_dyntick(TPS("Start"), oldval
, rdtp
->dynticks_nesting
);
373 if (!user
&& !is_idle_task(current
)) {
374 struct task_struct
*idle __maybe_unused
=
375 idle_task(smp_processor_id());
377 trace_rcu_dyntick(TPS("Error on entry: not idle task"), oldval
, 0);
378 ftrace_dump(DUMP_ORIG
);
379 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
380 current
->pid
, current
->comm
,
381 idle
->pid
, idle
->comm
); /* must be idle task! */
383 rcu_prepare_for_idle(smp_processor_id());
384 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
385 smp_mb__before_atomic_inc(); /* See above. */
386 atomic_inc(&rdtp
->dynticks
);
387 smp_mb__after_atomic_inc(); /* Force ordering with next sojourn. */
388 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
391 * It is illegal to enter an extended quiescent state while
392 * in an RCU read-side critical section.
394 rcu_lockdep_assert(!lock_is_held(&rcu_lock_map
),
395 "Illegal idle entry in RCU read-side critical section.");
396 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
),
397 "Illegal idle entry in RCU-bh read-side critical section.");
398 rcu_lockdep_assert(!lock_is_held(&rcu_sched_lock_map
),
399 "Illegal idle entry in RCU-sched read-side critical section.");
403 * Enter an RCU extended quiescent state, which can be either the
404 * idle loop or adaptive-tickless usermode execution.
406 static void rcu_eqs_enter(bool user
)
409 struct rcu_dynticks
*rdtp
;
411 rdtp
= this_cpu_ptr(&rcu_dynticks
);
412 oldval
= rdtp
->dynticks_nesting
;
413 WARN_ON_ONCE((oldval
& DYNTICK_TASK_NEST_MASK
) == 0);
414 if ((oldval
& DYNTICK_TASK_NEST_MASK
) == DYNTICK_TASK_NEST_VALUE
)
415 rdtp
->dynticks_nesting
= 0;
417 rdtp
->dynticks_nesting
-= DYNTICK_TASK_NEST_VALUE
;
418 rcu_eqs_enter_common(rdtp
, oldval
, user
);
422 * rcu_idle_enter - inform RCU that current CPU is entering idle
424 * Enter idle mode, in other words, -leave- the mode in which RCU
425 * read-side critical sections can occur. (Though RCU read-side
426 * critical sections can occur in irq handlers in idle, a possibility
427 * handled by irq_enter() and irq_exit().)
429 * We crowbar the ->dynticks_nesting field to zero to allow for
430 * the possibility of usermode upcalls having messed up our count
431 * of interrupt nesting level during the prior busy period.
433 void rcu_idle_enter(void)
437 local_irq_save(flags
);
438 rcu_eqs_enter(false);
439 rcu_sysidle_enter(this_cpu_ptr(&rcu_dynticks
), 0);
440 local_irq_restore(flags
);
442 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
444 #ifdef CONFIG_RCU_USER_QS
446 * rcu_user_enter - inform RCU that we are resuming userspace.
448 * Enter RCU idle mode right before resuming userspace. No use of RCU
449 * is permitted between this call and rcu_user_exit(). This way the
450 * CPU doesn't need to maintain the tick for RCU maintenance purposes
451 * when the CPU runs in userspace.
453 void rcu_user_enter(void)
457 #endif /* CONFIG_RCU_USER_QS */
460 * rcu_irq_exit - inform RCU that current CPU is exiting irq towards idle
462 * Exit from an interrupt handler, which might possibly result in entering
463 * idle mode, in other words, leaving the mode in which read-side critical
464 * sections can occur.
466 * This code assumes that the idle loop never does anything that might
467 * result in unbalanced calls to irq_enter() and irq_exit(). If your
468 * architecture violates this assumption, RCU will give you what you
469 * deserve, good and hard. But very infrequently and irreproducibly.
471 * Use things like work queues to work around this limitation.
473 * You have been warned.
475 void rcu_irq_exit(void)
479 struct rcu_dynticks
*rdtp
;
481 local_irq_save(flags
);
482 rdtp
= this_cpu_ptr(&rcu_dynticks
);
483 oldval
= rdtp
->dynticks_nesting
;
484 rdtp
->dynticks_nesting
--;
485 WARN_ON_ONCE(rdtp
->dynticks_nesting
< 0);
486 if (rdtp
->dynticks_nesting
)
487 trace_rcu_dyntick(TPS("--="), oldval
, rdtp
->dynticks_nesting
);
489 rcu_eqs_enter_common(rdtp
, oldval
, true);
490 rcu_sysidle_enter(rdtp
, 1);
491 local_irq_restore(flags
);
495 * rcu_eqs_exit_common - current CPU moving away from extended quiescent state
497 * If the new value of the ->dynticks_nesting counter was previously zero,
498 * we really have exited idle, and must do the appropriate accounting.
499 * The caller must have disabled interrupts.
501 static void rcu_eqs_exit_common(struct rcu_dynticks
*rdtp
, long long oldval
,
504 smp_mb__before_atomic_inc(); /* Force ordering w/previous sojourn. */
505 atomic_inc(&rdtp
->dynticks
);
506 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
507 smp_mb__after_atomic_inc(); /* See above. */
508 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
509 rcu_cleanup_after_idle(smp_processor_id());
510 trace_rcu_dyntick(TPS("End"), oldval
, rdtp
->dynticks_nesting
);
511 if (!user
&& !is_idle_task(current
)) {
512 struct task_struct
*idle __maybe_unused
=
513 idle_task(smp_processor_id());
515 trace_rcu_dyntick(TPS("Error on exit: not idle task"),
516 oldval
, rdtp
->dynticks_nesting
);
517 ftrace_dump(DUMP_ORIG
);
518 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
519 current
->pid
, current
->comm
,
520 idle
->pid
, idle
->comm
); /* must be idle task! */
525 * Exit an RCU extended quiescent state, which can be either the
526 * idle loop or adaptive-tickless usermode execution.
528 static void rcu_eqs_exit(bool user
)
530 struct rcu_dynticks
*rdtp
;
533 rdtp
= this_cpu_ptr(&rcu_dynticks
);
534 oldval
= rdtp
->dynticks_nesting
;
535 WARN_ON_ONCE(oldval
< 0);
536 if (oldval
& DYNTICK_TASK_NEST_MASK
)
537 rdtp
->dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
539 rdtp
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
540 rcu_eqs_exit_common(rdtp
, oldval
, user
);
544 * rcu_idle_exit - inform RCU that current CPU is leaving idle
546 * Exit idle mode, in other words, -enter- the mode in which RCU
547 * read-side critical sections can occur.
549 * We crowbar the ->dynticks_nesting field to DYNTICK_TASK_NEST to
550 * allow for the possibility of usermode upcalls messing up our count
551 * of interrupt nesting level during the busy period that is just
554 void rcu_idle_exit(void)
558 local_irq_save(flags
);
560 rcu_sysidle_exit(this_cpu_ptr(&rcu_dynticks
), 0);
561 local_irq_restore(flags
);
563 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
565 #ifdef CONFIG_RCU_USER_QS
567 * rcu_user_exit - inform RCU that we are exiting userspace.
569 * Exit RCU idle mode while entering the kernel because it can
570 * run a RCU read side critical section anytime.
572 void rcu_user_exit(void)
576 #endif /* CONFIG_RCU_USER_QS */
579 * rcu_irq_enter - inform RCU that current CPU is entering irq away from idle
581 * Enter an interrupt handler, which might possibly result in exiting
582 * idle mode, in other words, entering the mode in which read-side critical
583 * sections can occur.
585 * Note that the Linux kernel is fully capable of entering an interrupt
586 * handler that it never exits, for example when doing upcalls to
587 * user mode! This code assumes that the idle loop never does upcalls to
588 * user mode. If your architecture does do upcalls from the idle loop (or
589 * does anything else that results in unbalanced calls to the irq_enter()
590 * and irq_exit() functions), RCU will give you what you deserve, good
591 * and hard. But very infrequently and irreproducibly.
593 * Use things like work queues to work around this limitation.
595 * You have been warned.
597 void rcu_irq_enter(void)
600 struct rcu_dynticks
*rdtp
;
603 local_irq_save(flags
);
604 rdtp
= this_cpu_ptr(&rcu_dynticks
);
605 oldval
= rdtp
->dynticks_nesting
;
606 rdtp
->dynticks_nesting
++;
607 WARN_ON_ONCE(rdtp
->dynticks_nesting
== 0);
609 trace_rcu_dyntick(TPS("++="), oldval
, rdtp
->dynticks_nesting
);
611 rcu_eqs_exit_common(rdtp
, oldval
, true);
612 rcu_sysidle_exit(rdtp
, 1);
613 local_irq_restore(flags
);
617 * rcu_nmi_enter - inform RCU of entry to NMI context
619 * If the CPU was idle with dynamic ticks active, and there is no
620 * irq handler running, this updates rdtp->dynticks_nmi to let the
621 * RCU grace-period handling know that the CPU is active.
623 void rcu_nmi_enter(void)
625 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
627 if (rdtp
->dynticks_nmi_nesting
== 0 &&
628 (atomic_read(&rdtp
->dynticks
) & 0x1))
630 rdtp
->dynticks_nmi_nesting
++;
631 smp_mb__before_atomic_inc(); /* Force delay from prior write. */
632 atomic_inc(&rdtp
->dynticks
);
633 /* CPUs seeing atomic_inc() must see later RCU read-side crit sects */
634 smp_mb__after_atomic_inc(); /* See above. */
635 WARN_ON_ONCE(!(atomic_read(&rdtp
->dynticks
) & 0x1));
639 * rcu_nmi_exit - inform RCU of exit from NMI context
641 * If the CPU was idle with dynamic ticks active, and there is no
642 * irq handler running, this updates rdtp->dynticks_nmi to let the
643 * RCU grace-period handling know that the CPU is no longer active.
645 void rcu_nmi_exit(void)
647 struct rcu_dynticks
*rdtp
= this_cpu_ptr(&rcu_dynticks
);
649 if (rdtp
->dynticks_nmi_nesting
== 0 ||
650 --rdtp
->dynticks_nmi_nesting
!= 0)
652 /* CPUs seeing atomic_inc() must see prior RCU read-side crit sects */
653 smp_mb__before_atomic_inc(); /* See above. */
654 atomic_inc(&rdtp
->dynticks
);
655 smp_mb__after_atomic_inc(); /* Force delay to next write. */
656 WARN_ON_ONCE(atomic_read(&rdtp
->dynticks
) & 0x1);
660 * __rcu_is_watching - are RCU read-side critical sections safe?
662 * Return true if RCU is watching the running CPU, which means that
663 * this CPU can safely enter RCU read-side critical sections. Unlike
664 * rcu_is_watching(), the caller of __rcu_is_watching() must have at
665 * least disabled preemption.
667 bool notrace
__rcu_is_watching(void)
669 return atomic_read(this_cpu_ptr(&rcu_dynticks
.dynticks
)) & 0x1;
673 * rcu_is_watching - see if RCU thinks that the current CPU is idle
675 * If the current CPU is in its idle loop and is neither in an interrupt
676 * or NMI handler, return true.
678 bool notrace
rcu_is_watching(void)
683 ret
= __rcu_is_watching();
687 EXPORT_SYMBOL_GPL(rcu_is_watching
);
689 #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
692 * Is the current CPU online? Disable preemption to avoid false positives
693 * that could otherwise happen due to the current CPU number being sampled,
694 * this task being preempted, its old CPU being taken offline, resuming
695 * on some other CPU, then determining that its old CPU is now offline.
696 * It is OK to use RCU on an offline processor during initial boot, hence
697 * the check for rcu_scheduler_fully_active. Note also that it is OK
698 * for a CPU coming online to use RCU for one jiffy prior to marking itself
699 * online in the cpu_online_mask. Similarly, it is OK for a CPU going
700 * offline to continue to use RCU for one jiffy after marking itself
701 * offline in the cpu_online_mask. This leniency is necessary given the
702 * non-atomic nature of the online and offline processing, for example,
703 * the fact that a CPU enters the scheduler after completing the CPU_DYING
706 * This is also why RCU internally marks CPUs online during the
707 * CPU_UP_PREPARE phase and offline during the CPU_DEAD phase.
709 * Disable checking if in an NMI handler because we cannot safely report
710 * errors from NMI handlers anyway.
712 bool rcu_lockdep_current_cpu_online(void)
714 struct rcu_data
*rdp
;
715 struct rcu_node
*rnp
;
721 rdp
= this_cpu_ptr(&rcu_sched_data
);
723 ret
= (rdp
->grpmask
& rnp
->qsmaskinit
) ||
724 !rcu_scheduler_fully_active
;
728 EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online
);
730 #endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
733 * rcu_is_cpu_rrupt_from_idle - see if idle or immediately interrupted from idle
735 * If the current CPU is idle or running at a first-level (not nested)
736 * interrupt from idle, return true. The caller must have at least
737 * disabled preemption.
739 static int rcu_is_cpu_rrupt_from_idle(void)
741 return __this_cpu_read(rcu_dynticks
.dynticks_nesting
) <= 1;
745 * Snapshot the specified CPU's dynticks counter so that we can later
746 * credit them with an implicit quiescent state. Return 1 if this CPU
747 * is in dynticks idle mode, which is an extended quiescent state.
749 static int dyntick_save_progress_counter(struct rcu_data
*rdp
,
750 bool *isidle
, unsigned long *maxj
)
752 rdp
->dynticks_snap
= atomic_add_return(0, &rdp
->dynticks
->dynticks
);
753 rcu_sysidle_check_cpu(rdp
, isidle
, maxj
);
754 return (rdp
->dynticks_snap
& 0x1) == 0;
758 * This function really isn't for public consumption, but RCU is special in
759 * that context switches can allow the state machine to make progress.
