Root/kernel/rcutree_plugin.h

1/*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
4 * or preemptable semantics.
5 *
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.
10 *
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.
15 *
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.
19 *
20 * Copyright Red Hat, 2009
21 * Copyright IBM Corporation, 2009
22 *
23 * Author: Ingo Molnar <mingo@elte.hu>
24 * Paul E. McKenney <paulmck@linux.vnet.ibm.com>
25 */
26
27#include <linux/delay.h>
28
29#ifdef CONFIG_TREE_PREEMPT_RCU
30
31struct rcu_state rcu_preempt_state = RCU_STATE_INITIALIZER(rcu_preempt_state);
32DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
33
34static int rcu_preempted_readers_exp(struct rcu_node *rnp);
35
36/*
37 * Tell them what RCU they are running.
38 */
39static void __init rcu_bootup_announce(void)
40{
41    printk(KERN_INFO
42           "Experimental preemptable hierarchical RCU implementation.\n");
43}
44
45/*
46 * Return the number of RCU-preempt batches processed thus far
47 * for debug and statistics.
48 */
49long rcu_batches_completed_preempt(void)
50{
51    return rcu_preempt_state.completed;
52}
53EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
54
55/*
56 * Return the number of RCU batches processed thus far for debug & stats.
57 */
58long rcu_batches_completed(void)
59{
60    return rcu_batches_completed_preempt();
61}
62EXPORT_SYMBOL_GPL(rcu_batches_completed);
63
64/*
65 * Force a quiescent state for preemptible RCU.
66 */
67void rcu_force_quiescent_state(void)
68{
69    force_quiescent_state(&rcu_preempt_state, 0);
70}
71EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
72
73/*
74 * Record a preemptable-RCU quiescent state for the specified CPU. Note
75 * that this just means that the task currently running on the CPU is
76 * not in a quiescent state. There might be any number of tasks blocked
77 * while in an RCU read-side critical section.
78 */
79static void rcu_preempt_qs(int cpu)
80{
81    struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
82    rdp->passed_quiesc_completed = rdp->gpnum - 1;
83    barrier();
84    rdp->passed_quiesc = 1;
85}
86
87/*
88 * We have entered the scheduler, and the current task might soon be
89 * context-switched away from. If this task is in an RCU read-side
90 * critical section, we will no longer be able to rely on the CPU to
91 * record that fact, so we enqueue the task on the appropriate entry
92 * of the blocked_tasks[] array. The task will dequeue itself when
93 * it exits the outermost enclosing RCU read-side critical section.
94 * Therefore, the current grace period cannot be permitted to complete
95 * until the blocked_tasks[] entry indexed by the low-order bit of
96 * rnp->gpnum empties.
97 *
98 * Caller must disable preemption.
99 */
100static void rcu_preempt_note_context_switch(int cpu)
101{
102    struct task_struct *t = current;
103    unsigned long flags;
104    int phase;
105    struct rcu_data *rdp;
106    struct rcu_node *rnp;
107
108    if (t->rcu_read_lock_nesting &&
109        (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
110
111        /* Possibly blocking in an RCU read-side critical section. */
112        rdp = rcu_preempt_state.rda[cpu];
113        rnp = rdp->mynode;
114        raw_spin_lock_irqsave(&rnp->lock, flags);
115        t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
116        t->rcu_blocked_node = rnp;
117
118        /*
119         * If this CPU has already checked in, then this task
120         * will hold up the next grace period rather than the
121         * current grace period. Queue the task accordingly.
122         * If the task is queued for the current grace period
123         * (i.e., this CPU has not yet passed through a quiescent
124         * state for the current grace period), then as long
125         * as that task remains queued, the current grace period
126         * cannot end.
127         *
128         * But first, note that the current CPU must still be
129         * on line!
130         */
131        WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
132        WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
133        phase = (rnp->gpnum + !(rnp->qsmask & rdp->grpmask)) & 0x1;
134        list_add(&t->rcu_node_entry, &rnp->blocked_tasks[phase]);
135        raw_spin_unlock_irqrestore(&rnp->lock, flags);
136    }
137
138    /*
139     * Either we were not in an RCU read-side critical section to
140     * begin with, or we have now recorded that critical section
141     * globally. Either way, we can now note a quiescent state
142     * for this CPU. Again, if we were in an RCU read-side critical
143     * section, and if that critical section was blocking the current
144     * grace period, then the fact that the task has been enqueued
145     * means that we continue to block the current grace period.
