blob: 7f3244c0df014a7673831159ae1dbc25ceff55c8 [file] [log] [blame]
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001/*
2 * Read-Copy Update mechanism for mutual exclusion (tree-based version)
3 * Internal non-public definitions that provide either classic
Paul E. McKenney6cc68792011-03-02 13:15:15 -08004 * or preemptible semantics.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07005 *
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
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -080027#include <linux/delay.h>
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070028
Mike Galbraith5b61b0b2011-08-19 11:39:11 -070029#define RCU_KTHREAD_PRIO 1
30
31#ifdef CONFIG_RCU_BOOST
32#define RCU_BOOST_PRIO CONFIG_RCU_BOOST_PRIO
33#else
34#define RCU_BOOST_PRIO RCU_KTHREAD_PRIO
35#endif
36
Paul E. McKenney26845c22010-04-13 14:19:23 -070037/*
38 * Check the RCU kernel configuration parameters and print informative
39 * messages about anything out of the ordinary. If you like #ifdef, you
40 * will love this function.
41 */
42static void __init rcu_bootup_announce_oddness(void)
43{
44#ifdef CONFIG_RCU_TRACE
45 printk(KERN_INFO "\tRCU debugfs-based tracing is enabled.\n");
46#endif
47#if (defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 64) || (!defined(CONFIG_64BIT) && CONFIG_RCU_FANOUT != 32)
48 printk(KERN_INFO "\tCONFIG_RCU_FANOUT set to non-default value of %d\n",
49 CONFIG_RCU_FANOUT);
50#endif
51#ifdef CONFIG_RCU_FANOUT_EXACT
52 printk(KERN_INFO "\tHierarchical RCU autobalancing is disabled.\n");
53#endif
54#ifdef CONFIG_RCU_FAST_NO_HZ
55 printk(KERN_INFO
56 "\tRCU dyntick-idle grace-period acceleration is enabled.\n");
57#endif
58#ifdef CONFIG_PROVE_RCU
59 printk(KERN_INFO "\tRCU lockdep checking is enabled.\n");
60#endif
61#ifdef CONFIG_RCU_TORTURE_TEST_RUNNABLE
62 printk(KERN_INFO "\tRCU torture testing starts during boot.\n");
63#endif
Paul E. McKenney81a294c2010-08-30 09:52:50 -070064#if defined(CONFIG_TREE_PREEMPT_RCU) && !defined(CONFIG_RCU_CPU_STALL_VERBOSE)
Paul E. McKenneya858af22012-01-16 13:29:10 -080065 printk(KERN_INFO "\tDump stacks of tasks blocking RCU-preempt GP.\n");
66#endif
67#if defined(CONFIG_RCU_CPU_STALL_INFO)
68 printk(KERN_INFO "\tAdditional per-CPU info printed with stalls.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070069#endif
70#if NUM_RCU_LVL_4 != 0
Paul E. McKenneycc5df652012-06-15 18:16:00 -070071 printk(KERN_INFO "\tFour-level hierarchy is enabled.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070072#endif
Paul E. McKenneyf885b7f2012-04-23 15:52:53 -070073 if (rcu_fanout_leaf != CONFIG_RCU_FANOUT_LEAF)
74 printk(KERN_INFO "\tExperimental boot-time adjustment of leaf fanout to %d.\n", rcu_fanout_leaf);
Paul E. McKenneycca6f392012-05-08 21:00:28 -070075 if (nr_cpu_ids != NR_CPUS)
76 printk(KERN_INFO "\tRCU restricting CPUs from NR_CPUS=%d to nr_cpu_ids=%d.\n", NR_CPUS, nr_cpu_ids);
Paul E. McKenney26845c22010-04-13 14:19:23 -070077}
78
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070079#ifdef CONFIG_TREE_PREEMPT_RCU
80
Paul E. McKenney037b64e2012-05-28 23:26:01 -070081struct rcu_state rcu_preempt_state =
82 RCU_STATE_INITIALIZER(rcu_preempt, call_rcu);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070083DEFINE_PER_CPU(struct rcu_data, rcu_preempt_data);
Paul E. McKenney27f4d282011-02-07 12:47:15 -080084static struct rcu_state *rcu_state = &rcu_preempt_state;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070085
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -080086static int rcu_preempted_readers_exp(struct rcu_node *rnp);
87
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070088/*
89 * Tell them what RCU they are running.
90 */
Paul E. McKenney0e0fc1c2009-11-11 11:28:06 -080091static void __init rcu_bootup_announce(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070092{
Paul E. McKenney6cc68792011-03-02 13:15:15 -080093 printk(KERN_INFO "Preemptible hierarchical RCU implementation.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -070094 rcu_bootup_announce_oddness();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -070095}
96
97/*
98 * Return the number of RCU-preempt batches processed thus far
99 * for debug and statistics.
100 */
101long rcu_batches_completed_preempt(void)
102{
103 return rcu_preempt_state.completed;
104}
105EXPORT_SYMBOL_GPL(rcu_batches_completed_preempt);
106
107/*
108 * Return the number of RCU batches processed thus far for debug & stats.
109 */
110long rcu_batches_completed(void)
111{
112 return rcu_batches_completed_preempt();
113}
114EXPORT_SYMBOL_GPL(rcu_batches_completed);
115
116/*
Paul E. McKenneybf66f182010-01-04 15:09:10 -0800117 * Force a quiescent state for preemptible RCU.
118 */
119void rcu_force_quiescent_state(void)
120{
121 force_quiescent_state(&rcu_preempt_state, 0);
122}
123EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
124
125/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800126 * Record a preemptible-RCU quiescent state for the specified CPU. Note
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700127 * that this just means that the task currently running on the CPU is
128 * not in a quiescent state. There might be any number of tasks blocked
129 * while in an RCU read-side critical section.
Paul E. McKenney25502a62010-04-01 17:37:01 -0700130 *
131 * Unlike the other rcu_*_qs() functions, callers to this function
132 * must disable irqs in order to protect the assignment to
133 * ->rcu_read_unlock_special.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700134 */
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700135static void rcu_preempt_qs(int cpu)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700136{
137 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
Paul E. McKenney25502a62010-04-01 17:37:01 -0700138
Paul E. McKenneye4cc1f22011-06-27 00:17:43 -0700139 rdp->passed_quiesce_gpnum = rdp->gpnum;
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700140 barrier();
Paul E. McKenneye4cc1f22011-06-27 00:17:43 -0700141 if (rdp->passed_quiesce == 0)
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700142 trace_rcu_grace_period("rcu_preempt", rdp->gpnum, "cpuqs");
Paul E. McKenneye4cc1f22011-06-27 00:17:43 -0700143 rdp->passed_quiesce = 1;
Paul E. McKenney25502a62010-04-01 17:37:01 -0700144 current->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_NEED_QS;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700145}
146
147/*
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700148 * We have entered the scheduler, and the current task might soon be
149 * context-switched away from. If this task is in an RCU read-side
150 * critical section, we will no longer be able to rely on the CPU to
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800151 * record that fact, so we enqueue the task on the blkd_tasks list.
152 * The task will dequeue itself when it exits the outermost enclosing
153 * RCU read-side critical section. Therefore, the current grace period
154 * cannot be permitted to complete until the blkd_tasks list entries
155 * predating the current grace period drain, in other words, until
156 * rnp->gp_tasks becomes NULL.
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700157 *
158 * Caller must disable preemption.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700159 */
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700160static void rcu_preempt_note_context_switch(int cpu)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700161{
162 struct task_struct *t = current;
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700163 unsigned long flags;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700164 struct rcu_data *rdp;
165 struct rcu_node *rnp;
166
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700167 if (t->rcu_read_lock_nesting > 0 &&
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700168 (t->rcu_read_unlock_special & RCU_READ_UNLOCK_BLOCKED) == 0) {
169
170 /* Possibly blocking in an RCU read-side critical section. */
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700171 rdp = per_cpu_ptr(rcu_preempt_state.rda, cpu);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700172 rnp = rdp->mynode;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800173 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700174 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_BLOCKED;
Paul E. McKenney86848962009-08-27 15:00:12 -0700175 t->rcu_blocked_node = rnp;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700176
177 /*
178 * If this CPU has already checked in, then this task
179 * will hold up the next grace period rather than the
180 * current grace period. Queue the task accordingly.
181 * If the task is queued for the current grace period
182 * (i.e., this CPU has not yet passed through a quiescent
183 * state for the current grace period), then as long
184 * as that task remains queued, the current grace period
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800185 * cannot end. Note that there is some uncertainty as
186 * to exactly when the current grace period started.
187 * We take a conservative approach, which can result
188 * in unnecessarily waiting on tasks that started very
189 * slightly after the current grace period began. C'est
190 * la vie!!!
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700191 *
192 * But first, note that the current CPU must still be
193 * on line!
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700194 */
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700195 WARN_ON_ONCE((rdp->grpmask & rnp->qsmaskinit) == 0);
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700196 WARN_ON_ONCE(!list_empty(&t->rcu_node_entry));
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800197 if ((rnp->qsmask & rdp->grpmask) && rnp->gp_tasks != NULL) {
198 list_add(&t->rcu_node_entry, rnp->gp_tasks->prev);
199 rnp->gp_tasks = &t->rcu_node_entry;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800200#ifdef CONFIG_RCU_BOOST
201 if (rnp->boost_tasks != NULL)
202 rnp->boost_tasks = rnp->gp_tasks;
203#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800204 } else {
205 list_add(&t->rcu_node_entry, &rnp->blkd_tasks);
206 if (rnp->qsmask & rdp->grpmask)
207 rnp->gp_tasks = &t->rcu_node_entry;
208 }
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700209 trace_rcu_preempt_task(rdp->rsp->name,
210 t->pid,
211 (rnp->qsmask & rdp->grpmask)
212 ? rnp->gpnum
213 : rnp->gpnum + 1);
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800214 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700215 } else if (t->rcu_read_lock_nesting < 0 &&
216 t->rcu_read_unlock_special) {
217
218 /*
219 * Complete exit from RCU read-side critical section on
220 * behalf of preempted instance of __rcu_read_unlock().
221 */
222 rcu_read_unlock_special(t);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700223 }
224
225 /*
226 * Either we were not in an RCU read-side critical section to
227 * begin with, or we have now recorded that critical section
228 * globally. Either way, we can now note a quiescent state
229 * for this CPU. Again, if we were in an RCU read-side critical
230 * section, and if that critical section was blocking the current
231 * grace period, then the fact that the task has been enqueued
232 * means that we continue to block the current grace period.
233 */
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700234 local_irq_save(flags);
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700235 rcu_preempt_qs(cpu);
Paul E. McKenneye7d88422009-09-18 09:50:18 -0700236 local_irq_restore(flags);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700237}
238
239/*
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700240 * Check for preempted RCU readers blocking the current grace period
241 * for the specified rcu_node structure. If the caller needs a reliable
242 * answer, it must hold the rcu_node's ->lock.
243 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800244static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700245{
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800246 return rnp->gp_tasks != NULL;
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700247}
248
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800249/*
250 * Record a quiescent state for all tasks that were previously queued
251 * on the specified rcu_node structure and that were blocking the current
252 * RCU grace period. The caller must hold the specified rnp->lock with
253 * irqs disabled, and this lock is released upon return, but irqs remain
254 * disabled.
255 */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800256static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800257 __releases(rnp->lock)
258{
259 unsigned long mask;
260 struct rcu_node *rnp_p;
261
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800262 if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800263 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800264 return; /* Still need more quiescent states! */
265 }
266
267 rnp_p = rnp->parent;
268 if (rnp_p == NULL) {
269 /*
270 * Either there is only one rcu_node in the tree,
271 * or tasks were kicked up to root rcu_node due to
272 * CPUs going offline.
