net: dev_close() should check IFF_UP
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / rcutiny_plugin.h
blob015abaea962ad4087130014506b72dc19b33b43d
1 /*
2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition
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 (c) 2010 Linaro
22 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 #include <linux/kthread.h>
26 #include <linux/debugfs.h>
27 #include <linux/seq_file.h>
29 #ifdef CONFIG_RCU_TRACE
30 #define RCU_TRACE(stmt) stmt
31 #else /* #ifdef CONFIG_RCU_TRACE */
32 #define RCU_TRACE(stmt)
33 #endif /* #else #ifdef CONFIG_RCU_TRACE */
35 /* Global control variables for rcupdate callback mechanism. */
36 struct rcu_ctrlblk {
37 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
38 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
39 struct rcu_head **curtail; /* ->next pointer of last CB. */
40 RCU_TRACE(long qlen); /* Number of pending CBs. */
43 /* Definition for rcupdate control block. */
44 static struct rcu_ctrlblk rcu_sched_ctrlblk = {
45 .donetail = &rcu_sched_ctrlblk.rcucblist,
46 .curtail = &rcu_sched_ctrlblk.rcucblist,
49 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
50 .donetail = &rcu_bh_ctrlblk.rcucblist,
51 .curtail = &rcu_bh_ctrlblk.rcucblist,
54 #ifdef CONFIG_DEBUG_LOCK_ALLOC
55 int rcu_scheduler_active __read_mostly;
56 EXPORT_SYMBOL_GPL(rcu_scheduler_active);
57 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
59 #ifdef CONFIG_TINY_PREEMPT_RCU
61 #include <linux/delay.h>
63 /* Global control variables for preemptible RCU. */
64 struct rcu_preempt_ctrlblk {
65 struct rcu_ctrlblk rcb; /* curtail: ->next ptr of last CB for GP. */
66 struct rcu_head **nexttail;
67 /* Tasks blocked in a preemptible RCU */
68 /* read-side critical section while an */
69 /* preemptible-RCU grace period is in */
70 /* progress must wait for a later grace */
71 /* period. This pointer points to the */
72 /* ->next pointer of the last task that */
73 /* must wait for a later grace period, or */
74 /* to &->rcb.rcucblist if there is no */
75 /* such task. */
76 struct list_head blkd_tasks;
77 /* Tasks blocked in RCU read-side critical */
78 /* section. Tasks are placed at the head */
79 /* of this list and age towards the tail. */
80 struct list_head *gp_tasks;
81 /* Pointer to the first task blocking the */
82 /* current grace period, or NULL if there */
83 /* is no such task. */
84 struct list_head *exp_tasks;
85 /* Pointer to first task blocking the */
86 /* current expedited grace period, or NULL */
87 /* if there is no such task. If there */
88 /* is no current expedited grace period, */
89 /* then there cannot be any such task. */
90 #ifdef CONFIG_RCU_BOOST
91 struct list_head *boost_tasks;
92 /* Pointer to first task that needs to be */
93 /* priority-boosted, or NULL if no priority */
94 /* boosting is needed. If there is no */
95 /* current or expedited grace period, there */
96 /* can be no such task. */
97 #endif /* #ifdef CONFIG_RCU_BOOST */
98 u8 gpnum; /* Current grace period. */
99 u8 gpcpu; /* Last grace period blocked by the CPU. */
100 u8 completed; /* Last grace period completed. */
101 /* If all three are equal, RCU is idle. */
102 #ifdef CONFIG_RCU_BOOST
103 s8 boosted_this_gp; /* Has boosting already happened? */
104 unsigned long boost_time; /* When to start boosting (jiffies) */
105 #endif /* #ifdef CONFIG_RCU_BOOST */
106 #ifdef CONFIG_RCU_TRACE
107 unsigned long n_grace_periods;
108 #ifdef CONFIG_RCU_BOOST
109 unsigned long n_tasks_boosted;
110 unsigned long n_exp_boosts;
111 unsigned long n_normal_boosts;
112 unsigned long n_normal_balk_blkd_tasks;
113 unsigned long n_normal_balk_gp_tasks;
114 unsigned long n_normal_balk_boost_tasks;
115 unsigned long n_normal_balk_boosted;
116 unsigned long n_normal_balk_notyet;
117 unsigned long n_normal_balk_nos;
118 unsigned long n_exp_balk_blkd_tasks;
119 unsigned long n_exp_balk_nos;
120 #endif /* #ifdef CONFIG_RCU_BOOST */
121 #endif /* #ifdef CONFIG_RCU_TRACE */
124 static struct rcu_preempt_ctrlblk rcu_preempt_ctrlblk = {
125 .rcb.donetail = &rcu_preempt_ctrlblk.rcb.rcucblist,
126 .rcb.curtail = &rcu_preempt_ctrlblk.rcb.rcucblist,
127 .nexttail = &rcu_preempt_ctrlblk.rcb.rcucblist,
128 .blkd_tasks = LIST_HEAD_INIT(rcu_preempt_ctrlblk.blkd_tasks),
131 static int rcu_preempted_readers_exp(void);
132 static void rcu_report_exp_done(void);
135 * Return true if the CPU has not yet responded to the current grace period.