761 extern void resched_cpu(int cpu
);
764 * Return true if the specified CPU has passed through a quiescent
765 * state by virtue of being in or having passed through an dynticks
766 * idle state since the last call to dyntick_save_progress_counter()
767 * for this same CPU, or by virtue of having been offline.
769 static int rcu_implicit_dynticks_qs(struct rcu_data
*rdp
,
770 bool *isidle
, unsigned long *maxj
)
775 curr
= (unsigned int)atomic_add_return(0, &rdp
->dynticks
->dynticks
);
776 snap
= (unsigned int)rdp
->dynticks_snap
;
779 * If the CPU passed through or entered a dynticks idle phase with
780 * no active irq/NMI handlers, then we can safely pretend that the CPU
781 * already acknowledged the request to pass through a quiescent
782 * state. Either way, that CPU cannot possibly be in an RCU
783 * read-side critical section that started before the beginning
784 * of the current RCU grace period.
786 if ((curr
& 0x1) == 0 || UINT_CMP_GE(curr
, snap
+ 2)) {
787 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("dti"));
793 * Check for the CPU being offline, but only if the grace period
794 * is old enough. We don't need to worry about the CPU changing
795 * state: If we see it offline even once, it has been through a
798 * The reason for insisting that the grace period be at least
799 * one jiffy old is that CPUs that are not quite online and that
800 * have just gone offline can still execute RCU read-side critical
803 if (ULONG_CMP_GE(rdp
->rsp
->gp_start
+ 2, jiffies
))
804 return 0; /* Grace period is not old enough. */
806 if (cpu_is_offline(rdp
->cpu
)) {
807 trace_rcu_fqs(rdp
->rsp
->name
, rdp
->gpnum
, rdp
->cpu
, TPS("ofl"));
813 * There is a possibility that a CPU in adaptive-ticks state
814 * might run in the kernel with the scheduling-clock tick disabled
815 * for an extended time period. Invoke rcu_kick_nohz_cpu() to
816 * force the CPU to restart the scheduling-clock tick in this
817 * CPU is in this state.
819 rcu_kick_nohz_cpu(rdp
->cpu
);
822 * Alternatively, the CPU might be running in the kernel
823 * for an extended period of time without a quiescent state.
824 * Attempt to force the CPU through the scheduler to gain the
825 * needed quiescent state, but only if the grace period has gone
826 * on for an uncommonly long time. If there are many stuck CPUs,
827 * we will beat on the first one until it gets unstuck, then move
828 * to the next. Only do this for the primary flavor of RCU.
830 if (rdp
->rsp
== rcu_state
&&
831 ULONG_CMP_GE(ACCESS_ONCE(jiffies
), rdp
->rsp
->jiffies_resched
)) {
832 rdp
->rsp
->jiffies_resched
+= 5;
833 resched_cpu(rdp
->cpu
);
839 static void record_gp_stall_check_time(struct rcu_state
*rsp
)
841 unsigned long j
= ACCESS_ONCE(jiffies
);
845 smp_wmb(); /* Record start time before stall time. */
846 j1
= rcu_jiffies_till_stall_check();
847 rsp
->jiffies_stall
= j
+ j1
;
848 rsp
->jiffies_resched
= j
+ j1
/ 2;
852 * Dump stacks of all tasks running on stalled CPUs. This is a fallback
853 * for architectures that do not implement trigger_all_cpu_backtrace().
854 * The NMI-triggered stack traces are more accurate because they are
855 * printed by the target CPU.
857 static void rcu_dump_cpu_stacks(struct rcu_state
*rsp
)
861 struct rcu_node
*rnp
;
863 rcu_for_each_leaf_node(rsp
, rnp
) {
864 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
865 if (rnp
->qsmask
!= 0) {
866 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
867 if (rnp
->qsmask
& (1UL << cpu
))
868 dump_cpu_task(rnp
->grplo
+ cpu
);
870 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
874 static void print_other_cpu_stall(struct rcu_state
*rsp
)
880 struct rcu_node
*rnp
= rcu_get_root(rsp
);
883 /* Only let one CPU complain about others per time interval. */
885 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
886 delta
= jiffies
- rsp
->jiffies_stall
;
887 if (delta
< RCU_STALL_RAT_DELAY
|| !rcu_gp_in_progress(rsp
)) {
888 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
891 rsp
->jiffies_stall
= jiffies
+ 3 * rcu_jiffies_till_stall_check() + 3;
892 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
895 * OK, time to rat on our buddy...
896 * See Documentation/RCU/stallwarn.txt for info on how to debug
897 * RCU CPU stall warnings.
899 pr_err("INFO: %s detected stalls on CPUs/tasks:",
901 print_cpu_stall_info_begin();
902 rcu_for_each_leaf_node(rsp
, rnp
) {
903 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
904 ndetected
+= rcu_print_task_stall(rnp
);
905 if (rnp
->qsmask
!= 0) {
906 for (cpu
= 0; cpu
<= rnp
->grphi
- rnp
->grplo
; cpu
++)
907 if (rnp
->qsmask
& (1UL << cpu
)) {
908 print_cpu_stall_info(rsp
,
913 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
917 * Now rat on any tasks that got kicked up to the root rcu_node
918 * due to CPU offlining.
920 rnp
= rcu_get_root(rsp
);
921 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
922 ndetected
+= rcu_print_task_stall(rnp
);
923 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
925 print_cpu_stall_info_end();
926 for_each_possible_cpu(cpu
)
927 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
928 pr_cont("(detected by %d, t=%ld jiffies, g=%lu, c=%lu, q=%lu)\n",
929 smp_processor_id(), (long)(jiffies
- rsp
->gp_start
),
930 rsp
->gpnum
, rsp
->completed
, totqlen
);
932 pr_err("INFO: Stall ended before state dump start\n");
933 else if (!trigger_all_cpu_backtrace())
934 rcu_dump_cpu_stacks(rsp
);
936 /* Complain about tasks blocking the grace period. */
938 rcu_print_detail_task_stall(rsp
);
940 force_quiescent_state(rsp
); /* Kick them all. */
944 * This function really isn't for public consumption, but RCU is special in
945 * that context switches can allow the state machine to make progress.
947 extern void resched_cpu(int cpu
);
949 static void print_cpu_stall(struct rcu_state
*rsp
)
953 struct rcu_node
*rnp
= rcu_get_root(rsp
);
957 * OK, time to rat on ourselves...
958 * See Documentation/RCU/stallwarn.txt for info on how to debug
959 * RCU CPU stall warnings.
961 pr_err("INFO: %s self-detected stall on CPU", rsp
->name
);
962 print_cpu_stall_info_begin();
963 print_cpu_stall_info(rsp
, smp_processor_id());
964 print_cpu_stall_info_end();
965 for_each_possible_cpu(cpu
)
966 totqlen
+= per_cpu_ptr(rsp
->rda
, cpu
)->qlen
;
967 pr_cont(" (t=%lu jiffies g=%lu c=%lu q=%lu)\n",
968 jiffies
- rsp
->gp_start
, rsp
->gpnum
, rsp
->completed
, totqlen
);
969 if (!trigger_all_cpu_backtrace())
972 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
973 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_stall
))
974 rsp
->jiffies_stall
= jiffies
+
975 3 * rcu_jiffies_till_stall_check() + 3;
976 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
979 * Attempt to revive the RCU machinery by forcing a context switch.
981 * A context switch would normally allow the RCU state machine to make
982 * progress and it could be we're stuck in kernel space without context
983 * switches for an entirely unreasonable amount of time.
985 resched_cpu(smp_processor_id());
988 static void check_cpu_stall(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
990 unsigned long completed
;
995 struct rcu_node
*rnp
;
997 if (rcu_cpu_stall_suppress
|| !rcu_gp_in_progress(rsp
))
999 j
= ACCESS_ONCE(jiffies
);
1002 * Lots of memory barriers to reject false positives.
1004 * The idea is to pick up rsp->gpnum, then rsp->jiffies_stall,
1005 * then rsp->gp_start, and finally rsp->completed. These values
1006 * are updated in the opposite order with memory barriers (or
1007 * equivalent) during grace-period initialization and cleanup.
1008 * Now, a false positive can occur if we get an new value of
1009 * rsp->gp_start and a old value of rsp->jiffies_stall. But given
1010 * the memory barriers, the only way that this can happen is if one
1011 * grace period ends and another starts between these two fetches.
1012 * Detect this by comparing rsp->completed with the previous fetch
1015 * Given this check, comparisons of jiffies, rsp->jiffies_stall,
1016 * and rsp->gp_start suffice to forestall false positives.
1018 gpnum
= ACCESS_ONCE(rsp
->gpnum
);
1019 smp_rmb(); /* Pick up ->gpnum first... */
1020 js
= ACCESS_ONCE(rsp
->jiffies_stall
);
1021 smp_rmb(); /* ...then ->jiffies_stall before the rest... */
1022 gps
= ACCESS_ONCE(rsp
->gp_start
);
1023 smp_rmb(); /* ...and finally ->gp_start before ->completed. */
1024 completed
= ACCESS_ONCE(rsp
->completed
);
1025 if (ULONG_CMP_GE(completed
, gpnum
) ||
1026 ULONG_CMP_LT(j
, js
) ||
1027 ULONG_CMP_GE(gps
, js
))
1028 return; /* No stall or GP completed since entering function. */
1030 if (rcu_gp_in_progress(rsp
) &&
1031 (ACCESS_ONCE(rnp
->qsmask
) & rdp
->grpmask
)) {
1033 /* We haven't checked in, so go dump stack. */
1034 print_cpu_stall(rsp
);
1036 } else if (rcu_gp_in_progress(rsp
) &&
1037 ULONG_CMP_GE(j
, js
+ RCU_STALL_RAT_DELAY
)) {
1039 /* They had a few time units to dump stack, so complain. */
1040 print_other_cpu_stall(rsp
);
1045 * rcu_cpu_stall_reset - prevent further stall warnings in current grace period
1047 * Set the stall-warning timeout way off into the future, thus preventing
1048 * any RCU CPU stall-warning messages from appearing in the current set of
1049 * RCU grace periods.
1051 * The caller must disable hard irqs.
1053 void rcu_cpu_stall_reset(void)
1055 struct rcu_state
*rsp
;
1057 for_each_rcu_flavor(rsp
)
1058 rsp
->jiffies_stall
= jiffies
+ ULONG_MAX
/ 2;
1062 * Initialize the specified rcu_data structure's callback list to empty.
1064 static void init_callback_list(struct rcu_data
*rdp
)
1068 if (init_nocb_callback_list(rdp
))
1070 rdp
->nxtlist
= NULL
;
1071 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
1072 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
1076 * Determine the value that ->completed will have at the end of the
1077 * next subsequent grace period. This is used to tag callbacks so that
1078 * a CPU can invoke callbacks in a timely fashion even if that CPU has
1079 * been dyntick-idle for an extended period with callbacks under the
1080 * influence of RCU_FAST_NO_HZ.
1082 * The caller must hold rnp->lock with interrupts disabled.
1084 static unsigned long rcu_cbs_completed(struct rcu_state
*rsp
,
1085 struct rcu_node
*rnp
)
1088 * If RCU is idle, we just wait for the next grace period.
1089 * But we can only be sure that RCU is idle if we are looking
1090 * at the root rcu_node structure -- otherwise, a new grace
1091 * period might have started, but just not yet gotten around
1092 * to initializing the current non-root rcu_node structure.
1094 if (rcu_get_root(rsp
) == rnp
&& rnp
->gpnum
== rnp
->completed
)
1095 return rnp
->completed
+ 1;
1098 * Otherwise, wait for a possible partial grace period and
1099 * then the subsequent full grace period.
1101 return rnp
->completed
+ 2;
1105 * Trace-event helper function for rcu_start_future_gp() and
1106 * rcu_nocb_wait_gp().
1108 static void trace_rcu_future_gp(struct rcu_node
*rnp
, struct rcu_data
*rdp
,
1109 unsigned long c
, const char *s
)
1111 trace_rcu_future_grace_period(rdp
->rsp
->name
, rnp
->gpnum
,
1112 rnp
->completed
, c
, rnp
->level
,
1113 rnp
->grplo
, rnp
->grphi
, s
);
1117 * Start some future grace period, as needed to handle newly arrived
1118 * callbacks. The required future grace periods are recorded in each
1119 * rcu_node structure's ->need_future_gp field.
1121 * The caller must hold the specified rcu_node structure's ->lock.
1123 static unsigned long __maybe_unused
1124 rcu_start_future_gp(struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1128 struct rcu_node
*rnp_root
= rcu_get_root(rdp
->rsp
);
1131 * Pick up grace-period number for new callbacks. If this
1132 * grace period is already marked as needed, return to the caller.
1134 c
= rcu_cbs_completed(rdp
->rsp
, rnp
);
1135 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startleaf"));
1136 if (rnp
->need_future_gp
[c
& 0x1]) {
1137 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Prestartleaf"));
1142 * If either this rcu_node structure or the root rcu_node structure
1143 * believe that a grace period is in progress, then we must wait
1144 * for the one following, which is in "c". Because our request
1145 * will be noticed at the end of the current grace period, we don't
1146 * need to explicitly start one.
1148 if (rnp
->gpnum
!= rnp
->completed
||
1149 ACCESS_ONCE(rnp
->gpnum
) != ACCESS_ONCE(rnp
->completed
)) {
1150 rnp
->need_future_gp
[c
& 0x1]++;
1151 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedleaf"));
1156 * There might be no grace period in progress. If we don't already
1157 * hold it, acquire the root rcu_node structure's lock in order to
1158 * start one (if needed).
1160 if (rnp
!= rnp_root
)
1161 raw_spin_lock(&rnp_root
->lock
);
1164 * Get a new grace-period number. If there really is no grace
1165 * period in progress, it will be smaller than the one we obtained
1166 * earlier. Adjust callbacks as needed. Note that even no-CBs
1167 * CPUs have a ->nxtcompleted[] array, so no no-CBs checks needed.