146     */
147    rcu_preempt_qs(cpu);
148    local_irq_save(flags);
149    t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
150    local_irq_restore(flags);
151}
152
153/*
154 * Tree-preemptable RCU implementation for rcu_read_lock().
155 * Just increment ->rcu_read_lock_nesting, shared state will be updated
156 * if we block.
157 */
158void __rcu_read_lock(void)
159{
160    ACCESS_ONCE(current->rcu_read_lock_nesting)++;
161    barrier(); /* needed if we ever invoke rcu_read_lock in rcutree.c */
162}
163EXPORT_SYMBOL_GPL(__rcu_read_lock);
164
165/*
166 * Check for preempted RCU readers blocking the current grace period
167 * for the specified rcu_node structure. If the caller needs a reliable
168 * answer, it must hold the rcu_node's ->lock.
169 */
170static int rcu_preempted_readers(struct rcu_node *rnp)
171{
172    int phase = rnp->gpnum & 0x1;
173
174    return !list_empty(&rnp->blocked_tasks[phase]) ||
175           !list_empty(&rnp->blocked_tasks[phase + 2]);
176}
177
178/*
179 * Record a quiescent state for all tasks that were previously queued
180 * on the specified rcu_node structure and that were blocking the current
181 * RCU grace period. The caller must hold the specified rnp->lock with
182 * irqs disabled, and this lock is released upon return, but irqs remain
183 * disabled.
184 */
185static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
186    __releases(rnp->lock)
187{
188    unsigned long mask;
189    struct rcu_node *rnp_p;
190
191    if (rnp->qsmask != 0 || rcu_preempted_readers(rnp)) {
192        raw_spin_unlock_irqrestore(&rnp->lock, flags);
193        return; /* Still need more quiescent states! */
194    }
195
196    rnp_p = rnp->parent;
197    if (rnp_p == NULL) {
198        /*
199         * Either there is only one rcu_node in the tree,
200         * or tasks were kicked up to root rcu_node due to
201         * CPUs going offline.
202         */
203        rcu_report_qs_rsp(&rcu_preempt_state, flags);
204        return;
205    }
206
207    /* Report up the rest of the hierarchy. */
208    mask = rnp->grpmask;
209    raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
210    raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
211    rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
212}
213
214/*
215 * Handle special cases during rcu_read_unlock(), such as needing to
216 * notify RCU core processing or task having blocked during the RCU
217 * read-side critical section.
218 */
219static void rcu_read_unlock_special(struct task_struct *t)
220{
221    int empty;
222    int empty_exp;
223    unsigned long flags;
224    struct rcu_node *rnp;
225    int special;
226
227    /* NMI handlers cannot block and cannot safely manipulate state. */
228    if (in_nmi())
229        return;
230
231    local_irq_save(flags);
232
233    /*
234     * If RCU core is waiting for this CPU to exit critical section,
235     * let it know that we have done so.
236     */
237    special = t->rcu_read_unlock_special;
238    if (special & RCU_READ_UNLOCK_NEED_QS) {
239        t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
240        rcu_preempt_qs(smp_processor_id());
241    }
242
243    /* Hardware IRQ handlers cannot block. */
244    if (in_irq()) {
245        local_irq_restore(flags);
246        return;
247    }
248
249    /* Clean up if blocked during RCU read-side critical section. */
250    if (special & RCU_READ_UNLOCK_BLOCKED) {
251        t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
252
253        /*
254         * Remove this task from the list it blocked on. The
255         * task can migrate while we acquire the lock, but at
256         * most one time. So at most two passes through loop.
257         */
258        for (;;) {
259            rnp = t->rcu_blocked_node;
260            raw_spin_lock(&rnp->lock); /* irqs already disabled. */
261            if (rnp == t->rcu_blocked_node)
262                break;
263            raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
264        }
265        empty = !rcu_preempted_readers(rnp);
266        empty_exp = !rcu_preempted_readers_exp(rnp);
267        smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
268        list_del_init(&t->rcu_node_entry);
269        t->rcu_blocked_node = NULL;
270
271        /*
272         * If this was the last task on the current list, and if
273         * we aren't waiting on any CPUs, report the quiescent state.
274         * Note that rcu_report_unblock_qs_rnp() releases rnp->lock.
275         */
276        if (empty)
277            raw_spin_unlock_irqrestore(&rnp->lock, flags);
278        else
279            rcu_report_unblock_qs_rnp(rnp, flags);
280
281        /*
282         * If this was the last task on the expedited lists,
283         * then we need to report up the rcu_node hierarchy.
