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 (C) IBM Corporation, 2001
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
33 #include <linux/types.h>
34 #include <linux/kernel.h>
35 #include <linux/init.h>
36 #include <linux/spinlock.h>
37 #include <linux/smp.h>
38 #include <linux/rcupdate.h>
39 #include <linux/interrupt.h>
40 #include <linux/sched.h>
41 #include <asm/atomic.h>
42 #include <linux/bitops.h>
43 #include <linux/module.h>
44 #include <linux/completion.h>
45 #include <linux/moduleparam.h>
46 #include <linux/percpu.h>
47 #include <linux/notifier.h>
48 #include <linux/rcupdate.h>
49 #include <linux/cpu.h>
50 #include <linux/mutex.h>
52 #ifdef CONFIG_DEBUG_LOCK_ALLOC
53 static struct lock_class_key rcu_lock_key;
54 struct lockdep_map rcu_lock_map =
55 STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key);
57 EXPORT_SYMBOL_GPL(rcu_lock_map);
60 /* Definition for rcupdate control block. */
61 static struct rcu_ctrlblk rcu_ctrlblk = {
64 .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
65 .cpumask = CPU_MASK_NONE,
67 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
70 .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
71 .cpumask = CPU_MASK_NONE,
74 DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
75 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
77 /* Fake initialization required by compiler */
78 static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
79 static int blimit = 10;
80 static int qhimark = 10000;
81 static int qlowmark = 100;
83 static atomic_t rcu_barrier_cpu_count;
84 static DEFINE_MUTEX(rcu_barrier_mutex);
85 static struct completion rcu_barrier_completion;
88 static void force_quiescent_state(struct rcu_data *rdp,
89 struct rcu_ctrlblk *rcp)
94 if (unlikely(!rcp->signaled)) {
97 * Don't send IPI to itself. With irqs disabled,
98 * rdp->cpu is the current cpu.
100 cpumask = rcp->cpumask;
101 cpu_clear(rdp->cpu, cpumask);
102 for_each_cpu_mask(cpu, cpumask)
103 smp_send_reschedule(cpu);
107 static inline void force_quiescent_state(struct rcu_data *rdp,
108 struct rcu_ctrlblk *rcp)
115 * call_rcu - Queue an RCU callback for invocation after a grace period.
116 * @head: structure to be used for queueing the RCU updates.
117 * @func: actual update function to be invoked after the grace period
119 * The update function will be invoked some time after a full grace
120 * period elapses, in other words after all currently executing RCU
121 * read-side critical sections have completed. RCU read-side critical
122 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
125 void fastcall call_rcu(struct rcu_head *head,
126 void (*func)(struct rcu_head *rcu))
129 struct rcu_data *rdp;
133 local_irq_save(flags);
134 rdp = &__get_cpu_var(rcu_data);
135 *rdp->nxttail = head;
136 rdp->nxttail = &head->next;
137 if (unlikely(++rdp->qlen > qhimark)) {
138 rdp->blimit = INT_MAX;
139 force_quiescent_state(rdp, &rcu_ctrlblk);
141 local_irq_restore(flags);
145 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
146 * @head: structure to be used for queueing the RCU updates.
147 * @func: actual update function to be invoked after the grace period
149 * The update function will be invoked some time after a full grace
150 * period elapses, in other words after all currently executing RCU
151 * read-side critical sections have completed. call_rcu_bh() assumes
152 * that the read-side critical sections end on completion of a softirq
153 * handler. This means that read-side critical sections in process
154 * context must not be interrupted by softirqs. This interface is to be
155 * used when most of the read-side critical sections are in softirq context.
156 * RCU read-side critical sections are delimited by rcu_read_lock() and
157 * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
158 * and rcu_read_unlock_bh(), if in process context. These may be nested.
160 void fastcall call_rcu_bh(struct rcu_head *head,
161 void (*func)(struct rcu_head *rcu))
164 struct rcu_data *rdp;
168 local_irq_save(flags);
169 rdp = &__get_cpu_var(rcu_bh_data);
170 *rdp->nxttail = head;
171 rdp->nxttail = &head->next;
173 if (unlikely(++rdp->qlen > qhimark)) {
174 rdp->blimit = INT_MAX;
175 force_quiescent_state(rdp, &rcu_bh_ctrlblk);
178 local_irq_restore(flags);
182 * Return the number of RCU batches processed thus far. Useful
183 * for debug and statistics.
185 long rcu_batches_completed(void)
187 return rcu_ctrlblk.completed;
191 * Return the number of RCU batches processed thus far. Useful
192 * for debug and statistics.
194 long rcu_batches_completed_bh(void)
196 return rcu_bh_ctrlblk.completed;
199 static void rcu_barrier_callback(struct rcu_head *notused)
201 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
202 complete(&rcu_barrier_completion);
206 * Called with preemption disabled, and from cross-cpu IRQ context.
208 static void rcu_barrier_func(void *notused)
210 int cpu = smp_processor_id();
211 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
212 struct rcu_head *head;
214 head = &rdp->barrier;
215 atomic_inc(&rcu_barrier_cpu_count);
216 call_rcu(head, rcu_barrier_callback);
220 * rcu_barrier - Wait until all the in-flight RCUs are complete.