273 */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800274 rcu_report_qs_rsp(&rcu_preempt_state, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800275 return;
276 }
277
278 /* Report up the rest of the hierarchy. */
279 mask = rnp->grpmask;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800280 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
281 raw_spin_lock(&rnp_p->lock); /* irqs already disabled. */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800282 rcu_report_qs_rnp(mask, &rcu_preempt_state, rnp_p, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800283}
284
285/*
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800286 * Advance a ->blkd_tasks-list pointer to the next entry, instead
287 * returning NULL if at the end of the list.
288 */
289static struct list_head *rcu_next_node_entry(struct task_struct *t,
290 struct rcu_node *rnp)
291{
292 struct list_head *np;
293
294 np = t->rcu_node_entry.next;
295 if (np == &rnp->blkd_tasks)
296 np = NULL;
297 return np;
298}
299
300/*
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800301 * Handle special cases during rcu_read_unlock(), such as needing to
302 * notify RCU core processing or task having blocked during the RCU
303 * read-side critical section.
304 */
Paul E. McKenney2a3fa842012-05-21 11:58:36 -0700305void rcu_read_unlock_special(struct task_struct *t)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700306{
307 int empty;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800308 int empty_exp;
Paul E. McKenney389abd42011-09-21 14:41:37 -0700309 int empty_exp_now;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700310 unsigned long flags;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800311 struct list_head *np;
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700312#ifdef CONFIG_RCU_BOOST
313 struct rt_mutex *rbmp = NULL;
314#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700315 struct rcu_node *rnp;
316 int special;
317
318 /* NMI handlers cannot block and cannot safely manipulate state. */
319 if (in_nmi())
320 return;
321
322 local_irq_save(flags);
323
324 /*
325 * If RCU core is waiting for this CPU to exit critical section,
326 * let it know that we have done so.
327 */
328 special = t->rcu_read_unlock_special;
329 if (special & RCU_READ_UNLOCK_NEED_QS) {
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700330 rcu_preempt_qs(smp_processor_id());
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700331 }
332
333 /* Hardware IRQ handlers cannot block. */
Peter Zijlstraec433f02011-07-19 15:32:00 -0700334 if (in_irq() || in_serving_softirq()) {
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700335 local_irq_restore(flags);
336 return;
337 }
338
339 /* Clean up if blocked during RCU read-side critical section. */
340 if (special & RCU_READ_UNLOCK_BLOCKED) {
341 t->rcu_read_unlock_special &= ~RCU_READ_UNLOCK_BLOCKED;
342
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700343 /*
344 * Remove this task from the list it blocked on. The
345 * task can migrate while we acquire the lock, but at
346 * most one time. So at most two passes through loop.
347 */
348 for (;;) {
Paul E. McKenney86848962009-08-27 15:00:12 -0700349 rnp = t->rcu_blocked_node;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800350 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
Paul E. McKenney86848962009-08-27 15:00:12 -0700351 if (rnp == t->rcu_blocked_node)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700352 break;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800353 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700354 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800355 empty = !rcu_preempt_blocked_readers_cgp(rnp);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800356 empty_exp = !rcu_preempted_readers_exp(rnp);
357 smp_mb(); /* ensure expedited fastpath sees end of RCU c-s. */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800358 np = rcu_next_node_entry(t, rnp);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700359 list_del_init(&t->rcu_node_entry);
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700360 t->rcu_blocked_node = NULL;
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700361 trace_rcu_unlock_preempted_task("rcu_preempt",
362 rnp->gpnum, t->pid);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800363 if (&t->rcu_node_entry == rnp->gp_tasks)
364 rnp->gp_tasks = np;
365 if (&t->rcu_node_entry == rnp->exp_tasks)
366 rnp->exp_tasks = np;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800367#ifdef CONFIG_RCU_BOOST
368 if (&t->rcu_node_entry == rnp->boost_tasks)
369 rnp->boost_tasks = np;
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700370 /* Snapshot/clear ->rcu_boost_mutex with rcu_node lock held. */
371 if (t->rcu_boost_mutex) {
372 rbmp = t->rcu_boost_mutex;
373 t->rcu_boost_mutex = NULL;
Paul E. McKenney7765be22011-07-14 12:24:11 -0700374 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800375#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700376
377 /*
378 * If this was the last task on the current list, and if
379 * we aren't waiting on any CPUs, report the quiescent state.
Paul E. McKenney389abd42011-09-21 14:41:37 -0700380 * Note that rcu_report_unblock_qs_rnp() releases rnp->lock,
381 * so we must take a snapshot of the expedited state.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700382 */
Paul E. McKenney389abd42011-09-21 14:41:37 -0700383 empty_exp_now = !rcu_preempted_readers_exp(rnp);
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700384 if (!empty && !rcu_preempt_blocked_readers_cgp(rnp)) {
385 trace_rcu_quiescent_state_report("preempt_rcu",
386 rnp->gpnum,
387 0, rnp->qsmask,
388 rnp->level,
389 rnp->grplo,
390 rnp->grphi,
391 !!rnp->gp_tasks);
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800392 rcu_report_unblock_qs_rnp(rnp, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700393 } else {
Paul E. McKenneyd4c08f22011-06-25 06:36:56 -0700394 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700395 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800396
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800397#ifdef CONFIG_RCU_BOOST
398 /* Unboost if we were boosted. */
Paul E. McKenney82e78d82011-08-04 07:55:34 -0700399 if (rbmp)
400 rt_mutex_unlock(rbmp);
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800401#endif /* #ifdef CONFIG_RCU_BOOST */
402
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800403 /*
404 * If this was the last task on the expedited lists,
405 * then we need to report up the rcu_node hierarchy.
406 */
Paul E. McKenney389abd42011-09-21 14:41:37 -0700407 if (!empty_exp && empty_exp_now)
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700408 rcu_report_exp_rnp(&rcu_preempt_state, rnp, true);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800409 } else {
410 local_irq_restore(flags);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700411 }
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700412}
413
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800414#ifdef CONFIG_RCU_CPU_STALL_VERBOSE
415
416/*
417 * Dump detailed information for all tasks blocking the current RCU
418 * grace period on the specified rcu_node structure.
419 */
420static void rcu_print_detail_task_stall_rnp(struct rcu_node *rnp)
421{
422 unsigned long flags;
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800423 struct task_struct *t;
424
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800425 if (!rcu_preempt_blocked_readers_cgp(rnp))
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800426 return;
427 raw_spin_lock_irqsave(&rnp->lock, flags);
428 t = list_entry(rnp->gp_tasks,
429 struct task_struct, rcu_node_entry);
430 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry)
431 sched_show_task(t);
432 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800433}
434
435/*
436 * Dump detailed information for all tasks blocking the current RCU
437 * grace period.
438 */
439static void rcu_print_detail_task_stall(struct rcu_state *rsp)
440{
441 struct rcu_node *rnp = rcu_get_root(rsp);
442
443 rcu_print_detail_task_stall_rnp(rnp);
444 rcu_for_each_leaf_node(rsp, rnp)
445 rcu_print_detail_task_stall_rnp(rnp);
446}
447
448#else /* #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
449
450static void rcu_print_detail_task_stall(struct rcu_state *rsp)
451{
452}
453
454#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_VERBOSE */
455
Paul E. McKenneya858af22012-01-16 13:29:10 -0800456#ifdef CONFIG_RCU_CPU_STALL_INFO
457
458static void rcu_print_task_stall_begin(struct rcu_node *rnp)
459{
460 printk(KERN_ERR "\tTasks blocked on level-%d rcu_node (CPUs %d-%d):",
461 rnp->level, rnp->grplo, rnp->grphi);
462}
463
464static void rcu_print_task_stall_end(void)
465{
466 printk(KERN_CONT "\n");
467}
468
469#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
470
471static void rcu_print_task_stall_begin(struct rcu_node *rnp)
472{
473}
474
475static void rcu_print_task_stall_end(void)
476{
477}
478
479#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */
480
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700481/*
482 * Scan the current list of tasks blocked within RCU read-side critical
483 * sections, printing out the tid of each.
484 */
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700485static int rcu_print_task_stall(struct rcu_node *rnp)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700486{
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700487 struct task_struct *t;
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700488 int ndetected = 0;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700489
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800490 if (!rcu_preempt_blocked_readers_cgp(rnp))
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700491 return 0;
Paul E. McKenneya858af22012-01-16 13:29:10 -0800492 rcu_print_task_stall_begin(rnp);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800493 t = list_entry(rnp->gp_tasks,
494 struct task_struct, rcu_node_entry);
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700495 list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) {
Paul E. McKenneya858af22012-01-16 13:29:10 -0800496 printk(KERN_CONT " P%d", t->pid);
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700497 ndetected++;
498 }
Paul E. McKenneya858af22012-01-16 13:29:10 -0800499 rcu_print_task_stall_end();
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700500 return ndetected;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700501}
502
Paul E. McKenney53d84e02010-08-10 14:28:53 -0700503/*
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700504 * Check that the list of blocked tasks for the newly completed grace
505 * period is in fact empty. It is a serious bug to complete a grace
506 * period that still has RCU readers blocked! This function must be
507 * invoked -before- updating this rnp's ->gpnum, and the rnp's ->lock
508 * must be held by the caller.
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800509 *
510 * Also, if there are blocked tasks on the list, they automatically
511 * block the newly created grace period, so set up ->gp_tasks accordingly.
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700512 */
513static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
514{
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800515 WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp));
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800516 if (!list_empty(&rnp->blkd_tasks))
517 rnp->gp_tasks = rnp->blkd_tasks.next;
Paul E. McKenney28ecd582009-09-18 09:50:17 -0700518 WARN_ON_ONCE(rnp->qsmask);
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700519}
520
Paul E. McKenney33f76142009-08-24 09:42:01 -0700521#ifdef CONFIG_HOTPLUG_CPU
522
523/*
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700524 * Handle tasklist migration for case in which all CPUs covered by the
525 * specified rcu_node have gone offline. Move them up to the root
526 * rcu_node. The reason for not just moving them to the immediate
527 * parent is to remove the need for rcu_read_unlock_special() to
528 * make more than two attempts to acquire the target rcu_node's lock.
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800529 * Returns true if there were tasks blocking the current RCU grace
530 * period.
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700531 *
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700532 * Returns 1 if there was previously a task blocking the current grace
533 * period on the specified rcu_node structure.
534 *
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700535 * The caller must hold rnp->lock with irqs disabled.
536 */
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700537static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
538 struct rcu_node *rnp,
539 struct rcu_data *rdp)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700540{
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700541 struct list_head *lp;
542 struct list_head *lp_root;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800543 int retval = 0;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700544 struct rcu_node *rnp_root = rcu_get_root(rsp);
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800545 struct task_struct *t;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700546
Paul E. McKenney86848962009-08-27 15:00:12 -0700547 if (rnp == rnp_root) {
548 WARN_ONCE(1, "Last CPU thought to be offlined?");
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700549 return 0; /* Shouldn't happen: at least one CPU online. */
Paul E. McKenney86848962009-08-27 15:00:12 -0700550 }
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800551
552 /* If we are on an internal node, complain bitterly. */
553 WARN_ON_ONCE(rnp != rdp->mynode);
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700554
555 /*
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800556 * Move tasks up to root rcu_node. Don't try to get fancy for
557 * this corner-case operation -- just put this node's tasks
558 * at the head of the root node's list, and update the root node's
559 * ->gp_tasks and ->exp_tasks pointers to those of this node's,
560 * if non-NULL. This might result in waiting for more tasks than
561 * absolutely necessary, but this is a good performance/complexity
562 * tradeoff.