137 static int rcu_cpu_blocking_cur_gp(void)
139 return rcu_preempt_ctrlblk.gpcpu != rcu_preempt_ctrlblk.gpnum;
143 * Check for a running RCU reader. Because there is only one CPU,
144 * there can be but one running RCU reader at a time. ;-)
146 static int rcu_preempt_running_reader(void)
148 return current->rcu_read_lock_nesting;
152 * Check for preempted RCU readers blocking any grace period.
153 * If the caller needs a reliable answer, it must disable hard irqs.
155 static int rcu_preempt_blocked_readers_any(void)
157 return !list_empty(&rcu_preempt_ctrlblk.blkd_tasks);
161 * Check for preempted RCU readers blocking the current grace period.
162 * If the caller needs a reliable answer, it must disable hard irqs.
164 static int rcu_preempt_blocked_readers_cgp(void)
166 return rcu_preempt_ctrlblk.gp_tasks != NULL;
170 * Return true if another preemptible-RCU grace period is needed.
172 static int rcu_preempt_needs_another_gp(void)
174 return *rcu_preempt_ctrlblk.rcb.curtail != NULL;
178 * Return true if a preemptible-RCU grace period is in progress.
179 * The caller must disable hardirqs.
181 static int rcu_preempt_gp_in_progress(void)
183 return rcu_preempt_ctrlblk.completed != rcu_preempt_ctrlblk.gpnum;
187 * Advance a ->blkd_tasks-list pointer to the next entry, instead
188 * returning NULL if at the end of the list.
190 static struct list_head *rcu_next_node_entry(struct task_struct *t)
192 struct list_head *np;
194 np = t->rcu_node_entry.next;
195 if (np == &rcu_preempt_ctrlblk.blkd_tasks)
196 np = NULL;
197 return np;
200 #ifdef CONFIG_RCU_TRACE
202 #ifdef CONFIG_RCU_BOOST
203 static void rcu_initiate_boost_trace(void);
204 static void rcu_initiate_exp_boost_trace(void);
205 #endif /* #ifdef CONFIG_RCU_BOOST */
208 * Dump additional statistice for TINY_PREEMPT_RCU.
210 static void show_tiny_preempt_stats(struct seq_file *m)
212 seq_printf(m, "rcu_preempt: qlen=%ld gp=%lu g%u/p%u/c%u tasks=%c%c%c\n",
213 rcu_preempt_ctrlblk.rcb.qlen,
214 rcu_preempt_ctrlblk.n_grace_periods,
215 rcu_preempt_ctrlblk.gpnum,
216 rcu_preempt_ctrlblk.gpcpu,
217 rcu_preempt_ctrlblk.completed,
218 "T."[list_empty(&rcu_preempt_ctrlblk.blkd_tasks)],
219 "N."[!rcu_preempt_ctrlblk.gp_tasks],
220 "E."[!rcu_preempt_ctrlblk.exp_tasks]);
221 #ifdef CONFIG_RCU_BOOST
222 seq_printf(m, " ttb=%c btg=",
223 "B."[!rcu_preempt_ctrlblk.boost_tasks]);
224 switch (rcu_preempt_ctrlblk.boosted_this_gp) {
225 case -1:
226 seq_puts(m, "exp");
227 break;
228 case 0:
229 seq_puts(m, "no");
230 break;
231 case 1:
232 seq_puts(m, "begun");
233 break;
234 case 2:
235 seq_puts(m, "done");
236 break;
237 default:
238 seq_printf(m, "?%d?", rcu_preempt_ctrlblk.boosted_this_gp);
240 seq_printf(m, " ntb=%lu neb=%lu nnb=%lu j=%04x bt=%04x\n",
241 rcu_preempt_ctrlblk.n_tasks_boosted,
242 rcu_preempt_ctrlblk.n_exp_boosts,
243 rcu_preempt_ctrlblk.n_normal_boosts,
244 (int)(jiffies & 0xffff),
245 (int)(rcu_preempt_ctrlblk.boost_time & 0xffff));
246 seq_printf(m, " %s: nt=%lu gt=%lu bt=%lu b=%lu ny=%lu nos=%lu\n",
247 "normal balk",
248 rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks,
249 rcu_preempt_ctrlblk.n_normal_balk_gp_tasks,
250 rcu_preempt_ctrlblk.n_normal_balk_boost_tasks,
251 rcu_preempt_ctrlblk.n_normal_balk_boosted,
252 rcu_preempt_ctrlblk.n_normal_balk_notyet,
253 rcu_preempt_ctrlblk.n_normal_balk_nos);
254 seq_printf(m, " exp balk: bt=%lu nos=%lu\n",
255 rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks,
256 rcu_preempt_ctrlblk.n_exp_balk_nos);
257 #endif /* #ifdef CONFIG_RCU_BOOST */
260 #endif /* #ifdef CONFIG_RCU_TRACE */
262 #ifdef CONFIG_RCU_BOOST
264 #include "rtmutex_common.h"
267 * Carry out RCU priority boosting on the task indicated by ->boost_tasks,
268 * and advance ->boost_tasks to the next task in the ->blkd_tasks list.
