ia64/linux-2.6.18-xen.hg

view kernel/rcupdate.c @ 912:dd42cdb0ab89

[IA64] Build blktap2 driver by default in x86 builds.

add CONFIG_XEN_BLKDEV_TAP2=y to buildconfigs/linux-defconfig_xen_ia64.

Signed-off-by: Isaku Yamahata <yamahata@valinux.co.jp>
author Isaku Yamahata <yamahata@valinux.co.jp>
date Mon Jun 29 12:09:16 2009 +0900 (2009-06-29)
parents 831230e53067
children
line source
1 /*
2 * Read-Copy Update mechanism for mutual exclusion
3 *
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.
8 *
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.
13 *
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.
17 *
18 * Copyright (C) IBM Corporation, 2001
19 *
20 * Authors: Dipankar Sarma <dipankar@in.ibm.com>
21 * Manfred Spraul <manfred@colorfullife.com>
22 *
23 * Based on the original work by Paul McKenney <paulmck@us.ibm.com>
24 * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
25 * Papers:
26 * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
27 * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
28 *
29 * For detailed explanation of Read-Copy Update mechanism see -
30 * http://lse.sourceforge.net/locking/rcupdate.html
31 *
32 */
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 /* Definition for rcupdate control block. */
53 static struct rcu_ctrlblk rcu_ctrlblk = {
54 .cur = -300,
55 .completed = -300,
56 .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
57 .cpumask = CPU_MASK_NONE,
58 };
59 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
60 .cur = -300,
61 .completed = -300,
62 .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
63 .cpumask = CPU_MASK_NONE,
64 };
66 DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
67 DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
69 /* Fake initialization required by compiler */
70 static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
71 static int blimit = 10;
72 static int qhimark = 10000;
73 static int qlowmark = 100;
74 #ifdef CONFIG_SMP
75 static int rsinterval = 1000;
76 #endif
78 static atomic_t rcu_barrier_cpu_count;
79 static DEFINE_MUTEX(rcu_barrier_mutex);
80 static struct completion rcu_barrier_completion;
82 #ifdef CONFIG_SMP
83 static void force_quiescent_state(struct rcu_data *rdp,
84 struct rcu_ctrlblk *rcp)
85 {
86 int cpu;
87 cpumask_t cpumask;
88 set_need_resched();
89 if (unlikely(rdp->qlen - rdp->last_rs_qlen > rsinterval)) {
90 rdp->last_rs_qlen = rdp->qlen;
91 /*
92 * Don't send IPI to itself. With irqs disabled,
93 * rdp->cpu is the current cpu.
94 */
95 cpumask = rcp->cpumask;
96 cpu_clear(rdp->cpu, cpumask);
97 for_each_cpu_mask(cpu, cpumask)
98 smp_send_reschedule(cpu);
99 }
100 }
101 #else
102 static inline void force_quiescent_state(struct rcu_data *rdp,
103 struct rcu_ctrlblk *rcp)
104 {
105 set_need_resched();
106 }
107 #endif
109 /**
110 * call_rcu - Queue an RCU callback for invocation after a grace period.
111 * @head: structure to be used for queueing the RCU updates.
112 * @func: actual update function to be invoked after the grace period
113 *
114 * The update function will be invoked some time after a full grace
115 * period elapses, in other words after all currently executing RCU
116 * read-side critical sections have completed. RCU read-side critical
117 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
118 * and may be nested.
119 */
120 void fastcall call_rcu(struct rcu_head *head,
121 void (*func)(struct rcu_head *rcu))
122 {
123 unsigned long flags;
124 struct rcu_data *rdp;
126 head->func = func;
127 head->next = NULL;
128 local_irq_save(flags);
129 rdp = &__get_cpu_var(rcu_data);
130 *rdp->nxttail = head;
131 rdp->nxttail = &head->next;
132 if (unlikely(++rdp->qlen > qhimark)) {
133 rdp->blimit = INT_MAX;
134 force_quiescent_state(rdp, &rcu_ctrlblk);
135 }
136 local_irq_restore(flags);
137 }
139 /**
140 * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
141 * @head: structure to be used for queueing the RCU updates.