1169 c
= rcu_cbs_completed(rdp
->rsp
, rnp_root
);
1170 for (i
= RCU_DONE_TAIL
; i
< RCU_NEXT_TAIL
; i
++)
1171 if (ULONG_CMP_LT(c
, rdp
->nxtcompleted
[i
]))
1172 rdp
->nxtcompleted
[i
] = c
;
1175 * If the needed for the required grace period is already
1176 * recorded, trace and leave.
1178 if (rnp_root
->need_future_gp
[c
& 0x1]) {
1179 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Prestartedroot"));
1183 /* Record the need for the future grace period. */
1184 rnp_root
->need_future_gp
[c
& 0x1]++;
1186 /* If a grace period is not already in progress, start one. */
1187 if (rnp_root
->gpnum
!= rnp_root
->completed
) {
1188 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedleafroot"));
1190 trace_rcu_future_gp(rnp
, rdp
, c
, TPS("Startedroot"));
1191 rcu_start_gp_advanced(rdp
->rsp
, rnp_root
, rdp
);
1194 if (rnp
!= rnp_root
)
1195 raw_spin_unlock(&rnp_root
->lock
);
1200 * Clean up any old requests for the just-ended grace period. Also return
1201 * whether any additional grace periods have been requested. Also invoke
1202 * rcu_nocb_gp_cleanup() in order to wake up any no-callbacks kthreads
1203 * waiting for this grace period to complete.
1205 static int rcu_future_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
1207 int c
= rnp
->completed
;
1209 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1211 rcu_nocb_gp_cleanup(rsp
, rnp
);
1212 rnp
->need_future_gp
[c
& 0x1] = 0;
1213 needmore
= rnp
->need_future_gp
[(c
+ 1) & 0x1];
1214 trace_rcu_future_gp(rnp
, rdp
, c
,
1215 needmore
? TPS("CleanupMore") : TPS("Cleanup"));
1220 * If there is room, assign a ->completed number to any callbacks on
1221 * this CPU that have not already been assigned. Also accelerate any
1222 * callbacks that were previously assigned a ->completed number that has
1223 * since proven to be too conservative, which can happen if callbacks get
1224 * assigned a ->completed number while RCU is idle, but with reference to
1225 * a non-root rcu_node structure. This function is idempotent, so it does
1226 * not hurt to call it repeatedly.
1228 * The caller must hold rnp->lock with interrupts disabled.
1230 static void rcu_accelerate_cbs(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1231 struct rcu_data
*rdp
)
1236 /* If the CPU has no callbacks, nothing to do. */
1237 if (!rdp
->nxttail
[RCU_NEXT_TAIL
] || !*rdp
->nxttail
[RCU_DONE_TAIL
])
1241 * Starting from the sublist containing the callbacks most
1242 * recently assigned a ->completed number and working down, find the
1243 * first sublist that is not assignable to an upcoming grace period.
1244 * Such a sublist has something in it (first two tests) and has
1245 * a ->completed number assigned that will complete sooner than
1246 * the ->completed number for newly arrived callbacks (last test).
1248 * The key point is that any later sublist can be assigned the
1249 * same ->completed number as the newly arrived callbacks, which
1250 * means that the callbacks in any of these later sublist can be
1251 * grouped into a single sublist, whether or not they have already
1252 * been assigned a ->completed number.
1254 c
= rcu_cbs_completed(rsp
, rnp
);
1255 for (i
= RCU_NEXT_TAIL
- 1; i
> RCU_DONE_TAIL
; i
--)
1256 if (rdp
->nxttail
[i
] != rdp
->nxttail
[i
- 1] &&
1257 !ULONG_CMP_GE(rdp
->nxtcompleted
[i
], c
))
1261 * If there are no sublist for unassigned callbacks, leave.
1262 * At the same time, advance "i" one sublist, so that "i" will
1263 * index into the sublist where all the remaining callbacks should
1266 if (++i
>= RCU_NEXT_TAIL
)
1270 * Assign all subsequent callbacks' ->completed number to the next
1271 * full grace period and group them all in the sublist initially
1274 for (; i
<= RCU_NEXT_TAIL
; i
++) {
1275 rdp
->nxttail
[i
] = rdp
->nxttail
[RCU_NEXT_TAIL
];
1276 rdp
->nxtcompleted
[i
] = c
;
1278 /* Record any needed additional grace periods. */
1279 rcu_start_future_gp(rnp
, rdp
);
1281 /* Trace depending on how much we were able to accelerate. */
1282 if (!*rdp
->nxttail
[RCU_WAIT_TAIL
])
1283 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("AccWaitCB"));
1285 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("AccReadyCB"));
1289 * Move any callbacks whose grace period has completed to the
1290 * RCU_DONE_TAIL sublist, then compact the remaining sublists and
1291 * assign ->completed numbers to any callbacks in the RCU_NEXT_TAIL
1292 * sublist. This function is idempotent, so it does not hurt to
1293 * invoke it repeatedly. As long as it is not invoked -too- often...
1295 * The caller must hold rnp->lock with interrupts disabled.
1297 static void rcu_advance_cbs(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1298 struct rcu_data
*rdp
)
1302 /* If the CPU has no callbacks, nothing to do. */
1303 if (!rdp
->nxttail
[RCU_NEXT_TAIL
] || !*rdp
->nxttail
[RCU_DONE_TAIL
])
1307 * Find all callbacks whose ->completed numbers indicate that they
1308 * are ready to invoke, and put them into the RCU_DONE_TAIL sublist.
1310 for (i
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++) {
1311 if (ULONG_CMP_LT(rnp
->completed
, rdp
->nxtcompleted
[i
]))
1313 rdp
->nxttail
[RCU_DONE_TAIL
] = rdp
->nxttail
[i
];
1315 /* Clean up any sublist tail pointers that were misordered above. */
1316 for (j
= RCU_WAIT_TAIL
; j
< i
; j
++)
1317 rdp
->nxttail
[j
] = rdp
->nxttail
[RCU_DONE_TAIL
];
1319 /* Copy down callbacks to fill in empty sublists. */
1320 for (j
= RCU_WAIT_TAIL
; i
< RCU_NEXT_TAIL
; i
++, j
++) {
1321 if (rdp
->nxttail
[j
] == rdp
->nxttail
[RCU_NEXT_TAIL
])
1323 rdp
->nxttail
[j
] = rdp
->nxttail
[i
];
1324 rdp
->nxtcompleted
[j
] = rdp
->nxtcompleted
[i
];
1327 /* Classify any remaining callbacks. */
1328 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1332 * Update CPU-local rcu_data state to record the beginnings and ends of
1333 * grace periods. The caller must hold the ->lock of the leaf rcu_node
1334 * structure corresponding to the current CPU, and must have irqs disabled.
1336 static void __note_gp_changes(struct rcu_state
*rsp
, struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1338 /* Handle the ends of any preceding grace periods first. */
1339 if (rdp
->completed
== rnp
->completed
) {
1341 /* No grace period end, so just accelerate recent callbacks. */
1342 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1346 /* Advance callbacks. */
1347 rcu_advance_cbs(rsp
, rnp
, rdp
);
1349 /* Remember that we saw this grace-period completion. */
1350 rdp
->completed
= rnp
->completed
;
1351 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpuend"));
1354 if (rdp
->gpnum
!= rnp
->gpnum
) {
1356 * If the current grace period is waiting for this CPU,
1357 * set up to detect a quiescent state, otherwise don't
1358 * go looking for one.
1360 rdp
->gpnum
= rnp
->gpnum
;
1361 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpustart"));
1362 rdp
->passed_quiesce
= 0;
1363 rdp
->qs_pending
= !!(rnp
->qsmask
& rdp
->grpmask
);
1364 zero_cpu_stall_ticks(rdp
);
1368 static void note_gp_changes(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1370 unsigned long flags
;
1371 struct rcu_node
*rnp
;
1373 local_irq_save(flags
);
1375 if ((rdp
->gpnum
== ACCESS_ONCE(rnp
->gpnum
) &&
1376 rdp
->completed
== ACCESS_ONCE(rnp
->completed
)) || /* w/out lock. */
1377 !raw_spin_trylock(&rnp
->lock
)) { /* irqs already off, so later. */
1378 local_irq_restore(flags
);
1381 __note_gp_changes(rsp
, rnp
, rdp
);
1382 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1386 * Initialize a new grace period. Return 0 if no grace period required.
1388 static int rcu_gp_init(struct rcu_state
*rsp
)
1390 struct rcu_data
*rdp
;
1391 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1393 rcu_bind_gp_kthread();
1394 raw_spin_lock_irq(&rnp
->lock
);
1395 if (rsp
->gp_flags
== 0) {
1396 /* Spurious wakeup, tell caller to go back to sleep. */
1397 raw_spin_unlock_irq(&rnp
->lock
);
1400 rsp
->gp_flags
= 0; /* Clear all flags: New grace period. */
1402 if (WARN_ON_ONCE(rcu_gp_in_progress(rsp
))) {
1404 * Grace period already in progress, don't start another.
1405 * Not supposed to be able to happen.
1407 raw_spin_unlock_irq(&rnp
->lock
);
1411 /* Advance to a new grace period and initialize state. */
1412 record_gp_stall_check_time(rsp
);
1413 smp_wmb(); /* Record GP times before starting GP. */
1415 trace_rcu_grace_period(rsp
->name
, rsp
->gpnum
, TPS("start"));
1416 raw_spin_unlock_irq(&rnp
->lock
);
1418 /* Exclude any concurrent CPU-hotplug operations. */
1419 mutex_lock(&rsp
->onoff_mutex
);
1422 * Set the quiescent-state-needed bits in all the rcu_node
1423 * structures for all currently online CPUs in breadth-first order,
1424 * starting from the root rcu_node structure, relying on the layout
1425 * of the tree within the rsp->node[] array. Note that other CPUs
1426 * will access only the leaves of the hierarchy, thus seeing that no
1427 * grace period is in progress, at least until the corresponding
1428 * leaf node has been initialized. In addition, we have excluded
1429 * CPU-hotplug operations.
1431 * The grace period cannot complete until the initialization
1432 * process finishes, because this kthread handles both.
1434 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1435 raw_spin_lock_irq(&rnp
->lock
);
1436 rdp
= this_cpu_ptr(rsp
->rda
);
1437 rcu_preempt_check_blocked_tasks(rnp
);
1438 rnp
->qsmask
= rnp
->qsmaskinit
;
1439 ACCESS_ONCE(rnp
->gpnum
) = rsp
->gpnum
;
1440 WARN_ON_ONCE(rnp
->completed
!= rsp
->completed
);
1441 ACCESS_ONCE(rnp
->completed
) = rsp
->completed
;
1442 if (rnp
== rdp
->mynode
)
1443 __note_gp_changes(rsp
, rnp
, rdp
);
1444 rcu_preempt_boost_start_gp(rnp
);
1445 trace_rcu_grace_period_init(rsp
->name
, rnp
->gpnum
,
1446 rnp
->level
, rnp
->grplo
,
1447 rnp
->grphi
, rnp
->qsmask
);
1448 raw_spin_unlock_irq(&rnp
->lock
);
1449 #ifdef CONFIG_PROVE_RCU_DELAY
1450 if ((prandom_u32() % (rcu_num_nodes
+ 1)) == 0 &&
1451 system_state
== SYSTEM_RUNNING
)
1453 #endif /* #ifdef CONFIG_PROVE_RCU_DELAY */
1457 mutex_unlock(&rsp
->onoff_mutex
);
1462 * Do one round of quiescent-state forcing.
1464 static int rcu_gp_fqs(struct rcu_state
*rsp
, int fqs_state_in
)
1466 int fqs_state
= fqs_state_in
;
1467 bool isidle
= false;
1469 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1472 if (fqs_state
== RCU_SAVE_DYNTICK
) {
1473 /* Collect dyntick-idle snapshots. */
1474 if (is_sysidle_rcu_state(rsp
)) {
1476 maxj
= jiffies
- ULONG_MAX
/ 4;
1478 force_qs_rnp(rsp
, dyntick_save_progress_counter
,
1480 rcu_sysidle_report_gp(rsp
, isidle
, maxj
);
1481 fqs_state
= RCU_FORCE_QS
;
1483 /* Handle dyntick-idle and offline CPUs. */
1485 force_qs_rnp(rsp
, rcu_implicit_dynticks_qs
, &isidle
, &maxj
);
1487 /* Clear flag to prevent immediate re-entry. */
1488 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
1489 raw_spin_lock_irq(&rnp
->lock
);
1490 rsp
->gp_flags
&= ~RCU_GP_FLAG_FQS
;
1491 raw_spin_unlock_irq(&rnp
->lock
);
1497 * Clean up after the old grace period.
1499 static void rcu_gp_cleanup(struct rcu_state
*rsp
)
1501 unsigned long gp_duration
;
1503 struct rcu_data
*rdp
;
1504 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1506 raw_spin_lock_irq(&rnp
->lock
);
1507 gp_duration
= jiffies
- rsp
->gp_start
;
1508 if (gp_duration
> rsp
->gp_max
)
1509 rsp
->gp_max
= gp_duration
;
1512 * We know the grace period is complete, but to everyone else
1513 * it appears to still be ongoing. But it is also the case
1514 * that to everyone else it looks like there is nothing that
1515 * they can do to advance the grace period. It is therefore
1516 * safe for us to drop the lock in order to mark the grace
1517 * period as completed in all of the rcu_node structures.
1519 raw_spin_unlock_irq(&rnp
->lock
);
1522 * Propagate new ->completed value to rcu_node structures so
1523 * that other CPUs don't have to wait until the start of the next
1524 * grace period to process their callbacks. This also avoids
1525 * some nasty RCU grace-period initialization races by forcing
1526 * the end of the current grace period to be completely recorded in
1527 * all of the rcu_node structures before the beginning of the next
1528 * grace period is recorded in any of the rcu_node structures.