270 static int rcu_boost(void)
272 unsigned long flags;
273 struct rt_mutex mtx;
274 struct list_head *np;
275 struct task_struct *t;
277 if (rcu_preempt_ctrlblk.boost_tasks == NULL)
278 return 0; /* Nothing to boost. */
279 raw_local_irq_save(flags);
280 rcu_preempt_ctrlblk.boosted_this_gp++;
281 t = container_of(rcu_preempt_ctrlblk.boost_tasks, struct task_struct,
282 rcu_node_entry);
283 np = rcu_next_node_entry(t);
284 rt_mutex_init_proxy_locked(&mtx, t);
285 t->rcu_boost_mutex = &mtx;
286 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BOOSTED;
287 raw_local_irq_restore(flags);
288 rt_mutex_lock(&mtx);
289 RCU_TRACE(rcu_preempt_ctrlblk.n_tasks_boosted++);
290 rcu_preempt_ctrlblk.boosted_this_gp++;
291 rt_mutex_unlock(&mtx);
292 return rcu_preempt_ctrlblk.boost_tasks != NULL;
296 * Check to see if it is now time to start boosting RCU readers blocking
297 * the current grace period, and, if so, tell the rcu_kthread_task to
298 * start boosting them. If there is an expedited boost in progress,
299 * we wait for it to complete.
301 * If there are no blocked readers blocking the current grace period,
302 * return 0 to let the caller know, otherwise return 1. Note that this
303 * return value is independent of whether or not boosting was done.
305 static int rcu_initiate_boost(void)
307 if (!rcu_preempt_blocked_readers_cgp()) {
308 RCU_TRACE(rcu_preempt_ctrlblk.n_normal_balk_blkd_tasks++);
309 return 0;
311 if (rcu_preempt_ctrlblk.gp_tasks != NULL &&
312 rcu_preempt_ctrlblk.boost_tasks == NULL &&
313 rcu_preempt_ctrlblk.boosted_this_gp == 0 &&
314 ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time)) {
315 rcu_preempt_ctrlblk.boost_tasks = rcu_preempt_ctrlblk.gp_tasks;
316 invoke_rcu_kthread();
317 RCU_TRACE(rcu_preempt_ctrlblk.n_normal_boosts++);
318 } else
319 RCU_TRACE(rcu_initiate_boost_trace());
320 return 1;
324 * Initiate boosting for an expedited grace period.
326 static void rcu_initiate_expedited_boost(void)
328 unsigned long flags;
330 raw_local_irq_save(flags);
331 if (!list_empty(&rcu_preempt_ctrlblk.blkd_tasks)) {
332 rcu_preempt_ctrlblk.boost_tasks =
333 rcu_preempt_ctrlblk.blkd_tasks.next;
334 rcu_preempt_ctrlblk.boosted_this_gp = -1;
335 invoke_rcu_kthread();
336 RCU_TRACE(rcu_preempt_ctrlblk.n_exp_boosts++);
337 } else
338 RCU_TRACE(rcu_initiate_exp_boost_trace());
339 raw_local_irq_restore(flags);
342 #define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000);
345 * Do priority-boost accounting for the start of a new grace period.
347 static void rcu_preempt_boost_start_gp(void)
349 rcu_preempt_ctrlblk.boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
350 if (rcu_preempt_ctrlblk.boosted_this_gp > 0)
351 rcu_preempt_ctrlblk.boosted_this_gp = 0;
354 #else /* #ifdef CONFIG_RCU_BOOST */
357 * If there is no RCU priority boosting, we don't boost.