284         */
285        if (!empty_exp && !rcu_preempted_readers_exp(rnp))
286            rcu_report_exp_rnp(&rcu_preempt_state, rnp);
287    } else {
288        local_irq_restore(flags);
289    }
290}
291
292/*
293 * Tree-preemptable RCU implementation for rcu_read_unlock().
294 * Decrement ->rcu_read_lock_nesting. If the result is zero (outermost
295 * rcu_read_unlock()) and ->rcu_read_unlock_special is non-zero, then
296 * invoke rcu_read_unlock_special() to clean up after a context switch
297 * in an RCU read-side critical section and other special cases.
298 */
299void __rcu_read_unlock(void)
300{
301    struct task_struct *t = current;
302
303    barrier(); /* needed if we ever invoke rcu_read_unlock in rcutree.c */
304    if (--ACCESS_ONCE(t->rcu_read_lock_nesting) == 0 &&
305        unlikely(ACCESS_ONCE(t->rcu_read_unlock_special)))
306        rcu_read_unlock_special(t);
307#ifdef CONFIG_PROVE_LOCKING
308    WARN_ON_ONCE(ACCESS_ONCE(t->rcu_read_lock_nesting) < 0);
309#endif /* #ifdef CONFIG_PROVE_LOCKING */
310}
311EXPORT_SYMBOL_GPL(__rcu_read_unlock);
312
313#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
314
315#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
316
317/*
318 * Dump detailed information for all tasks blocking the current RCU
319 * grace period on the specified rcu_node structure.
320 */
321static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
322{
323    unsigned long flags;
324    struct list_head *lp;
325    int phase;
326    struct task_struct *t;
327
328    if (rcu_preempted_readers(rnp)) {
329        raw_spin_lock_irqsave(&rnp->lock, flags);
330        phase = rnp->gpnum & 0x1;
331        lp = &rnp->blocked_tasks[phase];
332        list_for_each_entry(t, lp, rcu_node_entry)
333            sched_show_task(t);
334        raw_spin_unlock_irqrestore(&rnp->lock, flags);
335    }
336}
337
338/*
339 * Dump detailed information for all tasks blocking the current RCU
340 * grace period.
341 */
342static void rcu_print_detail_task_stall(struct rcu_state *rsp)
343{
344    struct rcu_node *rnp = rcu_get_root(rsp);
345
346    rcu_print_detail_task_stall_rnp(rnp);
347    rcu_for_each_leaf_node(rsp, rnp)
348        rcu_print_detail_task_stall_rnp(rnp);
349}
350
351#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
352
353static void rcu_print_detail_task_stall(struct rcu_state *rsp)
354{
355}
356
357#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
358
359/*
360 * Scan the current list of tasks blocked within RCU read-side critical
361 * sections, printing out the tid of each.
362 */
363static void rcu_print_task_stall(struct rcu_node *rnp)
364{
365    struct list_head *lp;
366    int phase;
367    struct task_struct *t;
368
369    if (rcu_preempted_readers(rnp)) {
370        phase = rnp->gpnum & 0x1;
371        lp = &rnp->blocked_tasks[phase];
372        list_for_each_entry(t, lp, rcu_node_entry)
373            printk(" P%d", t->pid);
374    }
375}
376
377#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
378
379/*
380 * Check that the list of blocked tasks for the newly completed grace
381 * period is in fact empty. It is a serious bug to complete a grace
382 * period that still has RCU readers blocked! This function must be
383 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
384 * must be held by the caller.
385 */
386static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
387{
388    WARN_ON_ONCE(rcu_preempted_readers(rnp));
389    WARN_ON_ONCE(rnp->qsmask);
390}
391
392#ifdef CONFIG_HOTPLUG_CPU
393
394/*
395 * Handle tasklist migration for case in which all CPUs covered by the
396 * specified rcu_node have gone offline. Move them up to the root
397 * rcu_node. The reason for not just moving them to the immediate
398 * parent is to remove the need for rcu_read_unlock_special() to
399 * make more than two attempts to acquire the target rcu_node's lock.
400 * Returns true if there were tasks blocking the current RCU grace
401 * period.
402 *
403 * Returns 1 if there was previously a task blocking the current grace
404 * period on the specified rcu_node structure.
405 *
406 * The caller must hold rnp->lock with irqs disabled.
