2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptible semantics.
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
27 #include <linux/delay.h>
28 #include <linux/gfp.h>
29 #include <linux/oom.h>
30 #include <linux/smpboot.h>
32 #define RCU_KTHREAD_PRIO 1
34 #ifdef CONFIG_RCU_BOOST
35 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
37 #define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
40 #ifdef CONFIG_RCU_NOCB_CPU
41 static cpumask_var_t rcu_nocb_mask
; /* CPUs to have callbacks offloaded. */
42 static bool have_rcu_nocb_mask
; /* Was rcu_nocb_mask allocated? */
43 static bool __read_mostly rcu_nocb_poll
; /* Offload kthread are to poll. */
44 static char __initdata nocb_buf
[NR_CPUS
* 5];
45 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
48 * Check the RCU kernel configuration parameters and print informative
49 * messages about anything out of the ordinary. If you like #ifdef, you
50 * will love this function.
52 static void __init
rcu_bootup_announce_oddness(void)
54 #ifdef CONFIG_RCU_TRACE
55 printk(KERN_INFO
"\tRCU debugfs-based tracing is enabled.\n");
57 #if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
58 printk(KERN_INFO
"\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
61 #ifdef CONFIG_RCU_FANOUT_EXACT
62 printk(KERN_INFO
"\tHierarchical RCU autobalancing is disabled.\n");
64 #ifdef CONFIG_RCU_FAST_NO_HZ
66 "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
68 #ifdef CONFIG_PROVE_RCU
69 printk(KERN_INFO
"\tRCU lockdep checking is enabled.\n");
71 #ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
72 printk(KERN_INFO
"\tRCU torture testing starts during boot.\n");
74 #if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
75 printk(KERN_INFO
"\tDump stacks of tasks blocking RCU-preempt GP.\n");
77 #if defined(CONFIG_RCU_CPU_STALL_INFO)
78 printk(KERN_INFO
"\tAdditional per-CPU info printed with stalls.\n");
80 #if NUM_RCU_LVL_4 != 0
81 printk(KERN_INFO
"\tFour-level hierarchy is enabled.\n");
83 if (rcu_fanout_leaf
!= CONFIG_RCU_FANOUT_LEAF
)
84 printk(KERN_INFO
"\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf
);
85 if (nr_cpu_ids
!= NR_CPUS
)
86 printk(KERN_INFO
"\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS
, nr_cpu_ids
);
87 #ifdef CONFIG_RCU_NOCB_CPU
88 #ifndef CONFIG_RCU_NOCB_CPU_NONE
89 if (!have_rcu_nocb_mask
) {
90 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
91 have_rcu_nocb_mask
= true;
93 #ifdef CONFIG_RCU_NOCB_CPU_ZERO
94 pr_info("\tExperimental no-CBs CPU 0\n");
95 cpumask_set_cpu(0, rcu_nocb_mask
);
96 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ZERO */
97 #ifdef CONFIG_RCU_NOCB_CPU_ALL
98 pr_info("\tExperimental no-CBs for all CPUs\n");
99 cpumask_setall(rcu_nocb_mask
);
100 #endif /* #ifdef CONFIG_RCU_NOCB_CPU_ALL */
101 #endif /* #ifndef CONFIG_RCU_NOCB_CPU_NONE */
102 if (have_rcu_nocb_mask
) {
103 cpulist_scnprintf(nocb_buf
, sizeof(nocb_buf
), rcu_nocb_mask
);
104 pr_info("\tExperimental no-CBs CPUs: %s.\n", nocb_buf
);
106 pr_info("\tExperimental polled no-CBs CPUs.\n");
108 #endif /* #ifdef CONFIG_RCU_NOCB_CPU */
111 #ifdef CONFIG_TREE_PREEMPT_RCU
113 struct rcu_state rcu_preempt_state
=
114 RCU_STATE_INITIALIZER(rcu_preempt
, 'p', call_rcu
);
115 DEFINE_PER_CPU(struct rcu_data
, rcu_preempt_data
);
116 static struct rcu_state
*rcu_state
= &rcu_preempt_state
;
118 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
);
121 * Tell them what RCU they are running.
123 static void __init
rcu_bootup_announce(void)
125 printk(KERN_INFO
"Preemptible hierarchical RCU implementation.\n");
126 rcu_bootup_announce_oddness();
130 * Return the number of RCU-preempt batches processed thus far
131 * for debug and statistics.
133 long rcu_batches_completed_preempt(void)
135 return rcu_preempt_state
.completed
;
137 EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt
);
140 * Return the number of RCU batches processed thus far for debug & stats.
142 long rcu_batches_completed(void)
144 return rcu_batches_completed_preempt();
146 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
149 * Force a quiescent state for preemptible RCU.
151 void rcu_force_quiescent_state(void)
153 force_quiescent_state(&rcu_preempt_state
);
155 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state
);
158 * Record a preemptible-RCU quiescent state for the specified CPU. Note
159 * that this just means that the task currently running on the CPU is
160 * not in a quiescent state. There might be any number of tasks blocked
161 * while in an RCU read-side critical section.
163 * Unlike the other rcu_*_qs() functions, callers to this function
164 * must disable irqs in order to protect the assignment to
165 * ->rcu_read_unlock_special.
167 static void rcu_preempt_qs(int cpu
)
169 struct rcu_data
*rdp
= &per_cpu(rcu_preempt_data
, cpu
);
171 if (rdp
->passed_quiesce
== 0)
172 trace_rcu_grace_period("rcu_preempt", rdp
->gpnum
, "cpuqs");
173 rdp
->passed_quiesce
= 1;
174 current
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_NEED_QS
;
178 * We have entered the scheduler, and the current task might soon be
179 * context-switched away from. If this task is in an RCU read-side
180 * critical section, we will no longer be able to rely on the CPU to
181 * record that fact, so we enqueue the task on the blkd_tasks list.
182 * The task will dequeue itself when it exits the outermost enclosing
183 * RCU read-side critical section. Therefore, the current grace period
184 * cannot be permitted to complete until the blkd_tasks list entries
185 * predating the current grace period drain, in other words, until
186 * rnp->gp_tasks becomes NULL.
188 * Caller must disable preemption.
190 static void rcu_preempt_note_context_switch(int cpu
)
192 struct task_struct
*t
= current
;
194 struct rcu_data
*rdp
;
195 struct rcu_node
*rnp
;
197 if (t
->rcu_read_lock_nesting
> 0 &&
198 (t
->rcu_read_unlock_special
& RCU_READ_UNLOCK_BLOCKED
) == 0) {
200 /* Possibly blocking in an RCU read-side critical section. */
201 rdp
= per_cpu_ptr(rcu_preempt_state
.rda
, cpu
);
203 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
204 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_BLOCKED
;
205 t
->rcu_blocked_node
= rnp
;
208 * If this CPU has already checked in, then this task
209 * will hold up the next grace period rather than the
210 * current grace period. Queue the task accordingly.
211 * If the task is queued for the current grace period
212 * (i.e., this CPU has not yet passed through a quiescent
213 * state for the current grace period), then as long
214 * as that task remains queued, the current grace period
215 * cannot end. Note that there is some uncertainty as
216 * to exactly when the current grace period started.
217 * We take a conservative approach, which can result
218 * in unnecessarily waiting on tasks that started very
219 * slightly after the current grace period began. C'est
222 * But first, note that the current CPU must still be
225 WARN_ON_ONCE((rdp
->grpmask
& rnp
->qsmaskinit
) == 0);
226 WARN_ON_ONCE(!list_empty(&t
->rcu_node_entry
));
227 if ((rnp
->qsmask
& rdp
->grpmask
) && rnp
->gp_tasks
!= NULL
) {
228 list_add(&t
->rcu_node_entry
, rnp
->gp_tasks
->prev
);
229 rnp
->gp_tasks
= &t
->rcu_node_entry
;
230 #ifdef CONFIG_RCU_BOOST
231 if (rnp
->boost_tasks
!= NULL
)
232 rnp
->boost_tasks
= rnp
->gp_tasks
;
233 #endif /* #ifdef CONFIG_RCU_BOOST */
235 list_add(&t
->rcu_node_entry
, &rnp
->blkd_tasks
);
236 if (rnp
->qsmask
& rdp
->grpmask
)
237 rnp
->gp_tasks
= &t
->rcu_node_entry
;
239 trace_rcu_preempt_task(rdp
->rsp
->name
,
241 (rnp
->qsmask
& rdp
->grpmask
)
244 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
245 } else if (t
->rcu_read_lock_nesting
< 0 &&
246 t
->rcu_read_unlock_special
) {
249 * Complete exit from RCU read-side critical section on
250 * behalf of preempted instance of __rcu_read_unlock().
252 rcu_read_unlock_special(t
);
256 * Either we were not in an RCU read-side critical section to
257 * begin with, or we have now recorded that critical section
258 * globally. Either way, we can now note a quiescent state
259 * for this CPU. Again, if we were in an RCU read-side critical
260 * section, and if that critical section was blocking the current
261 * grace period, then the fact that the task has been enqueued
262 * means that we continue to block the current grace period.
264 local_irq_save(flags
);
266 local_irq_restore(flags
);
270 * Check for preempted RCU readers blocking the current grace period
271 * for the specified rcu_node structure. If the caller needs a reliable
272 * answer, it must hold the rcu_node's ->lock.