359 static int rcu_boost(void)
361 return 0;
365 * If there is no RCU priority boosting, we don't initiate boosting,
366 * but we do indicate whether there are blocked readers blocking the
367 * current grace period.
369 static int rcu_initiate_boost(void)
371 return rcu_preempt_blocked_readers_cgp();
375 * If there is no RCU priority boosting, we don't initiate expedited boosting.
377 static void rcu_initiate_expedited_boost(void)
382 * If there is no RCU priority boosting, nothing to do at grace-period start.
384 static void rcu_preempt_boost_start_gp(void)
388 #endif /* else #ifdef CONFIG_RCU_BOOST */
391 * Record a preemptible-RCU quiescent state for the specified CPU. Note
392 * that this just means that the task currently running on the CPU is
393 * in a quiescent state. There might be any number of tasks blocked
394 * while in an RCU read-side critical section.
396 * Unlike the other rcu_*_qs() functions, callers to this function
397 * must disable irqs in order to protect the assignment to
398 * ->rcu_read_unlock_special.
400 * Because this is a single-CPU implementation, the only way a grace
401 * period can end is if the CPU is in a quiescent state. The reason is
402 * that a blocked preemptible-RCU reader can exit its critical section
403 * only if the CPU is running it at the time. Therefore, when the
404 * last task blocking the current grace period exits its RCU read-side
405 * critical section, neither the CPU nor blocked tasks will be stopping
406 * the current grace period. (In contrast, SMP implementations
407 * might have CPUs running in RCU read-side critical sections that
408 * block later grace periods -- but this is not possible given only
409 * one CPU.)
411 static void rcu_preempt_cpu_qs(void)
413 /* Record both CPU and task as having responded to current GP. */
414 rcu_preempt_ctrlblk.gpcpu = rcu_preempt_ctrlblk.gpnum;
415 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
417 /* If there is no GP then there is nothing more to do. */
418 if (!rcu_preempt_gp_in_progress())
419 return;
421 * Check up on boosting. If there are no readers blocking the
422 * current grace period, leave.
424 if (rcu_initiate_boost())
425 return;
427 /* Advance callbacks. */
428 rcu_preempt_ctrlblk.completed = rcu_preempt_ctrlblk.gpnum;
429 rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.rcb.curtail;
430 rcu_preempt_ctrlblk.rcb.curtail = rcu_preempt_ctrlblk.nexttail;
432 /* If there are no blocked readers, next GP is done instantly. */
433 if (!rcu_preempt_blocked_readers_any())
434 rcu_preempt_ctrlblk.rcb.donetail = rcu_preempt_ctrlblk.nexttail;
436 /* If there are done callbacks, cause them to be invoked. */
437 if (*rcu_preempt_ctrlblk.rcb.donetail != NULL)
438 invoke_rcu_kthread();
442 * Start a new RCU grace period if warranted. Hard irqs must be disabled.
444 static void rcu_preempt_start_gp(void)
446 if (!rcu_preempt_gp_in_progress() && rcu_preempt_needs_another_gp()) {
448 /* Official start of GP. */
449 rcu_preempt_ctrlblk.gpnum++;
450 RCU_TRACE(rcu_preempt_ctrlblk.n_grace_periods++);
452 /* Any blocked RCU readers block new GP. */
453 if (rcu_preempt_blocked_readers_any())
454 rcu_preempt_ctrlblk.gp_tasks =
455 rcu_preempt_ctrlblk.blkd_tasks.next;
457 /* Set up for RCU priority boosting. */
458 rcu_preempt_boost_start_gp();
460 /* If there is no running reader, CPU is done with GP. */
461 if (!rcu_preempt_running_reader())
462 rcu_preempt_cpu_qs();
467 * We have entered the scheduler, and the current task might soon be
468 * context-switched away from. If this task is in an RCU read-side
469 * critical section, we will no longer be able to rely on the CPU to
470 * record that fact, so we enqueue the task on the blkd_tasks list.
471 * If the task started after the current grace period began, as recorded
472 * by ->gpcpu, we enqueue at the beginning of the list. Otherwise
473 * before the element referenced by ->gp_tasks (or at the tail if
474 * ->gp_tasks is NULL) and point ->gp_tasks at the newly added element.
475 * The task will dequeue itself when it exits the outermost enclosing
476 * RCU read-side critical section. Therefore, the current grace period
477 * cannot be permitted to complete until the ->gp_tasks pointer becomes
478 * NULL.