1530 rcu_for_each_node_breadth_first(rsp
, rnp
) {
1531 raw_spin_lock_irq(&rnp
->lock
);
1532 ACCESS_ONCE(rnp
->completed
) = rsp
->gpnum
;
1533 rdp
= this_cpu_ptr(rsp
->rda
);
1534 if (rnp
== rdp
->mynode
)
1535 __note_gp_changes(rsp
, rnp
, rdp
);
1536 nocb
+= rcu_future_gp_cleanup(rsp
, rnp
);
1537 raw_spin_unlock_irq(&rnp
->lock
);
1540 rnp
= rcu_get_root(rsp
);
1541 raw_spin_lock_irq(&rnp
->lock
);
1542 rcu_nocb_gp_set(rnp
, nocb
);
1544 rsp
->completed
= rsp
->gpnum
; /* Declare grace period done. */
1545 trace_rcu_grace_period(rsp
->name
, rsp
->completed
, TPS("end"));
1546 rsp
->fqs_state
= RCU_GP_IDLE
;
1547 rdp
= this_cpu_ptr(rsp
->rda
);
1548 rcu_advance_cbs(rsp
, rnp
, rdp
); /* Reduce false positives below. */
1549 if (cpu_needs_another_gp(rsp
, rdp
)) {
1550 rsp
->gp_flags
= RCU_GP_FLAG_INIT
;
1551 trace_rcu_grace_period(rsp
->name
,
1552 ACCESS_ONCE(rsp
->gpnum
),
1555 raw_spin_unlock_irq(&rnp
->lock
);
1559 * Body of kthread that handles grace periods.
1561 static int __noreturn
rcu_gp_kthread(void *arg
)
1567 struct rcu_state
*rsp
= arg
;
1568 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1572 /* Handle grace-period start. */
1574 trace_rcu_grace_period(rsp
->name
,
1575 ACCESS_ONCE(rsp
->gpnum
),
1577 wait_event_interruptible(rsp
->gp_wq
,
1578 ACCESS_ONCE(rsp
->gp_flags
) &
1580 if (rcu_gp_init(rsp
))
1583 flush_signals(current
);
1584 trace_rcu_grace_period(rsp
->name
,
1585 ACCESS_ONCE(rsp
->gpnum
),
1589 /* Handle quiescent-state forcing. */
1590 fqs_state
= RCU_SAVE_DYNTICK
;
1591 j
= jiffies_till_first_fqs
;
1594 jiffies_till_first_fqs
= HZ
;
1599 rsp
->jiffies_force_qs
= jiffies
+ j
;
1600 trace_rcu_grace_period(rsp
->name
,
1601 ACCESS_ONCE(rsp
->gpnum
),
1603 ret
= wait_event_interruptible_timeout(rsp
->gp_wq
,
1604 ((gf
= ACCESS_ONCE(rsp
->gp_flags
)) &
1606 (!ACCESS_ONCE(rnp
->qsmask
) &&
1607 !rcu_preempt_blocked_readers_cgp(rnp
)),
1609 /* If grace period done, leave loop. */
1610 if (!ACCESS_ONCE(rnp
->qsmask
) &&
1611 !rcu_preempt_blocked_readers_cgp(rnp
))
1613 /* If time for quiescent-state forcing, do it. */
1614 if (ULONG_CMP_GE(jiffies
, rsp
->jiffies_force_qs
) ||
1615 (gf
& RCU_GP_FLAG_FQS
)) {
1616 trace_rcu_grace_period(rsp
->name
,
1617 ACCESS_ONCE(rsp
->gpnum
),
1619 fqs_state
= rcu_gp_fqs(rsp
, fqs_state
);
1620 trace_rcu_grace_period(rsp
->name
,
1621 ACCESS_ONCE(rsp
->gpnum
),
1625 /* Deal with stray signal. */
1627 flush_signals(current
);
1628 trace_rcu_grace_period(rsp
->name
,
1629 ACCESS_ONCE(rsp
->gpnum
),
1632 j
= jiffies_till_next_fqs
;
1635 jiffies_till_next_fqs
= HZ
;
1638 jiffies_till_next_fqs
= 1;
1642 /* Handle grace-period end. */
1643 rcu_gp_cleanup(rsp
);
1647 static void rsp_wakeup(struct irq_work
*work
)
1649 struct rcu_state
*rsp
= container_of(work
, struct rcu_state
, wakeup_work
);
1651 /* Wake up rcu_gp_kthread() to start the grace period. */
1652 wake_up(&rsp
->gp_wq
);
1656 * Start a new RCU grace period if warranted, re-initializing the hierarchy
1657 * in preparation for detecting the next grace period. The caller must hold
1658 * the root node's ->lock and hard irqs must be disabled.
1660 * Note that it is legal for a dying CPU (which is marked as offline) to
1661 * invoke this function. This can happen when the dying CPU reports its
1665 rcu_start_gp_advanced(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1666 struct rcu_data
*rdp
)
1668 if (!rsp
->gp_kthread
|| !cpu_needs_another_gp(rsp
, rdp
)) {
1670 * Either we have not yet spawned the grace-period
1671 * task, this CPU does not need another grace period,
1672 * or a grace period is already in progress.
1673 * Either way, don't start a new grace period.
1677 rsp
->gp_flags
= RCU_GP_FLAG_INIT
;
1678 trace_rcu_grace_period(rsp
->name
, ACCESS_ONCE(rsp
->gpnum
),
1682 * We can't do wakeups while holding the rnp->lock, as that
1683 * could cause possible deadlocks with the rq->lock. Defer
1684 * the wakeup to interrupt context. And don't bother waking
1685 * up the running kthread.
1687 if (current
!= rsp
->gp_kthread
)
1688 irq_work_queue(&rsp
->wakeup_work
);
1692 * Similar to rcu_start_gp_advanced(), but also advance the calling CPU's
1693 * callbacks. Note that rcu_start_gp_advanced() cannot do this because it
1694 * is invoked indirectly from rcu_advance_cbs(), which would result in
1695 * endless recursion -- or would do so if it wasn't for the self-deadlock
1696 * that is encountered beforehand.
1699 rcu_start_gp(struct rcu_state
*rsp
)
1701 struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
);
1702 struct rcu_node
*rnp
= rcu_get_root(rsp
);
1705 * If there is no grace period in progress right now, any
1706 * callbacks we have up to this point will be satisfied by the
1707 * next grace period. Also, advancing the callbacks reduces the
1708 * probability of false positives from cpu_needs_another_gp()
1709 * resulting in pointless grace periods. So, advance callbacks
1710 * then start the grace period!
1712 rcu_advance_cbs(rsp
, rnp
, rdp
);
1713 rcu_start_gp_advanced(rsp
, rnp
, rdp
);
1717 * Report a full set of quiescent states to the specified rcu_state
1718 * data structure. This involves cleaning up after the prior grace
1719 * period and letting rcu_start_gp() start up the next grace period
1720 * if one is needed. Note that the caller must hold rnp->lock, which
1721 * is released before return.
1723 static void rcu_report_qs_rsp(struct rcu_state
*rsp
, unsigned long flags
)
1724 __releases(rcu_get_root(rsp
)->lock
)
1726 WARN_ON_ONCE(!rcu_gp_in_progress(rsp
));
1727 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
1728 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
1732 * Similar to rcu_report_qs_rdp(), for which it is a helper function.
1733 * Allows quiescent states for a group of CPUs to be reported at one go
1734 * to the specified rcu_node structure, though all the CPUs in the group
1735 * must be represented by the same rcu_node structure (which need not be
1736 * a leaf rcu_node structure, though it often will be). That structure's
1737 * lock must be held upon entry, and it is released before return.
1740 rcu_report_qs_rnp(unsigned long mask
, struct rcu_state
*rsp
,
1741 struct rcu_node
*rnp
, unsigned long flags
)
1742 __releases(rnp
->lock
)
1744 struct rcu_node
*rnp_c
;
1746 /* Walk up the rcu_node hierarchy. */
1748 if (!(rnp
->qsmask
& mask
)) {
1750 /* Our bit has already been cleared, so done. */
1751 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1754 rnp
->qsmask
&= ~mask
;
1755 trace_rcu_quiescent_state_report(rsp
->name
, rnp
->gpnum
,
1756 mask
, rnp
->qsmask
, rnp
->level
,
1757 rnp
->grplo
, rnp
->grphi
,
1759 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
1761 /* Other bits still set at this level, so done. */
1762 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1765 mask
= rnp
->grpmask
;
1766 if (rnp
->parent
== NULL
) {
1768 /* No more levels. Exit loop holding root lock. */
1772 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1775 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1776 WARN_ON_ONCE(rnp_c
->qsmask
);
1780 * Get here if we are the last CPU to pass through a quiescent
1781 * state for this grace period. Invoke rcu_report_qs_rsp()
1782 * to clean up and start the next grace period if one is needed.
1784 rcu_report_qs_rsp(rsp
, flags
); /* releases rnp->lock. */
1788 * Record a quiescent state for the specified CPU to that CPU's rcu_data
1789 * structure. This must be either called from the specified CPU, or
1790 * called when the specified CPU is known to be offline (and when it is
1791 * also known that no other CPU is concurrently trying to help the offline
1792 * CPU). The lastcomp argument is used to make sure we are still in the
1793 * grace period of interest. We don't want to end the current grace period
1794 * based on quiescent states detected in an earlier grace period!
1797 rcu_report_qs_rdp(int cpu
, struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1799 unsigned long flags
;
1801 struct rcu_node
*rnp
;
1804 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1805 if (rdp
->passed_quiesce
== 0 || rdp
->gpnum
!= rnp
->gpnum
||
1806 rnp
->completed
== rnp
->gpnum
) {
1809 * The grace period in which this quiescent state was
1810 * recorded has ended, so don't report it upwards.
1811 * We will instead need a new quiescent state that lies
1812 * within the current grace period.
1814 rdp
->passed_quiesce
= 0; /* need qs for new gp. */
1815 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1818 mask
= rdp
->grpmask
;
1819 if ((rnp
->qsmask
& mask
) == 0) {
1820 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1822 rdp
->qs_pending
= 0;
1825 * This GP can't end until cpu checks in, so all of our
1826 * callbacks can be processed during the next GP.
1828 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1830 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
); /* rlses rnp->lock */
1835 * Check to see if there is a new grace period of which this CPU
1836 * is not yet aware, and if so, set up local rcu_data state for it.
1837 * Otherwise, see if this CPU has just passed through its first
1838 * quiescent state for this grace period, and record that fact if so.
1841 rcu_check_quiescent_state(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
1843 /* Check for grace-period ends and beginnings. */
1844 note_gp_changes(rsp
, rdp
);
1847 * Does this CPU still need to do its part for current grace period?
1848 * If no, return and let the other CPUs do their part as well.
1850 if (!rdp
->qs_pending
)
1854 * Was there a quiescent state since the beginning of the grace
1855 * period? If no, then exit and wait for the next call.
1857 if (!rdp
->passed_quiesce
)
1861 * Tell RCU we are done (but rcu_report_qs_rdp() will be the
1864 rcu_report_qs_rdp(rdp
->cpu
, rsp
, rdp
);
1867 #ifdef CONFIG_HOTPLUG_CPU
1870 * Send the specified CPU's RCU callbacks to the orphanage. The
1871 * specified CPU must be offline, and the caller must hold the
1875 rcu_send_cbs_to_orphanage(int cpu
, struct rcu_state
*rsp
,
1876 struct rcu_node
*rnp
, struct rcu_data
*rdp
)
1878 /* No-CBs CPUs do not have orphanable callbacks. */
1879 if (rcu_is_nocb_cpu(rdp
->cpu
))
1883 * Orphan the callbacks. First adjust the counts. This is safe
1884 * because _rcu_barrier() excludes CPU-hotplug operations, so it
1885 * cannot be running now. Thus no memory barrier is required.
1887 if (rdp
->nxtlist
!= NULL
) {
1888 rsp
->qlen_lazy
+= rdp
->qlen_lazy
;
1889 rsp
->qlen
+= rdp
->qlen
;
1890 rdp
->n_cbs_orphaned
+= rdp
->qlen
;
1892 ACCESS_ONCE(rdp
->qlen
) = 0;
1896 * Next, move those callbacks still needing a grace period to
1897 * the orphanage, where some other CPU will pick them up.
1898 * Some of the callbacks might have gone partway through a grace
1899 * period, but that is too bad. They get to start over because we
1900 * cannot assume that grace periods are synchronized across CPUs.
1901 * We don't bother updating the ->nxttail[] array yet, instead
1902 * we just reset the whole thing later on.
1904 if (*rdp
->nxttail
[RCU_DONE_TAIL
] != NULL
) {
1905 *rsp
->orphan_nxttail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1906 rsp
->orphan_nxttail
= rdp
->nxttail
[RCU_NEXT_TAIL
];
1907 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
1911 * Then move the ready-to-invoke callbacks to the orphanage,
1912 * where some other CPU will pick them up. These will not be
1913 * required to pass though another grace period: They are done.
1915 if (rdp
->nxtlist
!= NULL
) {
1916 *rsp
->orphan_donetail
= rdp
->nxtlist
;
1917 rsp
->orphan_donetail
= rdp
->nxttail
[RCU_DONE_TAIL
];
1920 /* Finally, initialize the rcu_data structure's list to empty. */
1921 init_callback_list(rdp
);
1925 * Adopt the RCU callbacks from the specified rcu_state structure's
1926 * orphanage. The caller must hold the ->orphan_lock.
1928 static void rcu_adopt_orphan_cbs(struct rcu_state
*rsp
)
1931 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
1933 /* No-CBs CPUs are handled specially. */
1934 if (rcu_nocb_adopt_orphan_cbs(rsp
, rdp
))
1937 /* Do the accounting first. */
1938 rdp
->qlen_lazy
+= rsp
->qlen_lazy
;
1939 rdp
->qlen
+= rsp
->qlen
;
1940 rdp
->n_cbs_adopted
+= rsp
->qlen
;
1941 if (rsp
->qlen_lazy
!= rsp
->qlen
)
1942 rcu_idle_count_callbacks_posted();
1947 * We do not need a memory barrier here because the only way we
1948 * can get here if there is an rcu_barrier() in flight is if
1949 * we are the task doing the rcu_barrier().