407 */
408static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
409                     struct rcu_node *rnp,
410                     struct rcu_data *rdp)
411{
412    int i;
413    struct list_head *lp;
414    struct list_head *lp_root;
415    int retval = 0;
416    struct rcu_node *rnp_root = rcu_get_root(rsp);
417    struct task_struct *tp;
418
419    if (rnp == rnp_root) {
420        WARN_ONCE(1, "Last CPU thought to be offlined?");
421        return 0; /* Shouldn't happen: at least one CPU online. */
422    }
423    WARN_ON_ONCE(rnp != rdp->mynode &&
424             (!list_empty(&rnp->blocked_tasks[0]) ||
425              !list_empty(&rnp->blocked_tasks[1]) ||
426              !list_empty(&rnp->blocked_tasks[2]) ||
427              !list_empty(&rnp->blocked_tasks[3])));
428
429    /*
430     * Move tasks up to root rcu_node. Rely on the fact that the
431     * root rcu_node can be at most one ahead of the rest of the
432     * rcu_nodes in terms of gp_num value. This fact allows us to
433     * move the blocked_tasks[] array directly, element by element.
434     */
435    if (rcu_preempted_readers(rnp))
436        retval |= RCU_OFL_TASKS_NORM_GP;
437    if (rcu_preempted_readers_exp(rnp))
438        retval |= RCU_OFL_TASKS_EXP_GP;
439    for (i = 0; i < 4; i++) {
440        lp = &rnp->blocked_tasks[i];
441        lp_root = &rnp_root->blocked_tasks[i];
442        while (!list_empty(lp)) {
443            tp = list_entry(lp->next, typeof(*tp), rcu_node_entry);
444            raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
445            list_del(&tp->rcu_node_entry);
446            tp->rcu_blocked_node = rnp_root;
447            list_add(&tp->rcu_node_entry, lp_root);
448            raw_spin_unlock(&rnp_root->lock); /* irqs remain disabled */
449        }
450    }
451    return retval;
452}
453
454/*
455 * Do CPU-offline processing for preemptable RCU.
456 */
457static void rcu_preempt_offline_cpu(int cpu)
458{
459    __rcu_offline_cpu(cpu, &rcu_preempt_state);
460}
461
462#endif /* #ifdef CONFIG_HOTPLUG_CPU */
463
464/*
465 * Check for a quiescent state from the current CPU. When a task blocks,
466 * the task is recorded in the corresponding CPU's rcu_node structure,
467 * which is checked elsewhere.
468 *
469 * Caller must disable hard irqs.
470 */
471static void rcu_preempt_check_callbacks(int cpu)
472{
473    struct task_struct *t = current;
474
475    if (t->rcu_read_lock_nesting == 0) {
476        t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
477        rcu_preempt_qs(cpu);
478        return;
479    }
480    if (per_cpu(rcu_preempt_data, cpu).qs_pending)
481        t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
482}
483
484/*
485 * Process callbacks for preemptable RCU.
486 */
487static void rcu_preempt_process_callbacks(void)
488{
489    __rcu_process_callbacks(&rcu_preempt_state,
490                &__get_cpu_var(rcu_preempt_data));
491}
492
493/*
494 * Queue a preemptable-RCU callback for invocation after a grace period.
495 */
496void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
497{
498    __call_rcu(head, func, &rcu_preempt_state);
499}
500EXPORT_SYMBOL_GPL(call_rcu);
501
502/**
503 * synchronize_rcu - wait until a grace period has elapsed.
504 *
505 * Control will return to the caller some time after a full grace
506 * period has elapsed, in other words after all currently executing RCU
507 * read-side critical sections have completed. RCU read-side critical
508 * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
509 * and may be nested.
510 */
511void synchronize_rcu(void)
512{
513    struct rcu_synchronize rcu;
514
515    if (!rcu_scheduler_active)
516        return;
517
518    init_completion(&rcu.completion);
519    /* Will wake me after RCU finished. */
520    call_rcu(&rcu.head, wakeme_after_rcu);
521    /* Wait for it. */
522    wait_for_completion(&rcu.completion);
523}
524EXPORT_SYMBOL_GPL(synchronize_rcu);
525
526static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
527static long sync_rcu_preempt_exp_count;
528static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
529
530/*
531 * Return non-zero if there are any tasks in RCU read-side critical
532 * sections blocking the current preemptible-RCU expedited grace period.
533 * If there is no preemptible-RCU expedited grace period currently in
534 * progress, returns zero unconditionally.