274 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
276 return rnp
->gp_tasks
!= NULL
;
280 * Record a quiescent state for all tasks that were previously queued
281 * on the specified rcu_node structure and that were blocking the current
282 * RCU grace period. The caller must hold the specified rnp->lock with
283 * irqs disabled, and this lock is released upon return, but irqs remain
286 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
287 __releases(rnp
->lock
)
290 struct rcu_node
*rnp_p
;
292 if (rnp
->qsmask
!= 0 || rcu_preempt_blocked_readers_cgp(rnp
)) {
293 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
294 return; /* Still need more quiescent states! */
300 * Either there is only one rcu_node in the tree,
301 * or tasks were kicked up to root rcu_node due to
302 * CPUs going offline.
304 rcu_report_qs_rsp(&rcu_preempt_state
, flags
);
308 /* Report up the rest of the hierarchy. */
310 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
311 raw_spin_lock(&rnp_p
->lock
); /* irqs already disabled. */
312 rcu_report_qs_rnp(mask
, &rcu_preempt_state
, rnp_p
, flags
);
316 * Advance a ->blkd_tasks-list pointer to the next entry, instead
317 * returning NULL if at the end of the list.
319 static struct list_head
*rcu_next_node_entry(struct task_struct
*t
,
320 struct rcu_node
*rnp
)
322 struct list_head
*np
;
324 np
= t
->rcu_node_entry
.next
;
325 if (np
== &rnp
->blkd_tasks
)
331 * Handle special cases during rcu_read_unlock(), such as needing to
332 * notify RCU core processing or task having blocked during the RCU
333 * read-side critical section.
335 void rcu_read_unlock_special(struct task_struct
*t
)
341 struct list_head
*np
;
342 #ifdef CONFIG_RCU_BOOST
343 struct rt_mutex
*rbmp
= NULL
;
344 #endif /* #ifdef CONFIG_RCU_BOOST */
345 struct rcu_node
*rnp
;
348 /* NMI handlers cannot block and cannot safely manipulate state. */
352 local_irq_save(flags
);
355 * If RCU core is waiting for this CPU to exit critical section,
356 * let it know that we have done so.
358 special
= t
->rcu_read_unlock_special
;
359 if (special
& RCU_READ_UNLOCK_NEED_QS
) {
360 rcu_preempt_qs(smp_processor_id());
363 /* Hardware IRQ handlers cannot block. */
364 if (in_irq() || in_serving_softirq()) {
365 local_irq_restore(flags
);
369 /* Clean up if blocked during RCU read-side critical section. */
370 if (special
& RCU_READ_UNLOCK_BLOCKED
) {
371 t
->rcu_read_unlock_special
&= ~RCU_READ_UNLOCK_BLOCKED
;
374 * Remove this task from the list it blocked on. The
375 * task can migrate while we acquire the lock, but at
376 * most one time. So at most two passes through loop.
379 rnp
= t
->rcu_blocked_node
;
380 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
381 if (rnp
== t
->rcu_blocked_node
)
383 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
385 empty
= !rcu_preempt_blocked_readers_cgp(rnp
);
386 empty_exp
= !rcu_preempted_readers_exp(rnp
);
387 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
388 np
= rcu_next_node_entry(t
, rnp
);
389 list_del_init(&t
->rcu_node_entry
);
390 t
->rcu_blocked_node
= NULL
;
391 trace_rcu_unlock_preempted_task("rcu_preempt",
393 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
395 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
397 #ifdef CONFIG_RCU_BOOST
398 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
399 rnp
->boost_tasks
= np
;
400 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
401 if (t
->rcu_boost_mutex
) {
402 rbmp
= t
->rcu_boost_mutex
;
403 t
->rcu_boost_mutex
= NULL
;
405 #endif /* #ifdef CONFIG_RCU_BOOST */
408 * If this was the last task on the current list, and if
409 * we aren't waiting on any CPUs, report the quiescent state.
410 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
411 * so we must take a snapshot of the expedited state.
413 empty_exp_now
= !rcu_preempted_readers_exp(rnp
);
414 if (!empty
&& !rcu_preempt_blocked_readers_cgp(rnp
)) {
415 trace_rcu_quiescent_state_report("preempt_rcu",
422 rcu_report_unblock_qs_rnp(rnp
, flags
);
424 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
427 #ifdef CONFIG_RCU_BOOST
428 /* Unboost if we were boosted. */
430 rt_mutex_unlock(rbmp
);
431 #endif /* #ifdef CONFIG_RCU_BOOST */
434 * If this was the last task on the expedited lists,
435 * then we need to report up the rcu_node hierarchy.
437 if (!empty_exp
&& empty_exp_now
)
438 rcu_report_exp_rnp(&rcu_preempt_state
, rnp
, true);
440 local_irq_restore(flags
);
444 #ifdef CONFIG_RCU_CPU_STALL_VERBOSE
447 * Dump detailed information for all tasks blocking the current RCU
448 * grace period on the specified rcu_node structure.
450 static void rcu_print_detail_task_stall_rnp(struct rcu_node
*rnp
)
453 struct task_struct
*t
;
455 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
456 if (!rcu_preempt_blocked_readers_cgp(rnp
)) {
457 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
460 t
= list_entry(rnp
->gp_tasks
,
461 struct task_struct
, rcu_node_entry
);
462 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
)
464 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
468 * Dump detailed information for all tasks blocking the current RCU
471 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
473 struct rcu_node
*rnp
= rcu_get_root(rsp
);
475 rcu_print_detail_task_stall_rnp(rnp
);
476 rcu_for_each_leaf_node(rsp
, rnp
)
477 rcu_print_detail_task_stall_rnp(rnp
);
480 #else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
482 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
486 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
488 #ifdef CONFIG_RCU_CPU_STALL_INFO
490 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
492 printk(KERN_ERR
"\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
493 rnp
->level
, rnp
->grplo
, rnp
->grphi
);
496 static void rcu_print_task_stall_end(void)
498 printk(KERN_CONT
"\n");
501 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
503 static void rcu_print_task_stall_begin(struct rcu_node
*rnp
)
507 static void rcu_print_task_stall_end(void)
511 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
514 * Scan the current list of tasks blocked within RCU read-side critical
515 * sections, printing out the tid of each.
517 static int rcu_print_task_stall(struct rcu_node
*rnp
)
519 struct task_struct
*t
;
522 if (!rcu_preempt_blocked_readers_cgp(rnp
))
524 rcu_print_task_stall_begin(rnp
);
525 t
= list_entry(rnp
->gp_tasks
,
526 struct task_struct
, rcu_node_entry
);
527 list_for_each_entry_continue(t
, &rnp
->blkd_tasks
, rcu_node_entry
) {
528 printk(KERN_CONT
" P%d", t
->pid
);
531 rcu_print_task_stall_end();
536 * Check that the list of blocked tasks for the newly completed grace
537 * period is in fact empty. It is a serious bug to complete a grace
538 * period that still has RCU readers blocked! This function must be
539 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
540 * must be held by the caller.
542 * Also, if there are blocked tasks on the list, they automatically
543 * block the newly created grace period, so set up ->gp_tasks accordingly.
545 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
547 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp
));
548 if (!list_empty(&rnp
->blkd_tasks
))
549 rnp
->gp_tasks
= rnp
->blkd_tasks
.next
;
550 WARN_ON_ONCE(rnp
->qsmask
);
553 #ifdef CONFIG_HOTPLUG_CPU
556 * Handle tasklist migration for case in which all CPUs covered by the
557 * specified rcu_node have gone offline. Move them up to the root
558 * rcu_node. The reason for not just moving them to the immediate
559 * parent is to remove the need for rcu_read_unlock_special() to
560 * make more than two attempts to acquire the target rcu_node's lock.
561 * Returns true if there were tasks blocking the current RCU grace
564 * Returns 1 if there was previously a task blocking the current grace
565 * period on the specified rcu_node structure.
567 * The caller must hold rnp->lock with irqs disabled.
569 static int rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
570 struct rcu_node
*rnp
,
571 struct rcu_data
*rdp
)
573 struct list_head
*lp
;
574 struct list_head
*lp_root
;
576 struct rcu_node
*rnp_root
= rcu_get_root(rsp
);
577 struct task_struct
*t
;
579 if (rnp
== rnp_root
) {
580 WARN_ONCE(1, "Last CPU thought to be offlined?");
581 return 0; /* Shouldn't happen: at least one CPU online. */
584 /* If we are on an internal node, complain bitterly. */
585 WARN_ON_ONCE(rnp
!= rdp
->mynode
);
588 * Move tasks up to root rcu_node. Don't try to get fancy for
589 * this corner-case operation -- just put this node's tasks
590 * at the head of the root node's list, and update the root node's
591 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
592 * if non-NULL. This might result in waiting for more tasks than
593 * absolutely necessary, but this is a good performance/complexity
596 if (rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->qsmask
== 0)
597 retval
|= RCU_OFL_TASKS_NORM_GP
;
598 if (rcu_preempted_readers_exp(rnp
))
599 retval
|= RCU_OFL_TASKS_EXP_GP
;
600 lp
= &rnp
->blkd_tasks
;
601 lp_root
= &rnp_root
->blkd_tasks
;
602 while (!list_empty(lp
)) {
603 t
= list_entry(lp
->next
, typeof(*t
), rcu_node_entry
);
604 raw_spin_lock(&rnp_root
->lock
); /* irqs already disabled */
605 list_del(&t
->rcu_node_entry
);
606 t
->rcu_blocked_node
= rnp_root
;
607 list_add(&t
->rcu_node_entry
, lp_root
);
608 if (&t
->rcu_node_entry
== rnp
->gp_tasks
)
609 rnp_root
->gp_tasks
= rnp
->gp_tasks
;
610 if (&t
->rcu_node_entry
== rnp
->exp_tasks
)
611 rnp_root
->exp_tasks
= rnp
->exp_tasks
;
612 #ifdef CONFIG_RCU_BOOST
613 if (&t
->rcu_node_entry
== rnp
->boost_tasks
)
614 rnp_root
->boost_tasks
= rnp
->boost_tasks
;
615 #endif /* #ifdef CONFIG_RCU_BOOST */
616 raw_spin_unlock(&rnp_root
->lock
); /* irqs still disabled */
619 rnp
->gp_tasks
= NULL
;
620 rnp
->exp_tasks
= NULL
;
621 #ifdef CONFIG_RCU_BOOST
622 rnp
->boost_tasks
= NULL
;
624 * In case root is being boosted and leaf was not. Make sure
625 * that we boost the tasks blocking the current grace period
628 raw_spin_lock(&rnp_root
->lock
); /* irqs already disabled */
629 if (rnp_root
->boost_tasks
!= NULL
&&
630 rnp_root
->boost_tasks
!= rnp_root
->gp_tasks
&&
631 rnp_root
->boost_tasks
!= rnp_root
->exp_tasks
)
632 rnp_root
->boost_tasks
= rnp_root
->gp_tasks
;
633 raw_spin_unlock(&rnp_root
->lock
); /* irqs still disabled */
634 #endif /* #ifdef CONFIG_RCU_BOOST */
639 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
642 * Check for a quiescent state from the current CPU. When a task blocks,
643 * the task is recorded in the corresponding CPU's rcu_node structure,
644 * which is checked elsewhere.