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700563 */
Paul E. McKenney2036d942012-01-30 17:02:47 -0800564 if (rcu_preempt_blocked_readers_cgp(rnp) && rnp->qsmask == 0)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800565 retval |= RCU_OFL_TASKS_NORM_GP;
566 if (rcu_preempted_readers_exp(rnp))
567 retval |= RCU_OFL_TASKS_EXP_GP;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800568 lp = &rnp->blkd_tasks;
569 lp_root = &rnp_root->blkd_tasks;
570 while (!list_empty(lp)) {
571 t = list_entry(lp->next, typeof(*t), rcu_node_entry);
572 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
573 list_del(&t->rcu_node_entry);
574 t->rcu_blocked_node = rnp_root;
575 list_add(&t->rcu_node_entry, lp_root);
576 if (&t->rcu_node_entry == rnp->gp_tasks)
577 rnp_root->gp_tasks = rnp->gp_tasks;
578 if (&t->rcu_node_entry == rnp->exp_tasks)
579 rnp_root->exp_tasks = rnp->exp_tasks;
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800580#ifdef CONFIG_RCU_BOOST
581 if (&t->rcu_node_entry == rnp->boost_tasks)
582 rnp_root->boost_tasks = rnp->boost_tasks;
583#endif /* #ifdef CONFIG_RCU_BOOST */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800584 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700585 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800586
587#ifdef CONFIG_RCU_BOOST
588 /* In case root is being boosted and leaf is not. */
589 raw_spin_lock(&rnp_root->lock); /* irqs already disabled */
590 if (rnp_root->boost_tasks != NULL &&
591 rnp_root->boost_tasks != rnp_root->gp_tasks)
592 rnp_root->boost_tasks = rnp_root->gp_tasks;
593 raw_spin_unlock(&rnp_root->lock); /* irqs still disabled */
594#endif /* #ifdef CONFIG_RCU_BOOST */
595
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800596 rnp->gp_tasks = NULL;
597 rnp->exp_tasks = NULL;
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700598 return retval;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700599}
600
Paul E. McKenneye5601402012-01-07 11:03:57 -0800601#endif /* #ifdef CONFIG_HOTPLUG_CPU */
602
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700603/*
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700604 * Check for a quiescent state from the current CPU. When a task blocks,
605 * the task is recorded in the corresponding CPU's rcu_node structure,
606 * which is checked elsewhere.
607 *
608 * Caller must disable hard irqs.
609 */
610static void rcu_preempt_check_callbacks(int cpu)
611{
612 struct task_struct *t = current;
613
614 if (t->rcu_read_lock_nesting == 0) {
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700615 rcu_preempt_qs(cpu);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700616 return;
617 }
Paul E. McKenney10f39bb2011-07-17 21:14:35 -0700618 if (t->rcu_read_lock_nesting > 0 &&
619 per_cpu(rcu_preempt_data, cpu).qs_pending)
Paul E. McKenneyc3422be2009-09-13 09:15:10 -0700620 t->rcu_read_unlock_special |= RCU_READ_UNLOCK_NEED_QS;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700621}
622
Paul E. McKenneya46e0892011-06-15 15:47:09 -0700623#ifdef CONFIG_RCU_BOOST
624
Shaohua Li09223372011-06-14 13:26:25 +0800625static void rcu_preempt_do_callbacks(void)
626{
627 rcu_do_batch(&rcu_preempt_state, &__get_cpu_var(rcu_preempt_data));
628}
629
Paul E. McKenneya46e0892011-06-15 15:47:09 -0700630#endif /* #ifdef CONFIG_RCU_BOOST */
631
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700632/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800633 * Queue a preemptible-RCU callback for invocation after a grace period.
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700634 */
635void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
636{
Paul E. McKenney486e2592012-01-06 14:11:30 -0800637 __call_rcu(head, func, &rcu_preempt_state, 0);
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700638}
639EXPORT_SYMBOL_GPL(call_rcu);
640
Paul E. McKenney486e2592012-01-06 14:11:30 -0800641/*
642 * Queue an RCU callback for lazy invocation after a grace period.
643 * This will likely be later named something like "call_rcu_lazy()",
644 * but this change will require some way of tagging the lazy RCU
645 * callbacks in the list of pending callbacks. Until then, this
646 * function may only be called from __kfree_rcu().
647 */
648void kfree_call_rcu(struct rcu_head *head,
649 void (*func)(struct rcu_head *rcu))
650{
651 __call_rcu(head, func, &rcu_preempt_state, 1);
652}
653EXPORT_SYMBOL_GPL(kfree_call_rcu);
654
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800655/**
656 * synchronize_rcu - wait until a grace period has elapsed.
657 *
658 * Control will return to the caller some time after a full grace
659 * period has elapsed, in other words after all currently executing RCU
Paul E. McKenney77d84852010-07-08 17:38:59 -0700660 * read-side critical sections have completed. Note, however, that
661 * upon return from synchronize_rcu(), the caller might well be executing
662 * concurrently with new RCU read-side critical sections that began while
663 * synchronize_rcu() was waiting. RCU read-side critical sections are
664 * delimited by rcu_read_lock() and rcu_read_unlock(), and may be nested.
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800665 */
666void synchronize_rcu(void)
667{
Paul E. McKenneyfe15d702012-01-04 13:30:33 -0800668 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
669 !lock_is_held(&rcu_lock_map) &&
670 !lock_is_held(&rcu_sched_lock_map),
671 "Illegal synchronize_rcu() in RCU read-side critical section");
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800672 if (!rcu_scheduler_active)
673 return;
Paul E. McKenney2c428182011-05-26 22:14:36 -0700674 wait_rcu_gp(call_rcu);
Paul E. McKenney6ebb2372009-11-22 08:53:50 -0800675}
676EXPORT_SYMBOL_GPL(synchronize_rcu);
677
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800678static DECLARE_WAIT_QUEUE_HEAD(sync_rcu_preempt_exp_wq);
679static long sync_rcu_preempt_exp_count;
680static DEFINE_MUTEX(sync_rcu_preempt_exp_mutex);
681
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700682/*
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800683 * Return non-zero if there are any tasks in RCU read-side critical
684 * sections blocking the current preemptible-RCU expedited grace period.
685 * If there is no preemptible-RCU expedited grace period currently in
686 * progress, returns zero unconditionally.
687 */
688static int rcu_preempted_readers_exp(struct rcu_node *rnp)
689{
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800690 return rnp->exp_tasks != NULL;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800691}
692
693/*
694 * return non-zero if there is no RCU expedited grace period in progress
695 * for the specified rcu_node structure, in other words, if all CPUs and
696 * tasks covered by the specified rcu_node structure have done their bit
697 * for the current expedited grace period. Works only for preemptible
698 * RCU -- other RCU implementation use other means.
699 *
700 * Caller must hold sync_rcu_preempt_exp_mutex.
701 */
702static int sync_rcu_preempt_exp_done(struct rcu_node *rnp)
703{
704 return !rcu_preempted_readers_exp(rnp) &&
705 ACCESS_ONCE(rnp->expmask) == 0;
706}
707
708/*
709 * Report the exit from RCU read-side critical section for the last task
710 * that queued itself during or before the current expedited preemptible-RCU
711 * grace period. This event is reported either to the rcu_node structure on
712 * which the task was queued or to one of that rcu_node structure's ancestors,
713 * recursively up the tree. (Calm down, calm down, we do the recursion
714 * iteratively!)
715 *
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700716 * Most callers will set the "wake" flag, but the task initiating the
717 * expedited grace period need not wake itself.
718 *
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800719 * Caller must hold sync_rcu_preempt_exp_mutex.
720 */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700721static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
722 bool wake)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800723{
724 unsigned long flags;
725 unsigned long mask;
726
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800727 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800728 for (;;) {
Paul E. McKenney131906b2011-07-17 02:05:49 -0700729 if (!sync_rcu_preempt_exp_done(rnp)) {
730 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800731 break;
Paul E. McKenney131906b2011-07-17 02:05:49 -0700732 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800733 if (rnp->parent == NULL) {
Paul E. McKenney131906b2011-07-17 02:05:49 -0700734 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700735 if (wake)
736 wake_up(&sync_rcu_preempt_exp_wq);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800737 break;
738 }
739 mask = rnp->grpmask;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800740 raw_spin_unlock(&rnp->lock); /* irqs remain disabled */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800741 rnp = rnp->parent;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800742 raw_spin_lock(&rnp->lock); /* irqs already disabled */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800743 rnp->expmask &= ~mask;
744 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800745}
746
747/*
748 * Snapshot the tasks blocking the newly started preemptible-RCU expedited
749 * grace period for the specified rcu_node structure. If there are no such
750 * tasks, report it up the rcu_node hierarchy.
751 *
752 * Caller must hold sync_rcu_preempt_exp_mutex and rsp->onofflock.
753 */
754static void
755sync_rcu_preempt_exp_init(struct rcu_state *rsp, struct rcu_node *rnp)
756{
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700757 unsigned long flags;
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800758 int must_wait = 0;
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800759
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700760 raw_spin_lock_irqsave(&rnp->lock, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700761 if (list_empty(&rnp->blkd_tasks)) {
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700762 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700763 } else {
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800764 rnp->exp_tasks = rnp->blkd_tasks.next;
Paul E. McKenney1217ed12011-05-04 21:43:49 -0700765 rcu_initiate_boost(rnp, flags); /* releases rnp->lock */
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800766 must_wait = 1;
767 }
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800768 if (!must_wait)
Thomas Gleixnerb40d2932011-10-22 07:12:34 -0700769 rcu_report_exp_rnp(rsp, rnp, false); /* Don't wake self. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800770}
771
Paul E. McKenney236fefa2012-01-31 14:00:41 -0800772/**
773 * synchronize_rcu_expedited - Brute-force RCU grace period
774 *
775 * Wait for an RCU-preempt grace period, but expedite it. The basic
776 * idea is to invoke synchronize_sched_expedited() to push all the tasks to
777 * the ->blkd_tasks lists and wait for this list to drain. This consumes
778 * significant time on all CPUs and is unfriendly to real-time workloads,
779 * so is thus not recommended for any sort of common-case code.
780 * In fact, if you are using synchronize_rcu_expedited() in a loop,
781 * please restructure your code to batch your updates, and then Use a
782 * single synchronize_rcu() instead.
783 *
784 * Note that it is illegal to call this function while holding any lock
785 * that is acquired by a CPU-hotplug notifier. And yes, it is also illegal
786 * to call this function from a CPU-hotplug notifier. Failing to observe
787 * these restriction will result in deadlock.
Paul E. McKenney019129d52009-10-14 10:15:56 -0700788 */
789void synchronize_rcu_expedited(void)
790{
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800791 unsigned long flags;
792 struct rcu_node *rnp;
793 struct rcu_state *rsp = &rcu_preempt_state;
794 long snap;
795 int trycount = 0;
796
797 smp_mb(); /* Caller's modifications seen first by other CPUs. */
798 snap = ACCESS_ONCE(sync_rcu_preempt_exp_count) + 1;
799 smp_mb(); /* Above access cannot bleed into critical section. */
800
801 /*
802 * Acquire lock, falling back to synchronize_rcu() if too many
803 * lock-acquisition failures. Of course, if someone does the
804 * expedited grace period for us, just leave.
805 */
806 while (!mutex_trylock(&sync_rcu_preempt_exp_mutex)) {
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700807 if (trycount++ < 10) {
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800808 udelay(trycount * num_online_cpus());
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -0700809 } else {
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800810 synchronize_rcu();
811 return;
812 }
813 if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
814 goto mb_ret; /* Others did our work for us. */
815 }
816 if ((ACCESS_ONCE(sync_rcu_preempt_exp_count) - snap) > 0)
817 goto unlock_mb_ret; /* Others did our work for us. */
818
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800819 /* force all RCU readers onto ->blkd_tasks lists. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800820 synchronize_sched_expedited();
821
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800822 raw_spin_lock_irqsave(&rsp->onofflock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800823
824 /* Initialize ->expmask for all non-leaf rcu_node structures. */
825 rcu_for_each_nonleaf_node_breadth_first(rsp, rnp) {
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800826 raw_spin_lock(&rnp->lock); /* irqs already disabled. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800827 rnp->expmask = rnp->qsmaskinit;
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800828 raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800829 }
830
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800831 /* Snapshot current state of ->blkd_tasks lists. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800832 rcu_for_each_leaf_node(rsp, rnp)
833 sync_rcu_preempt_exp_init(rsp, rnp);
834 if (NUM_RCU_NODES > 1)
835 sync_rcu_preempt_exp_init(rsp, rcu_get_root(rsp));
836
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800837 raw_spin_unlock_irqrestore(&rsp->onofflock, flags);
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800838
Paul E. McKenney12f5f522010-11-29 21:56:39 -0800839 /* Wait for snapshotted ->blkd_tasks lists to drain. */
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -0800840 rnp = rcu_get_root(rsp);
841 wait_event(sync_rcu_preempt_exp_wq,
842 sync_rcu_preempt_exp_done(rnp));
843
844 /* Clean up and exit. */
845 smp_mb(); /* ensure expedited GP seen before counter increment. */
846 ACCESS_ONCE(sync_rcu_preempt_exp_count)++;
847unlock_mb_ret:
848 mutex_unlock(&sync_rcu_preempt_exp_mutex);
849mb_ret:
850 smp_mb(); /* ensure subsequent action seen after grace period. */
Paul E. McKenney019129d52009-10-14 10:15:56 -0700851}
852EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
853
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700854/**
855 * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete.