1952 /* First adopt the ready-to-invoke callbacks. */
1953 if (rsp
->orphan_donelist
!= NULL
) {
1954 *rsp
->orphan_donetail
= *rdp
->nxttail
[RCU_DONE_TAIL
];
1955 *rdp
->nxttail
[RCU_DONE_TAIL
] = rsp
->orphan_donelist
;
1956 for (i
= RCU_NEXT_SIZE
- 1; i
>= RCU_DONE_TAIL
; i
--)
1957 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
1958 rdp
->nxttail
[i
] = rsp
->orphan_donetail
;
1959 rsp
->orphan_donelist
= NULL
;
1960 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
1963 /* And then adopt the callbacks that still need a grace period. */
1964 if (rsp
->orphan_nxtlist
!= NULL
) {
1965 *rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxtlist
;
1966 rdp
->nxttail
[RCU_NEXT_TAIL
] = rsp
->orphan_nxttail
;
1967 rsp
->orphan_nxtlist
= NULL
;
1968 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
1973 * Trace the fact that this CPU is going offline.
1975 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
1977 RCU_TRACE(unsigned long mask
);
1978 RCU_TRACE(struct rcu_data
*rdp
= this_cpu_ptr(rsp
->rda
));
1979 RCU_TRACE(struct rcu_node
*rnp
= rdp
->mynode
);
1981 RCU_TRACE(mask
= rdp
->grpmask
);
1982 trace_rcu_grace_period(rsp
->name
,
1983 rnp
->gpnum
+ 1 - !!(rnp
->qsmask
& mask
),
1988 * The CPU has been completely removed, and some other CPU is reporting
1989 * this fact from process context. Do the remainder of the cleanup,
1990 * including orphaning the outgoing CPU's RCU callbacks, and also
1991 * adopting them. There can only be one CPU hotplug operation at a time,
1992 * so no other CPU can be attempting to update rcu_cpu_kthread_task.
1994 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
1996 unsigned long flags
;
1998 int need_report
= 0;
1999 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2000 struct rcu_node
*rnp
= rdp
->mynode
; /* Outgoing CPU's rdp & rnp. */
2002 /* Adjust any no-longer-needed kthreads. */
2003 rcu_boost_kthread_setaffinity(rnp
, -1);
2005 /* Remove the dead CPU from the bitmasks in the rcu_node hierarchy. */
2007 /* Exclude any attempts to start a new grace period. */
2008 mutex_lock(&rsp
->onoff_mutex
);
2009 raw_spin_lock_irqsave(&rsp
->orphan_lock
, flags
);
2011 /* Orphan the dead CPU's callbacks, and adopt them if appropriate. */
2012 rcu_send_cbs_to_orphanage(cpu
, rsp
, rnp
, rdp
);
2013 rcu_adopt_orphan_cbs(rsp
);
2015 /* Remove the outgoing CPU from the masks in the rcu_node hierarchy. */
2016 mask
= rdp
->grpmask
; /* rnp->grplo is constant. */
2018 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
2019 rnp
->qsmaskinit
&= ~mask
;
2020 if (rnp
->qsmaskinit
!= 0) {
2021 if (rnp
!= rdp
->mynode
)
2022 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2025 if (rnp
== rdp
->mynode
)
2026 need_report
= rcu_preempt_offline_tasks(rsp
, rnp
, rdp
);
2028 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
2029 mask
= rnp
->grpmask
;
2031 } while (rnp
!= NULL
);
2034 * We still hold the leaf rcu_node structure lock here, and
2035 * irqs are still disabled. The reason for this subterfuge is
2036 * because invoking rcu_report_unblock_qs_rnp() with ->orphan_lock
2037 * held leads to deadlock.
2039 raw_spin_unlock(&rsp
->orphan_lock
); /* irqs remain disabled. */
2041 if (need_report
& RCU_OFL_TASKS_NORM_GP
)
2042 rcu_report_unblock_qs_rnp(rnp
, flags
);
2044 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2045 if (need_report
& RCU_OFL_TASKS_EXP_GP
)
2046 rcu_report_exp_rnp(rsp
, rnp
, true);
2047 WARN_ONCE(rdp
->qlen
!= 0 || rdp
->nxtlist
!= NULL
,
2048 "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, nxtlist=%p\n",
2049 cpu
, rdp
->qlen
, rdp
->nxtlist
);
2050 init_callback_list(rdp
);
2051 /* Disallow further callbacks on this CPU. */
2052 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2053 mutex_unlock(&rsp
->onoff_mutex
);
2056 #else /* #ifdef CONFIG_HOTPLUG_CPU */
2058 static void rcu_cleanup_dying_cpu(struct rcu_state
*rsp
)
2062 static void rcu_cleanup_dead_cpu(int cpu
, struct rcu_state
*rsp
)
2066 #endif /* #else #ifdef CONFIG_HOTPLUG_CPU */
2069 * Invoke any RCU callbacks that have made it to the end of their grace
2070 * period. Thottle as specified by rdp->blimit.
2072 static void rcu_do_batch(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2074 unsigned long flags
;
2075 struct rcu_head
*next
, *list
, **tail
;
2076 long bl
, count
, count_lazy
;
2079 /* If no callbacks are ready, just return. */
2080 if (!cpu_has_callbacks_ready_to_invoke(rdp
)) {
2081 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, 0);
2082 trace_rcu_batch_end(rsp
->name
, 0, !!ACCESS_ONCE(rdp
->nxtlist
),
2083 need_resched(), is_idle_task(current
),
2084 rcu_is_callbacks_kthread());
2089 * Extract the list of ready callbacks, disabling to prevent
2090 * races with call_rcu() from interrupt handlers.
2092 local_irq_save(flags
);
2093 WARN_ON_ONCE(cpu_is_offline(smp_processor_id()));
2095 trace_rcu_batch_start(rsp
->name
, rdp
->qlen_lazy
, rdp
->qlen
, bl
);
2096 list
= rdp
->nxtlist
;
2097 rdp
->nxtlist
= *rdp
->nxttail
[RCU_DONE_TAIL
];
2098 *rdp
->nxttail
[RCU_DONE_TAIL
] = NULL
;
2099 tail
= rdp
->nxttail
[RCU_DONE_TAIL
];
2100 for (i
= RCU_NEXT_SIZE
- 1; i
>= 0; i
--)
2101 if (rdp
->nxttail
[i
] == rdp
->nxttail
[RCU_DONE_TAIL
])
2102 rdp
->nxttail
[i
] = &rdp
->nxtlist
;
2103 local_irq_restore(flags
);
2105 /* Invoke callbacks. */
2106 count
= count_lazy
= 0;
2110 debug_rcu_head_unqueue(list
);
2111 if (__rcu_reclaim(rsp
->name
, list
))
2114 /* Stop only if limit reached and CPU has something to do. */
2115 if (++count
>= bl
&&
2117 (!is_idle_task(current
) && !rcu_is_callbacks_kthread())))
2121 local_irq_save(flags
);
2122 trace_rcu_batch_end(rsp
->name
, count
, !!list
, need_resched(),
2123 is_idle_task(current
),
2124 rcu_is_callbacks_kthread());
2126 /* Update count, and requeue any remaining callbacks. */
2128 *tail
= rdp
->nxtlist
;
2129 rdp
->nxtlist
= list
;
2130 for (i
= 0; i
< RCU_NEXT_SIZE
; i
++)
2131 if (&rdp
->nxtlist
== rdp
->nxttail
[i
])
2132 rdp
->nxttail
[i
] = tail
;
2136 smp_mb(); /* List handling before counting for rcu_barrier(). */
2137 rdp
->qlen_lazy
-= count_lazy
;
2138 ACCESS_ONCE(rdp
->qlen
) -= count
;
2139 rdp
->n_cbs_invoked
+= count
;
2141 /* Reinstate batch limit if we have worked down the excess. */
2142 if (rdp
->blimit
== LONG_MAX
&& rdp
->qlen
<= qlowmark
)
2143 rdp
->blimit
= blimit
;
2145 /* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */
2146 if (rdp
->qlen
== 0 && rdp
->qlen_last_fqs_check
!= 0) {
2147 rdp
->qlen_last_fqs_check
= 0;
2148 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2149 } else if (rdp
->qlen
< rdp
->qlen_last_fqs_check
- qhimark
)
2150 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2151 WARN_ON_ONCE((rdp
->nxtlist
== NULL
) != (rdp
->qlen
== 0));
2153 local_irq_restore(flags
);
2155 /* Re-invoke RCU core processing if there are callbacks remaining. */
2156 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2161 * Check to see if this CPU is in a non-context-switch quiescent state
2162 * (user mode or idle loop for rcu, non-softirq execution for rcu_bh).
2163 * Also schedule RCU core processing.
2165 * This function must be called from hardirq context. It is normally
2166 * invoked from the scheduling-clock interrupt. If rcu_pending returns
2167 * false, there is no point in invoking rcu_check_callbacks().
2169 void rcu_check_callbacks(int cpu
, int user
)
2171 trace_rcu_utilization(TPS("Start scheduler-tick"));
2172 increment_cpu_stall_ticks();
2173 if (user
|| rcu_is_cpu_rrupt_from_idle()) {
2176 * Get here if this CPU took its interrupt from user
2177 * mode or from the idle loop, and if this is not a
2178 * nested interrupt. In this case, the CPU is in
2179 * a quiescent state, so note it.
2181 * No memory barrier is required here because both
2182 * rcu_sched_qs() and rcu_bh_qs() reference only CPU-local
2183 * variables that other CPUs neither access nor modify,
2184 * at least not while the corresponding CPU is online.
2190 } else if (!in_softirq()) {
2193 * Get here if this CPU did not take its interrupt from
2194 * softirq, in other words, if it is not interrupting
2195 * a rcu_bh read-side critical section. This is an _bh
2196 * critical section, so note it.
2201 rcu_preempt_check_callbacks(cpu
);
2202 if (rcu_pending(cpu
))
2204 trace_rcu_utilization(TPS("End scheduler-tick"));
2208 * Scan the leaf rcu_node structures, processing dyntick state for any that
2209 * have not yet encountered a quiescent state, using the function specified.
2210 * Also initiate boosting for any threads blocked on the root rcu_node.
2212 * The caller must have suppressed start of new grace periods.
2214 static void force_qs_rnp(struct rcu_state
*rsp
,
2215 int (*f
)(struct rcu_data
*rsp
, bool *isidle
,
2216 unsigned long *maxj
),
2217 bool *isidle
, unsigned long *maxj
)
2221 unsigned long flags
;
2223 struct rcu_node
*rnp
;
2225 rcu_for_each_leaf_node(rsp
, rnp
) {
2228 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2229 if (!rcu_gp_in_progress(rsp
)) {
2230 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2233 if (rnp
->qsmask
== 0) {
2234 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
2239 for (; cpu
<= rnp
->grphi
; cpu
++, bit
<<= 1) {
2240 if ((rnp
->qsmask
& bit
) != 0) {
2241 if ((rnp
->qsmaskinit
& bit
) != 0)
2243 if (f(per_cpu_ptr(rsp
->rda
, cpu
), isidle
, maxj
))
2249 /* rcu_report_qs_rnp() releases rnp->lock. */
2250 rcu_report_qs_rnp(mask
, rsp
, rnp
, flags
);
2253 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2255 rnp
= rcu_get_root(rsp
);
2256 if (rnp
->qsmask
== 0) {
2257 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2258 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock. */
2263 * Force quiescent states on reluctant CPUs, and also detect which
2264 * CPUs are in dyntick-idle mode.
2266 static void force_quiescent_state(struct rcu_state
*rsp
)
2268 unsigned long flags
;
2270 struct rcu_node
*rnp
;
2271 struct rcu_node
*rnp_old
= NULL
;
2273 /* Funnel through hierarchy to reduce memory contention. */
2274 rnp
= per_cpu_ptr(rsp
->rda
, raw_smp_processor_id())->mynode
;
2275 for (; rnp
!= NULL
; rnp
= rnp
->parent
) {
2276 ret
= (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) ||
2277 !raw_spin_trylock(&rnp
->fqslock
);
2278 if (rnp_old
!= NULL
)
2279 raw_spin_unlock(&rnp_old
->fqslock
);
2281 rsp
->n_force_qs_lh
++;
2286 /* rnp_old == rcu_get_root(rsp), rnp == NULL. */
2288 /* Reached the root of the rcu_node tree, acquire lock. */
2289 raw_spin_lock_irqsave(&rnp_old
->lock
, flags
);
2290 raw_spin_unlock(&rnp_old
->fqslock
);
2291 if (ACCESS_ONCE(rsp
->gp_flags
) & RCU_GP_FLAG_FQS
) {
2292 rsp
->n_force_qs_lh
++;
2293 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2294 return; /* Someone beat us to it. */
2296 rsp
->gp_flags
|= RCU_GP_FLAG_FQS
;
2297 raw_spin_unlock_irqrestore(&rnp_old
->lock
, flags
);
2298 wake_up(&rsp
->gp_wq
); /* Memory barrier implied by wake_up() path. */
2302 * This does the RCU core processing work for the specified rcu_state
2303 * and rcu_data structures. This may be called only from the CPU to
2304 * whom the rdp belongs.
2307 __rcu_process_callbacks(struct rcu_state
*rsp
)
2309 unsigned long flags
;
2310 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2312 WARN_ON_ONCE(rdp
->beenonline
== 0);
2314 /* Update RCU state based on any recent quiescent states. */
2315 rcu_check_quiescent_state(rsp
, rdp
);
2317 /* Does this CPU require a not-yet-started grace period? */
2318 local_irq_save(flags
);
2319 if (cpu_needs_another_gp(rsp
, rdp
)) {
2320 raw_spin_lock(&rcu_get_root(rsp
)->lock
); /* irqs disabled. */
2322 raw_spin_unlock_irqrestore(&rcu_get_root(rsp
)->lock
, flags
);
2324 local_irq_restore(flags
);
2327 /* If there are callbacks ready, invoke them. */
2328 if (cpu_has_callbacks_ready_to_invoke(rdp
))
2329 invoke_rcu_callbacks(rsp
, rdp
);
2333 * Do RCU core processing for the current CPU.