535 */
536static int rcu_preempted_readers_exp(struct rcu_node *rnp)
537{
538    return !list_empty(&rnp->blocked_tasks[2]) ||
539           !list_empty(&rnp->blocked_tasks[3]);
540}
541
542/*
543 * return non-zero if there is no RCU expedited grace period in progress
544 * for the specified rcu_node structure, in other words, if all CPUs and
545 * tasks covered by the specified rcu_node structure have done their bit
546 * for the current expedited grace period. Works only for preemptible
547 * RCU -- other RCU implementation use other means.
548 *
549 * Caller must hold sync_rcu_preempt_exp_mutex.
550 */
551static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
552{
553    return !rcu_preempted_readers_exp(rnp) &&
554           ACCESS_ONCE(rnp->expmask) == 0;
555}
556
557/*
558 * Report the exit from RCU read-side critical section for the last task
559 * that queued itself during or before the current expedited preemptible-RCU
560 * grace period. This event is reported either to the rcu_node structure on
561 * which the task was queued or to one of that rcu_node structure's ancestors,
562 * recursively up the tree. (Calm down, calm down, we do the recursion
563 * iteratively!)
564 *
565 * Caller must hold sync_rcu_preempt_exp_mutex.
566 */
567static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
568{
569    unsigned long flags;
570    unsigned long mask;
571
572    raw_spin_lock_irqsave(&rnp->lock, flags);
573    for (;;) {
574        if (!sync_rcu_preempt_exp_done(rnp))
575            break;
576        if (rnp->parent == NULL) {
577            wake_up(&sync_rcu_preempt_exp_wq);
578            break;
579        }
580        mask = rnp->grpmask;
581        raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
582        rnp = rnp->parent;
583        raw_spin_lock(&rnp->lock); /* irqs already disabled */
584        rnp->expmask &= ~mask;
585    }
586    raw_spin_unlock_irqrestore(&rnp->lock, flags);
587}
588
589/*
590 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
591 * grace period for the specified rcu_node structure. If there are no such
592 * tasks, report it up the rcu_node hierarchy.
593 *
594 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
595 */
596static void
597sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
598{
599    int must_wait;
600
601    raw_spin_lock(&rnp->lock); /* irqs already disabled */
602    list_splice_init(&rnp->blocked_tasks[0], &rnp->blocked_tasks[2]);
603    list_splice_init(&rnp->blocked_tasks[1], &rnp->blocked_tasks[3]);
604    must_wait = rcu_preempted_readers_exp(rnp);
605    raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
606    if (!must_wait)
607        rcu_report_exp_rnp(rsp, rnp);
608}
609
610/*
611 * Wait for an rcu-preempt grace period, but expedite it. The basic idea
612 * is to invoke synchronize_sched_expedited() to push all the tasks to
613 * the ->blocked_tasks[] lists, move all entries from the first set of
614 * ->blocked_tasks[] lists to the second set, and finally wait for this
615 * second set to drain.
616 */
617void synchronize_rcu_expedited(void)
618{
619    unsigned long flags;
620    struct rcu_node *rnp;
621    struct rcu_state *rsp = &rcu_preempt_state;
622    long snap;
623    int trycount = 0;
624
625    smp_mb(); /* Caller's modifications seen first by other CPUs. */
626    snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
627    smp_mb(); /* Above access cannot bleed into critical section. */
628
629    /*
630     * Acquire lock, falling back to synchronize_rcu() if too many
631     * lock-acquisition failures. Of course, if someone does the
632     * expedited grace period for us, just leave.
633     */
634    while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
635        if (trycount++ < 10)
636            udelay(trycount * num_online_cpus());
637        else {
638            synchronize_rcu();
639            return;
640        }
641        if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
642            goto mb_ret; /* Others did our work for us. */
643    }
644    if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
645        goto unlock_mb_ret; /* Others did our work for us. */
646
647    /* force all RCU readers onto blocked_tasks[]. */
648    synchronize_sched_expedited();
649
650    raw_spin_lock_irqsave(&rsp->onofflock, flags);
651
652    /* Initialize ->expmask for all non-leaf rcu_node structures. */
653    rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
654        raw_spin_lock(&rnp->lock); /* irqs already disabled. */
655        rnp->expmask = rnp->qsmaskinit;
656        raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
657    }
658
659    /* Snapshot current state of ->blocked_tasks[] lists. */
660    rcu_for_each_leaf_node(rsp, rnp)
661        sync_rcu_preempt_exp_init(rsp, rnp);
662    if (NUM_RCU_NODES > 1)
663        sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
664
665    raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
666
667    /* Wait for snapshotted ->blocked_tasks[] lists to drain. */
668    rnp = rcu_get_root(rsp);
669    wait_event(sync_rcu_preempt_exp_wq,
670           sync_rcu_preempt_exp_done(rnp));
671
672    /* Clean up and exit. */
673    smp_mb(); /* ensure expedited GP seen before counter increment. */
674    ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
675unlock_mb_ret:
676    mutex_unlock(&sync_rcu_preempt_exp_mutex);
677mb_ret:
678    smp_mb(); /* ensure subsequent action seen after grace period. */
679}
680EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
681
682/*
683 * Check to see if there is any immediate preemptable-RCU-related work
684 * to be done.