222 void rcu_barrier(void)
224 BUG_ON(in_interrupt());
225 /* Take cpucontrol mutex to protect against CPU hotplug */
226 mutex_lock(&rcu_barrier_mutex);
227 init_completion(&rcu_barrier_completion);
228 atomic_set(&rcu_barrier_cpu_count, 0);
229 on_each_cpu(rcu_barrier_func, NULL, 0, 1);
230 wait_for_completion(&rcu_barrier_completion);
231 mutex_unlock(&rcu_barrier_mutex);
233 EXPORT_SYMBOL_GPL(rcu_barrier);
236 * Invoke the completed RCU callbacks. They are expected to be in
239 static void rcu_do_batch(struct rcu_data *rdp)
241 struct rcu_head *next, *list;
244 list = rdp->donelist;
250 if (++count >= rdp->blimit)
253 rdp->donelist = list;
258 if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
259 rdp->blimit = blimit;
262 rdp->donetail = &rdp->donelist;
264 tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
268 * Grace period handling:
269 * The grace period handling consists out of two steps:
270 * - A new grace period is started.
271 * This is done by rcu_start_batch. The start is not broadcasted to
272 * all cpus, they must pick this up by comparing rcp->cur with
273 * rdp->quiescbatch. All cpus are recorded in the
274 * rcu_ctrlblk.cpumask bitmap.
275 * - All cpus must go through a quiescent state.
276 * Since the start of the grace period is not broadcasted, at least two
277 * calls to rcu_check_quiescent_state are required:
278 * The first call just notices that a new grace period is running. The
279 * following calls check if there was a quiescent state since the beginning
280 * of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
281 * the bitmap is empty, then the grace period is completed.
282 * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
283 * period (if necessary).
286 * Register a new batch of callbacks, and start it up if there is currently no
287 * active batch and the batch to be registered has not already occurred.
288 * Caller must hold rcu_ctrlblk.lock.
290 static void rcu_start_batch(struct rcu_ctrlblk *rcp)
292 if (rcp->next_pending &&
293 rcp->completed == rcp->cur) {
294 rcp->next_pending = 0;
296 * next_pending == 0 must be visible in
297 * __rcu_process_callbacks() before it can see new value of cur.
303 * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
304 * Barrier Otherwise it can cause tickless idle CPUs to be
305 * included in rcp->cpumask, which will extend graceperiods
309 cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
316 * cpu went through a quiescent state since the beginning of the grace period.
317 * Clear it from the cpu mask and complete the grace period if it was the last
318 * cpu. Start another grace period if someone has further entries pending
320 static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
322 cpu_clear(cpu, rcp->cpumask);
323 if (cpus_empty(rcp->cpumask)) {
324 /* batch completed ! */
325 rcp->completed = rcp->cur;
326 rcu_start_batch(rcp);
331 * Check if the cpu has gone through a quiescent state (say context
332 * switch). If so and if it already hasn't done so in this RCU
333 * quiescent cycle, then indicate that it has done so.
335 static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
336 struct rcu_data *rdp)
338 if (rdp->quiescbatch != rcp->cur) {
339 /* start new grace period: */
341 rdp->passed_quiesc = 0;
342 rdp->quiescbatch = rcp->cur;
346 /* Grace period already completed for this cpu?
347 * qs_pending is checked instead of the actual bitmap to avoid
348 * cacheline trashing.
350 if (!rdp->qs_pending)
354 * Was there a quiescent state since the beginning of the grace
355 * period? If no, then exit and wait for the next call.
357 if (!rdp->passed_quiesc)
361 spin_lock(&rcp->lock);
363 * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
364 * during cpu startup. Ignore the quiescent state.
366 if (likely(rdp->quiescbatch == rcp->cur))
367 cpu_quiet(rdp->cpu, rcp);
369 spin_unlock(&rcp->lock);
373 #ifdef CONFIG_HOTPLUG_CPU
375 /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
376 * locking requirements, the list it's pulling from has to belong to a cpu
377 * which is dead and hence not processing interrupts.
379 static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
380 struct rcu_head **tail)
383 *this_rdp->nxttail = list;
385 this_rdp->nxttail = tail;
389 static void __rcu_offline_cpu(struct rcu_data *this_rdp,
390 struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
392 /* if the cpu going offline owns the grace period
393 * we can block indefinitely waiting for it, so flush
396 spin_lock_bh(&rcp->lock);
397 if (rcp->cur != rcp->completed)
398 cpu_quiet(rdp->cpu, rcp);
399 spin_unlock_bh(&rcp->lock);
400 rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
401 rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
402 rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
405 static void rcu_offline_cpu(int cpu)
407 struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
408 struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
410 __rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
411 &per_cpu(rcu_data, cpu));
412 __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
413 &per_cpu(rcu_bh_data, cpu));
414 put_cpu_var(rcu_data);
415 put_cpu_var(rcu_bh_data);
416 tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
421 static void rcu_offline_cpu(int cpu)
428 * This does the RCU processing work from tasklet context.