856 */
857void rcu_barrier(void)
858{
Paul E. McKenney037b64e2012-05-28 23:26:01 -0700859 _rcu_barrier(&rcu_preempt_state);
Paul E. McKenneye74f4c42009-10-06 21:48:17 -0700860}
861EXPORT_SYMBOL_GPL(rcu_barrier);
862
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700863/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800864 * Initialize preemptible RCU's state structures.
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700865 */
866static void __init __rcu_init_preempt(void)
867{
Lai Jiangshan394f99a2010-06-28 16:25:04 +0800868 rcu_init_one(&rcu_preempt_state, &rcu_preempt_data);
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700869}
870
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700871#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
872
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800873static struct rcu_state *rcu_state = &rcu_sched_state;
874
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700875/*
876 * Tell them what RCU they are running.
877 */
Paul E. McKenney0e0fc1c2009-11-11 11:28:06 -0800878static void __init rcu_bootup_announce(void)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700879{
880 printk(KERN_INFO "Hierarchical RCU implementation.\n");
Paul E. McKenney26845c22010-04-13 14:19:23 -0700881 rcu_bootup_announce_oddness();
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700882}
883
884/*
885 * Return the number of RCU batches processed thus far for debug & stats.
886 */
887long rcu_batches_completed(void)
888{
889 return rcu_batches_completed_sched();
890}
891EXPORT_SYMBOL_GPL(rcu_batches_completed);
892
893/*
Paul E. McKenneybf66f182010-01-04 15:09:10 -0800894 * Force a quiescent state for RCU, which, because there is no preemptible
895 * RCU, becomes the same as rcu-sched.
896 */
897void rcu_force_quiescent_state(void)
898{
899 rcu_sched_force_quiescent_state();
900}
901EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
902
903/*
Paul E. McKenneycba6d0d2012-07-02 07:08:42 -0700904 * Because preemptible RCU does not exist, we never have to check for
905 * CPUs being in quiescent states.
906 */
907static void rcu_preempt_note_context_switch(int cpu)
908{
909}
910
911/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800912 * Because preemptible RCU does not exist, there are never any preempted
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700913 * RCU readers.
914 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -0800915static int rcu_preempt_blocked_readers_cgp(struct rcu_node *rnp)
Paul E. McKenneyfc2219d2009-09-23 09:50:41 -0700916{
917 return 0;
918}
919
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800920#ifdef CONFIG_HOTPLUG_CPU
921
922/* Because preemptible RCU does not exist, no quieting of tasks. */
Paul E. McKenneyd3f6bad2009-12-02 12:10:13 -0800923static void rcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800924{
Paul E. McKenney1304afb2010-02-22 17:05:02 -0800925 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenneyb668c9c2009-11-22 08:53:48 -0800926}
927
928#endif /* #ifdef CONFIG_HOTPLUG_CPU */
929
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700930/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800931 * Because preemptible RCU does not exist, we never have to check for
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700932 * tasks blocked within RCU read-side critical sections.
933 */
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800934static void rcu_print_detail_task_stall(struct rcu_state *rsp)
935{
936}
937
938/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800939 * Because preemptible RCU does not exist, we never have to check for
Paul E. McKenney1ed509a2010-02-22 17:05:05 -0800940 * tasks blocked within RCU read-side critical sections.
941 */
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700942static int rcu_print_task_stall(struct rcu_node *rnp)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700943{
Paul E. McKenney9bc8b552011-08-13 13:31:47 -0700944 return 0;
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700945}
946
Paul E. McKenney53d84e02010-08-10 14:28:53 -0700947/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800948 * Because there is no preemptible RCU, there can be no readers blocked,
Paul E. McKenney49e29122009-09-18 09:50:19 -0700949 * so there is no need to check for blocked tasks. So check only for
950 * bogus qsmask values.
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700951 */
952static void rcu_preempt_check_blocked_tasks(struct rcu_node *rnp)
953{
Paul E. McKenney49e29122009-09-18 09:50:19 -0700954 WARN_ON_ONCE(rnp->qsmask);
Paul E. McKenneyb0e165c2009-09-13 09:15:09 -0700955}
956
Paul E. McKenney33f76142009-08-24 09:42:01 -0700957#ifdef CONFIG_HOTPLUG_CPU
958
959/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800960 * Because preemptible RCU does not exist, it never needs to migrate
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700961 * tasks that were blocked within RCU read-side critical sections, and
962 * such non-existent tasks cannot possibly have been blocking the current
963 * grace period.
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700964 */
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700965static int rcu_preempt_offline_tasks(struct rcu_state *rsp,
966 struct rcu_node *rnp,
967 struct rcu_data *rdp)
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700968{
Paul E. McKenney237c80c2009-10-15 09:26:14 -0700969 return 0;
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700970}
971
Paul E. McKenneye5601402012-01-07 11:03:57 -0800972#endif /* #ifdef CONFIG_HOTPLUG_CPU */
973
Paul E. McKenneydd5d19b2009-08-27 14:58:16 -0700974/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -0800975 * Because preemptible RCU does not exist, it never has any callbacks
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700976 * to check.
977 */
Paul E. McKenney1eba8f82009-09-23 09:50:42 -0700978static void rcu_preempt_check_callbacks(int cpu)
Paul E. McKenneyf41d9112009-08-22 13:56:52 -0700979{
980}
981
982/*
Paul E. McKenney486e2592012-01-06 14:11:30 -0800983 * Queue an RCU callback for lazy invocation after a grace period.
984 * This will likely be later named something like "call_rcu_lazy()",
985 * but this change will require some way of tagging the lazy RCU
986 * callbacks in the list of pending callbacks. Until then, this
987 * function may only be called from __kfree_rcu().
988 *
989 * Because there is no preemptible RCU, we use RCU-sched instead.
990 */
991void kfree_call_rcu(struct rcu_head *head,
992 void (*func)(struct rcu_head *rcu))
993{
994 __call_rcu(head, func, &rcu_sched_state, 1);
995}
996EXPORT_SYMBOL_GPL(kfree_call_rcu);
997
998/*
Paul E. McKenney019129d52009-10-14 10:15:56 -0700999 * Wait for an rcu-preempt grace period, but make it happen quickly.
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001000 * But because preemptible RCU does not exist, map to rcu-sched.
Paul E. McKenney019129d52009-10-14 10:15:56 -07001001 */
1002void synchronize_rcu_expedited(void)
1003{
1004 synchronize_sched_expedited();
1005}
1006EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
1007
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001008#ifdef CONFIG_HOTPLUG_CPU
1009
1010/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001011 * Because preemptible RCU does not exist, there is never any need to
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001012 * report on tasks preempted in RCU read-side critical sections during
1013 * expedited RCU grace periods.
1014 */
Thomas Gleixnerb40d2932011-10-22 07:12:34 -07001015static void rcu_report_exp_rnp(struct rcu_state *rsp, struct rcu_node *rnp,
1016 bool wake)
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001017{
Paul E. McKenneyd9a3da02009-12-02 12:10:15 -08001018}
1019
1020#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1021
Paul E. McKenney019129d52009-10-14 10:15:56 -07001022/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001023 * Because preemptible RCU does not exist, rcu_barrier() is just
Paul E. McKenneye74f4c42009-10-06 21:48:17 -07001024 * another name for rcu_barrier_sched().
1025 */
1026void rcu_barrier(void)
1027{
1028 rcu_barrier_sched();
1029}
1030EXPORT_SYMBOL_GPL(rcu_barrier);
1031
1032/*
Paul E. McKenney6cc68792011-03-02 13:15:15 -08001033 * Because preemptible RCU does not exist, it need not be initialized.
Paul E. McKenney1eba8f82009-09-23 09:50:42 -07001034 */
1035static void __init __rcu_init_preempt(void)
1036{
1037}
1038
Paul E. McKenneyf41d9112009-08-22 13:56:52 -07001039#endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001040
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001041#ifdef CONFIG_RCU_BOOST
1042
1043#include "rtmutex_common.h"
1044
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001045#ifdef CONFIG_RCU_TRACE
1046
1047static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1048{
1049 if (list_empty(&rnp->blkd_tasks))
1050 rnp->n_balk_blkd_tasks++;
1051 else if (rnp->exp_tasks == NULL && rnp->gp_tasks == NULL)
1052 rnp->n_balk_exp_gp_tasks++;
1053 else if (rnp->gp_tasks != NULL && rnp->boost_tasks != NULL)
1054 rnp->n_balk_boost_tasks++;
1055 else if (rnp->gp_tasks != NULL && rnp->qsmask != 0)
1056 rnp->n_balk_notblocked++;
1057 else if (rnp->gp_tasks != NULL &&
Paul E. McKenneya9f47932011-05-02 03:46:10 -07001058 ULONG_CMP_LT(jiffies, rnp->boost_time))
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001059 rnp->n_balk_notyet++;
1060 else
1061 rnp->n_balk_nos++;
1062}
1063
1064#else /* #ifdef CONFIG_RCU_TRACE */
1065
1066static void rcu_initiate_boost_trace(struct rcu_node *rnp)
1067{
1068}
1069
1070#endif /* #else #ifdef CONFIG_RCU_TRACE */
1071
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001072/*
1073 * Carry out RCU priority boosting on the task indicated by ->exp_tasks
1074 * or ->boost_tasks, advancing the pointer to the next task in the
1075 * ->blkd_tasks list.
1076 *
1077 * Note that irqs must be enabled: boosting the task can block.
1078 * Returns 1 if there are more tasks needing to be boosted.
1079 */
1080static int rcu_boost(struct rcu_node *rnp)
1081{
1082 unsigned long flags;
1083 struct rt_mutex mtx;
1084 struct task_struct *t;
1085 struct list_head *tb;
1086
1087 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL)
1088 return 0; /* Nothing left to boost. */
1089
1090 raw_spin_lock_irqsave(&rnp->lock, flags);
1091
1092 /*
1093 * Recheck under the lock: all tasks in need of boosting
1094 * might exit their RCU read-side critical sections on their own.
1095 */
1096 if (rnp->exp_tasks == NULL && rnp->boost_tasks == NULL) {
1097 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1098 return 0;
1099 }
1100
1101 /*
1102 * Preferentially boost tasks blocking expedited grace periods.
1103 * This cannot starve the normal grace periods because a second
1104 * expedited grace period must boost all blocked tasks, including
1105 * those blocking the pre-existing normal grace period.
1106 */
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001107 if (rnp->exp_tasks != NULL) {
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001108 tb = rnp->exp_tasks;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001109 rnp->n_exp_boosts++;
1110 } else {
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001111 tb = rnp->boost_tasks;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001112 rnp->n_normal_boosts++;
1113 }
1114 rnp->n_tasks_boosted++;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001115
1116 /*
1117 * We boost task t by manufacturing an rt_mutex that appears to
1118 * be held by task t. We leave a pointer to that rt_mutex where
1119 * task t can find it, and task t will release the mutex when it
1120 * exits its outermost RCU read-side critical section. Then
1121 * simply acquiring this artificial rt_mutex will boost task
1122 * t's priority. (Thanks to tglx for suggesting this approach!)