685 */
686static int rcu_preempt_pending(int cpu)
687{
688    return __rcu_pending(&rcu_preempt_state,
689                 &per_cpu(rcu_preempt_data, cpu));
690}
691
692/*
693 * Does preemptable RCU need the CPU to stay out of dynticks mode?
694 */
695static int rcu_preempt_needs_cpu(int cpu)
696{
697    return !!per_cpu(rcu_preempt_data, cpu).nxtlist;
698}
699
700/**
701 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
702 */
703void rcu_barrier(void)
704{
705    _rcu_barrier(&rcu_preempt_state, call_rcu);
706}
707EXPORT_SYMBOL_GPL(rcu_barrier);
708
709/*
710 * Initialize preemptable RCU's per-CPU data.
711 */
712static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
713{
714    rcu_init_percpu_data(cpu, &rcu_preempt_state, 1);
715}
716
717/*
718 * Move preemptable RCU's callbacks to ->orphan_cbs_list.
719 */
720static void rcu_preempt_send_cbs_to_orphanage(void)
721{
722    rcu_send_cbs_to_orphanage(&rcu_preempt_state);
723}
724
725/*
726 * Initialize preemptable RCU's state structures.
727 */
728static void __init __rcu_init_preempt(void)
729{
730    RCU_INIT_FLAVOR(&rcu_preempt_state, rcu_preempt_data);
731}
732
733/*
734 * Check for a task exiting while in a preemptable-RCU read-side
735 * critical section, clean up if so. No need to issue warnings,
736 * as debug_check_no_locks_held() already does this if lockdep
737 * is enabled.
738 */
739void exit_rcu(void)
740{
741    struct task_struct *t = current;
742
743    if (t->rcu_read_lock_nesting == 0)
744        return;
745    t->rcu_read_lock_nesting = 1;
746    rcu_read_unlock();
747}
748
749#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
750
751/*
752 * Tell them what RCU they are running.
753 */
754static void __init rcu_bootup_announce(void)
755{
756    printk(KERN_INFO "Hierarchical RCU implementation.\n");
757}
758
759/*
760 * Return the number of RCU batches processed thus far for debug & stats.
761 */
762long rcu_batches_completed(void)
763{
764    return rcu_batches_completed_sched();
765}
766EXPORT_SYMBOL_GPL(rcu_batches_completed);
767
768/*
769 * Force a quiescent state for RCU, which, because there is no preemptible
770 * RCU, becomes the same as rcu-sched.
771 */
772void rcu_force_quiescent_state(void)
773{
774    rcu_sched_force_quiescent_state();
775}
776EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
777
778/*
779 * Because preemptable RCU does not exist, we never have to check for
780 * CPUs being in quiescent states.
781 */
782static void rcu_preempt_note_context_switch(int cpu)
783{
784}
785
786/*
787 * Because preemptable RCU does not exist, there are never any preempted
788 * RCU readers.
789 */
790static int rcu_preempted_readers(struct rcu_node *rnp)
791{
792    return 0;
793}
794
795#ifdef CONFIG_HOTPLUG_CPU
796
797/* Because preemptible RCU does not exist, no quieting of tasks. */
798static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
799{
800    raw_spin_unlock_irqrestore(&rnp->lock, flags);
801}
802
803#endif /* #ifdef CONFIG_HOTPLUG_CPU */
804
805#ifdef CONFIG_RCU_CPU_STALL_DETECTOR
806
807/*
808 * Because preemptable RCU does not exist, we never have to check for
809 * tasks blocked within RCU read-side critical sections.
810 */
811static void rcu_print_detail_task_stall(struct rcu_state *rsp)
812{
813}
814
815/*
816 * Because preemptable RCU does not exist, we never have to check for
817 * tasks blocked within RCU read-side critical sections.
818 */
819static void rcu_print_task_stall(struct rcu_node *rnp)
820{
821}
822
823#endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */
824
825/*
826 * Because there is no preemptable RCU, there can be no readers blocked,
827 * so there is no need to check for blocked tasks. So check only for
828 * bogus qsmask values.