480 * Caller must disable preemption.
482 void rcu_preempt_note_context_switch(void)
484 struct task_struct *t = current;
485 unsigned long flags;
487 local_irq_save(flags); /* must exclude scheduler_tick(). */
488 if (rcu_preempt_running_reader() &&
489 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
491 /* Possibly blocking in an RCU read-side critical section. */
492 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
495 * If this CPU has already checked in, then this task
496 * will hold up the next grace period rather than the
497 * current grace period. Queue the task accordingly.
498 * If the task is queued for the current grace period
499 * (i.e., this CPU has not yet passed through a quiescent
500 * state for the current grace period), then as long
501 * as that task remains queued, the current grace period
502 * cannot end.
504 list_add(&t->rcu_node_entry, &rcu_preempt_ctrlblk.blkd_tasks);
505 if (rcu_cpu_blocking_cur_gp())
506 rcu_preempt_ctrlblk.gp_tasks = &t->rcu_node_entry;
510 * Either we were not in an RCU read-side critical section to
511 * begin with, or we have now recorded that critical section
512 * globally. Either way, we can now note a quiescent state
513 * for this CPU. Again, if we were in an RCU read-side critical
514 * section, and if that critical section was blocking the current
515 * grace period, then the fact that the task has been enqueued
516 * means that current grace period continues to be blocked.
518 rcu_preempt_cpu_qs();
519 local_irq_restore(flags);
523 * Tiny-preemptible RCU implementation for rcu_read_lock().
524 * Just increment ->rcu_read_lock_nesting, shared state will be updated
525 * if we block.
527 void __rcu_read_lock(void)
529 current->rcu_read_lock_nesting++;
530 barrier(); /* needed if we ever invoke rcu_read_lock in rcutiny.c */
532 EXPORT_SYMBOL_GPL(__rcu_read_lock);
535 * Handle special cases during rcu_read_unlock(), such as needing to
536 * notify RCU core processing or task having blocked during the RCU
537 * read-side critical section.
539 static void rcu_read_unlock_special(struct task_struct *t)
541 int empty;
542 int empty_exp;
543 unsigned long flags;
544 struct list_head *np;
545 int special;
548 * NMI handlers cannot block and cannot safely manipulate state.
549 * They therefore cannot possibly be special, so just leave.
551 if (in_nmi())
552 return;
554 local_irq_save(flags);
557 * If RCU core is waiting for this CPU to exit critical section,
558 * let it know that we have done so.
560 special = t->rcu_read_unlock_special;
561 if (special & RCU_READ_UNLOCK_NEED_QS)
562 rcu_preempt_cpu_qs();
564 /* Hardware IRQ handlers cannot block. */
565 if (in_irq()) {
566 local_irq_restore(flags);
567 return;
570 /* Clean up if blocked during RCU read-side critical section. */
571 if (special & RCU_READ_UNLOCK_BLOCKED) {
572 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
575 * Remove this task from the ->blkd_tasks list and adjust
576 * any pointers that might have been referencing it.
578 empty = !rcu_preempt_blocked_readers_cgp();
579 empty_exp = rcu_preempt_ctrlblk.exp_tasks == NULL;
580 np = rcu_next_node_entry(t);
581 list_del(&t->rcu_node_entry);
582 if (&t->rcu_node_entry == rcu_preempt_ctrlblk.gp_tasks)
583 rcu_preempt_ctrlblk.gp_tasks = np;
584 if (&t->rcu_node_entry == rcu_preempt_ctrlblk.exp_tasks)
585 rcu_preempt_ctrlblk.exp_tasks = np;
586 #ifdef CONFIG_RCU_BOOST
587 if (&t->rcu_node_entry == rcu_preempt_ctrlblk.boost_tasks)
588 rcu_preempt_ctrlblk.boost_tasks = np;
589 #endif /* #ifdef CONFIG_RCU_BOOST */
590 INIT_LIST_HEAD(&t->rcu_node_entry);
593 * If this was the last task on the current list, and if
594 * we aren't waiting on the CPU, report the quiescent state
595 * and start a new grace period if needed.
597 if (!empty && !rcu_preempt_blocked_readers_cgp()) {
598 rcu_preempt_cpu_qs();
599 rcu_preempt_start_gp();
603 * If this was the last task on the expedited lists,
604 * then we need wake up the waiting task.