1123 *
1124 * Note that task t must acquire rnp->lock to remove itself from
1125 * the ->blkd_tasks list, which it will do from exit() if from
1126 * nowhere else. We therefore are guaranteed that task t will
1127 * stay around at least until we drop rnp->lock. Note that
1128 * rnp->lock also resolves races between our priority boosting
1129 * and task t's exiting its outermost RCU read-side critical
1130 * section.
1131 */
1132 t = container_of(tb, struct task_struct, rcu_node_entry);
1133 rt_mutex_init_proxy_locked(&mtx, t);
1134 t->rcu_boost_mutex = &mtx;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001135 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1136 rt_mutex_lock(&mtx); /* Side effect: boosts task t's priority. */
1137 rt_mutex_unlock(&mtx); /* Keep lockdep happy. */
1138
Paul E. McKenney4f89b332011-12-09 14:43:47 -08001139 return ACCESS_ONCE(rnp->exp_tasks) != NULL ||
1140 ACCESS_ONCE(rnp->boost_tasks) != NULL;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001141}
1142
1143/*
1144 * Timer handler to initiate waking up of boost kthreads that
1145 * have yielded the CPU due to excessive numbers of tasks to
1146 * boost. We wake up the per-rcu_node kthread, which in turn
1147 * will wake up the booster kthread.
1148 */
1149static void rcu_boost_kthread_timer(unsigned long arg)
1150{
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001151 invoke_rcu_node_kthread((struct rcu_node *)arg);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001152}
1153
1154/*
1155 * Priority-boosting kthread. One per leaf rcu_node and one for the
1156 * root rcu_node.
1157 */
1158static int rcu_boost_kthread(void *arg)
1159{
1160 struct rcu_node *rnp = (struct rcu_node *)arg;
1161 int spincnt = 0;
1162 int more2boost;
1163
Paul E. McKenney385680a2011-06-21 22:43:26 -07001164 trace_rcu_utilization("Start boost kthread@init");
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001165 for (;;) {
Paul E. McKenneyd71df902011-03-29 17:48:28 -07001166 rnp->boost_kthread_status = RCU_KTHREAD_WAITING;
Paul E. McKenney385680a2011-06-21 22:43:26 -07001167 trace_rcu_utilization("End boost kthread@rcu_wait");
Peter Zijlstra08bca602011-05-20 16:06:29 -07001168 rcu_wait(rnp->boost_tasks || rnp->exp_tasks);
Paul E. McKenney385680a2011-06-21 22:43:26 -07001169 trace_rcu_utilization("Start boost kthread@rcu_wait");
Paul E. McKenneyd71df902011-03-29 17:48:28 -07001170 rnp->boost_kthread_status = RCU_KTHREAD_RUNNING;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001171 more2boost = rcu_boost(rnp);
1172 if (more2boost)
1173 spincnt++;
1174 else
1175 spincnt = 0;
1176 if (spincnt > 10) {
Paul E. McKenney385680a2011-06-21 22:43:26 -07001177 trace_rcu_utilization("End boost kthread@rcu_yield");
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001178 rcu_yield(rcu_boost_kthread_timer, (unsigned long)rnp);
Paul E. McKenney385680a2011-06-21 22:43:26 -07001179 trace_rcu_utilization("Start boost kthread@rcu_yield");
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001180 spincnt = 0;
1181 }
1182 }
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001183 /* NOTREACHED */
Paul E. McKenney385680a2011-06-21 22:43:26 -07001184 trace_rcu_utilization("End boost kthread@notreached");
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001185 return 0;
1186}
1187
1188/*
1189 * Check to see if it is time to start boosting RCU readers that are
1190 * blocking the current grace period, and, if so, tell the per-rcu_node
1191 * kthread to start boosting them. If there is an expedited grace
1192 * period in progress, it is always time to boost.
1193 *
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001194 * The caller must hold rnp->lock, which this function releases,
1195 * but irqs remain disabled. The ->boost_kthread_task is immortal,
1196 * so we don't need to worry about it going away.
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001197 */
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001198static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001199{
1200 struct task_struct *t;
1201
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001202 if (!rcu_preempt_blocked_readers_cgp(rnp) && rnp->exp_tasks == NULL) {
1203 rnp->n_balk_exp_gp_tasks++;
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001204 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001205 return;
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001206 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001207 if (rnp->exp_tasks != NULL ||
1208 (rnp->gp_tasks != NULL &&
1209 rnp->boost_tasks == NULL &&
1210 rnp->qsmask == 0 &&
1211 ULONG_CMP_GE(jiffies, rnp->boost_time))) {
1212 if (rnp->exp_tasks == NULL)
1213 rnp->boost_tasks = rnp->gp_tasks;
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001214 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001215 t = rnp->boost_kthread_task;
1216 if (t != NULL)
1217 wake_up_process(t);
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001218 } else {
Paul E. McKenney0ea1f2e2011-02-22 13:42:43 -08001219 rcu_initiate_boost_trace(rnp);
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001220 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1221 }
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001222}
1223
Paul E. McKenney0f962a52011-04-14 12:13:53 -07001224/*
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001225 * Wake up the per-CPU kthread to invoke RCU callbacks.
1226 */
1227static void invoke_rcu_callbacks_kthread(void)
1228{
1229 unsigned long flags;
1230
1231 local_irq_save(flags);
1232 __this_cpu_write(rcu_cpu_has_work, 1);
Shaohua Li1eb52122011-06-16 16:02:54 -07001233 if (__this_cpu_read(rcu_cpu_kthread_task) != NULL &&
1234 current != __this_cpu_read(rcu_cpu_kthread_task))
1235 wake_up_process(__this_cpu_read(rcu_cpu_kthread_task));
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001236 local_irq_restore(flags);
1237}
1238
1239/*
Paul E. McKenneydff16722011-11-29 15:57:13 -08001240 * Is the current CPU running the RCU-callbacks kthread?
1241 * Caller must have preemption disabled.
1242 */
1243static bool rcu_is_callbacks_kthread(void)
1244{
1245 return __get_cpu_var(rcu_cpu_kthread_task) == current;
1246}
1247
1248/*
Paul E. McKenney0f962a52011-04-14 12:13:53 -07001249 * Set the affinity of the boost kthread. The CPU-hotplug locks are
1250 * held, so no one should be messing with the existence of the boost
1251 * kthread.
1252 */
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001253static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp,
1254 cpumask_var_t cm)
1255{
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001256 struct task_struct *t;
1257
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001258 t = rnp->boost_kthread_task;
1259 if (t != NULL)
1260 set_cpus_allowed_ptr(rnp->boost_kthread_task, cm);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001261}
1262
1263#define RCU_BOOST_DELAY_JIFFIES DIV_ROUND_UP(CONFIG_RCU_BOOST_DELAY * HZ, 1000)
1264
1265/*
1266 * Do priority-boost accounting for the start of a new grace period.
1267 */
1268static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1269{
1270 rnp->boost_time = jiffies + RCU_BOOST_DELAY_JIFFIES;
1271}
1272
1273/*
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001274 * Create an RCU-boost kthread for the specified node if one does not
1275 * already exist. We only create this kthread for preemptible RCU.
1276 * Returns zero if all is well, a negated errno otherwise.
1277 */
1278static int __cpuinit rcu_spawn_one_boost_kthread(struct rcu_state *rsp,
1279 struct rcu_node *rnp,
1280 int rnp_index)
1281{
1282 unsigned long flags;
1283 struct sched_param sp;
1284 struct task_struct *t;
1285
1286 if (&rcu_preempt_state != rsp)
1287 return 0;
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001288 rsp->boost = 1;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001289 if (rnp->boost_kthread_task != NULL)
1290 return 0;
1291 t = kthread_create(rcu_boost_kthread, (void *)rnp,
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001292 "rcub/%d", rnp_index);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001293 if (IS_ERR(t))
1294 return PTR_ERR(t);
1295 raw_spin_lock_irqsave(&rnp->lock, flags);
1296 rnp->boost_kthread_task = t;
1297 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001298 sp.sched_priority = RCU_BOOST_PRIO;
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001299 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
Paul E. McKenney9a432732011-05-30 20:38:55 -07001300 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001301 return 0;
1302}
1303
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001304#ifdef CONFIG_HOTPLUG_CPU
1305
1306/*
1307 * Stop the RCU's per-CPU kthread when its CPU goes offline,.
1308 */
1309static void rcu_stop_cpu_kthread(int cpu)
1310{
1311 struct task_struct *t;
1312
1313 /* Stop the CPU's kthread. */
1314 t = per_cpu(rcu_cpu_kthread_task, cpu);
1315 if (t != NULL) {
1316 per_cpu(rcu_cpu_kthread_task, cpu) = NULL;
1317 kthread_stop(t);
1318 }
1319}
1320
1321#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1322
1323static void rcu_kthread_do_work(void)
1324{
1325 rcu_do_batch(&rcu_sched_state, &__get_cpu_var(rcu_sched_data));
1326 rcu_do_batch(&rcu_bh_state, &__get_cpu_var(rcu_bh_data));
1327 rcu_preempt_do_callbacks();
1328}
1329
1330/*
1331 * Wake up the specified per-rcu_node-structure kthread.
1332 * Because the per-rcu_node kthreads are immortal, we don't need
1333 * to do anything to keep them alive.
1334 */
1335static void invoke_rcu_node_kthread(struct rcu_node *rnp)
1336{
1337 struct task_struct *t;
1338
1339 t = rnp->node_kthread_task;
1340 if (t != NULL)
1341 wake_up_process(t);
1342}
1343
1344/*
1345 * Set the specified CPU's kthread to run RT or not, as specified by
1346 * the to_rt argument. The CPU-hotplug locks are held, so the task
1347 * is not going away.
1348 */
1349static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
1350{
1351 int policy;
1352 struct sched_param sp;
1353 struct task_struct *t;
1354
1355 t = per_cpu(rcu_cpu_kthread_task, cpu);
1356 if (t == NULL)
1357 return;
1358 if (to_rt) {
1359 policy = SCHED_FIFO;
1360 sp.sched_priority = RCU_KTHREAD_PRIO;
1361 } else {
1362 policy = SCHED_NORMAL;
1363 sp.sched_priority = 0;
1364 }
1365 sched_setscheduler_nocheck(t, policy, &sp);
1366}
1367
1368/*
1369 * Timer handler to initiate the waking up of per-CPU kthreads that
1370 * have yielded the CPU due to excess numbers of RCU callbacks.
1371 * We wake up the per-rcu_node kthread, which in turn will wake up
1372 * the booster kthread.
1373 */
1374static void rcu_cpu_kthread_timer(unsigned long arg)
1375{
1376 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, arg);
1377 struct rcu_node *rnp = rdp->mynode;
1378
1379 atomic_or(rdp->grpmask, &rnp->wakemask);
1380 invoke_rcu_node_kthread(rnp);
1381}
1382
1383/*
1384 * Drop to non-real-time priority and yield, but only after posting a
1385 * timer that will cause us to regain our real-time priority if we
1386 * remain preempted. Either way, we restore our real-time priority
1387 * before returning.
1388 */
1389static void rcu_yield(void (*f)(unsigned long), unsigned long arg)
1390{
1391 struct sched_param sp;
1392 struct timer_list yield_timer;
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001393 int prio = current->rt_priority;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001394
1395 setup_timer_on_stack(&yield_timer, f, arg);
1396 mod_timer(&yield_timer, jiffies + 2);
1397 sp.sched_priority = 0;
1398 sched_setscheduler_nocheck(current, SCHED_NORMAL, &sp);
1399 set_user_nice(current, 19);
1400 schedule();
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001401 set_user_nice(current, 0);
1402 sp.sched_priority = prio;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001403 sched_setscheduler_nocheck(current, SCHED_FIFO, &sp);
1404 del_timer(&yield_timer);
1405}
1406
1407/*
1408 * Handle cases where the rcu_cpu_kthread() ends up on the wrong CPU.