829 */
830static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
831{
832    WARN_ON_ONCE(rnp->qsmask);
833}
834
835#ifdef CONFIG_HOTPLUG_CPU
836
837/*
838 * Because preemptable RCU does not exist, it never needs to migrate
839 * tasks that were blocked within RCU read-side critical sections, and
840 * such non-existent tasks cannot possibly have been blocking the current
841 * grace period.
842 */
843static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
844                     struct rcu_node *rnp,
845                     struct rcu_data *rdp)
846{
847    return 0;
848}
849
850/*
851 * Because preemptable RCU does not exist, it never needs CPU-offline
852 * processing.
853 */
854static void rcu_preempt_offline_cpu(int cpu)
855{
856}
857
858#endif /* #ifdef CONFIG_HOTPLUG_CPU */
859
860/*
861 * Because preemptable RCU does not exist, it never has any callbacks
862 * to check.
863 */
864static void rcu_preempt_check_callbacks(int cpu)
865{
866}
867
868/*
869 * Because preemptable RCU does not exist, it never has any callbacks
870 * to process.
871 */
872static void rcu_preempt_process_callbacks(void)
873{
874}
875
876/*
877 * In classic RCU, call_rcu() is just call_rcu_sched().
878 */
879void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
880{
881    call_rcu_sched(head, func);
882}
883EXPORT_SYMBOL_GPL(call_rcu);
884
885/*
886 * Wait for an rcu-preempt grace period, but make it happen quickly.
887 * But because preemptable RCU does not exist, map to rcu-sched.
888 */
889void synchronize_rcu_expedited(void)
890{
891    synchronize_sched_expedited();
892}
893EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
894
895#ifdef CONFIG_HOTPLUG_CPU
896
897/*
898 * Because preemptable RCU does not exist, there is never any need to
899 * report on tasks preempted in RCU read-side critical sections during
900 * expedited RCU grace periods.
901 */
902static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp)
903{
904    return;
905}
906
907#endif /* #ifdef CONFIG_HOTPLUG_CPU */
908
909/*
910 * Because preemptable RCU does not exist, it never has any work to do.
911 */
912static int rcu_preempt_pending(int cpu)
913{
914    return 0;
915}
916
917/*
918 * Because preemptable RCU does not exist, it never needs any CPU.
919 */
920static int rcu_preempt_needs_cpu(int cpu)
921{
922    return 0;
923}
924
925/*
926 * Because preemptable RCU does not exist, rcu_barrier() is just
927 * another name for rcu_barrier_sched().
928 */
929void rcu_barrier(void)
930{
931    rcu_barrier_sched();
932}
933EXPORT_SYMBOL_GPL(rcu_barrier);
934
935/*
936 * Because preemptable RCU does not exist, there is no per-CPU
937 * data to initialize.
938 */
939static void __cpuinit rcu_preempt_init_percpu_data(int cpu)
940{
941}
942
943/*
944 * Because there is no preemptable RCU, there are no callbacks to move.
945 */
946static void rcu_preempt_send_cbs_to_orphanage(void)
947{
948}
949
950/*
951 * Because preemptable RCU does not exist, it need not be initialized.
952 */
953static void __init __rcu_init_preempt(void)
954{
955}
956
957#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
958
959#if !defined(CONFIG_RCU_FAST_NO_HZ)
960
961/*
962 * Check to see if any future RCU-related work will need to be done
963 * by the current CPU, even if none need be done immediately, returning
964 * 1 if so. This function is part of the RCU implementation; it is -not-
965 * an exported member of the RCU API.
966 *
967 * Because we have preemptible RCU, just check whether this CPU needs
968 * any flavor of RCU. Do not chew up lots of CPU cycles with preemption
969 * disabled in a most-likely vain attempt to cause RCU not to need this CPU.
970 */
971int rcu_needs_cpu(int cpu)
972{
973    return rcu_needs_cpu_quick_check(cpu);
974}
975
976/*
977 * Check to see if we need to continue a callback-flush operations to
978 * allow the last CPU to enter dyntick-idle mode. But fast dyntick-idle
979 * entry is not configured, so we never do need to.
980 */
981static void rcu_needs_cpu_flush(void)
982{
983}
984
985#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
986
987#define RCU_NEEDS_CPU_FLUSHES 5
988static DEFINE_PER_CPU(int, rcu_dyntick_drain);
989static DEFINE_PER_CPU(unsigned long, rcu_dyntick_holdoff);
990
991/*
992 * Check to see if any future RCU-related work will need to be done
993 * by the current CPU, even if none need be done immediately, returning
994 * 1 if so. This function is part of the RCU implementation; it is -not-
995 * an exported member of the RCU API.