430 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
431 struct rcu_data *rdp)
433 if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
434 *rdp->donetail = rdp->curlist;
435 rdp->donetail = rdp->curtail;
437 rdp->curtail = &rdp->curlist;
440 if (rdp->nxtlist && !rdp->curlist) {
442 rdp->curlist = rdp->nxtlist;
443 rdp->curtail = rdp->nxttail;
445 rdp->nxttail = &rdp->nxtlist;
449 * start the next batch of callbacks
452 /* determine batch number */
453 rdp->batch = rcp->cur + 1;
454 /* see the comment and corresponding wmb() in
455 * the rcu_start_batch()
459 if (!rcp->next_pending) {
460 /* and start it/schedule start if it's a new batch */
461 spin_lock(&rcp->lock);
462 rcp->next_pending = 1;
463 rcu_start_batch(rcp);
464 spin_unlock(&rcp->lock);
468 rcu_check_quiescent_state(rcp, rdp);
473 static void rcu_process_callbacks(unsigned long unused)
475 __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
476 __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
479 static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
481 /* This cpu has pending rcu entries and the grace period
482 * for them has completed.
484 if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
487 /* This cpu has no pending entries, but there are new entries */
488 if (!rdp->curlist && rdp->nxtlist)
491 /* This cpu has finished callbacks to invoke */
495 /* The rcu core waits for a quiescent state from the cpu */
496 if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
504 * Check to see if there is any immediate RCU-related work to be done
505 * by the current CPU, returning 1 if so. This function is part of the
506 * RCU implementation; it is -not- an exported member of the RCU API.
508 int rcu_pending(int cpu)
510 return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
511 __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
515 * Check to see if any future RCU-related work will need to be done
516 * by the current CPU, even if none need be done immediately, returning
517 * 1 if so. This function is part of the RCU implementation; it is -not-
518 * an exported member of the RCU API.
520 int rcu_needs_cpu(int cpu)
522 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
523 struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
525 return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
528 void rcu_check_callbacks(int cpu, int user)
531 (idle_cpu(cpu) && !in_softirq() &&
532 hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
534 rcu_bh_qsctr_inc(cpu);
535 } else if (!in_softirq())
536 rcu_bh_qsctr_inc(cpu);
537 tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
540 static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
541 struct rcu_data *rdp)
543 memset(rdp, 0, sizeof(*rdp));
544 rdp->curtail = &rdp->curlist;
545 rdp->nxttail = &rdp->nxtlist;
546 rdp->donetail = &rdp->donelist;
547 rdp->quiescbatch = rcp->completed;
550 rdp->blimit = blimit;
553 static void __devinit rcu_online_cpu(int cpu)
555 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
556 struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
558 rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
559 rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
560 tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
563 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
564 unsigned long action, void *hcpu)
566 long cpu = (long)hcpu;
569 case CPU_UP_PREPARE_FROZEN:
573 case CPU_DEAD_FROZEN:
574 rcu_offline_cpu(cpu);
582 static struct notifier_block __cpuinitdata rcu_nb = {
583 .notifier_call = rcu_cpu_notify,
587 * Initializes rcu mechanism. Assumed to be called early.
588 * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
589 * Note that rcu_qsctr and friends are implicitly
590 * initialized due to the choice of ``0'' for RCU_CTR_INVALID.
592 void __init rcu_init(void)
594 rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
595 (void *)(long)smp_processor_id());
596 /* Register notifier for non-boot CPUs */
597 register_cpu_notifier(&rcu_nb);
600 struct rcu_synchronize {
601 struct rcu_head head;
602 struct completion completion;
605 /* Because of FASTCALL declaration of complete, we use this wrapper */
606 static void wakeme_after_rcu(struct rcu_head *head)
608 struct rcu_synchronize *rcu;
610 rcu = container_of(head, struct rcu_synchronize, head);
611 complete(&rcu->completion);
615 * synchronize_rcu - wait until a grace period has elapsed.
617 * Control will return to the caller some time after a full grace
618 * period has elapsed, in other words after all currently executing RCU
619 * read-side critical sections have completed. RCU read-side critical
620 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
623 * If your read-side code is not protected by rcu_read_lock(), do -not-
624 * use synchronize_rcu().
626 void synchronize_rcu(void)
628 struct rcu_synchronize rcu;
630 init_completion(&rcu.completion);
631 /* Will wake me after RCU finished */
632 call_rcu(&rcu.head, wakeme_after_rcu);
635 wait_for_completion(&rcu.completion);
638 module_param(blimit, int, 0);
639 module_param(qhimark, int, 0);
640 module_param(qlowmark, int, 0);
641 EXPORT_SYMBOL_GPL(rcu_batches_completed);
642 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
643 EXPORT_SYMBOL_GPL(call_rcu);
644 EXPORT_SYMBOL_GPL(call_rcu_bh);
645 EXPORT_SYMBOL_GPL(synchronize_rcu);