142 * @func: actual update function to be invoked after the grace period
143 *
144 * The update function will be invoked some time after a full grace
145 * period elapses, in other words after all currently executing RCU
146 * read-side critical sections have completed. call_rcu_bh() assumes
147 * that the read-side critical sections end on completion of a softirq
148 * handler. This means that read-side critical sections in process
149 * context must not be interrupted by softirqs. This interface is to be
150 * used when most of the read-side critical sections are in softirq context.
151 * RCU read-side critical sections are delimited by rcu_read_lock() and
152 * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
153 * and rcu_read_unlock_bh(), if in process context. These may be nested.
154 */
155 void fastcall call_rcu_bh(struct rcu_head *head,
156 void (*func)(struct rcu_head *rcu))
157 {
158 unsigned long flags;
159 struct rcu_data *rdp;
161 head->func = func;
162 head->next = NULL;
163 local_irq_save(flags);
164 rdp = &__get_cpu_var(rcu_bh_data);
165 *rdp->nxttail = head;
166 rdp->nxttail = &head->next;
168 if (unlikely(++rdp->qlen > qhimark)) {
169 rdp->blimit = INT_MAX;
170 force_quiescent_state(rdp, &rcu_bh_ctrlblk);
171 }
173 local_irq_restore(flags);
174 }
176 /*
177 * Return the number of RCU batches processed thus far. Useful
178 * for debug and statistics.
179 */
180 long rcu_batches_completed(void)
181 {
182 return rcu_ctrlblk.completed;
183 }
185 /*
186 * Return the number of RCU batches processed thus far. Useful
187 * for debug and statistics.
188 */
189 long rcu_batches_completed_bh(void)
190 {
191 return rcu_bh_ctrlblk.completed;
192 }
194 static void rcu_barrier_callback(struct rcu_head *notused)
195 {
196 if (atomic_dec_and_test(&rcu_barrier_cpu_count))
197 complete(&rcu_barrier_completion);
198 }
200 /*
201 * Called with preemption disabled, and from cross-cpu IRQ context.
202 */
203 static void rcu_barrier_func(void *notused)
204 {
205 int cpu = smp_processor_id();
206 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
207 struct rcu_head *head;
209 head = &rdp->barrier;
210 atomic_inc(&rcu_barrier_cpu_count);
211 call_rcu(head, rcu_barrier_callback);
212 }
214 /**
215 * rcu_barrier - Wait until all the in-flight RCUs are complete.
216 */
217 void rcu_barrier(void)
218 {
219 BUG_ON(in_interrupt());
220 /* Take cpucontrol mutex to protect against CPU hotplug */
221 mutex_lock(&rcu_barrier_mutex);
222 init_completion(&rcu_barrier_completion);
223 atomic_set(&rcu_barrier_cpu_count, 0);
224 on_each_cpu(rcu_barrier_func, NULL, 0, 1);
225 wait_for_completion(&rcu_barrier_completion);
226 mutex_unlock(&rcu_barrier_mutex);
227 }
228 EXPORT_SYMBOL_GPL(rcu_barrier);
230 /*
231 * Invoke the completed RCU callbacks. They are expected to be in
232 * a per-cpu list.
233 */
234 static void rcu_do_batch(struct rcu_data *rdp)
235 {
236 struct rcu_head *next, *list;
237 int count = 0;
239 list = rdp->donelist;
240 while (list) {
241 next = rdp->donelist = list->next;
242 list->func(list);
243 list = next;
244 if (++count >= rdp->blimit)
245 break;
246 }
248 local_irq_disable();
249 rdp->qlen -= count;
250 local_irq_enable();
251 if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
252 rdp->blimit = blimit;
254 if (!rdp->donelist)
255 rdp->donetail = &rdp->donelist;
256 else
257 tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
258 }
260 /*
261 * Grace period handling:
262 * The grace period handling consists out of two steps:
263 * - A new grace period is started.