646 * Caller must disable hard irqs.
648 static void rcu_preempt_check_callbacks(int cpu
)
650 struct task_struct
*t
= current
;
652 if (t
->rcu_read_lock_nesting
== 0) {
656 if (t
->rcu_read_lock_nesting
> 0 &&
657 per_cpu(rcu_preempt_data
, cpu
).qs_pending
)
658 t
->rcu_read_unlock_special
|= RCU_READ_UNLOCK_NEED_QS
;
661 #ifdef CONFIG_RCU_BOOST
663 static void rcu_preempt_do_callbacks(void)
665 rcu_do_batch(&rcu_preempt_state
, &__get_cpu_var(rcu_preempt_data
));
668 #endif /* #ifdef CONFIG_RCU_BOOST */
671 * Queue a preemptible-RCU callback for invocation after a grace period.
673 void call_rcu(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
675 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 0);
677 EXPORT_SYMBOL_GPL(call_rcu
);
680 * Queue an RCU callback for lazy invocation after a grace period.
681 * This will likely be later named something like "call_rcu_lazy()",
682 * but this change will require some way of tagging the lazy RCU
683 * callbacks in the list of pending callbacks. Until then, this
684 * function may only be called from __kfree_rcu().
686 void kfree_call_rcu(struct rcu_head
*head
,
687 void (*func
)(struct rcu_head
*rcu
))
689 __call_rcu(head
, func
, &rcu_preempt_state
, -1, 1);
691 EXPORT_SYMBOL_GPL(kfree_call_rcu
);
694 * synchronize_rcu - wait until a grace period has elapsed.
696 * Control will return to the caller some time after a full grace
697 * period has elapsed, in other words after all currently executing RCU
698 * read-side critical sections have completed. Note, however, that
699 * upon return from synchronize_rcu(), the caller might well be executing
700 * concurrently with new RCU read-side critical sections that began while
701 * synchronize_rcu() was waiting. RCU read-side critical sections are
702 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
704 * See the description of synchronize_sched() for more detailed information
705 * on memory ordering guarantees.
707 void synchronize_rcu(void)
709 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
710 !lock_is_held(&rcu_lock_map
) &&
711 !lock_is_held(&rcu_sched_lock_map
),
712 "Illegal synchronize_rcu() in RCU read-side critical section");
713 if (!rcu_scheduler_active
)
716 synchronize_rcu_expedited();
718 wait_rcu_gp(call_rcu
);
720 EXPORT_SYMBOL_GPL(synchronize_rcu
);
722 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq
);
723 static unsigned long sync_rcu_preempt_exp_count
;
724 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex
);
727 * Return non-zero if there are any tasks in RCU read-side critical
728 * sections blocking the current preemptible-RCU expedited grace period.
729 * If there is no preemptible-RCU expedited grace period currently in
730 * progress, returns zero unconditionally.
732 static int rcu_preempted_readers_exp(struct rcu_node
*rnp
)
734 return rnp
->exp_tasks
!= NULL
;
738 * return non-zero if there is no RCU expedited grace period in progress
739 * for the specified rcu_node structure, in other words, if all CPUs and
740 * tasks covered by the specified rcu_node structure have done their bit
741 * for the current expedited grace period. Works only for preemptible
742 * RCU -- other RCU implementation use other means.
744 * Caller must hold sync_rcu_preempt_exp_mutex.
746 static int sync_rcu_preempt_exp_done(struct rcu_node
*rnp
)
748 return !rcu_preempted_readers_exp(rnp
) &&
749 ACCESS_ONCE(rnp
->expmask
) == 0;
753 * Report the exit from RCU read-side critical section for the last task
754 * that queued itself during or before the current expedited preemptible-RCU
755 * grace period. This event is reported either to the rcu_node structure on
756 * which the task was queued or to one of that rcu_node structure's ancestors,
757 * recursively up the tree. (Calm down, calm down, we do the recursion
760 * Most callers will set the "wake" flag, but the task initiating the
761 * expedited grace period need not wake itself.
763 * Caller must hold sync_rcu_preempt_exp_mutex.
765 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
771 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
773 if (!sync_rcu_preempt_exp_done(rnp
)) {
774 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
777 if (rnp
->parent
== NULL
) {
778 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
780 wake_up(&sync_rcu_preempt_exp_wq
);
784 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled */
786 raw_spin_lock(&rnp
->lock
); /* irqs already disabled */
787 rnp
->expmask
&= ~mask
;
792 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
793 * grace period for the specified rcu_node structure. If there are no such
794 * tasks, report it up the rcu_node hierarchy.
796 * Caller must hold sync_rcu_preempt_exp_mutex and must exclude
797 * CPU hotplug operations.
800 sync_rcu_preempt_exp_init(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
805 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
806 if (list_empty(&rnp
->blkd_tasks
)) {
807 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
809 rnp
->exp_tasks
= rnp
->blkd_tasks
.next
;
810 rcu_initiate_boost(rnp
, flags
); /* releases rnp->lock */
814 rcu_report_exp_rnp(rsp
, rnp
, false); /* Don't wake self. */
818 * synchronize_rcu_expedited - Brute-force RCU grace period
820 * Wait for an RCU-preempt grace period, but expedite it. The basic
821 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
822 * the ->blkd_tasks lists and wait for this list to drain. This consumes
823 * significant time on all CPUs and is unfriendly to real-time workloads,
824 * so is thus not recommended for any sort of common-case code.
825 * In fact, if you are using synchronize_rcu_expedited() in a loop,
826 * please restructure your code to batch your updates, and then Use a
827 * single synchronize_rcu() instead.
829 * Note that it is illegal to call this function while holding any lock
830 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
831 * to call this function from a CPU-hotplug notifier. Failing to observe
832 * these restriction will result in deadlock.
834 void synchronize_rcu_expedited(void)
837 struct rcu_node
*rnp
;
838 struct rcu_state
*rsp
= &rcu_preempt_state
;
842 smp_mb(); /* Caller's modifications seen first by other CPUs. */
843 snap
= ACCESS_ONCE(sync_rcu_preempt_exp_count
) + 1;
844 smp_mb(); /* Above access cannot bleed into critical section. */
847 * Block CPU-hotplug operations. This means that any CPU-hotplug
848 * operation that finds an rcu_node structure with tasks in the
849 * process of being boosted will know that all tasks blocking
850 * this expedited grace period will already be in the process of
851 * being boosted. This simplifies the process of moving tasks
852 * from leaf to root rcu_node structures.
857 * Acquire lock, falling back to synchronize_rcu() if too many
858 * lock-acquisition failures. Of course, if someone does the
859 * expedited grace period for us, just leave.
861 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex
)) {
862 if (ULONG_CMP_LT(snap
,
863 ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
865 goto mb_ret
; /* Others did our work for us. */
867 if (trycount
++ < 10) {
868 udelay(trycount
* num_online_cpus());
871 wait_rcu_gp(call_rcu
);
875 if (ULONG_CMP_LT(snap
, ACCESS_ONCE(sync_rcu_preempt_exp_count
))) {
877 goto unlock_mb_ret
; /* Others did our work for us. */
880 /* force all RCU readers onto ->blkd_tasks lists. */
881 synchronize_sched_expedited();
883 /* Initialize ->expmask for all non-leaf rcu_node structures. */
884 rcu_for_each_nonleaf_node_breadth_first(rsp
, rnp
) {
885 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
886 rnp
->expmask
= rnp
->qsmaskinit
;
887 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
890 /* Snapshot current state of ->blkd_tasks lists. */
891 rcu_for_each_leaf_node(rsp
, rnp
)
892 sync_rcu_preempt_exp_init(rsp
, rnp
);
893 if (NUM_RCU_NODES
> 1)
894 sync_rcu_preempt_exp_init(rsp
, rcu_get_root(rsp
));
898 /* Wait for snapshotted ->blkd_tasks lists to drain. */
899 rnp
= rcu_get_root(rsp
);
900 wait_event(sync_rcu_preempt_exp_wq
,
901 sync_rcu_preempt_exp_done(rnp
));
903 /* Clean up and exit. */
904 smp_mb(); /* ensure expedited GP seen before counter increment. */
905 ACCESS_ONCE(sync_rcu_preempt_exp_count
)++;
907 mutex_unlock(&sync_rcu_preempt_exp_mutex
);
909 smp_mb(); /* ensure subsequent action seen after grace period. */
911 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
914 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
916 * Note that this primitive does not necessarily wait for an RCU grace period
917 * to complete. For example, if there are no RCU callbacks queued anywhere
918 * in the system, then rcu_barrier() is within its rights to return
919 * immediately, without waiting for anything, much less an RCU grace period.