2335 static void rcu_process_callbacks(struct softirq_action
*unused
)
2337 struct rcu_state
*rsp
;
2339 if (cpu_is_offline(smp_processor_id()))
2341 trace_rcu_utilization(TPS("Start RCU core"));
2342 for_each_rcu_flavor(rsp
)
2343 __rcu_process_callbacks(rsp
);
2344 trace_rcu_utilization(TPS("End RCU core"));
2348 * Schedule RCU callback invocation. If the specified type of RCU
2349 * does not support RCU priority boosting, just do a direct call,
2350 * otherwise wake up the per-CPU kernel kthread. Note that because we
2351 * are running on the current CPU with interrupts disabled, the
2352 * rcu_cpu_kthread_task cannot disappear out from under us.
2354 static void invoke_rcu_callbacks(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2356 if (unlikely(!ACCESS_ONCE(rcu_scheduler_fully_active
)))
2358 if (likely(!rsp
->boost
)) {
2359 rcu_do_batch(rsp
, rdp
);
2362 invoke_rcu_callbacks_kthread();
2365 static void invoke_rcu_core(void)
2367 if (cpu_online(smp_processor_id()))
2368 raise_softirq(RCU_SOFTIRQ
);
2372 * Handle any core-RCU processing required by a call_rcu() invocation.
2374 static void __call_rcu_core(struct rcu_state
*rsp
, struct rcu_data
*rdp
,
2375 struct rcu_head
*head
, unsigned long flags
)
2378 * If called from an extended quiescent state, invoke the RCU
2379 * core in order to force a re-evaluation of RCU's idleness.
2381 if (!rcu_is_watching() && cpu_online(smp_processor_id()))
2384 /* If interrupts were disabled or CPU offline, don't invoke RCU core. */
2385 if (irqs_disabled_flags(flags
) || cpu_is_offline(smp_processor_id()))
2389 * Force the grace period if too many callbacks or too long waiting.
2390 * Enforce hysteresis, and don't invoke force_quiescent_state()
2391 * if some other CPU has recently done so. Also, don't bother
2392 * invoking force_quiescent_state() if the newly enqueued callback
2393 * is the only one waiting for a grace period to complete.
2395 if (unlikely(rdp
->qlen
> rdp
->qlen_last_fqs_check
+ qhimark
)) {
2397 /* Are we ignoring a completed grace period? */
2398 note_gp_changes(rsp
, rdp
);
2400 /* Start a new grace period if one not already started. */
2401 if (!rcu_gp_in_progress(rsp
)) {
2402 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
2404 raw_spin_lock(&rnp_root
->lock
);
2406 raw_spin_unlock(&rnp_root
->lock
);
2408 /* Give the grace period a kick. */
2409 rdp
->blimit
= LONG_MAX
;
2410 if (rsp
->n_force_qs
== rdp
->n_force_qs_snap
&&
2411 *rdp
->nxttail
[RCU_DONE_TAIL
] != head
)
2412 force_quiescent_state(rsp
);
2413 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
2414 rdp
->qlen_last_fqs_check
= rdp
->qlen
;
2420 * RCU callback function to leak a callback.
2422 static void rcu_leak_callback(struct rcu_head
*rhp
)
2427 * Helper function for call_rcu() and friends. The cpu argument will
2428 * normally be -1, indicating "currently running CPU". It may specify
2429 * a CPU only if that CPU is a no-CBs CPU. Currently, only _rcu_barrier()
2430 * is expected to specify a CPU.
2433 __call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
),
2434 struct rcu_state
*rsp
, int cpu
, bool lazy
)
2436 unsigned long flags
;
2437 struct rcu_data
*rdp
;
2439 WARN_ON_ONCE((unsigned long)head
& 0x3); /* Misaligned rcu_head! */
2440 if (debug_rcu_head_queue(head
)) {
2441 /* Probable double call_rcu(), so leak the callback. */
2442 ACCESS_ONCE(head
->func
) = rcu_leak_callback
;
2443 WARN_ONCE(1, "__call_rcu(): Leaked duplicate callback\n");
2450 * Opportunistically note grace-period endings and beginnings.
2451 * Note that we might see a beginning right after we see an
2452 * end, but never vice versa, since this CPU has to pass through
2453 * a quiescent state betweentimes.
2455 local_irq_save(flags
);
2456 rdp
= this_cpu_ptr(rsp
->rda
);
2458 /* Add the callback to our list. */
2459 if (unlikely(rdp
->nxttail
[RCU_NEXT_TAIL
] == NULL
) || cpu
!= -1) {
2463 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2464 offline
= !__call_rcu_nocb(rdp
, head
, lazy
);
2465 WARN_ON_ONCE(offline
);
2466 /* _call_rcu() is illegal on offline CPU; leak the callback. */
2467 local_irq_restore(flags
);
2470 ACCESS_ONCE(rdp
->qlen
)++;
2474 rcu_idle_count_callbacks_posted();
2475 smp_mb(); /* Count before adding callback for rcu_barrier(). */
2476 *rdp
->nxttail
[RCU_NEXT_TAIL
] = head
;
2477 rdp
->nxttail
[RCU_NEXT_TAIL
] = &head
->next
;
2479 if (__is_kfree_rcu_offset((unsigned long)func
))
2480 trace_rcu_kfree_callback(rsp
->name
, head
, (unsigned long)func
,
2481 rdp
->qlen_lazy
, rdp
->qlen
);
2483 trace_rcu_callback(rsp
->name
, head
, rdp
->qlen_lazy
, rdp
->qlen
);
2485 /* Go handle any RCU core processing required. */
2486 __call_rcu_core(rsp
, rdp
, head
, flags
);
2487 local_irq_restore(flags
);
2491 * Queue an RCU-sched callback for invocation after a grace period.
2493 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2495 __call_rcu(head
, func
, &rcu_sched_state
, -1, 0);
2497 EXPORT_SYMBOL_GPL(call_rcu_sched
);
2500 * Queue an RCU callback for invocation after a quicker grace period.
2502 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
2504 __call_rcu(head
, func
, &rcu_bh_state
, -1, 0);
2506 EXPORT_SYMBOL_GPL(call_rcu_bh
);
2509 * Because a context switch is a grace period for RCU-sched and RCU-bh,
2510 * any blocking grace-period wait automatically implies a grace period
2511 * if there is only one CPU online at any point time during execution
2512 * of either synchronize_sched() or synchronize_rcu_bh(). It is OK to
2513 * occasionally incorrectly indicate that there are multiple CPUs online
2514 * when there was in fact only one the whole time, as this just adds
2515 * some overhead: RCU still operates correctly.
2517 static inline int rcu_blocking_is_gp(void)
2521 might_sleep(); /* Check for RCU read-side critical section. */
2523 ret
= num_online_cpus() <= 1;
2529 * synchronize_sched - wait until an rcu-sched grace period has elapsed.
2531 * Control will return to the caller some time after a full rcu-sched
2532 * grace period has elapsed, in other words after all currently executing
2533 * rcu-sched read-side critical sections have completed. These read-side
2534 * critical sections are delimited by rcu_read_lock_sched() and
2535 * rcu_read_unlock_sched(), and may be nested. Note that preempt_disable(),
2536 * local_irq_disable(), and so on may be used in place of
2537 * rcu_read_lock_sched().
2539 * This means that all preempt_disable code sequences, including NMI and
2540 * non-threaded hardware-interrupt handlers, in progress on entry will
2541 * have completed before this primitive returns. However, this does not
2542 * guarantee that softirq handlers will have completed, since in some
2543 * kernels, these handlers can run in process context, and can block.
2545 * Note that this guarantee implies further memory-ordering guarantees.
2546 * On systems with more than one CPU, when synchronize_sched() returns,
2547 * each CPU is guaranteed to have executed a full memory barrier since the
2548 * end of its last RCU-sched read-side critical section whose beginning
2549 * preceded the call to synchronize_sched(). In addition, each CPU having
2550 * an RCU read-side critical section that extends beyond the return from
2551 * synchronize_sched() is guaranteed to have executed a full memory barrier
2552 * after the beginning of synchronize_sched() and before the beginning of
2553 * that RCU read-side critical section. Note that these guarantees include
2554 * CPUs that are offline, idle, or executing in user mode, as well as CPUs
2555 * that are executing in the kernel.
2557 * Furthermore, if CPU A invoked synchronize_sched(), which returned
2558 * to its caller on CPU B, then both CPU A and CPU B are guaranteed
2559 * to have executed a full memory barrier during the execution of
2560 * synchronize_sched() -- even if CPU A and CPU B are the same CPU (but
2561 * again only if the system has more than one CPU).
2563 * This primitive provides the guarantees made by the (now removed)
2564 * synchronize_kernel() API. In contrast, synchronize_rcu() only
2565 * guarantees that rcu_read_lock() sections will have completed.
2566 * In "classic RCU", these two guarantees happen to be one and
2567 * the same, but can differ in realtime RCU implementations.
2569 void synchronize_sched(void)
2571 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2572 !lock_is_held(&rcu_lock_map
) &&
2573 !lock_is_held(&rcu_sched_lock_map
),
2574 "Illegal synchronize_sched() in RCU-sched read-side critical section");
2575 if (rcu_blocking_is_gp())
2578 synchronize_sched_expedited();
2580 wait_rcu_gp(call_rcu_sched
);
2582 EXPORT_SYMBOL_GPL(synchronize_sched
);
2585 * synchronize_rcu_bh - wait until an rcu_bh grace period has elapsed.
2587 * Control will return to the caller some time after a full rcu_bh grace
2588 * period has elapsed, in other words after all currently executing rcu_bh
2589 * read-side critical sections have completed. RCU read-side critical
2590 * sections are delimited by rcu_read_lock_bh() and rcu_read_unlock_bh(),
2591 * and may be nested.
2593 * See the description of synchronize_sched() for more detailed information
2594 * on memory ordering guarantees.
2596 void synchronize_rcu_bh(void)
2598 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
2599 !lock_is_held(&rcu_lock_map
) &&
2600 !lock_is_held(&rcu_sched_lock_map
),
2601 "Illegal synchronize_rcu_bh() in RCU-bh read-side critical section");
2602 if (rcu_blocking_is_gp())
2605 synchronize_rcu_bh_expedited();
2607 wait_rcu_gp(call_rcu_bh
);
2609 EXPORT_SYMBOL_GPL(synchronize_rcu_bh
);
2611 static int synchronize_sched_expedited_cpu_stop(void *data
)
2614 * There must be a full memory barrier on each affected CPU
2615 * between the time that try_stop_cpus() is called and the
2616 * time that it returns.
2618 * In the current initial implementation of cpu_stop, the
2619 * above condition is already met when the control reaches
2620 * this point and the following smp_mb() is not strictly
2621 * necessary. Do smp_mb() anyway for documentation and
2622 * robustness against future implementation changes.
2624 smp_mb(); /* See above comment block. */
2629 * synchronize_sched_expedited - Brute-force RCU-sched grace period
2631 * Wait for an RCU-sched grace period to elapse, but use a "big hammer"
2632 * approach to force the grace period to end quickly. This consumes
2633 * significant time on all CPUs and is unfriendly to real-time workloads,
2634 * so is thus not recommended for any sort of common-case code. In fact,
2635 * if you are using synchronize_sched_expedited() in a loop, please
2636 * restructure your code to batch your updates, and then use a single
2637 * synchronize_sched() instead.
2639 * Note that it is illegal to call this function while holding any lock
2640 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
2641 * to call this function from a CPU-hotplug notifier. Failing to observe
2642 * these restriction will result in deadlock.
2644 * This implementation can be thought of as an application of ticket
2645 * locking to RCU, with sync_sched_expedited_started and
2646 * sync_sched_expedited_done taking on the roles of the halves
2647 * of the ticket-lock word. Each task atomically increments
2648 * sync_sched_expedited_started upon entry, snapshotting the old value,
2649 * then attempts to stop all the CPUs. If this succeeds, then each
2650 * CPU will have executed a context switch, resulting in an RCU-sched
2651 * grace period. We are then done, so we use atomic_cmpxchg() to
2652 * update sync_sched_expedited_done to match our snapshot -- but
2653 * only if someone else has not already advanced past our snapshot.
2655 * On the other hand, if try_stop_cpus() fails, we check the value
2656 * of sync_sched_expedited_done. If it has advanced past our
2657 * initial snapshot, then someone else must have forced a grace period
2658 * some time after we took our snapshot. In this case, our work is
2659 * done for us, and we can simply return. Otherwise, we try again,
2660 * but keep our initial snapshot for purposes of checking for someone
2661 * doing our work for us.
2663 * If we fail too many times in a row, we fall back to synchronize_sched().
2665 void synchronize_sched_expedited(void)
2667 long firstsnap
, s
, snap
;
2669 struct rcu_state
*rsp
= &rcu_sched_state
;
2672 * If we are in danger of counter wrap, just do synchronize_sched().
2673 * By allowing sync_sched_expedited_started to advance no more than
2674 * ULONG_MAX/8 ahead of sync_sched_expedited_done, we are ensuring
2675 * that more than 3.5 billion CPUs would be required to force a
2676 * counter wrap on a 32-bit system. Quite a few more CPUs would of
2677 * course be required on a 64-bit system.
2679 if (ULONG_CMP_GE((ulong
)atomic_long_read(&rsp
->expedited_start
),
2680 (ulong
)atomic_long_read(&rsp
->expedited_done
) +
2682 synchronize_sched();
2683 atomic_long_inc(&rsp
->expedited_wrap
);
2688 * Take a ticket. Note that atomic_inc_return() implies a
2689 * full memory barrier.