606 if (!empty_exp && rcu_preempt_ctrlblk.exp_tasks == NULL)
607 rcu_report_exp_done();
609 #ifdef CONFIG_RCU_BOOST
610 /* Unboost self if was boosted. */
611 if (special & RCU_READ_UNLOCK_BOOSTED) {
612 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BOOSTED;
613 rt_mutex_unlock(t->rcu_boost_mutex);
614 t->rcu_boost_mutex = NULL;
616 #endif /* #ifdef CONFIG_RCU_BOOST */
617 local_irq_restore(flags);
621 * Tiny-preemptible RCU implementation for rcu_read_unlock().
622 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
623 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
624 * invoke rcu_read_unlock_special() to clean up after a context switch
625 * in an RCU read-side critical section and other special cases.
627 void __rcu_read_unlock(void)
629 struct task_struct *t = current;
631 barrier(); /* needed if we ever invoke rcu_read_unlock in rcutiny.c */
632 --t->rcu_read_lock_nesting;
633 barrier(); /* decrement before load of ->rcu_read_unlock_special */
634 if (t->rcu_read_lock_nesting == 0 &&
635 unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
636 rcu_read_unlock_special(t);
637 #ifdef CONFIG_PROVE_LOCKING
638 WARN_ON_ONCE(t->rcu_read_lock_nesting < 0);
639 #endif /* #ifdef CONFIG_PROVE_LOCKING */
641 EXPORT_SYMBOL_GPL(__rcu_read_unlock);
644 * Check for a quiescent state from the current CPU. When a task blocks,
645 * the task is recorded in the rcu_preempt_ctrlblk structure, which is
646 * checked elsewhere. This is called from the scheduling-clock interrupt.
648 * Caller must disable hard irqs.
650 static void rcu_preempt_check_callbacks(void)
652 struct task_struct *t = current;
654 if (rcu_preempt_gp_in_progress() &&
655 (!rcu_preempt_running_reader() ||
656 !rcu_cpu_blocking_cur_gp()))
657 rcu_preempt_cpu_qs();
658 if (&rcu_preempt_ctrlblk.rcb.rcucblist !=
659 rcu_preempt_ctrlblk.rcb.donetail)
660 invoke_rcu_kthread();
661 if (rcu_preempt_gp_in_progress() &&
662 rcu_cpu_blocking_cur_gp() &&
663 rcu_preempt_running_reader())
664 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
668 * TINY_PREEMPT_RCU has an extra callback-list tail pointer to
669 * update, so this is invoked from rcu_process_callbacks() to
670 * handle that case. Of course, it is invoked for all flavors of
671 * RCU, but RCU callbacks can appear only on one of the lists, and
672 * neither ->nexttail nor ->donetail can possibly be NULL, so there
673 * is no need for an explicit check.
675 static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
677 if (rcu_preempt_ctrlblk.nexttail == rcp->donetail)
678 rcu_preempt_ctrlblk.nexttail = &rcp->rcucblist;
682 * Process callbacks for preemptible RCU.
684 static void rcu_preempt_process_callbacks(void)
686 rcu_process_callbacks(&rcu_preempt_ctrlblk.rcb);
690 * Queue a preemptible -RCU callback for invocation after a grace period.
692 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
694 unsigned long flags;
696 debug_rcu_head_queue(head);
697 head->func = func;
698 head->next = NULL;
700 local_irq_save(flags);
701 *rcu_preempt_ctrlblk.nexttail = head;
702 rcu_preempt_ctrlblk.nexttail = &head->next;
703 RCU_TRACE(rcu_preempt_ctrlblk.rcb.qlen++);
704 rcu_preempt_start_gp(); /* checks to see if GP needed. */
705 local_irq_restore(flags);
707 EXPORT_SYMBOL_GPL(call_rcu);
709 void rcu_barrier(void)
711 struct rcu_synchronize rcu;
713 init_rcu_head_on_stack(&rcu.head);
714 init_completion(&rcu.completion);
715 /* Will wake me after RCU finished. */
716 call_rcu(&rcu.head, wakeme_after_rcu);
717 /* Wait for it. */
718 wait_for_completion(&rcu.completion);
719 destroy_rcu_head_on_stack(&rcu.head);
721 EXPORT_SYMBOL_GPL(rcu_barrier);
724 * synchronize_rcu - wait until a grace period has elapsed.
726 * Control will return to the caller some time after a full grace
727 * period has elapsed, in other words after all currently executing RCU
728 * read-side critical sections have completed. RCU read-side critical
729 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
730 * and may be nested.