921 void rcu_barrier(void)
923 _rcu_barrier(&rcu_preempt_state
);
925 EXPORT_SYMBOL_GPL(rcu_barrier
);
928 * Initialize preemptible RCU's state structures.
930 static void __init
__rcu_init_preempt(void)
932 rcu_init_one(&rcu_preempt_state
, &rcu_preempt_data
);
935 #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
937 static struct rcu_state
*rcu_state
= &rcu_sched_state
;
940 * Tell them what RCU they are running.
942 static void __init
rcu_bootup_announce(void)
944 printk(KERN_INFO
"Hierarchical RCU implementation.\n");
945 rcu_bootup_announce_oddness();
949 * Return the number of RCU batches processed thus far for debug & stats.
951 long rcu_batches_completed(void)
953 return rcu_batches_completed_sched();
955 EXPORT_SYMBOL_GPL(rcu_batches_completed
);
958 * Force a quiescent state for RCU, which, because there is no preemptible
959 * RCU, becomes the same as rcu-sched.
961 void rcu_force_quiescent_state(void)
963 rcu_sched_force_quiescent_state();
965 EXPORT_SYMBOL_GPL(rcu_force_quiescent_state
);
968 * Because preemptible RCU does not exist, we never have to check for
969 * CPUs being in quiescent states.
971 static void rcu_preempt_note_context_switch(int cpu
)
976 * Because preemptible RCU does not exist, there are never any preempted
979 static int rcu_preempt_blocked_readers_cgp(struct rcu_node
*rnp
)
984 #ifdef CONFIG_HOTPLUG_CPU
986 /* Because preemptible RCU does not exist, no quieting of tasks. */
987 static void rcu_report_unblock_qs_rnp(struct rcu_node
*rnp
, unsigned long flags
)
989 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
992 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
995 * Because preemptible RCU does not exist, we never have to check for
996 * tasks blocked within RCU read-side critical sections.
998 static void rcu_print_detail_task_stall(struct rcu_state
*rsp
)
1003 * Because preemptible RCU does not exist, we never have to check for
1004 * tasks blocked within RCU read-side critical sections.
1006 static int rcu_print_task_stall(struct rcu_node
*rnp
)
1012 * Because there is no preemptible RCU, there can be no readers blocked,
1013 * so there is no need to check for blocked tasks. So check only for
1014 * bogus qsmask values.
1016 static void rcu_preempt_check_blocked_tasks(struct rcu_node
*rnp
)
1018 WARN_ON_ONCE(rnp
->qsmask
);
1021 #ifdef CONFIG_HOTPLUG_CPU
1024 * Because preemptible RCU does not exist, it never needs to migrate
1025 * tasks that were blocked within RCU read-side critical sections, and
1026 * such non-existent tasks cannot possibly have been blocking the current
1029 static int rcu_preempt_offline_tasks(struct rcu_state
*rsp
,
1030 struct rcu_node
*rnp
,
1031 struct rcu_data
*rdp
)
1036 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1039 * Because preemptible RCU does not exist, it never has any callbacks
1042 static void rcu_preempt_check_callbacks(int cpu
)
1047 * Queue an RCU callback for lazy invocation after a grace period.
1048 * This will likely be later named something like "call_rcu_lazy()",
1049 * but this change will require some way of tagging the lazy RCU
1050 * callbacks in the list of pending callbacks. Until then, this
1051 * function may only be called from __kfree_rcu().
1053 * Because there is no preemptible RCU, we use RCU-sched instead.
1055 void kfree_call_rcu(struct rcu_head
*head
,
1056 void (*func
)(struct rcu_head
*rcu
))
1058 __call_rcu(head
, func
, &rcu_sched_state
, -1, 1);
1060 EXPORT_SYMBOL_GPL(kfree_call_rcu
);
1063 * Wait for an rcu-preempt grace period, but make it happen quickly.
1064 * But because preemptible RCU does not exist, map to rcu-sched.
1066 void synchronize_rcu_expedited(void)
1068 synchronize_sched_expedited();
1070 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited
);
1072 #ifdef CONFIG_HOTPLUG_CPU
1075 * Because preemptible RCU does not exist, there is never any need to
1076 * report on tasks preempted in RCU read-side critical sections during
1077 * expedited RCU grace periods.
1079 static void rcu_report_exp_rnp(struct rcu_state
*rsp
, struct rcu_node
*rnp
,
1084 #endif /* #ifdef CONFIG_HOTPLUG_CPU */
1087 * Because preemptible RCU does not exist, rcu_barrier() is just
1088 * another name for rcu_barrier_sched().
1090 void rcu_barrier(void)
1092 rcu_barrier_sched();
1094 EXPORT_SYMBOL_GPL(rcu_barrier
);
1097 * Because preemptible RCU does not exist, it need not be initialized.
1099 static void __init
__rcu_init_preempt(void)
1103 #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
1105 #ifdef CONFIG_RCU_BOOST
1107 #include "rtmutex_common.h"
1109 #ifdef CONFIG_RCU_TRACE
1111 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1113 if (list_empty(&rnp
->blkd_tasks
))
1114 rnp
->n_balk_blkd_tasks
++;
1115 else if (rnp
->exp_tasks
== NULL
&& rnp
->gp_tasks
== NULL
)
1116 rnp
->n_balk_exp_gp_tasks
++;
1117 else if (rnp
->gp_tasks
!= NULL
&& rnp
->boost_tasks
!= NULL
)
1118 rnp
->n_balk_boost_tasks
++;
1119 else if (rnp
->gp_tasks
!= NULL
&& rnp
->qsmask
!= 0)
1120 rnp
->n_balk_notblocked
++;
1121 else if (rnp
->gp_tasks
!= NULL
&&
1122 ULONG_CMP_LT(jiffies
, rnp
->boost_time
))
1123 rnp
->n_balk_notyet
++;
1128 #else /* #ifdef CONFIG_RCU_TRACE */
1130 static void rcu_initiate_boost_trace(struct rcu_node
*rnp
)
1134 #endif /* #else #ifdef CONFIG_RCU_TRACE */
1136 static void rcu_wake_cond(struct task_struct
*t
, int status
)
1139 * If the thread is yielding, only wake it when this
1140 * is invoked from idle
1142 if (status
!= RCU_KTHREAD_YIELDING
|| is_idle_task(current
))
1147 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1148 * or ->boost_tasks, advancing the pointer to the next task in the
1149 * ->blkd_tasks list.
1151 * Note that irqs must be enabled: boosting the task can block.
1152 * Returns 1 if there are more tasks needing to be boosted.
1154 static int rcu_boost(struct rcu_node
*rnp
)
1156 unsigned long flags
;
1157 struct rt_mutex mtx
;
1158 struct task_struct
*t
;
1159 struct list_head
*tb
;
1161 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
)
1162 return 0; /* Nothing left to boost. */
1164 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1167 * Recheck under the lock: all tasks in need of boosting
1168 * might exit their RCU read-side critical sections on their own.
1170 if (rnp
->exp_tasks
== NULL
&& rnp
->boost_tasks
== NULL
) {
1171 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1176 * Preferentially boost tasks blocking expedited grace periods.
1177 * This cannot starve the normal grace periods because a second
1178 * expedited grace period must boost all blocked tasks, including
1179 * those blocking the pre-existing normal grace period.
1181 if (rnp
->exp_tasks
!= NULL
) {
1182 tb
= rnp
->exp_tasks
;
1183 rnp
->n_exp_boosts
++;
1185 tb
= rnp
->boost_tasks
;
1186 rnp
->n_normal_boosts
++;
1188 rnp
->n_tasks_boosted
++;
1191 * We boost task t by manufacturing an rt_mutex that appears to
1192 * be held by task t. We leave a pointer to that rt_mutex where
1193 * task t can find it, and task t will release the mutex when it
1194 * exits its outermost RCU read-side critical section. Then
1195 * simply acquiring this artificial rt_mutex will boost task
1196 * t's priority. (Thanks to tglx for suggesting this approach!)