264 * This is done by rcu_start_batch. The start is not broadcasted to
265 * all cpus, they must pick this up by comparing rcp->cur with
266 * rdp->quiescbatch. All cpus are recorded in the
267 * rcu_ctrlblk.cpumask bitmap.
268 * - All cpus must go through a quiescent state.
269 * Since the start of the grace period is not broadcasted, at least two
270 * calls to rcu_check_quiescent_state are required:
271 * The first call just notices that a new grace period is running. The
272 * following calls check if there was a quiescent state since the beginning
273 * of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
274 * the bitmap is empty, then the grace period is completed.
275 * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
276 * period (if necessary).
277 */
278 /*
279 * Register a new batch of callbacks, and start it up if there is currently no
280 * active batch and the batch to be registered has not already occurred.
281 * Caller must hold rcu_ctrlblk.lock.
282 */
283 static void rcu_start_batch(struct rcu_ctrlblk *rcp)
284 {
285 if (rcp->next_pending &&
286 rcp->completed == rcp->cur) {
287 rcp->next_pending = 0;
288 /*
289 * next_pending == 0 must be visible in
290 * __rcu_process_callbacks() before it can see new value of cur.
291 */
292 smp_wmb();
293 rcp->cur++;
295 /*
296 * Accessing nohz_cpu_mask before incrementing rcp->cur needs a
297 * Barrier Otherwise it can cause tickless idle CPUs to be
298 * included in rcp->cpumask, which will extend graceperiods
299 * unnecessarily.
300 */
301 smp_mb();
302 cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
304 }
305 }
307 /*
308 * cpu went through a quiescent state since the beginning of the grace period.
309 * Clear it from the cpu mask and complete the grace period if it was the last
310 * cpu. Start another grace period if someone has further entries pending
311 */
312 static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
313 {
314 cpu_clear(cpu, rcp->cpumask);
315 if (cpus_empty(rcp->cpumask)) {
316 /* batch completed ! */
317 rcp->completed = rcp->cur;
318 rcu_start_batch(rcp);
319 }
320 }
322 /*
323 * Check if the cpu has gone through a quiescent state (say context
324 * switch). If so and if it already hasn't done so in this RCU
325 * quiescent cycle, then indicate that it has done so.
326 */
327 static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
328 struct rcu_data *rdp)
329 {
330 if (rdp->quiescbatch != rcp->cur) {
331 /* start new grace period: */
332 rdp->qs_pending = 1;
333 rdp->passed_quiesc = 0;
334 rdp->quiescbatch = rcp->cur;
335 return;
336 }
338 /* Grace period already completed for this cpu?
339 * qs_pending is checked instead of the actual bitmap to avoid
340 * cacheline trashing.
341 */
342 if (!rdp->qs_pending)
343 return;
345 /*
346 * Was there a quiescent state since the beginning of the grace
347 * period? If no, then exit and wait for the next call.
348 */
349 if (!rdp->passed_quiesc)
350 return;
351 rdp->qs_pending = 0;
353 spin_lock(&rcp->lock);
354 /*
355 * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
356 * during cpu startup. Ignore the quiescent state.
357 */
358 if (likely(rdp->quiescbatch == rcp->cur))
359 cpu_quiet(rdp->cpu, rcp);
361 spin_unlock(&rcp->lock);
362 }
365 #ifdef CONFIG_HOTPLUG_CPU
367 /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
368 * locking requirements, the list it's pulling from has to belong to a cpu
369 * which is dead and hence not processing interrupts.