996 *
997 * Because we are not supporting preemptible RCU, attempt to accelerate
998 * any current grace periods so that RCU no longer needs this CPU, but
999 * only if all other CPUs are already in dynticks-idle mode. This will
1000 * allow the CPU cores to be powered down immediately, as opposed to after
1001 * waiting many milliseconds for grace periods to elapse.
1002 *
1003 * Because it is not legal to invoke rcu_process_callbacks() with irqs
1004 * disabled, we do one pass of force_quiescent_state(), then do a
1005 * raise_softirq() to cause rcu_process_callbacks() to be invoked later.
1006 * The per-cpu rcu_dyntick_drain variable controls the sequencing.
1007 */
1008int rcu_needs_cpu(int cpu)
1009{
1010    int c = 0;
1011    int thatcpu;
1012
1013    /* Check for being in the holdoff period. */
1014    if (per_cpu(rcu_dyntick_holdoff, cpu) == jiffies)
1015        return rcu_needs_cpu_quick_check(cpu);
1016
1017    /* Don't bother unless we are the last non-dyntick-idle CPU. */
1018    for_each_cpu_not(thatcpu, nohz_cpu_mask)
1019        if (thatcpu != cpu) {
1020            per_cpu(rcu_dyntick_drain, cpu) = 0;
1021            per_cpu(rcu_dyntick_holdoff, cpu) = jiffies - 1;
1022            return rcu_needs_cpu_quick_check(cpu);
1023        }
1024
1025    /* Check and update the rcu_dyntick_drain sequencing. */
1026    if (per_cpu(rcu_dyntick_drain, cpu) <= 0) {
1027        /* First time through, initialize the counter. */
1028        per_cpu(rcu_dyntick_drain, cpu) = RCU_NEEDS_CPU_FLUSHES;
1029    } else if (--per_cpu(rcu_dyntick_drain, cpu) <= 0) {
1030        /* We have hit the limit, so time to give up. */
1031        per_cpu(rcu_dyntick_holdoff, cpu) = jiffies;
1032        return rcu_needs_cpu_quick_check(cpu);
1033    }
1034
1035    /* Do one step pushing remaining RCU callbacks through. */
1036    if (per_cpu(rcu_sched_data, cpu).nxtlist) {
1037        rcu_sched_qs(cpu);
1038        force_quiescent_state(&rcu_sched_state, 0);
1039        c = c || per_cpu(rcu_sched_data, cpu).nxtlist;
1040    }
1041    if (per_cpu(rcu_bh_data, cpu).nxtlist) {
1042        rcu_bh_qs(cpu);
1043        force_quiescent_state(&rcu_bh_state, 0);
1044        c = c || per_cpu(rcu_bh_data, cpu).nxtlist;
1045    }
1046
1047    /* If RCU callbacks are still pending, RCU still needs this CPU. */
1048    if (c)
1049        raise_softirq(RCU_SOFTIRQ);
1050    return c;
1051}
1052
1053/*
1054 * Check to see if we need to continue a callback-flush operations to
1055 * allow the last CPU to enter dyntick-idle mode.
1056 */
1057static void rcu_needs_cpu_flush(void)
1058{
1059    int cpu = smp_processor_id();
1060    unsigned long flags;
1061
1062    if (per_cpu(rcu_dyntick_drain, cpu) <= 0)
1063        return;
1064    local_irq_save(flags);
1065    (void)rcu_needs_cpu(cpu);
1066    local_irq_restore(flags);
1067}
1068
1069#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1070

Archive Download this file

Branches:
ben-wpan
ben-wpan-stefan
javiroman/ks7010
jz-2.6.34
jz-2.6.34-rc5
jz-2.6.34-rc6
jz-2.6.34-rc7
jz-2.6.35
jz-2.6.36
jz-2.6.37
jz-2.6.38
jz-2.6.39
jz-3.0
jz-3.1
jz-3.2
jz-3.3
jz-3.4
jz-3.5
jz-3.6
jz-3.6-rc2-pwm
jz-3.9
jz-3.9-rc8
jz47xx
jz47xx-2.6.38
master

Tags:
od-2011-09-04
od-2011-09-18
v2.6.34-rc5
v2.6.34-rc6
v2.6.34-rc7
v3.9



interactive