1198 * Note that task t must acquire rnp->lock to remove itself from
1199 * the ->blkd_tasks list, which it will do from exit() if from
1200 * nowhere else. We therefore are guaranteed that task t will
1201 * stay around at least until we drop rnp->lock. Note that
1202 * rnp->lock also resolves races between our priority boosting
1203 * and task t's exiting its outermost RCU read-side critical
1206 t
= container_of(tb
, struct task_struct
, rcu_node_entry
);
1207 rt_mutex_init_proxy_locked(&mtx
, t
);
1208 t
->rcu_boost_mutex
= &mtx
;
1209 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1210 rt_mutex_lock(&mtx
); /* Side effect: boosts task t's priority. */
1211 rt_mutex_unlock(&mtx
); /* Keep lockdep happy. */
1213 return ACCESS_ONCE(rnp
->exp_tasks
) != NULL
||
1214 ACCESS_ONCE(rnp
->boost_tasks
) != NULL
;
1218 * Priority-boosting kthread. One per leaf rcu_node and one for the
1221 static int rcu_boost_kthread(void *arg
)
1223 struct rcu_node
*rnp
= (struct rcu_node
*)arg
;
1227 trace_rcu_utilization("Start boost kthread@init");
1229 rnp
->boost_kthread_status
= RCU_KTHREAD_WAITING
;
1230 trace_rcu_utilization("End boost kthread@rcu_wait");
1231 rcu_wait(rnp
->boost_tasks
|| rnp
->exp_tasks
);
1232 trace_rcu_utilization("Start boost kthread@rcu_wait");
1233 rnp
->boost_kthread_status
= RCU_KTHREAD_RUNNING
;
1234 more2boost
= rcu_boost(rnp
);
1240 rnp
->boost_kthread_status
= RCU_KTHREAD_YIELDING
;
1241 trace_rcu_utilization("End boost kthread@rcu_yield");
1242 schedule_timeout_interruptible(2);
1243 trace_rcu_utilization("Start boost kthread@rcu_yield");
1248 trace_rcu_utilization("End boost kthread@notreached");
1253 * Check to see if it is time to start boosting RCU readers that are
1254 * blocking the current grace period, and, if so, tell the per-rcu_node
1255 * kthread to start boosting them. If there is an expedited grace
1256 * period in progress, it is always time to boost.
1258 * The caller must hold rnp->lock, which this function releases.
1259 * The ->boost_kthread_task is immortal, so we don't need to worry
1260 * about it going away.
1262 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1264 struct task_struct
*t
;
1266 if (!rcu_preempt_blocked_readers_cgp(rnp
) && rnp
->exp_tasks
== NULL
) {
1267 rnp
->n_balk_exp_gp_tasks
++;
1268 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1271 if (rnp
->exp_tasks
!= NULL
||
1272 (rnp
->gp_tasks
!= NULL
&&
1273 rnp
->boost_tasks
== NULL
&&
1275 ULONG_CMP_GE(jiffies
, rnp
->boost_time
))) {
1276 if (rnp
->exp_tasks
== NULL
)
1277 rnp
->boost_tasks
= rnp
->gp_tasks
;
1278 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1279 t
= rnp
->boost_kthread_task
;
1281 rcu_wake_cond(t
, rnp
->boost_kthread_status
);
1283 rcu_initiate_boost_trace(rnp
);
1284 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1289 * Wake up the per-CPU kthread to invoke RCU callbacks.
1291 static void invoke_rcu_callbacks_kthread(void)
1293 unsigned long flags
;
1295 local_irq_save(flags
);
1296 __this_cpu_write(rcu_cpu_has_work
, 1);
1297 if (__this_cpu_read(rcu_cpu_kthread_task
) != NULL
&&
1298 current
!= __this_cpu_read(rcu_cpu_kthread_task
)) {
1299 rcu_wake_cond(__this_cpu_read(rcu_cpu_kthread_task
),
1300 __this_cpu_read(rcu_cpu_kthread_status
));
1302 local_irq_restore(flags
);
1306 * Is the current CPU running the RCU-callbacks kthread?
1307 * Caller must have preemption disabled.
1309 static bool rcu_is_callbacks_kthread(void)
1311 return __get_cpu_var(rcu_cpu_kthread_task
) == current
;
1314 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1317 * Do priority-boost accounting for the start of a new grace period.
1319 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1321 rnp
->boost_time
= jiffies
+ RCU_BOOST_DELAY_JIFFIES
;
1325 * Create an RCU-boost kthread for the specified node if one does not
1326 * already exist. We only create this kthread for preemptible RCU.
1327 * Returns zero if all is well, a negated errno otherwise.
1329 static int __cpuinit
rcu_spawn_one_boost_kthread(struct rcu_state
*rsp
,
1330 struct rcu_node
*rnp
)
1332 int rnp_index
= rnp
- &rsp
->node
[0];
1333 unsigned long flags
;
1334 struct sched_param sp
;
1335 struct task_struct
*t
;
1337 if (&rcu_preempt_state
!= rsp
)
1340 if (!rcu_scheduler_fully_active
|| rnp
->qsmaskinit
== 0)
1344 if (rnp
->boost_kthread_task
!= NULL
)
1346 t
= kthread_create(rcu_boost_kthread
, (void *)rnp
,
1347 "rcub/%d", rnp_index
);
1350 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
1351 rnp
->boost_kthread_task
= t
;
1352 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1353 sp
.sched_priority
= RCU_BOOST_PRIO
;
1354 sched_setscheduler_nocheck(t
, SCHED_FIFO
, &sp
);
1355 wake_up_process(t
); /* get to TASK_INTERRUPTIBLE quickly. */
1359 static void rcu_kthread_do_work(void)
1361 rcu_do_batch(&rcu_sched_state
, &__get_cpu_var(rcu_sched_data
));
1362 rcu_do_batch(&rcu_bh_state
, &__get_cpu_var(rcu_bh_data
));
1363 rcu_preempt_do_callbacks();
1366 static void rcu_cpu_kthread_setup(unsigned int cpu
)
1368 struct sched_param sp
;
1370 sp
.sched_priority
= RCU_KTHREAD_PRIO
;
1371 sched_setscheduler_nocheck(current
, SCHED_FIFO
, &sp
);
1374 static void rcu_cpu_kthread_park(unsigned int cpu
)
1376 per_cpu(rcu_cpu_kthread_status
, cpu
) = RCU_KTHREAD_OFFCPU
;
1379 static int rcu_cpu_kthread_should_run(unsigned int cpu
)
1381 return __get_cpu_var(rcu_cpu_has_work
);
1385 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
1386 * RCU softirq used in flavors and configurations of RCU that do not
1387 * support RCU priority boosting.
1389 static void rcu_cpu_kthread(unsigned int cpu
)
1391 unsigned int *statusp
= &__get_cpu_var(rcu_cpu_kthread_status
);
1392 char work
, *workp
= &__get_cpu_var(rcu_cpu_has_work
);
1395 for (spincnt
= 0; spincnt
< 10; spincnt
++) {
1396 trace_rcu_utilization("Start CPU kthread@rcu_wait");
1398 *statusp
= RCU_KTHREAD_RUNNING
;
1399 this_cpu_inc(rcu_cpu_kthread_loops
);
1400 local_irq_disable();
1405 rcu_kthread_do_work();
1408 trace_rcu_utilization("End CPU kthread@rcu_wait");
1409 *statusp
= RCU_KTHREAD_WAITING
;
1413 *statusp
= RCU_KTHREAD_YIELDING
;
1414 trace_rcu_utilization("Start CPU kthread@rcu_yield");
1415 schedule_timeout_interruptible(2);
1416 trace_rcu_utilization("End CPU kthread@rcu_yield");
1417 *statusp
= RCU_KTHREAD_WAITING
;
1421 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1422 * served by the rcu_node in question. The CPU hotplug lock is still
1423 * held, so the value of rnp->qsmaskinit will be stable.
1425 * We don't include outgoingcpu in the affinity set, use -1 if there is
1426 * no outgoing CPU. If there are no CPUs left in the affinity set,
1427 * this function allows the kthread to execute on any CPU.
1429 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1431 struct task_struct
*t
= rnp
->boost_kthread_task
;
1432 unsigned long mask
= rnp
->qsmaskinit
;
1438 if (!zalloc_cpumask_var(&cm
, GFP_KERNEL
))
1440 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++, mask
>>= 1)
1441 if ((mask
& 0x1) && cpu
!= outgoingcpu
)
1442 cpumask_set_cpu(cpu
, cm
);
1443 if (cpumask_weight(cm
) == 0) {
1445 for (cpu
= rnp
->grplo
; cpu
<= rnp
->grphi
; cpu
++)
1446 cpumask_clear_cpu(cpu
, cm
);
1447 WARN_ON_ONCE(cpumask_weight(cm
) == 0);
1449 set_cpus_allowed_ptr(t
, cm
);
1450 free_cpumask_var(cm
);
1453 static struct smp_hotplug_thread rcu_cpu_thread_spec
= {
1454 .store
= &rcu_cpu_kthread_task
,
1455 .thread_should_run
= rcu_cpu_kthread_should_run
,
1456 .thread_fn
= rcu_cpu_kthread
,
1457 .thread_comm
= "rcuc/%u",
1458 .setup
= rcu_cpu_kthread_setup
,
1459 .park
= rcu_cpu_kthread_park
,
1463 * Spawn all kthreads -- called as soon as the scheduler is running.