1409 * This can happen while the corresponding CPU is either coming online
1410 * or going offline. We cannot wait until the CPU is fully online
1411 * before starting the kthread, because the various notifier functions
1412 * can wait for RCU grace periods. So we park rcu_cpu_kthread() until
1413 * the corresponding CPU is online.
1414 *
1415 * Return 1 if the kthread needs to stop, 0 otherwise.
1416 *
1417 * Caller must disable bh. This function can momentarily enable it.
1418 */
1419static int rcu_cpu_kthread_should_stop(int cpu)
1420{
1421 while (cpu_is_offline(cpu) ||
1422 !cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)) ||
1423 smp_processor_id() != cpu) {
1424 if (kthread_should_stop())
1425 return 1;
1426 per_cpu(rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;
1427 per_cpu(rcu_cpu_kthread_cpu, cpu) = raw_smp_processor_id();
1428 local_bh_enable();
1429 schedule_timeout_uninterruptible(1);
1430 if (!cpumask_equal(&current->cpus_allowed, cpumask_of(cpu)))
1431 set_cpus_allowed_ptr(current, cpumask_of(cpu));
1432 local_bh_disable();
1433 }
1434 per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
1435 return 0;
1436}
1437
1438/*
1439 * Per-CPU kernel thread that invokes RCU callbacks. This replaces the
Paul E. McKenneye0f23062011-06-21 01:29:39 -07001440 * RCU softirq used in flavors and configurations of RCU that do not
1441 * support RCU priority boosting.
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001442 */
1443static int rcu_cpu_kthread(void *arg)
1444{
1445 int cpu = (int)(long)arg;
1446 unsigned long flags;
1447 int spincnt = 0;
1448 unsigned int *statusp = &per_cpu(rcu_cpu_kthread_status, cpu);
1449 char work;
1450 char *workp = &per_cpu(rcu_cpu_has_work, cpu);
1451
Paul E. McKenney385680a2011-06-21 22:43:26 -07001452 trace_rcu_utilization("Start CPU kthread@init");
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001453 for (;;) {
1454 *statusp = RCU_KTHREAD_WAITING;
Paul E. McKenney385680a2011-06-21 22:43:26 -07001455 trace_rcu_utilization("End CPU kthread@rcu_wait");
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001456 rcu_wait(*workp != 0 || kthread_should_stop());
Paul E. McKenney385680a2011-06-21 22:43:26 -07001457 trace_rcu_utilization("Start CPU kthread@rcu_wait");
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001458 local_bh_disable();
1459 if (rcu_cpu_kthread_should_stop(cpu)) {
1460 local_bh_enable();
1461 break;
1462 }
1463 *statusp = RCU_KTHREAD_RUNNING;
1464 per_cpu(rcu_cpu_kthread_loops, cpu)++;
1465 local_irq_save(flags);
1466 work = *workp;
1467 *workp = 0;
1468 local_irq_restore(flags);
1469 if (work)
1470 rcu_kthread_do_work();
1471 local_bh_enable();
1472 if (*workp != 0)
1473 spincnt++;
1474 else
1475 spincnt = 0;
1476 if (spincnt > 10) {
1477 *statusp = RCU_KTHREAD_YIELDING;
Paul E. McKenney385680a2011-06-21 22:43:26 -07001478 trace_rcu_utilization("End CPU kthread@rcu_yield");
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001479 rcu_yield(rcu_cpu_kthread_timer, (unsigned long)cpu);
Paul E. McKenney385680a2011-06-21 22:43:26 -07001480 trace_rcu_utilization("Start CPU kthread@rcu_yield");
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001481 spincnt = 0;
1482 }
1483 }
1484 *statusp = RCU_KTHREAD_STOPPED;
Paul E. McKenney385680a2011-06-21 22:43:26 -07001485 trace_rcu_utilization("End CPU kthread@term");
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001486 return 0;
1487}
1488
1489/*
1490 * Spawn a per-CPU kthread, setting up affinity and priority.
1491 * Because the CPU hotplug lock is held, no other CPU will be attempting
1492 * to manipulate rcu_cpu_kthread_task. There might be another CPU
1493 * attempting to access it during boot, but the locking in kthread_bind()
1494 * will enforce sufficient ordering.
1495 *
1496 * Please note that we cannot simply refuse to wake up the per-CPU
1497 * kthread because kthreads are created in TASK_UNINTERRUPTIBLE state,
1498 * which can result in softlockup complaints if the task ends up being
1499 * idle for more than a couple of minutes.
1500 *
1501 * However, please note also that we cannot bind the per-CPU kthread to its
1502 * CPU until that CPU is fully online. We also cannot wait until the
1503 * CPU is fully online before we create its per-CPU kthread, as this would
1504 * deadlock the system when CPU notifiers tried waiting for grace
1505 * periods. So we bind the per-CPU kthread to its CPU only if the CPU
1506 * is online. If its CPU is not yet fully online, then the code in
1507 * rcu_cpu_kthread() will wait until it is fully online, and then do
1508 * the binding.
1509 */
1510static int __cpuinit rcu_spawn_one_cpu_kthread(int cpu)
1511{
1512 struct sched_param sp;
1513 struct task_struct *t;
1514
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001515 if (!rcu_scheduler_fully_active ||
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001516 per_cpu(rcu_cpu_kthread_task, cpu) != NULL)
1517 return 0;
Eric Dumazet1f288092011-06-16 15:53:18 -07001518 t = kthread_create_on_node(rcu_cpu_kthread,
1519 (void *)(long)cpu,
1520 cpu_to_node(cpu),
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001521 "rcuc/%d", cpu);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001522 if (IS_ERR(t))
1523 return PTR_ERR(t);
1524 if (cpu_online(cpu))
1525 kthread_bind(t, cpu);
1526 per_cpu(rcu_cpu_kthread_cpu, cpu) = cpu;
1527 WARN_ON_ONCE(per_cpu(rcu_cpu_kthread_task, cpu) != NULL);
1528 sp.sched_priority = RCU_KTHREAD_PRIO;
1529 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1530 per_cpu(rcu_cpu_kthread_task, cpu) = t;
1531 wake_up_process(t); /* Get to TASK_INTERRUPTIBLE quickly. */
1532 return 0;
1533}
1534
1535/*
1536 * Per-rcu_node kthread, which is in charge of waking up the per-CPU
1537 * kthreads when needed. We ignore requests to wake up kthreads
1538 * for offline CPUs, which is OK because force_quiescent_state()
1539 * takes care of this case.
1540 */
1541static int rcu_node_kthread(void *arg)
1542{
1543 int cpu;
1544 unsigned long flags;
1545 unsigned long mask;
1546 struct rcu_node *rnp = (struct rcu_node *)arg;
1547 struct sched_param sp;
1548 struct task_struct *t;
1549
1550 for (;;) {
1551 rnp->node_kthread_status = RCU_KTHREAD_WAITING;
1552 rcu_wait(atomic_read(&rnp->wakemask) != 0);
1553 rnp->node_kthread_status = RCU_KTHREAD_RUNNING;
1554 raw_spin_lock_irqsave(&rnp->lock, flags);
1555 mask = atomic_xchg(&rnp->wakemask, 0);
1556 rcu_initiate_boost(rnp, flags); /* releases rnp->lock. */
1557 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1) {
1558 if ((mask & 0x1) == 0)
1559 continue;
1560 preempt_disable();
1561 t = per_cpu(rcu_cpu_kthread_task, cpu);
1562 if (!cpu_online(cpu) || t == NULL) {
1563 preempt_enable();
1564 continue;
1565 }
1566 per_cpu(rcu_cpu_has_work, cpu) = 1;
1567 sp.sched_priority = RCU_KTHREAD_PRIO;
1568 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1569 preempt_enable();
1570 }
1571 }
1572 /* NOTREACHED */
1573 rnp->node_kthread_status = RCU_KTHREAD_STOPPED;
1574 return 0;
1575}
1576
1577/*
1578 * Set the per-rcu_node kthread's affinity to cover all CPUs that are
1579 * served by the rcu_node in question. The CPU hotplug lock is still
1580 * held, so the value of rnp->qsmaskinit will be stable.
1581 *
1582 * We don't include outgoingcpu in the affinity set, use -1 if there is
1583 * no outgoing CPU. If there are no CPUs left in the affinity set,
1584 * this function allows the kthread to execute on any CPU.
1585 */
1586static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1587{
1588 cpumask_var_t cm;
1589 int cpu;
1590 unsigned long mask = rnp->qsmaskinit;
1591
1592 if (rnp->node_kthread_task == NULL)
1593 return;
1594 if (!alloc_cpumask_var(&cm, GFP_KERNEL))
1595 return;
1596 cpumask_clear(cm);
1597 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++, mask >>= 1)
1598 if ((mask & 0x1) && cpu != outgoingcpu)
1599 cpumask_set_cpu(cpu, cm);
1600 if (cpumask_weight(cm) == 0) {
1601 cpumask_setall(cm);
1602 for (cpu = rnp->grplo; cpu <= rnp->grphi; cpu++)
1603 cpumask_clear_cpu(cpu, cm);
1604 WARN_ON_ONCE(cpumask_weight(cm) == 0);
1605 }
1606 set_cpus_allowed_ptr(rnp->node_kthread_task, cm);
1607 rcu_boost_kthread_setaffinity(rnp, cm);
1608 free_cpumask_var(cm);
1609}
1610
1611/*
1612 * Spawn a per-rcu_node kthread, setting priority and affinity.
1613 * Called during boot before online/offline can happen, or, if
1614 * during runtime, with the main CPU-hotplug locks held. So only
1615 * one of these can be executing at a time.
1616 */
1617static int __cpuinit rcu_spawn_one_node_kthread(struct rcu_state *rsp,
1618 struct rcu_node *rnp)
1619{
1620 unsigned long flags;
1621 int rnp_index = rnp - &rsp->node[0];
1622 struct sched_param sp;
1623 struct task_struct *t;
1624
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001625 if (!rcu_scheduler_fully_active ||
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001626 rnp->qsmaskinit == 0)
1627 return 0;
1628 if (rnp->node_kthread_task == NULL) {
1629 t = kthread_create(rcu_node_kthread, (void *)rnp,
Mike Galbraith5b61b0b2011-08-19 11:39:11 -07001630 "rcun/%d", rnp_index);
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001631 if (IS_ERR(t))
1632 return PTR_ERR(t);
1633 raw_spin_lock_irqsave(&rnp->lock, flags);
1634 rnp->node_kthread_task = t;
1635 raw_spin_unlock_irqrestore(&rnp->lock, flags);
1636 sp.sched_priority = 99;
1637 sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
1638 wake_up_process(t); /* get to TASK_INTERRUPTIBLE quickly. */
1639 }
1640 return rcu_spawn_one_boost_kthread(rsp, rnp, rnp_index);
1641}
1642
1643/*
1644 * Spawn all kthreads -- called as soon as the scheduler is running.