370 */
371 static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
372 struct rcu_head **tail)
373 {
374 local_irq_disable();
375 *this_rdp->nxttail = list;
376 if (list)
377 this_rdp->nxttail = tail;
378 local_irq_enable();
379 }
381 static void __rcu_offline_cpu(struct rcu_data *this_rdp,
382 struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
383 {
384 /* if the cpu going offline owns the grace period
385 * we can block indefinitely waiting for it, so flush
386 * it here
387 */
388 spin_lock_bh(&rcp->lock);
389 if (rcp->cur != rcp->completed)
390 cpu_quiet(rdp->cpu, rcp);
391 spin_unlock_bh(&rcp->lock);
392 rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
393 rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
394 rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
395 }
397 static void rcu_offline_cpu(int cpu)
398 {
399 struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
400 struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
402 __rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
403 &per_cpu(rcu_data, cpu));
404 __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
405 &per_cpu(rcu_bh_data, cpu));
406 put_cpu_var(rcu_data);
407 put_cpu_var(rcu_bh_data);
408 tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
409 }
411 #else
413 static void rcu_offline_cpu(int cpu)
414 {
415 }
417 #endif
419 /*
420 * This does the RCU processing work from tasklet context.
421 */
422 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
423 struct rcu_data *rdp)
424 {
425 if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
426 *rdp->donetail = rdp->curlist;
427 rdp->donetail = rdp->curtail;
428 rdp->curlist = NULL;
429 rdp->curtail = &rdp->curlist;
430 }
432 if (rdp->nxtlist && !rdp->curlist) {
433 local_irq_disable();
434 rdp->curlist = rdp->nxtlist;
435 rdp->curtail = rdp->nxttail;
436 rdp->nxtlist = NULL;
437 rdp->nxttail = &rdp->nxtlist;
438 local_irq_enable();
440 /*
441 * start the next batch of callbacks
442 */
444 /* determine batch number */
445 rdp->batch = rcp->cur + 1;
446 /* see the comment and corresponding wmb() in
447 * the rcu_start_batch()
448 */
449 smp_rmb();
451 if (!rcp->next_pending) {
452 /* and start it/schedule start if it's a new batch */
453 spin_lock(&rcp->lock);
454 rcp->next_pending = 1;
455 rcu_start_batch(rcp);
456 spin_unlock(&rcp->lock);
457 }
458 }
460 rcu_check_quiescent_state(rcp, rdp);
461 if (rdp->donelist)
462 rcu_do_batch(rdp);
463 }
465 static void rcu_process_callbacks(unsigned long unused)
466 {
467 __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
468 __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
469 }
471 static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
472 {
473 /* This cpu has pending rcu entries and the grace period
474 * for them has completed.
475 */
476 if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
477 return 1;
479 /* This cpu has no pending entries, but there are new entries */
480 if (!rdp->curlist && rdp->nxtlist)
481 return 1;
483 /* This cpu has finished callbacks to invoke */
484 if (rdp->donelist)
485 return 1;
487 /* The rcu core waits for a quiescent state from the cpu */
488 if (rdp->quiescbatch != rcp->cur || rdp->qs_pending)
489 return 1;
491 /* nothing to do */
492 return 0;
493 }
495 /*
496 * Check to see if there is any immediate RCU-related work to be done
497 * by the current CPU, returning 1 if so. This function is part of the
498 * RCU implementation; it is -not- an exported member of the RCU API.
499 */
500 int rcu_pending(int cpu)
501 {
502 return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) ||
503 __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu));
504 }
506 /*
507 * Check to see if any future RCU-related work will need to be done
508 * by the current CPU, even if none need be done immediately, returning
509 * 1 if so. This function is part of the RCU implementation; it is -not-
510 * an exported member of the RCU API.