1465 static int __init
rcu_spawn_kthreads(void)
1467 struct rcu_node
*rnp
;
1470 rcu_scheduler_fully_active
= 1;
1471 for_each_possible_cpu(cpu
)
1472 per_cpu(rcu_cpu_has_work
, cpu
) = 0;
1473 BUG_ON(smpboot_register_percpu_thread(&rcu_cpu_thread_spec
));
1474 rnp
= rcu_get_root(rcu_state
);
1475 (void)rcu_spawn_one_boost_kthread(rcu_state
, rnp
);
1476 if (NUM_RCU_NODES
> 1) {
1477 rcu_for_each_leaf_node(rcu_state
, rnp
)
1478 (void)rcu_spawn_one_boost_kthread(rcu_state
, rnp
);
1482 early_initcall(rcu_spawn_kthreads
);
1484 static void __cpuinit
rcu_prepare_kthreads(int cpu
)
1486 struct rcu_data
*rdp
= per_cpu_ptr(rcu_state
->rda
, cpu
);
1487 struct rcu_node
*rnp
= rdp
->mynode
;
1489 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
1490 if (rcu_scheduler_fully_active
)
1491 (void)rcu_spawn_one_boost_kthread(rcu_state
, rnp
);
1494 #else /* #ifdef CONFIG_RCU_BOOST */
1496 static void rcu_initiate_boost(struct rcu_node
*rnp
, unsigned long flags
)
1498 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
1501 static void invoke_rcu_callbacks_kthread(void)
1506 static bool rcu_is_callbacks_kthread(void)
1511 static void rcu_preempt_boost_start_gp(struct rcu_node
*rnp
)
1515 static void rcu_boost_kthread_setaffinity(struct rcu_node
*rnp
, int outgoingcpu
)
1519 static int __init
rcu_scheduler_really_started(void)
1521 rcu_scheduler_fully_active
= 1;
1524 early_initcall(rcu_scheduler_really_started
);
1526 static void __cpuinit
rcu_prepare_kthreads(int cpu
)
1530 #endif /* #else #ifdef CONFIG_RCU_BOOST */
1532 #if !defined(CONFIG_RCU_FAST_NO_HZ)
1535 * Check to see if any future RCU-related work will need to be done
1536 * by the current CPU, even if none need be done immediately, returning
1537 * 1 if so. This function is part of the RCU implementation; it is -not-
1538 * an exported member of the RCU API.
1540 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1541 * any flavor of RCU.
1543 int rcu_needs_cpu(int cpu
, unsigned long *delta_jiffies
)
1545 *delta_jiffies
= ULONG_MAX
;
1546 return rcu_cpu_has_callbacks(cpu
, NULL
);
1550 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1553 static void rcu_cleanup_after_idle(int cpu
)
1558 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
1561 static void rcu_prepare_for_idle(int cpu
)
1566 * Don't bother keeping a running count of the number of RCU callbacks
1567 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1569 static void rcu_idle_count_callbacks_posted(void)
1573 #else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1576 * This code is invoked when a CPU goes idle, at which point we want
1577 * to have the CPU do everything required for RCU so that it can enter
1578 * the energy-efficient dyntick-idle mode. This is handled by a
1579 * state machine implemented by rcu_prepare_for_idle() below.
1581 * The following three proprocessor symbols control this state machine:
1583 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1584 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1585 * is sized to be roughly one RCU grace period. Those energy-efficiency
1586 * benchmarkers who might otherwise be tempted to set this to a large
1587 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1588 * system. And if you are -that- concerned about energy efficiency,
1589 * just power the system down and be done with it!
1590 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1591 * permitted to sleep in dyntick-idle mode with only lazy RCU
1592 * callbacks pending. Setting this too high can OOM your system.
1594 * The values below work well in practice. If future workloads require
1595 * adjustment, they can be converted into kernel config parameters, though
1596 * making the state machine smarter might be a better option.
1598 #define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
1599 #define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
1601 static int rcu_idle_gp_delay
= RCU_IDLE_GP_DELAY
;
1602 module_param(rcu_idle_gp_delay
, int, 0644);
1603 static int rcu_idle_lazy_gp_delay
= RCU_IDLE_LAZY_GP_DELAY
;
1604 module_param(rcu_idle_lazy_gp_delay
, int, 0644);
1606 extern int tick_nohz_enabled
;
1609 * Try to advance callbacks for all flavors of RCU on the current CPU.
1610 * Afterwards, if there are any callbacks ready for immediate invocation,
1613 static bool rcu_try_advance_all_cbs(void)
1615 bool cbs_ready
= false;
1616 struct rcu_data
*rdp
;
1617 struct rcu_node
*rnp
;
1618 struct rcu_state
*rsp
;
1620 for_each_rcu_flavor(rsp
) {
1621 rdp
= this_cpu_ptr(rsp
->rda
);
1625 * Don't bother checking unless a grace period has
1626 * completed since we last checked and there are
1627 * callbacks not yet ready to invoke.
1629 if (rdp
->completed
!= rnp
->completed
&&
1630 rdp
->nxttail
[RCU_DONE_TAIL
] != rdp
->nxttail
[RCU_NEXT_TAIL
])
1631 rcu_process_gp_end(rsp
, rdp
);
1633 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1640 * Allow the CPU to enter dyntick-idle mode unless it has callbacks ready
1641 * to invoke. If the CPU has callbacks, try to advance them. Tell the
1642 * caller to set the timeout based on whether or not there are non-lazy
1645 * The caller must have disabled interrupts.
1647 int rcu_needs_cpu(int cpu
, unsigned long *dj
)
1649 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1651 /* Snapshot to detect later posting of non-lazy callback. */
1652 rdtp
->nonlazy_posted_snap
= rdtp
->nonlazy_posted
;
1654 /* If no callbacks, RCU doesn't need the CPU. */
1655 if (!rcu_cpu_has_callbacks(cpu
, &rdtp
->all_lazy
)) {
1660 /* Attempt to advance callbacks. */
1661 if (rcu_try_advance_all_cbs()) {
1662 /* Some ready to invoke, so initiate later invocation. */
1666 rdtp
->last_accelerate
= jiffies
;
1668 /* Request timer delay depending on laziness, and round. */
1669 if (rdtp
->all_lazy
) {
1670 *dj
= round_up(rcu_idle_gp_delay
+ jiffies
,
1671 rcu_idle_gp_delay
) - jiffies
;
1673 *dj
= round_jiffies(rcu_idle_lazy_gp_delay
+ jiffies
) - jiffies
;
1679 * Prepare a CPU for idle from an RCU perspective. The first major task
1680 * is to sense whether nohz mode has been enabled or disabled via sysfs.
1681 * The second major task is to check to see if a non-lazy callback has
1682 * arrived at a CPU that previously had only lazy callbacks. The third
1683 * major task is to accelerate (that is, assign grace-period numbers to)
1684 * any recently arrived callbacks.
1686 * The caller must have disabled interrupts.
1688 static void rcu_prepare_for_idle(int cpu
)
1690 struct rcu_data
*rdp
;
1691 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1692 struct rcu_node
*rnp
;
1693 struct rcu_state
*rsp
;
1696 /* Handle nohz enablement switches conservatively. */
1697 tne
= ACCESS_ONCE(tick_nohz_enabled
);
1698 if (tne
!= rdtp
->tick_nohz_enabled_snap
) {
1699 if (rcu_cpu_has_callbacks(cpu
, NULL
))
1700 invoke_rcu_core(); /* force nohz to see update. */
1701 rdtp
->tick_nohz_enabled_snap
= tne
;
1707 /* If this is a no-CBs CPU, no callbacks, just return. */
1708 if (is_nocb_cpu(cpu
))
1712 * If a non-lazy callback arrived at a CPU having only lazy
1713 * callbacks, invoke RCU core for the side-effect of recalculating
1714 * idle duration on re-entry to idle.
1716 if (rdtp
->all_lazy
&&
1717 rdtp
->nonlazy_posted
!= rdtp
->nonlazy_posted_snap
) {
1723 * If we have not yet accelerated this jiffy, accelerate all
1724 * callbacks on this CPU.
1726 if (rdtp
->last_accelerate
== jiffies
)
1728 rdtp
->last_accelerate
= jiffies
;
1729 for_each_rcu_flavor(rsp
) {
1730 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1731 if (!*rdp
->nxttail
[RCU_DONE_TAIL
])
1734 raw_spin_lock(&rnp
->lock
); /* irqs already disabled. */
1735 rcu_accelerate_cbs(rsp
, rnp
, rdp
);
1736 raw_spin_unlock(&rnp
->lock
); /* irqs remain disabled. */
1741 * Clean up for exit from idle. Attempt to advance callbacks based on
1742 * any grace periods that elapsed while the CPU was idle, and if any
1743 * callbacks are now ready to invoke, initiate invocation.
1745 static void rcu_cleanup_after_idle(int cpu
)
1747 struct rcu_data
*rdp
;
1748 struct rcu_state
*rsp
;
1750 if (is_nocb_cpu(cpu
))
1752 rcu_try_advance_all_cbs();
1753 for_each_rcu_flavor(rsp
) {
1754 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1755 if (cpu_has_callbacks_ready_to_invoke(rdp
))
1761 * Keep a running count of the number of non-lazy callbacks posted
1762 * on this CPU. This running counter (which is never decremented) allows
1763 * rcu_prepare_for_idle() to detect when something out of the idle loop
1764 * posts a callback, even if an equal number of callbacks are invoked.
1765 * Of course, callbacks should only be posted from within a trace event
1766 * designed to be called from idle or from within RCU_NONIDLE().
1768 static void rcu_idle_count_callbacks_posted(void)
1770 __this_cpu_add(rcu_dynticks
.nonlazy_posted
, 1);
1774 * Data for flushing lazy RCU callbacks at OOM time.
1776 static atomic_t oom_callback_count
;
1777 static DECLARE_WAIT_QUEUE_HEAD(oom_callback_wq
);
1780 * RCU OOM callback -- decrement the outstanding count and deliver the
1781 * wake-up if we are the last one.