1645 */
1646static int __init rcu_spawn_kthreads(void)
1647{
1648 int cpu;
1649 struct rcu_node *rnp;
1650
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001651 rcu_scheduler_fully_active = 1;
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001652 for_each_possible_cpu(cpu) {
1653 per_cpu(rcu_cpu_has_work, cpu) = 0;
1654 if (cpu_online(cpu))
1655 (void)rcu_spawn_one_cpu_kthread(cpu);
1656 }
1657 rnp = rcu_get_root(rcu_state);
1658 (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
1659 if (NUM_RCU_NODES > 1) {
1660 rcu_for_each_leaf_node(rcu_state, rnp)
1661 (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
1662 }
1663 return 0;
1664}
1665early_initcall(rcu_spawn_kthreads);
1666
1667static void __cpuinit rcu_prepare_kthreads(int cpu)
1668{
1669 struct rcu_data *rdp = per_cpu_ptr(rcu_state->rda, cpu);
1670 struct rcu_node *rnp = rdp->mynode;
1671
1672 /* Fire up the incoming CPU's kthread and leaf rcu_node kthread. */
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001673 if (rcu_scheduler_fully_active) {
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001674 (void)rcu_spawn_one_cpu_kthread(cpu);
1675 if (rnp->node_kthread_task == NULL)
1676 (void)rcu_spawn_one_node_kthread(rcu_state, rnp);
1677 }
1678}
1679
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001680#else /* #ifdef CONFIG_RCU_BOOST */
1681
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001682static void rcu_initiate_boost(struct rcu_node *rnp, unsigned long flags)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001683{
Paul E. McKenney1217ed12011-05-04 21:43:49 -07001684 raw_spin_unlock_irqrestore(&rnp->lock, flags);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001685}
1686
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001687static void invoke_rcu_callbacks_kthread(void)
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001688{
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001689 WARN_ON_ONCE(1);
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001690}
1691
Paul E. McKenneydff16722011-11-29 15:57:13 -08001692static bool rcu_is_callbacks_kthread(void)
1693{
1694 return false;
1695}
1696
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001697static void rcu_preempt_boost_start_gp(struct rcu_node *rnp)
1698{
1699}
1700
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001701#ifdef CONFIG_HOTPLUG_CPU
1702
1703static void rcu_stop_cpu_kthread(int cpu)
1704{
1705}
1706
1707#endif /* #ifdef CONFIG_HOTPLUG_CPU */
1708
1709static void rcu_node_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
1710{
1711}
1712
1713static void rcu_cpu_kthread_setrt(int cpu, int to_rt)
1714{
1715}
1716
Paul E. McKenneyb0d30412011-07-10 15:57:35 -07001717static int __init rcu_scheduler_really_started(void)
1718{
1719 rcu_scheduler_fully_active = 1;
1720 return 0;
1721}
1722early_initcall(rcu_scheduler_really_started);
1723
Paul E. McKenneyf8b7fc62011-06-16 08:26:32 -07001724static void __cpuinit rcu_prepare_kthreads(int cpu)
1725{
1726}
1727
Paul E. McKenney27f4d282011-02-07 12:47:15 -08001728#endif /* #else #ifdef CONFIG_RCU_BOOST */
1729
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001730#if !defined(CONFIG_RCU_FAST_NO_HZ)
1731
1732/*
1733 * Check to see if any future RCU-related work will need to be done
1734 * by the current CPU, even if none need be done immediately, returning
1735 * 1 if so. This function is part of the RCU implementation; it is -not-
1736 * an exported member of the RCU API.
1737 *
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001738 * Because we not have RCU_FAST_NO_HZ, just check whether this CPU needs
1739 * any flavor of RCU.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001740 */
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001741int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001742{
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001743 *delta_jiffies = ULONG_MAX;
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001744 return rcu_cpu_has_callbacks(cpu);
1745}
1746
1747/*
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001748 * Because we do not have RCU_FAST_NO_HZ, don't bother initializing for it.
1749 */
1750static void rcu_prepare_for_idle_init(int cpu)
1751{
1752}
1753
1754/*
1755 * Because we do not have RCU_FAST_NO_HZ, don't bother cleaning up
1756 * after it.
1757 */
1758static void rcu_cleanup_after_idle(int cpu)
1759{
1760}
1761
1762/*
Paul E. McKenneya858af22012-01-16 13:29:10 -08001763 * Do the idle-entry grace-period work, which, because CONFIG_RCU_FAST_NO_HZ=n,
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001764 * is nothing.
1765 */
1766static void rcu_prepare_for_idle(int cpu)
1767{
1768}
1769
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08001770/*
1771 * Don't bother keeping a running count of the number of RCU callbacks
1772 * posted because CONFIG_RCU_FAST_NO_HZ=n.
1773 */
1774static void rcu_idle_count_callbacks_posted(void)
1775{
1776}
1777
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001778#else /* #if !defined(CONFIG_RCU_FAST_NO_HZ) */
1779
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001780/*
1781 * This code is invoked when a CPU goes idle, at which point we want
1782 * to have the CPU do everything required for RCU so that it can enter
1783 * the energy-efficient dyntick-idle mode. This is handled by a
1784 * state machine implemented by rcu_prepare_for_idle() below.
1785 *
1786 * The following three proprocessor symbols control this state machine:
1787 *
1788 * RCU_IDLE_FLUSHES gives the maximum number of times that we will attempt
1789 * to satisfy RCU. Beyond this point, it is better to incur a periodic
1790 * scheduling-clock interrupt than to loop through the state machine
1791 * at full power.
1792 * RCU_IDLE_OPT_FLUSHES gives the number of RCU_IDLE_FLUSHES that are
1793 * optional if RCU does not need anything immediately from this
1794 * CPU, even if this CPU still has RCU callbacks queued. The first
1795 * times through the state machine are mandatory: we need to give
1796 * the state machine a chance to communicate a quiescent state
1797 * to the RCU core.
1798 * RCU_IDLE_GP_DELAY gives the number of jiffies that a CPU is permitted
1799 * to sleep in dyntick-idle mode with RCU callbacks pending. This
1800 * is sized to be roughly one RCU grace period. Those energy-efficiency
1801 * benchmarkers who might otherwise be tempted to set this to a large
1802 * number, be warned: Setting RCU_IDLE_GP_DELAY too high can hang your
1803 * system. And if you are -that- concerned about energy efficiency,
1804 * just power the system down and be done with it!
Paul E. McKenney778d2502012-01-10 14:13:24 -08001805 * RCU_IDLE_LAZY_GP_DELAY gives the number of jiffies that a CPU is
1806 * permitted to sleep in dyntick-idle mode with only lazy RCU
1807 * callbacks pending. Setting this too high can OOM your system.
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001808 *
1809 * The values below work well in practice. If future workloads require
1810 * adjustment, they can be converted into kernel config parameters, though
1811 * making the state machine smarter might be a better option.
1812 */
1813#define RCU_IDLE_FLUSHES 5 /* Number of dyntick-idle tries. */
1814#define RCU_IDLE_OPT_FLUSHES 3 /* Optional dyntick-idle tries. */
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001815#define RCU_IDLE_GP_DELAY 4 /* Roughly one grace period. */
Paul E. McKenney778d2502012-01-10 14:13:24 -08001816#define RCU_IDLE_LAZY_GP_DELAY (6 * HZ) /* Roughly six seconds. */
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08001817
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001818extern int tick_nohz_enabled;
1819
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001820/*
Paul E. McKenney486e2592012-01-06 14:11:30 -08001821 * Does the specified flavor of RCU have non-lazy callbacks pending on
1822 * the specified CPU? Both RCU flavor and CPU are specified by the
1823 * rcu_data structure.
1824 */
1825static bool __rcu_cpu_has_nonlazy_callbacks(struct rcu_data *rdp)
1826{
1827 return rdp->qlen != rdp->qlen_lazy;
1828}
1829
1830#ifdef CONFIG_TREE_PREEMPT_RCU
1831
1832/*
1833 * Are there non-lazy RCU-preempt callbacks? (There cannot be if there
1834 * is no RCU-preempt in the kernel.)
1835 */
1836static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
1837{
1838 struct rcu_data *rdp = &per_cpu(rcu_preempt_data, cpu);
1839
1840 return __rcu_cpu_has_nonlazy_callbacks(rdp);
1841}
1842
1843#else /* #ifdef CONFIG_TREE_PREEMPT_RCU */
1844
1845static bool rcu_preempt_cpu_has_nonlazy_callbacks(int cpu)
1846{
1847 return 0;
1848}
1849
1850#endif /* else #ifdef CONFIG_TREE_PREEMPT_RCU */
1851
1852/*
1853 * Does any flavor of RCU have non-lazy callbacks on the specified CPU?
1854 */
1855static bool rcu_cpu_has_nonlazy_callbacks(int cpu)
1856{
1857 return __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_sched_data, cpu)) ||
1858 __rcu_cpu_has_nonlazy_callbacks(&per_cpu(rcu_bh_data, cpu)) ||
1859 rcu_preempt_cpu_has_nonlazy_callbacks(cpu);
1860}
1861
1862/*
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001863 * Allow the CPU to enter dyntick-idle mode if either: (1) There are no
1864 * callbacks on this CPU, (2) this CPU has not yet attempted to enter
1865 * dyntick-idle mode, or (3) this CPU is in the process of attempting to
1866 * enter dyntick-idle mode. Otherwise, if we have recently tried and failed
1867 * to enter dyntick-idle mode, we refuse to try to enter it. After all,
1868 * it is better to incur scheduling-clock interrupts than to spin
1869 * continuously for the same time duration!
1870 *
1871 * The delta_jiffies argument is used to store the time when RCU is
1872 * going to need the CPU again if it still has callbacks. The reason
1873 * for this is that rcu_prepare_for_idle() might need to post a timer,
1874 * but if so, it will do so after tick_nohz_stop_sched_tick() has set
1875 * the wakeup time for this CPU. This means that RCU's timer can be
1876 * delayed until the wakeup time, which defeats the purpose of posting
1877 * a timer.
1878 */
1879int rcu_needs_cpu(int cpu, unsigned long *delta_jiffies)
1880{
1881 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1882
1883 /* Flag a new idle sojourn to the idle-entry state machine. */
1884 rdtp->idle_first_pass = 1;
1885 /* If no callbacks, RCU doesn't need the CPU. */
1886 if (!rcu_cpu_has_callbacks(cpu)) {
1887 *delta_jiffies = ULONG_MAX;
1888 return 0;
1889 }
1890 if (rdtp->dyntick_holdoff == jiffies) {
1891 /* RCU recently tried and failed, so don't try again. */
1892 *delta_jiffies = 1;
1893 return 1;
1894 }
1895 /* Set up for the possibility that RCU will post a timer. */
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07001896 if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
1897 *delta_jiffies = round_up(RCU_IDLE_GP_DELAY + jiffies,
1898 RCU_IDLE_GP_DELAY) - jiffies;
1899 } else {
1900 *delta_jiffies = jiffies + RCU_IDLE_LAZY_GP_DELAY;
1901 *delta_jiffies = round_jiffies(*delta_jiffies) - jiffies;
1902 }
Paul E. McKenneyaa9b16302012-05-10 16:41:44 -07001903 return 0;
1904}
1905
1906/*
Paul E. McKenney21e52e12012-04-30 14:16:19 -07001907 * Handler for smp_call_function_single(). The only point of this
1908 * handler is to wake the CPU up, so the handler does only tracing.
1909 */
1910void rcu_idle_demigrate(void *unused)
1911{
1912 trace_rcu_prep_idle("Demigrate");
1913}
1914
1915/*
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001916 * Timer handler used to force CPU to start pushing its remaining RCU
1917 * callbacks in the case where it entered dyntick-idle mode with callbacks
1918 * pending. The hander doesn't really need to do anything because the
1919 * real work is done upon re-entry to idle, or by the next scheduling-clock
1920 * interrupt should idle not be re-entered.
Paul E. McKenney21e52e12012-04-30 14:16:19 -07001921 *
1922 * One special case: the timer gets migrated without awakening the CPU
1923 * on which the timer was scheduled on. In this case, we must wake up
1924 * that CPU. We do so with smp_call_function_single().
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001925 */
Paul E. McKenney21e52e12012-04-30 14:16:19 -07001926static void rcu_idle_gp_timer_func(unsigned long cpu_in)
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001927{
Paul E. McKenney21e52e12012-04-30 14:16:19 -07001928 int cpu = (int)cpu_in;
1929
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001930 trace_rcu_prep_idle("Timer");
Paul E. McKenney21e52e12012-04-30 14:16:19 -07001931 if (cpu != smp_processor_id())
1932 smp_call_function_single(cpu, rcu_idle_demigrate, NULL, 0);
1933 else
1934 WARN_ON_ONCE(1); /* Getting here can hang the system... */
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001935}
1936
1937/*
1938 * Initialize the timer used to pull CPUs out of dyntick-idle mode.