732 void synchronize_rcu(void)
734 #ifdef CONFIG_DEBUG_LOCK_ALLOC
735 if (!rcu_scheduler_active)
736 return;
737 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
739 WARN_ON_ONCE(rcu_preempt_running_reader());
740 if (!rcu_preempt_blocked_readers_any())
741 return;
743 /* Once we get past the fastpath checks, same code as rcu_barrier(). */
744 rcu_barrier();
746 EXPORT_SYMBOL_GPL(synchronize_rcu);
748 static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
749 static unsigned long sync_rcu_preempt_exp_count;
750 static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
753 * Return non-zero if there are any tasks in RCU read-side critical
754 * sections blocking the current preemptible-RCU expedited grace period.
755 * If there is no preemptible-RCU expedited grace period currently in
756 * progress, returns zero unconditionally.
758 static int rcu_preempted_readers_exp(void)
760 return rcu_preempt_ctrlblk.exp_tasks != NULL;
764 * Report the exit from RCU read-side critical section for the last task
765 * that queued itself during or before the current expedited preemptible-RCU
766 * grace period.
768 static void rcu_report_exp_done(void)
770 wake_up(&sync_rcu_preempt_exp_wq);
774 * Wait for an rcu-preempt grace period, but expedite it. The basic idea
775 * is to rely in the fact that there is but one CPU, and that it is
776 * illegal for a task to invoke synchronize_rcu_expedited() while in a
777 * preemptible-RCU read-side critical section. Therefore, any such
778 * critical sections must correspond to blocked tasks, which must therefore
779 * be on the ->blkd_tasks list. So just record the current head of the
780 * list in the ->exp_tasks pointer, and wait for all tasks including and
781 * after the task pointed to by ->exp_tasks to drain.
783 void synchronize_rcu_expedited(void)
785 unsigned long flags;
786 struct rcu_preempt_ctrlblk *rpcp = &rcu_preempt_ctrlblk;
787 unsigned long snap;
789 barrier(); /* ensure prior action seen before grace period. */
791 WARN_ON_ONCE(rcu_preempt_running_reader());
794 * Acquire lock so that there is only one preemptible RCU grace
795 * period in flight. Of course, if someone does the expedited
796 * grace period for us while we are acquiring the lock, just leave.
798 snap = sync_rcu_preempt_exp_count + 1;
799 mutex_lock(&sync_rcu_preempt_exp_mutex);
800 if (ULONG_CMP_LT(snap, sync_rcu_preempt_exp_count))
801 goto unlock_mb_ret; /* Others did our work for us. */
803 local_irq_save(flags);
806 * All RCU readers have to already be on blkd_tasks because
807 * we cannot legally be executing in an RCU read-side critical
808 * section.
811 /* Snapshot current head of ->blkd_tasks list. */
812 rpcp->exp_tasks = rpcp->blkd_tasks.next;
813 if (rpcp->exp_tasks == &rpcp->blkd_tasks)
814 rpcp->exp_tasks = NULL;
815 local_irq_restore(flags);
817 /* Wait for tail of ->blkd_tasks list to drain. */
818 if (rcu_preempted_readers_exp())
819 rcu_initiate_expedited_boost();
820 wait_event(sync_rcu_preempt_exp_wq,
821 !rcu_preempted_readers_exp());
823 /* Clean up and exit. */
824 barrier(); /* ensure expedited GP seen before counter increment. */
825 sync_rcu_preempt_exp_count++;
826 unlock_mb_ret:
827 mutex_unlock(&sync_rcu_preempt_exp_mutex);
828 barrier(); /* ensure subsequent action seen after grace period. */
830 EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
833 * Does preemptible RCU need the CPU to stay out of dynticks mode?
835 int rcu_preempt_needs_cpu(void)
837 if (!rcu_preempt_running_reader())
838 rcu_preempt_cpu_qs();
839 return rcu_preempt_ctrlblk.rcb.rcucblist != NULL;
843 * Check for a task exiting while in a preemptible -RCU read-side
844 * critical section, clean up if so. No need to issue warnings,
845 * as debug_check_no_locks_held() already does this if lockdep
846 * is enabled.
848 void exit_rcu(void)
850 struct task_struct *t = current;
852 if (t->rcu_read_lock_nesting == 0)
853 return;
854 t->rcu_read_lock_nesting = 1;
855 rcu_read_unlock();
858 #else /* #ifdef CONFIG_TINY_PREEMPT_RCU */
860 #ifdef CONFIG_RCU_TRACE
863 * Because preemptible RCU does not exist, it is not necessary to
864 * dump out its statistics.
866 static void show_tiny_preempt_stats(struct seq_file *m)
870 #endif /* #ifdef CONFIG_RCU_TRACE */
873 * Because preemptible RCU does not exist, it is never necessary to
874 * boost preempted RCU readers.