1783 static void rcu_oom_callback(struct rcu_head
*rhp
)
1785 if (atomic_dec_and_test(&oom_callback_count
))
1786 wake_up(&oom_callback_wq
);
1790 * Post an rcu_oom_notify callback on the current CPU if it has at
1791 * least one lazy callback. This will unnecessarily post callbacks
1792 * to CPUs that already have a non-lazy callback at the end of their
1793 * callback list, but this is an infrequent operation, so accept some
1794 * extra overhead to keep things simple.
1796 static void rcu_oom_notify_cpu(void *unused
)
1798 struct rcu_state
*rsp
;
1799 struct rcu_data
*rdp
;
1801 for_each_rcu_flavor(rsp
) {
1802 rdp
= __this_cpu_ptr(rsp
->rda
);
1803 if (rdp
->qlen_lazy
!= 0) {
1804 atomic_inc(&oom_callback_count
);
1805 rsp
->call(&rdp
->oom_head
, rcu_oom_callback
);
1811 * If low on memory, ensure that each CPU has a non-lazy callback.
1812 * This will wake up CPUs that have only lazy callbacks, in turn
1813 * ensuring that they free up the corresponding memory in a timely manner.
1814 * Because an uncertain amount of memory will be freed in some uncertain
1815 * timeframe, we do not claim to have freed anything.
1817 static int rcu_oom_notify(struct notifier_block
*self
,
1818 unsigned long notused
, void *nfreed
)
1822 /* Wait for callbacks from earlier instance to complete. */
1823 wait_event(oom_callback_wq
, atomic_read(&oom_callback_count
) == 0);
1826 * Prevent premature wakeup: ensure that all increments happen
1827 * before there is a chance of the counter reaching zero.
1829 atomic_set(&oom_callback_count
, 1);
1832 for_each_online_cpu(cpu
) {
1833 smp_call_function_single(cpu
, rcu_oom_notify_cpu
, NULL
, 1);
1838 /* Unconditionally decrement: no need to wake ourselves up. */
1839 atomic_dec(&oom_callback_count
);
1844 static struct notifier_block rcu_oom_nb
= {
1845 .notifier_call
= rcu_oom_notify
1848 static int __init
rcu_register_oom_notifier(void)
1850 register_oom_notifier(&rcu_oom_nb
);
1853 early_initcall(rcu_register_oom_notifier
);
1855 #endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1857 #ifdef CONFIG_RCU_CPU_STALL_INFO
1859 #ifdef CONFIG_RCU_FAST_NO_HZ
1861 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1863 struct rcu_dynticks
*rdtp
= &per_cpu(rcu_dynticks
, cpu
);
1864 unsigned long nlpd
= rdtp
->nonlazy_posted
- rdtp
->nonlazy_posted_snap
;
1866 sprintf(cp
, "last_accelerate: %04lx/%04lx, nonlazy_posted: %ld, %c%c",
1867 rdtp
->last_accelerate
& 0xffff, jiffies
& 0xffff,
1869 rdtp
->all_lazy
? 'L' : '.',
1870 rdtp
->tick_nohz_enabled_snap
? '.' : 'D');
1873 #else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
1875 static void print_cpu_stall_fast_no_hz(char *cp
, int cpu
)
1880 #endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
1882 /* Initiate the stall-info list. */
1883 static void print_cpu_stall_info_begin(void)
1885 printk(KERN_CONT
"\n");
1889 * Print out diagnostic information for the specified stalled CPU.
1891 * If the specified CPU is aware of the current RCU grace period
1892 * (flavor specified by rsp), then print the number of scheduling
1893 * clock interrupts the CPU has taken during the time that it has
1894 * been aware. Otherwise, print the number of RCU grace periods
1895 * that this CPU is ignorant of, for example, "1" if the CPU was
1896 * aware of the previous grace period.
1898 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
1900 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1902 char fast_no_hz
[72];
1903 struct rcu_data
*rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
1904 struct rcu_dynticks
*rdtp
= rdp
->dynticks
;
1906 unsigned long ticks_value
;
1908 if (rsp
->gpnum
== rdp
->gpnum
) {
1909 ticks_title
= "ticks this GP";
1910 ticks_value
= rdp
->ticks_this_gp
;
1912 ticks_title
= "GPs behind";
1913 ticks_value
= rsp
->gpnum
- rdp
->gpnum
;
1915 print_cpu_stall_fast_no_hz(fast_no_hz
, cpu
);
1916 printk(KERN_ERR
"\t%d: (%lu %s) idle=%03x/%llx/%d softirq=%u/%u %s\n",
1917 cpu
, ticks_value
, ticks_title
,
1918 atomic_read(&rdtp
->dynticks
) & 0xfff,
1919 rdtp
->dynticks_nesting
, rdtp
->dynticks_nmi_nesting
,
1920 rdp
->softirq_snap
, kstat_softirqs_cpu(RCU_SOFTIRQ
, cpu
),
1924 /* Terminate the stall-info list. */
1925 static void print_cpu_stall_info_end(void)
1927 printk(KERN_ERR
"\t");
1930 /* Zero ->ticks_this_gp for all flavors of RCU. */
1931 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1933 rdp
->ticks_this_gp
= 0;
1934 rdp
->softirq_snap
= kstat_softirqs_cpu(RCU_SOFTIRQ
, smp_processor_id());
1937 /* Increment ->ticks_this_gp for all flavors of RCU. */
1938 static void increment_cpu_stall_ticks(void)
1940 struct rcu_state
*rsp
;
1942 for_each_rcu_flavor(rsp
)
1943 __this_cpu_ptr(rsp
->rda
)->ticks_this_gp
++;
1946 #else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
1948 static void print_cpu_stall_info_begin(void)
1950 printk(KERN_CONT
" {");
1953 static void print_cpu_stall_info(struct rcu_state
*rsp
, int cpu
)
1955 printk(KERN_CONT
" %d", cpu
);
1958 static void print_cpu_stall_info_end(void)
1960 printk(KERN_CONT
"} ");
1963 static void zero_cpu_stall_ticks(struct rcu_data
*rdp
)
1967 static void increment_cpu_stall_ticks(void)
1971 #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
1973 #ifdef CONFIG_RCU_NOCB_CPU
1976 * Offload callback processing from the boot-time-specified set of CPUs
1977 * specified by rcu_nocb_mask. For each CPU in the set, there is a
1978 * kthread created that pulls the callbacks from the corresponding CPU,
1979 * waits for a grace period to elapse, and invokes the callbacks.
1980 * The no-CBs CPUs do a wake_up() on their kthread when they insert
1981 * a callback into any empty list, unless the rcu_nocb_poll boot parameter
1982 * has been specified, in which case each kthread actively polls its
1983 * CPU. (Which isn't so great for energy efficiency, but which does
1984 * reduce RCU's overhead on that CPU.)
1986 * This is intended to be used in conjunction with Frederic Weisbecker's
1987 * adaptive-idle work, which would seriously reduce OS jitter on CPUs
1988 * running CPU-bound user-mode computations.
1990 * Offloading of callback processing could also in theory be used as
1991 * an energy-efficiency measure because CPUs with no RCU callbacks
1992 * queued are more aggressive about entering dyntick-idle mode.
1996 /* Parse the boot-time rcu_nocb_mask CPU list from the kernel parameters. */
1997 static int __init
rcu_nocb_setup(char *str
)
1999 alloc_bootmem_cpumask_var(&rcu_nocb_mask
);
2000 have_rcu_nocb_mask
= true;
2001 cpulist_parse(str
, rcu_nocb_mask
);
2004 __setup("rcu_nocbs=", rcu_nocb_setup
);
2006 static int __init
parse_rcu_nocb_poll(char *arg
)
2011 early_param("rcu_nocb_poll", parse_rcu_nocb_poll
);
2014 * Do any no-CBs CPUs need another grace period?
2016 * Interrupts must be disabled. If the caller does not hold the root
2017 * rnp_node structure's ->lock, the results are advisory only.
2019 static int rcu_nocb_needs_gp(struct rcu_state
*rsp
)
2021 struct rcu_node
*rnp
= rcu_get_root(rsp
);
2023 return rnp
->need_future_gp
[(ACCESS_ONCE(rnp
->completed
) + 1) & 0x1];
2027 * Wake up any no-CBs CPUs' kthreads that were waiting on the just-ended
2030 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2032 wake_up_all(&rnp
->nocb_gp_wq
[rnp
->completed
& 0x1]);
2036 * Set the root rcu_node structure's ->need_future_gp field
2037 * based on the sum of those of all rcu_node structures. This does
2038 * double-count the root rcu_node structure's requests, but this
2039 * is necessary to handle the possibility of a rcu_nocb_kthread()
2040 * having awakened during the time that the rcu_node structures
2041 * were being updated for the end of the previous grace period.
2043 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2045 rnp
->need_future_gp
[(rnp
->completed
+ 1) & 0x1] += nrq
;
2048 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2050 init_waitqueue_head(&rnp
->nocb_gp_wq
[0]);
2051 init_waitqueue_head(&rnp
->nocb_gp_wq
[1]);
2054 /* Is the specified CPU a no-CPUs CPU? */
2055 static bool is_nocb_cpu(int cpu
)
2057 if (have_rcu_nocb_mask
)
2058 return cpumask_test_cpu(cpu
, rcu_nocb_mask
);
2063 * Enqueue the specified string of rcu_head structures onto the specified
2064 * CPU's no-CBs lists. The CPU is specified by rdp, the head of the
2065 * string by rhp, and the tail of the string by rhtp. The non-lazy/lazy
2066 * counts are supplied by rhcount and rhcount_lazy.
2068 * If warranted, also wake up the kthread servicing this CPUs queues.