2691 snap
= atomic_long_inc_return(&rsp
->expedited_start
);
2694 WARN_ON_ONCE(cpu_is_offline(raw_smp_processor_id()));
2697 * Each pass through the following loop attempts to force a
2698 * context switch on each CPU.
2700 while (try_stop_cpus(cpu_online_mask
,
2701 synchronize_sched_expedited_cpu_stop
,
2704 atomic_long_inc(&rsp
->expedited_tryfail
);
2706 /* Check to see if someone else did our work for us. */
2707 s
= atomic_long_read(&rsp
->expedited_done
);
2708 if (ULONG_CMP_GE((ulong
)s
, (ulong
)firstsnap
)) {
2709 /* ensure test happens before caller kfree */
2710 smp_mb__before_atomic_inc(); /* ^^^ */
2711 atomic_long_inc(&rsp
->expedited_workdone1
);
2715 /* No joy, try again later. Or just synchronize_sched(). */
2716 if (trycount
++ < 10) {
2717 udelay(trycount
* num_online_cpus());
2719 wait_rcu_gp(call_rcu_sched
);
2720 atomic_long_inc(&rsp
->expedited_normal
);
2724 /* Recheck to see if someone else did our work for us. */
2725 s
= atomic_long_read(&rsp
->expedited_done
);
2726 if (ULONG_CMP_GE((ulong
)s
, (ulong
)firstsnap
)) {
2727 /* ensure test happens before caller kfree */
2728 smp_mb__before_atomic_inc(); /* ^^^ */
2729 atomic_long_inc(&rsp
->expedited_workdone2
);
2734 * Refetching sync_sched_expedited_started allows later
2735 * callers to piggyback on our grace period. We retry
2736 * after they started, so our grace period works for them,
2737 * and they started after our first try, so their grace
2738 * period works for us.
2741 snap
= atomic_long_read(&rsp
->expedited_start
);
2742 smp_mb(); /* ensure read is before try_stop_cpus(). */
2744 atomic_long_inc(&rsp
->expedited_stoppedcpus
);
2747 * Everyone up to our most recent fetch is covered by our grace
2748 * period. Update the counter, but only if our work is still
2749 * relevant -- which it won't be if someone who started later
2750 * than we did already did their update.
2753 atomic_long_inc(&rsp
->expedited_done_tries
);
2754 s
= atomic_long_read(&rsp
->expedited_done
);
2755 if (ULONG_CMP_GE((ulong
)s
, (ulong
)snap
)) {
2756 /* ensure test happens before caller kfree */
2757 smp_mb__before_atomic_inc(); /* ^^^ */
2758 atomic_long_inc(&rsp
->expedited_done_lost
);
2761 } while (atomic_long_cmpxchg(&rsp
->expedited_done
, s
, snap
) != s
);
2762 atomic_long_inc(&rsp
->expedited_done_exit
);
2766 EXPORT_SYMBOL_GPL(synchronize_sched_expedited
);
2769 * Check to see if there is any immediate RCU-related work to be done
2770 * by the current CPU, for the specified type of RCU, returning 1 if so.
2771 * The checks are in order of increasing expense: checks that can be
2772 * carried out against CPU-local state are performed first. However,
2773 * we must check for CPU stalls first, else we might not get a chance.
2775 static int __rcu_pending(struct rcu_state
*rsp
, struct rcu_data
*rdp
)
2777 struct rcu_node
*rnp
= rdp
->mynode
;
2779 rdp
->n_rcu_pending
++;
2781 /* Check for CPU stalls, if enabled. */
2782 check_cpu_stall(rsp
, rdp
);
2784 /* Is the RCU core waiting for a quiescent state from this CPU? */
2785 if (rcu_scheduler_fully_active
&&
2786 rdp
->qs_pending
&& !rdp
->passed_quiesce
) {
2787 rdp
->n_rp_qs_pending
++;
2788 } else if (rdp
->qs_pending
&& rdp
->passed_quiesce
) {
2789 rdp
->n_rp_report_qs
++;
2793 /* Does this CPU have callbacks ready to invoke? */
2794 if (cpu_has_callbacks_ready_to_invoke(rdp
)) {
2795 rdp
->n_rp_cb_ready
++;
2799 /* Has RCU gone idle with this CPU needing another grace period? */
2800 if (cpu_needs_another_gp(rsp
, rdp
)) {
2801 rdp
->n_rp_cpu_needs_gp
++;
2805 /* Has another RCU grace period completed? */
2806 if (ACCESS_ONCE(rnp
->completed
) != rdp
->completed
) { /* outside lock */
2807 rdp
->n_rp_gp_completed
++;
2811 /* Has a new RCU grace period started? */
2812 if (ACCESS_ONCE(rnp
->gpnum
) != rdp
->gpnum
) { /* outside lock */
2813 rdp
->n_rp_gp_started
++;
2818 rdp
->n_rp_need_nothing
++;
2823 * Check to see if there is any immediate RCU-related work to be done
2824 * by the current CPU, returning 1 if so. This function is part of the
2825 * RCU implementation; it is -not- an exported member of the RCU API.
2827 static int rcu_pending(int cpu
)
2829 struct rcu_state
*rsp
;
2831 for_each_rcu_flavor(rsp
)
2832 if (__rcu_pending(rsp
, per_cpu_ptr(rsp
->rda
, cpu
)))
2838 * Return true if the specified CPU has any callback. If all_lazy is
2839 * non-NULL, store an indication of whether all callbacks are lazy.
2840 * (If there are no callbacks, all of them are deemed to be lazy.)
2842 static int rcu_cpu_has_callbacks(int cpu
, bool *all_lazy
)
2846 struct rcu_data
*rdp
;
2847 struct rcu_state
*rsp
;
2849 for_each_rcu_flavor(rsp
) {
2850 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2854 if (rdp
->qlen
!= rdp
->qlen_lazy
|| !all_lazy
) {
2865 * Helper function for _rcu_barrier() tracing. If tracing is disabled,
2866 * the compiler is expected to optimize this away.
2868 static void _rcu_barrier_trace(struct rcu_state
*rsp
, const char *s
,
2869 int cpu
, unsigned long done
)
2871 trace_rcu_barrier(rsp
->name
, s
, cpu
,
2872 atomic_read(&rsp
->barrier_cpu_count
), done
);
2876 * RCU callback function for _rcu_barrier(). If we are last, wake
2877 * up the task executing _rcu_barrier().
2879 static void rcu_barrier_callback(struct rcu_head
*rhp
)
2881 struct rcu_data
*rdp
= container_of(rhp
, struct rcu_data
, barrier_head
);
2882 struct rcu_state
*rsp
= rdp
->rsp
;
2884 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
)) {
2885 _rcu_barrier_trace(rsp
, "LastCB", -1, rsp
->n_barrier_done
);
2886 complete(&rsp
->barrier_completion
);
2888 _rcu_barrier_trace(rsp
, "CB", -1, rsp
->n_barrier_done
);
2893 * Called with preemption disabled, and from cross-cpu IRQ context.
2895 static void rcu_barrier_func(void *type
)
2897 struct rcu_state
*rsp
= type
;
2898 struct rcu_data
*rdp
= __this_cpu_ptr(rsp
->rda
);
2900 _rcu_barrier_trace(rsp
, "IRQ", -1, rsp
->n_barrier_done
);
2901 atomic_inc(&rsp
->barrier_cpu_count
);
2902 rsp
->call(&rdp
->barrier_head
, rcu_barrier_callback
);
2906 * Orchestrate the specified type of RCU barrier, waiting for all
2907 * RCU callbacks of the specified type to complete.
2909 static void _rcu_barrier(struct rcu_state
*rsp
)
2912 struct rcu_data
*rdp
;
2913 unsigned long snap
= ACCESS_ONCE(rsp
->n_barrier_done
);
2914 unsigned long snap_done
;
2916 _rcu_barrier_trace(rsp
, "Begin", -1, snap
);
2918 /* Take mutex to serialize concurrent rcu_barrier() requests. */
2919 mutex_lock(&rsp
->barrier_mutex
);
2922 * Ensure that all prior references, including to ->n_barrier_done,
2923 * are ordered before the _rcu_barrier() machinery.
2925 smp_mb(); /* See above block comment. */
2928 * Recheck ->n_barrier_done to see if others did our work for us.
2929 * This means checking ->n_barrier_done for an even-to-odd-to-even
2930 * transition. The "if" expression below therefore rounds the old
2931 * value up to the next even number and adds two before comparing.
2933 snap_done
= rsp
->n_barrier_done
;
2934 _rcu_barrier_trace(rsp
, "Check", -1, snap_done
);
2937 * If the value in snap is odd, we needed to wait for the current
2938 * rcu_barrier() to complete, then wait for the next one, in other
2939 * words, we need the value of snap_done to be three larger than
2940 * the value of snap. On the other hand, if the value in snap is
2941 * even, we only had to wait for the next rcu_barrier() to complete,
2942 * in other words, we need the value of snap_done to be only two
2943 * greater than the value of snap. The "(snap + 3) & ~0x1" computes
2944 * this for us (thank you, Linus!).
2946 if (ULONG_CMP_GE(snap_done
, (snap
+ 3) & ~0x1)) {
2947 _rcu_barrier_trace(rsp
, "EarlyExit", -1, snap_done
);
2948 smp_mb(); /* caller's subsequent code after above check. */
2949 mutex_unlock(&rsp
->barrier_mutex
);
2954 * Increment ->n_barrier_done to avoid duplicate work. Use
2955 * ACCESS_ONCE() to prevent the compiler from speculating
2956 * the increment to precede the early-exit check.
2958 ACCESS_ONCE(rsp
->n_barrier_done
)++;
2959 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 1);
2960 _rcu_barrier_trace(rsp
, "Inc1", -1, rsp
->n_barrier_done
);
2961 smp_mb(); /* Order ->n_barrier_done increment with below mechanism. */
2964 * Initialize the count to one rather than to zero in order to
2965 * avoid a too-soon return to zero in case of a short grace period
2966 * (or preemption of this task). Exclude CPU-hotplug operations
2967 * to ensure that no offline CPU has callbacks queued.
2969 init_completion(&rsp
->barrier_completion
);
2970 atomic_set(&rsp
->barrier_cpu_count
, 1);
2974 * Force each CPU with callbacks to register a new callback.
2975 * When that callback is invoked, we will know that all of the
2976 * corresponding CPU's preceding callbacks have been invoked.
2978 for_each_possible_cpu(cpu
) {
2979 if (!cpu_online(cpu
) && !rcu_is_nocb_cpu(cpu
))
2981 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2982 if (rcu_is_nocb_cpu(cpu
)) {
2983 _rcu_barrier_trace(rsp
, "OnlineNoCB", cpu
,
2984 rsp
->n_barrier_done
);
2985 atomic_inc(&rsp
->barrier_cpu_count
);
2986 __call_rcu(&rdp
->barrier_head
, rcu_barrier_callback
,
2988 } else if (ACCESS_ONCE(rdp
->qlen
)) {
2989 _rcu_barrier_trace(rsp
, "OnlineQ", cpu
,
2990 rsp
->n_barrier_done
);
2991 smp_call_function_single(cpu
, rcu_barrier_func
, rsp
, 1);
2993 _rcu_barrier_trace(rsp
, "OnlineNQ", cpu
,
2994 rsp
->n_barrier_done
);
3000 * Now that we have an rcu_barrier_callback() callback on each
3001 * CPU, and thus each counted, remove the initial count.
3003 if (atomic_dec_and_test(&rsp
->barrier_cpu_count
))
3004 complete(&rsp
->barrier_completion
);
3006 /* Increment ->n_barrier_done to prevent duplicate work. */
3007 smp_mb(); /* Keep increment after above mechanism. */
3008 ACCESS_ONCE(rsp
->n_barrier_done
)++;
3009 WARN_ON_ONCE((rsp
->n_barrier_done
& 0x1) != 0);
3010 _rcu_barrier_trace(rsp
, "Inc2", -1, rsp
->n_barrier_done
);
3011 smp_mb(); /* Keep increment before caller's subsequent code. */
3013 /* Wait for all rcu_barrier_callback() callbacks to be invoked. */
3014 wait_for_completion(&rsp
->barrier_completion
);
3016 /* Other rcu_barrier() invocations can now safely proceed. */
3017 mutex_unlock(&rsp
->barrier_mutex
);
3021 * rcu_barrier_bh - Wait until all in-flight call_rcu_bh() callbacks complete.
3023 void rcu_barrier_bh(void)
3025 _rcu_barrier(&rcu_bh_state
);
3027 EXPORT_SYMBOL_GPL(rcu_barrier_bh
);
3030 * rcu_barrier_sched - Wait for in-flight call_rcu_sched() callbacks.
3032 void rcu_barrier_sched(void)
3034 _rcu_barrier(&rcu_sched_state
);
3036 EXPORT_SYMBOL_GPL(rcu_barrier_sched
);
3039 * Do boot-time initialization of a CPU's per-CPU RCU data.
3042 rcu_boot_init_percpu_data(int cpu
, struct rcu_state
*rsp
)
3044 unsigned long flags
;
3045 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3046 struct rcu_node
*rnp
= rcu_get_root(rsp
);
3048 /* Set up local state, ensuring consistent view of global state. */
3049 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3050 rdp
->grpmask
= 1UL << (cpu
- rdp
->mynode
->grplo
);
3051 init_callback_list(rdp
);
3053 ACCESS_ONCE(rdp
->qlen
) = 0;
3054 rdp
->dynticks
= &per_cpu(rcu_dynticks
, cpu
);
3055 WARN_ON_ONCE(rdp
->dynticks
->dynticks_nesting
!= DYNTICK_TASK_EXIT_IDLE
);
3056 WARN_ON_ONCE(atomic_read(&rdp
->dynticks
->dynticks
) != 1);
3059 rcu_boot_init_nocb_percpu_data(rdp
);
3060 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
3064 * Initialize a CPU's per-CPU RCU data. Note that only one online or
3065 * offline event can be happening at a given time. Note also that we
3066 * can accept some slop in the rsp->completed access due to the fact
3067 * that this CPU cannot possibly have any RCU callbacks in flight yet.