876 static int rcu_boost(void)
878 return 0;
882 * Because preemptible RCU does not exist, it never has any callbacks
883 * to check.
885 static void rcu_preempt_check_callbacks(void)
890 * Because preemptible RCU does not exist, it never has any callbacks
891 * to remove.
893 static void rcu_preempt_remove_callbacks(struct rcu_ctrlblk *rcp)
898 * Because preemptible RCU does not exist, it never has any callbacks
899 * to process.
901 static void rcu_preempt_process_callbacks(void)
905 #endif /* #else #ifdef CONFIG_TINY_PREEMPT_RCU */
907 #ifdef CONFIG_DEBUG_LOCK_ALLOC
908 #include <linux/kernel_stat.h>
911 * During boot, we forgive RCU lockdep issues. After this function is
912 * invoked, we start taking RCU lockdep issues seriously.
914 void __init rcu_scheduler_starting(void)
916 WARN_ON(nr_context_switches() > 0);
917 rcu_scheduler_active = 1;
920 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
922 #ifdef CONFIG_RCU_BOOST
923 #define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
924 #else /* #ifdef CONFIG_RCU_BOOST */
925 #define RCU_BOOST_PRIO 1
926 #endif /* #else #ifdef CONFIG_RCU_BOOST */
928 #ifdef CONFIG_RCU_TRACE
930 #ifdef CONFIG_RCU_BOOST
932 static void rcu_initiate_boost_trace(void)
934 if (rcu_preempt_ctrlblk.gp_tasks == NULL)
935 rcu_preempt_ctrlblk.n_normal_balk_gp_tasks++;
936 else if (rcu_preempt_ctrlblk.boost_tasks != NULL)
937 rcu_preempt_ctrlblk.n_normal_balk_boost_tasks++;
938 else if (rcu_preempt_ctrlblk.boosted_this_gp != 0)
939 rcu_preempt_ctrlblk.n_normal_balk_boosted++;
940 else if (!ULONG_CMP_GE(jiffies, rcu_preempt_ctrlblk.boost_time))
941 rcu_preempt_ctrlblk.n_normal_balk_notyet++;
942 else
943 rcu_preempt_ctrlblk.n_normal_balk_nos++;
946 static void rcu_initiate_exp_boost_trace(void)
948 if (list_empty(&rcu_preempt_ctrlblk.blkd_tasks))
949 rcu_preempt_ctrlblk.n_exp_balk_blkd_tasks++;
950 else
951 rcu_preempt_ctrlblk.n_exp_balk_nos++;
954 #endif /* #ifdef CONFIG_RCU_BOOST */
956 static void rcu_trace_sub_qlen(struct rcu_ctrlblk *rcp, int n)
958 unsigned long flags;
960 raw_local_irq_save(flags);
961 rcp->qlen -= n;
962 raw_local_irq_restore(flags);
966 * Dump statistics for TINY_RCU, such as they are.
968 static int show_tiny_stats(struct seq_file *m, void *unused)
970 show_tiny_preempt_stats(m);
971 seq_printf(m, "rcu_sched: qlen: %ld\n", rcu_sched_ctrlblk.qlen);
972 seq_printf(m, "rcu_bh: qlen: %ld\n", rcu_bh_ctrlblk.qlen);
973 return 0;
976 static int show_tiny_stats_open(struct inode *inode, struct file *file)
978 return single_open(file, show_tiny_stats, NULL);
981 static const struct file_operations show_tiny_stats_fops = {
982 .owner = THIS_MODULE,
983 .open = show_tiny_stats_open,
984 .read = seq_read,
985 .llseek = seq_lseek,
986 .release = single_release,
989 static struct dentry *rcudir;
991 static int __init rcutiny_trace_init(void)
993 struct dentry *retval;
995 rcudir = debugfs_create_dir("rcu", NULL);
996 if (!rcudir)
997 goto free_out;
998 retval = debugfs_create_file("rcudata", 0444, rcudir,
999 NULL, &show_tiny_stats_fops);
1000 if (!retval)
1001 goto free_out;
1002 return 0;
1003 free_out:
1004 debugfs_remove_recursive(rcudir);
1005 return 1;
1008 static void __exit rcutiny_trace_cleanup(void)
1010 debugfs_remove_recursive(rcudir);
1013 module_init(rcutiny_trace_init);
1014 module_exit(rcutiny_trace_cleanup);
1016 MODULE_AUTHOR("Paul E. McKenney");
1017 MODULE_DESCRIPTION("Read-Copy Update tracing for tiny implementation");
1018 MODULE_LICENSE("GPL");
1020 #endif /* #ifdef CONFIG_RCU_TRACE */