2070 static void __call_rcu_nocb_enqueue(struct rcu_data
*rdp
,
2071 struct rcu_head
*rhp
,
2072 struct rcu_head
**rhtp
,
2073 int rhcount
, int rhcount_lazy
)
2076 struct rcu_head
**old_rhpp
;
2077 struct task_struct
*t
;
2079 /* Enqueue the callback on the nocb list and update counts. */
2080 old_rhpp
= xchg(&rdp
->nocb_tail
, rhtp
);
2081 ACCESS_ONCE(*old_rhpp
) = rhp
;
2082 atomic_long_add(rhcount
, &rdp
->nocb_q_count
);
2083 atomic_long_add(rhcount_lazy
, &rdp
->nocb_q_count_lazy
);
2085 /* If we are not being polled and there is a kthread, awaken it ... */
2086 t
= ACCESS_ONCE(rdp
->nocb_kthread
);
2087 if (rcu_nocb_poll
| !t
)
2089 len
= atomic_long_read(&rdp
->nocb_q_count
);
2090 if (old_rhpp
== &rdp
->nocb_head
) {
2091 wake_up(&rdp
->nocb_wq
); /* ... only if queue was empty ... */
2092 rdp
->qlen_last_fqs_check
= 0;
2093 } else if (len
> rdp
->qlen_last_fqs_check
+ qhimark
) {
2094 wake_up_process(t
); /* ... or if many callbacks queued. */
2095 rdp
->qlen_last_fqs_check
= LONG_MAX
/ 2;
2101 * This is a helper for __call_rcu(), which invokes this when the normal
2102 * callback queue is inoperable. If this is not a no-CBs CPU, this
2103 * function returns failure back to __call_rcu(), which can complain
2106 * Otherwise, this function queues the callback where the corresponding
2107 * "rcuo" kthread can find it.
2109 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2113 if (!is_nocb_cpu(rdp
->cpu
))
2115 __call_rcu_nocb_enqueue(rdp
, rhp
, &rhp
->next
, 1, lazy
);
2116 if (__is_kfree_rcu_offset((unsigned long)rhp
->func
))
2117 trace_rcu_kfree_callback(rdp
->rsp
->name
, rhp
,
2118 (unsigned long)rhp
->func
,
2119 rdp
->qlen_lazy
, rdp
->qlen
);
2121 trace_rcu_callback(rdp
->rsp
->name
, rhp
,
2122 rdp
->qlen_lazy
, rdp
->qlen
);
2127 * Adopt orphaned callbacks on a no-CBs CPU, or return 0 if this is
2130 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2131 struct rcu_data
*rdp
)
2133 long ql
= rsp
->qlen
;
2134 long qll
= rsp
->qlen_lazy
;
2136 /* If this is not a no-CBs CPU, tell the caller to do it the old way. */
2137 if (!is_nocb_cpu(smp_processor_id()))
2142 /* First, enqueue the donelist, if any. This preserves CB ordering. */
2143 if (rsp
->orphan_donelist
!= NULL
) {
2144 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_donelist
,
2145 rsp
->orphan_donetail
, ql
, qll
);
2147 rsp
->orphan_donelist
= NULL
;
2148 rsp
->orphan_donetail
= &rsp
->orphan_donelist
;
2150 if (rsp
->orphan_nxtlist
!= NULL
) {
2151 __call_rcu_nocb_enqueue(rdp
, rsp
->orphan_nxtlist
,
2152 rsp
->orphan_nxttail
, ql
, qll
);
2154 rsp
->orphan_nxtlist
= NULL
;
2155 rsp
->orphan_nxttail
= &rsp
->orphan_nxtlist
;
2161 * If necessary, kick off a new grace period, and either way wait
2162 * for a subsequent grace period to complete.
2164 static void rcu_nocb_wait_gp(struct rcu_data
*rdp
)
2168 unsigned long flags
;
2169 struct rcu_node
*rnp
= rdp
->mynode
;
2171 raw_spin_lock_irqsave(&rnp
->lock
, flags
);
2172 c
= rcu_start_future_gp(rnp
, rdp
);
2173 raw_spin_unlock_irqrestore(&rnp
->lock
, flags
);
2176 * Wait for the grace period. Do so interruptibly to avoid messing
2177 * up the load average.
2179 trace_rcu_future_gp(rnp
, rdp
, c
, "StartWait");
2181 wait_event_interruptible(
2182 rnp
->nocb_gp_wq
[c
& 0x1],
2183 (d
= ULONG_CMP_GE(ACCESS_ONCE(rnp
->completed
), c
)));
2186 flush_signals(current
);
2187 trace_rcu_future_gp(rnp
, rdp
, c
, "ResumeWait");
2189 trace_rcu_future_gp(rnp
, rdp
, c
, "EndWait");
2190 smp_mb(); /* Ensure that CB invocation happens after GP end. */
2194 * Per-rcu_data kthread, but only for no-CBs CPUs. Each kthread invokes
2195 * callbacks queued by the corresponding no-CBs CPU.
2197 static int rcu_nocb_kthread(void *arg
)
2200 struct rcu_head
*list
;
2201 struct rcu_head
*next
;
2202 struct rcu_head
**tail
;
2203 struct rcu_data
*rdp
= arg
;
2205 /* Each pass through this loop invokes one batch of callbacks */
2207 /* If not polling, wait for next batch of callbacks. */
2209 wait_event_interruptible(rdp
->nocb_wq
, rdp
->nocb_head
);
2210 list
= ACCESS_ONCE(rdp
->nocb_head
);
2212 schedule_timeout_interruptible(1);
2213 flush_signals(current
);
2218 * Extract queued callbacks, update counts, and wait
2219 * for a grace period to elapse.
2221 ACCESS_ONCE(rdp
->nocb_head
) = NULL
;
2222 tail
= xchg(&rdp
->nocb_tail
, &rdp
->nocb_head
);
2223 c
= atomic_long_xchg(&rdp
->nocb_q_count
, 0);
2224 cl
= atomic_long_xchg(&rdp
->nocb_q_count_lazy
, 0);
2225 ACCESS_ONCE(rdp
->nocb_p_count
) += c
;
2226 ACCESS_ONCE(rdp
->nocb_p_count_lazy
) += cl
;
2227 rcu_nocb_wait_gp(rdp
);
2229 /* Each pass through the following loop invokes a callback. */
2230 trace_rcu_batch_start(rdp
->rsp
->name
, cl
, c
, -1);
2234 /* Wait for enqueuing to complete, if needed. */
2235 while (next
== NULL
&& &list
->next
!= tail
) {
2236 schedule_timeout_interruptible(1);
2239 debug_rcu_head_unqueue(list
);
2241 if (__rcu_reclaim(rdp
->rsp
->name
, list
))
2247 trace_rcu_batch_end(rdp
->rsp
->name
, c
, !!list
, 0, 0, 1);
2248 ACCESS_ONCE(rdp
->nocb_p_count
) -= c
;
2249 ACCESS_ONCE(rdp
->nocb_p_count_lazy
) -= cl
;
2250 rdp
->n_nocbs_invoked
+= c
;
2255 /* Initialize per-rcu_data variables for no-CBs CPUs. */
2256 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2258 rdp
->nocb_tail
= &rdp
->nocb_head
;
2259 init_waitqueue_head(&rdp
->nocb_wq
);
2262 /* Create a kthread for each RCU flavor for each no-CBs CPU. */
2263 static void __init
rcu_spawn_nocb_kthreads(struct rcu_state
*rsp
)
2266 struct rcu_data
*rdp
;
2267 struct task_struct
*t
;
2269 if (rcu_nocb_mask
== NULL
)
2271 for_each_cpu(cpu
, rcu_nocb_mask
) {
2272 rdp
= per_cpu_ptr(rsp
->rda
, cpu
);
2273 t
= kthread_run(rcu_nocb_kthread
, rdp
,
2274 "rcuo%c/%d", rsp
->abbr
, cpu
);
2276 ACCESS_ONCE(rdp
->nocb_kthread
) = t
;
2280 /* Prevent __call_rcu() from enqueuing callbacks on no-CBs CPUs */
2281 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2283 if (rcu_nocb_mask
== NULL
||
2284 !cpumask_test_cpu(rdp
->cpu
, rcu_nocb_mask
))
2286 rdp
->nxttail
[RCU_NEXT_TAIL
] = NULL
;
2290 #else /* #ifdef CONFIG_RCU_NOCB_CPU */
2292 static int rcu_nocb_needs_gp(struct rcu_state
*rsp
)
2297 static void rcu_nocb_gp_cleanup(struct rcu_state
*rsp
, struct rcu_node
*rnp
)
2301 static void rcu_nocb_gp_set(struct rcu_node
*rnp
, int nrq
)
2305 static void rcu_init_one_nocb(struct rcu_node
*rnp
)
2309 static bool is_nocb_cpu(int cpu
)
2314 static bool __call_rcu_nocb(struct rcu_data
*rdp
, struct rcu_head
*rhp
,
2320 static bool __maybe_unused
rcu_nocb_adopt_orphan_cbs(struct rcu_state
*rsp
,
2321 struct rcu_data
*rdp
)
2326 static void __init
rcu_boot_init_nocb_percpu_data(struct rcu_data
*rdp
)
2330 static void __init
rcu_spawn_nocb_kthreads(struct rcu_state
*rsp
)
2334 static bool init_nocb_callback_list(struct rcu_data
*rdp
)
2339 #endif /* #else #ifdef CONFIG_RCU_NOCB_CPU */