3070 rcu_init_percpu_data(int cpu
, struct rcu_state
*rsp
, int preemptible
)
3072 unsigned long flags
;
3074 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
3075 struct rcu_node
*rnp
= rcu_get_root(rsp
);
3077 /* Exclude new grace periods. */
3078 mutex_lock(&rsp
->onoff_mutex
);
3080 /* Set up local state, ensuring consistent view of global state. */
3081 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3082 rdp
->beenonline
= 1; /* We have now been online. */
3083 rdp
->preemptible
= preemptible
;
3084 rdp
->qlen_last_fqs_check
= 0;
3085 rdp
->n_force_qs_snap
= rsp
->n_force_qs
;
3086 rdp
->blimit
= blimit
;
3087 init_callback_list(rdp
); /* Re-enable callbacks on this CPU. */
3088 rdp
->dynticks
->dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
3089 rcu_sysidle_init_percpu_data(rdp
->dynticks
);
3090 atomic_set(&rdp
->dynticks
->dynticks
,
3091 (atomic_read(&rdp
->dynticks
->dynticks
) & ~0x1) + 1);
3092 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
3094 /* Add CPU to rcu_node bitmasks. */
3096 mask
= rdp
->grpmask
;
3098 /* Exclude any attempts to start a new GP on small systems. */
3099 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
3100 rnp
->qsmaskinit
|= mask
;
3101 mask
= rnp
->grpmask
;
3102 if (rnp
== rdp
->mynode
) {
3104 * If there is a grace period in progress, we will
3105 * set up to wait for it next time we run the
3108 rdp
->gpnum
= rnp
->completed
;
3109 rdp
->completed
= rnp
->completed
;
3110 rdp
->passed_quiesce
= 0;
3111 rdp
->qs_pending
= 0;
3112 trace_rcu_grace_period(rsp
->name
, rdp
->gpnum
, TPS("cpuonl"));
3114 raw_spin_unlock(&rnp
->lock
); /* irqs already disabled. */
3116 } while (rnp
!= NULL
&& !(rnp
->qsmaskinit
& mask
));
3117 local_irq_restore(flags
);
3119 mutex_unlock(&rsp
->onoff_mutex
);
3122 static void rcu_prepare_cpu(int cpu
)
3124 struct rcu_state
*rsp
;
3126 for_each_rcu_flavor(rsp
)
3127 rcu_init_percpu_data(cpu
, rsp
,
3128 strcmp(rsp
->name
, "rcu_preempt") == 0);
3132 * Handle CPU online/offline notification events.
3134 static int rcu_cpu_notify(struct notifier_block
*self
,
3135 unsigned long action
, void *hcpu
)
3137 long cpu
= (long)hcpu
;
3138 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
3139 struct rcu_node
*rnp
= rdp
->mynode
;
3140 struct rcu_state
*rsp
;
3142 trace_rcu_utilization(TPS("Start CPU hotplug"));
3144 case CPU_UP_PREPARE
:
3145 case CPU_UP_PREPARE_FROZEN
:
3146 rcu_prepare_cpu(cpu
);
3147 rcu_prepare_kthreads(cpu
);
3150 case CPU_DOWN_FAILED
:
3151 rcu_boost_kthread_setaffinity(rnp
, -1);
3153 case CPU_DOWN_PREPARE
:
3154 rcu_boost_kthread_setaffinity(rnp
, cpu
);
3157 case CPU_DYING_FROZEN
:
3158 for_each_rcu_flavor(rsp
)
3159 rcu_cleanup_dying_cpu(rsp
);
3162 case CPU_DEAD_FROZEN
:
3163 case CPU_UP_CANCELED
:
3164 case CPU_UP_CANCELED_FROZEN
:
3165 for_each_rcu_flavor(rsp
)
3166 rcu_cleanup_dead_cpu(cpu
, rsp
);
3171 trace_rcu_utilization(TPS("End CPU hotplug"));
3175 static int rcu_pm_notify(struct notifier_block
*self
,
3176 unsigned long action
, void *hcpu
)
3179 case PM_HIBERNATION_PREPARE
:
3180 case PM_SUSPEND_PREPARE
:
3181 if (nr_cpu_ids
<= 256) /* Expediting bad for large systems. */
3184 case PM_POST_HIBERNATION
:
3185 case PM_POST_SUSPEND
:
3195 * Spawn the kthread that handles this RCU flavor's grace periods.
3197 static int __init
rcu_spawn_gp_kthread(void)
3199 unsigned long flags
;
3200 struct rcu_node
*rnp
;
3201 struct rcu_state
*rsp
;
3202 struct task_struct
*t
;
3204 for_each_rcu_flavor(rsp
) {
3205 t
= kthread_run(rcu_gp_kthread
, rsp
, "%s", rsp
->name
);
3207 rnp
= rcu_get_root(rsp
);
3208 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
3209 rsp
->gp_kthread
= t
;
3210 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
3211 rcu_spawn_nocb_kthreads(rsp
);
3215 early_initcall(rcu_spawn_gp_kthread
);
3218 * This function is invoked towards the end of the scheduler's initialization
3219 * process. Before this is called, the idle task might contain
3220 * RCU read-side critical sections (during which time, this idle
3221 * task is booting the system). After this function is called, the
3222 * idle tasks are prohibited from containing RCU read-side critical
3223 * sections. This function also enables RCU lockdep checking.
3225 void rcu_scheduler_starting(void)
3227 WARN_ON(num_online_cpus() != 1);
3228 WARN_ON(nr_context_switches() > 0);
3229 rcu_scheduler_active
= 1;
3233 * Compute the per-level fanout, either using the exact fanout specified
3234 * or balancing the tree, depending on CONFIG_RCU_FANOUT_EXACT.
3236 #ifdef CONFIG_RCU_FANOUT_EXACT
3237 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
3241 for (i
= rcu_num_lvls
- 1; i
> 0; i
--)
3242 rsp
->levelspread
[i
] = CONFIG_RCU_FANOUT
;
3243 rsp
->levelspread
[0] = rcu_fanout_leaf
;
3245 #else /* #ifdef CONFIG_RCU_FANOUT_EXACT */
3246 static void __init
rcu_init_levelspread(struct rcu_state
*rsp
)
3253 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
3254 ccur
= rsp
->levelcnt
[i
];
3255 rsp
->levelspread
[i
] = (cprv
+ ccur
- 1) / ccur
;
3259 #endif /* #else #ifdef CONFIG_RCU_FANOUT_EXACT */
3262 * Helper function for rcu_init() that initializes one rcu_state structure.
3264 static void __init
rcu_init_one(struct rcu_state
*rsp
,
3265 struct rcu_data __percpu
*rda
)
3267 static char *buf
[] = { "rcu_node_0",
3270 "rcu_node_3" }; /* Match MAX_RCU_LVLS */
3271 static char *fqs
[] = { "rcu_node_fqs_0",
3274 "rcu_node_fqs_3" }; /* Match MAX_RCU_LVLS */
3278 struct rcu_node
*rnp
;
3280 BUILD_BUG_ON(MAX_RCU_LVLS
> ARRAY_SIZE(buf
)); /* Fix buf[] init! */
3282 /* Silence gcc 4.8 warning about array index out of range. */
3283 if (rcu_num_lvls
> RCU_NUM_LVLS
)
3284 panic("rcu_init_one: rcu_num_lvls overflow");
3286 /* Initialize the level-tracking arrays. */
3288 for (i
= 0; i
< rcu_num_lvls
; i
++)
3289 rsp
->levelcnt
[i
] = num_rcu_lvl
[i
];
3290 for (i
= 1; i
< rcu_num_lvls
; i
++)
3291 rsp
->level
[i
] = rsp
->level
[i
- 1] + rsp
->levelcnt
[i
- 1];
3292 rcu_init_levelspread(rsp
);
3294 /* Initialize the elements themselves, starting from the leaves. */
3296 for (i
= rcu_num_lvls
- 1; i
>= 0; i
--) {
3297 cpustride
*= rsp
->levelspread
[i
];
3298 rnp
= rsp
->level
[i
];
3299 for (j
= 0; j
< rsp
->levelcnt
[i
]; j
++, rnp
++) {
3300 raw_spin_lock_init(&rnp
->lock
);
3301 lockdep_set_class_and_name(&rnp
->lock
,
3302 &rcu_node_class
[i
], buf
[i
]);
3303 raw_spin_lock_init(&rnp
->fqslock
);
3304 lockdep_set_class_and_name(&rnp
->fqslock
,
3305 &rcu_fqs_class
[i
], fqs
[i
]);
3306 rnp
->gpnum
= rsp
->gpnum
;
3307 rnp
->completed
= rsp
->completed
;
3309 rnp
->qsmaskinit
= 0;
3310 rnp
->grplo
= j
* cpustride
;
3311 rnp
->grphi
= (j
+ 1) * cpustride
- 1;
3312 if (rnp
->grphi
>= NR_CPUS
)
3313 rnp
->grphi
= NR_CPUS
- 1;
3319 rnp
->grpnum
= j
% rsp
->levelspread
[i
- 1];
3320 rnp
->grpmask
= 1UL << rnp
->grpnum
;
3321 rnp
->parent
= rsp
->level
[i
- 1] +
3322 j
/ rsp
->levelspread
[i
- 1];
3325 INIT_LIST_HEAD(&rnp
->blkd_tasks
);
3326 rcu_init_one_nocb(rnp
);
3331 init_waitqueue_head(&rsp
->gp_wq
);
3332 init_irq_work(&rsp
->wakeup_work
, rsp_wakeup
);
3333 rnp
= rsp
->level
[rcu_num_lvls
- 1];
3334 for_each_possible_cpu(i
) {
3335 while (i
> rnp
->grphi
)
3337 per_cpu_ptr(rsp
->rda
, i
)->mynode
= rnp
;
3338 rcu_boot_init_percpu_data(i
, rsp
);
3340 list_add(&rsp
->flavors
, &rcu_struct_flavors
);
3344 * Compute the rcu_node tree geometry from kernel parameters. This cannot
3345 * replace the definitions in tree.h because those are needed to size
3346 * the ->node array in the rcu_state structure.
3348 static void __init
rcu_init_geometry(void)
3354 int rcu_capacity
[MAX_RCU_LVLS
+ 1];
3357 * Initialize any unspecified boot parameters.
3358 * The default values of jiffies_till_first_fqs and
3359 * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS
3360 * value, which is a function of HZ, then adding one for each
3361 * RCU_JIFFIES_FQS_DIV CPUs that might be on the system.
3363 d
= RCU_JIFFIES_TILL_FORCE_QS
+ nr_cpu_ids
/ RCU_JIFFIES_FQS_DIV
;
3364 if (jiffies_till_first_fqs
== ULONG_MAX
)
3365 jiffies_till_first_fqs
= d
;
3366 if (jiffies_till_next_fqs
== ULONG_MAX
)
3367 jiffies_till_next_fqs
= d
;
3369 /* If the compile-time values are accurate, just leave. */
3370 if (rcu_fanout_leaf
== CONFIG_RCU_FANOUT_LEAF
&&
3371 nr_cpu_ids
== NR_CPUS
)
3375 * Compute number of nodes that can be handled an rcu_node tree
3376 * with the given number of levels. Setting rcu_capacity[0] makes
3377 * some of the arithmetic easier.
3379 rcu_capacity
[0] = 1;
3380 rcu_capacity
[1] = rcu_fanout_leaf
;
3381 for (i
= 2; i
<= MAX_RCU_LVLS
; i
++)
3382 rcu_capacity
[i
] = rcu_capacity
[i
- 1] * CONFIG_RCU_FANOUT
;
3385 * The boot-time rcu_fanout_leaf parameter is only permitted
3386 * to increase the leaf-level fanout, not decrease it. Of course,
3387 * the leaf-level fanout cannot exceed the number of bits in
3388 * the rcu_node masks. Finally, the tree must be able to accommodate
3389 * the configured number of CPUs. Complain and fall back to the
3390 * compile-time values if these limits are exceeded.
3392 if (rcu_fanout_leaf
< CONFIG_RCU_FANOUT_LEAF
||
3393 rcu_fanout_leaf
> sizeof(unsigned long) * 8 ||
3394 n
> rcu_capacity
[MAX_RCU_LVLS
]) {
3399 /* Calculate the number of rcu_nodes at each level of the tree. */
3400 for (i
= 1; i
<= MAX_RCU_LVLS
; i
++)
3401 if (n
<= rcu_capacity
[i
]) {
3402 for (j
= 0; j
<= i
; j
++)
3404 DIV_ROUND_UP(n
, rcu_capacity
[i
- j
]);
3406 for (j
= i
+ 1; j
<= MAX_RCU_LVLS
; j
++)
3411 /* Calculate the total number of rcu_node structures. */
3413 for (i
= 0; i
<= MAX_RCU_LVLS
; i
++)
3414 rcu_num_nodes
+= num_rcu_lvl
[i
];
3418 void __init
rcu_init(void)
3422 rcu_bootup_announce();
3423 rcu_init_geometry();
3424 rcu_init_one(&rcu_bh_state
, &rcu_bh_data
);
3425 rcu_init_one(&rcu_sched_state
, &rcu_sched_data
);
3426 __rcu_init_preempt();
3427 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
3430 * We don't need protection against CPU-hotplug here because
3431 * this is called early in boot, before either interrupts
3432 * or the scheduler are operational.
3434 cpu_notifier(rcu_cpu_notify
, 0);
3435 pm_notifier(rcu_pm_notify
, 0);
3436 for_each_online_cpu(cpu
)
3437 rcu_cpu_notify(NULL
, CPU_UP_PREPARE
, (void *)(long)cpu
);
3440 #include "tree_plugin.h"