511 */
512 int rcu_needs_cpu(int cpu)
513 {
514 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
515 struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu);
517 return (!!rdp->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
518 }
520 void rcu_check_callbacks(int cpu, int user)
521 {
522 if (user ||
523 (idle_cpu(cpu) && !in_softirq() &&
524 hardirq_count() <= (1 << HARDIRQ_SHIFT))) {
525 rcu_qsctr_inc(cpu);
526 rcu_bh_qsctr_inc(cpu);
527 } else if (!in_softirq())
528 rcu_bh_qsctr_inc(cpu);
529 tasklet_schedule(&per_cpu(rcu_tasklet, cpu));
530 }
532 static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp,
533 struct rcu_data *rdp)
534 {
535 memset(rdp, 0, sizeof(*rdp));
536 rdp->curtail = &rdp->curlist;
537 rdp->nxttail = &rdp->nxtlist;
538 rdp->donetail = &rdp->donelist;
539 rdp->quiescbatch = rcp->completed;
540 rdp->qs_pending = 0;
541 rdp->cpu = cpu;
542 rdp->blimit = blimit;
543 }
545 static void __devinit rcu_online_cpu(int cpu)
546 {
547 struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
548 struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu);
550 rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp);
551 rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp);
552 tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL);
553 }
555 static int __cpuinit rcu_cpu_notify(struct notifier_block *self,
556 unsigned long action, void *hcpu)
557 {
558 long cpu = (long)hcpu;
559 switch (action) {
560 case CPU_UP_PREPARE:
561 rcu_online_cpu(cpu);
562 break;
563 case CPU_DEAD:
564 rcu_offline_cpu(cpu);
565 break;
566 default:
567 break;
568 }
569 return NOTIFY_OK;
570 }
572 static struct notifier_block __cpuinitdata rcu_nb = {
573 .notifier_call = rcu_cpu_notify,
574 };
576 /*
577 * Initializes rcu mechanism. Assumed to be called early.
578 * That is before local timer(SMP) or jiffie timer (uniproc) is setup.
579 * Note that rcu_qsctr and friends are implicitly
580 * initialized due to the choice of ``0'' for RCU_CTR_INVALID.
581 */
582 void __init rcu_init(void)
583 {
584 rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE,
585 (void *)(long)smp_processor_id());
586 /* Register notifier for non-boot CPUs */
587 register_cpu_notifier(&rcu_nb);
588 }
590 struct rcu_synchronize {
591 struct rcu_head head;
592 struct completion completion;
593 };
595 /* Because of FASTCALL declaration of complete, we use this wrapper */
596 static void wakeme_after_rcu(struct rcu_head *head)
597 {
598 struct rcu_synchronize *rcu;
600 rcu = container_of(head, struct rcu_synchronize, head);
601 complete(&rcu->completion);
602 }
604 /**
605 * synchronize_rcu - wait until a grace period has elapsed.
606 *
607 * Control will return to the caller some time after a full grace
608 * period has elapsed, in other words after all currently executing RCU
609 * read-side critical sections have completed. RCU read-side critical
610 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
611 * and may be nested.
612 *
613 * If your read-side code is not protected by rcu_read_lock(), do -not-
614 * use synchronize_rcu().
615 */
616 void synchronize_rcu(void)
617 {
618 struct rcu_synchronize rcu;
620 init_completion(&rcu.completion);
621 /* Will wake me after RCU finished */
622 call_rcu(&rcu.head, wakeme_after_rcu);
624 /* Wait for it */
625 wait_for_completion(&rcu.completion);
626 }
628 module_param(blimit, int, 0);
629 module_param(qhimark, int, 0);
630 module_param(qlowmark, int, 0);
631 #ifdef CONFIG_SMP
632 module_param(rsinterval, int, 0);
633 #endif
634 EXPORT_SYMBOL_GPL(rcu_batches_completed);
635 EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
636 EXPORT_SYMBOL_GPL(call_rcu);
637 EXPORT_SYMBOL_GPL(call_rcu_bh);
638 EXPORT_SYMBOL_GPL(synchronize_rcu);