1939 */
1940static void rcu_prepare_for_idle_init(int cpu)
1941{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001942 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1943
1944 rdtp->dyntick_holdoff = jiffies - 1;
1945 setup_timer(&rdtp->idle_gp_timer, rcu_idle_gp_timer_func, cpu);
1946 rdtp->idle_gp_timer_expires = jiffies - 1;
1947 rdtp->idle_first_pass = 1;
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001948}
1949
1950/*
1951 * Clean up for exit from idle. Because we are exiting from idle, there
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001952 * is no longer any point to ->idle_gp_timer, so cancel it. This will
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001953 * do nothing if this timer is not active, so just cancel it unconditionally.
1954 */
1955static void rcu_cleanup_after_idle(int cpu)
1956{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001957 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
1958
1959 del_timer(&rdtp->idle_gp_timer);
Paul E. McKenney2fdbb312012-02-23 15:58:29 -08001960 trace_rcu_prep_idle("Cleanup after idle");
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001961 rdtp->tick_nohz_enabled_snap = ACCESS_ONCE(tick_nohz_enabled);
Paul E. McKenney7cb92492011-11-28 12:28:34 -08001962}
1963
1964/*
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001965 * Check to see if any RCU-related work can be done by the current CPU,
1966 * and if so, schedule a softirq to get it done. This function is part
1967 * of the RCU implementation; it is -not- an exported member of the RCU API.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001968 *
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001969 * The idea is for the current CPU to clear out all work required by the
1970 * RCU core for the current grace period, so that this CPU can be permitted
1971 * to enter dyntick-idle mode. In some cases, it will need to be awakened
1972 * at the end of the grace period by whatever CPU ends the grace period.
1973 * This allows CPUs to go dyntick-idle more quickly, and to reduce the
1974 * number of wakeups by a modest integer factor.
Paul E. McKenneya47cd882010-02-26 16:38:56 -08001975 *
1976 * Because it is not legal to invoke rcu_process_callbacks() with irqs
1977 * disabled, we do one pass of force_quiescent_state(), then do a
Paul E. McKenneya46e0892011-06-15 15:47:09 -07001978 * invoke_rcu_core() to cause rcu_process_callbacks() to be invoked
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001979 * later. The ->dyntick_drain field controls the sequencing.
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001980 *
1981 * The caller must have disabled interrupts.
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001982 */
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07001983static void rcu_prepare_for_idle(int cpu)
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08001984{
Paul E. McKenneyf511fc62012-03-15 12:16:26 -07001985 struct timer_list *tp;
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07001986 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
Paul E. McKenney9d2ad242012-06-24 10:15:02 -07001987 int tne;
1988
1989 /* Handle nohz enablement switches conservatively. */
1990 tne = ACCESS_ONCE(tick_nohz_enabled);
1991 if (tne != rdtp->tick_nohz_enabled_snap) {
1992 if (rcu_cpu_has_callbacks(cpu))
1993 invoke_rcu_core(); /* force nohz to see update. */
1994 rdtp->tick_nohz_enabled_snap = tne;
1995 return;
1996 }
1997 if (!tne)
1998 return;
Paul E. McKenneyf511fc62012-03-15 12:16:26 -07001999
Paul E. McKenney3084f2f2011-11-22 17:07:11 -08002000 /*
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002001 * If this is an idle re-entry, for example, due to use of
2002 * RCU_NONIDLE() or the new idle-loop tracing API within the idle
2003 * loop, then don't take any state-machine actions, unless the
2004 * momentary exit from idle queued additional non-lazy callbacks.
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002005 * Instead, repost the ->idle_gp_timer if this CPU has callbacks
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002006 * pending.
2007 */
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002008 if (!rdtp->idle_first_pass &&
2009 (rdtp->nonlazy_posted == rdtp->nonlazy_posted_snap)) {
Paul E. McKenneyf511fc62012-03-15 12:16:26 -07002010 if (rcu_cpu_has_callbacks(cpu)) {
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002011 tp = &rdtp->idle_gp_timer;
2012 mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
Paul E. McKenneyf511fc62012-03-15 12:16:26 -07002013 }
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002014 return;
2015 }
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002016 rdtp->idle_first_pass = 0;
2017 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted - 1;
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002018
2019 /*
Paul E. McKenneyf535a602011-11-22 20:43:02 -08002020 * If there are no callbacks on this CPU, enter dyntick-idle mode.
2021 * Also reset state to avoid prejudicing later attempts.
Paul E. McKenney3084f2f2011-11-22 17:07:11 -08002022 */
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07002023 if (!rcu_cpu_has_callbacks(cpu)) {
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002024 rdtp->dyntick_holdoff = jiffies - 1;
2025 rdtp->dyntick_drain = 0;
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002026 trace_rcu_prep_idle("No callbacks");
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07002027 return;
Paul E. McKenney77e38ed2010-04-25 21:04:29 -07002028 }
Paul E. McKenney3084f2f2011-11-22 17:07:11 -08002029
2030 /*
2031 * If in holdoff mode, just return. We will presumably have
2032 * refrained from disabling the scheduling-clock tick.
2033 */
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002034 if (rdtp->dyntick_holdoff == jiffies) {
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002035 trace_rcu_prep_idle("In holdoff");
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07002036 return;
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002037 }
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08002038
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002039 /* Check and update the ->dyntick_drain sequencing. */
2040 if (rdtp->dyntick_drain <= 0) {
Paul E. McKenneya47cd882010-02-26 16:38:56 -08002041 /* First time through, initialize the counter. */
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002042 rdtp->dyntick_drain = RCU_IDLE_FLUSHES;
2043 } else if (rdtp->dyntick_drain <= RCU_IDLE_OPT_FLUSHES &&
Paul E. McKenneyc3ce9102012-02-14 10:12:54 -08002044 !rcu_pending(cpu) &&
2045 !local_softirq_pending()) {
Paul E. McKenney7cb92492011-11-28 12:28:34 -08002046 /* Can we go dyntick-idle despite still having callbacks? */
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002047 rdtp->dyntick_drain = 0;
2048 rdtp->dyntick_holdoff = jiffies;
Paul E. McKenneyfd4b3522012-05-05 19:10:35 -07002049 if (rcu_cpu_has_nonlazy_callbacks(cpu)) {
2050 trace_rcu_prep_idle("Dyntick with callbacks");
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002051 rdtp->idle_gp_timer_expires =
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07002052 round_up(jiffies + RCU_IDLE_GP_DELAY,
2053 RCU_IDLE_GP_DELAY);
Paul E. McKenneyfd4b3522012-05-05 19:10:35 -07002054 } else {
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002055 rdtp->idle_gp_timer_expires =
Paul E. McKenneye84c48a2012-06-04 20:45:10 -07002056 round_jiffies(jiffies + RCU_IDLE_LAZY_GP_DELAY);
Paul E. McKenneyfd4b3522012-05-05 19:10:35 -07002057 trace_rcu_prep_idle("Dyntick with lazy callbacks");
2058 }
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002059 tp = &rdtp->idle_gp_timer;
2060 mod_timer_pinned(tp, rdtp->idle_gp_timer_expires);
2061 rdtp->nonlazy_posted_snap = rdtp->nonlazy_posted;
Paul E. McKenneyf23f7fa2011-11-30 15:41:14 -08002062 return; /* Nothing more to do immediately. */
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002063 } else if (--(rdtp->dyntick_drain) <= 0) {
Paul E. McKenneya47cd882010-02-26 16:38:56 -08002064 /* We have hit the limit, so time to give up. */
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002065 rdtp->dyntick_holdoff = jiffies;
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002066 trace_rcu_prep_idle("Begin holdoff");
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07002067 invoke_rcu_core(); /* Force the CPU out of dyntick-idle. */
2068 return;
Paul E. McKenneya47cd882010-02-26 16:38:56 -08002069 }
2070
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07002071 /*
2072 * Do one step of pushing the remaining RCU callbacks through
2073 * the RCU core state machine.
2074 */
2075#ifdef CONFIG_TREE_PREEMPT_RCU
2076 if (per_cpu(rcu_preempt_data, cpu).nxtlist) {
2077 rcu_preempt_qs(cpu);
2078 force_quiescent_state(&rcu_preempt_state, 0);
Paul E. McKenneyaea1b352011-11-02 06:54:54 -07002079 }
2080#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
Paul E. McKenneya47cd882010-02-26 16:38:56 -08002081 if (per_cpu(rcu_sched_data, cpu).nxtlist) {
2082 rcu_sched_qs(cpu);
2083 force_quiescent_state(&rcu_sched_state, 0);
Paul E. McKenneya47cd882010-02-26 16:38:56 -08002084 }
2085 if (per_cpu(rcu_bh_data, cpu).nxtlist) {
2086 rcu_bh_qs(cpu);
2087 force_quiescent_state(&rcu_bh_state, 0);
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08002088 }
2089
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002090 /*
2091 * If RCU callbacks are still pending, RCU still needs this CPU.
2092 * So try forcing the callbacks through the grace period.
2093 */
Paul E. McKenney3ad0dec2011-11-22 21:08:13 -08002094 if (rcu_cpu_has_callbacks(cpu)) {
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002095 trace_rcu_prep_idle("More callbacks");
Paul E. McKenneya46e0892011-06-15 15:47:09 -07002096 invoke_rcu_core();
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -07002097 } else {
Paul E. McKenney433cddd2011-11-22 14:58:03 -08002098 trace_rcu_prep_idle("Callbacks drained");
Paul E. McKenneyc701d5d2012-06-28 08:08:25 -07002099 }
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08002100}
2101
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002102/*
Paul E. McKenney98248a02012-05-03 15:38:10 -07002103 * Keep a running count of the number of non-lazy callbacks posted
2104 * on this CPU. This running counter (which is never decremented) allows
2105 * rcu_prepare_for_idle() to detect when something out of the idle loop
2106 * posts a callback, even if an equal number of callbacks are invoked.
2107 * Of course, callbacks should only be posted from within a trace event
2108 * designed to be called from idle or from within RCU_NONIDLE().
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002109 */
2110static void rcu_idle_count_callbacks_posted(void)
2111{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002112 __this_cpu_add(rcu_dynticks.nonlazy_posted, 1);
Paul E. McKenneyc57afe82012-02-28 11:02:21 -08002113}
2114
Paul E. McKenney8bd93a22010-02-22 17:04:59 -08002115#endif /* #else #if !defined(CONFIG_RCU_FAST_NO_HZ) */
Paul E. McKenneya858af22012-01-16 13:29:10 -08002116
2117#ifdef CONFIG_RCU_CPU_STALL_INFO
2118
2119#ifdef CONFIG_RCU_FAST_NO_HZ
2120
2121static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
2122{
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002123 struct rcu_dynticks *rdtp = &per_cpu(rcu_dynticks, cpu);
2124 struct timer_list *tltp = &rdtp->idle_gp_timer;
Paul E. McKenneya858af22012-01-16 13:29:10 -08002125
Paul E. McKenney2ee3dc82012-02-23 17:13:19 -08002126 sprintf(cp, "drain=%d %c timer=%lu",
Paul E. McKenney5955f7e2012-05-09 12:07:05 -07002127 rdtp->dyntick_drain,
2128 rdtp->dyntick_holdoff == jiffies ? 'H' : '.',
Paul E. McKenney2ee3dc82012-02-23 17:13:19 -08002129 timer_pending(tltp) ? tltp->expires - jiffies : -1);
Paul E. McKenneya858af22012-01-16 13:29:10 -08002130}
2131
2132#else /* #ifdef CONFIG_RCU_FAST_NO_HZ */
2133
2134static void print_cpu_stall_fast_no_hz(char *cp, int cpu)
2135{
Carsten Emde1c17e4d2012-06-19 10:43:16 +02002136 *cp = '\0';
Paul E. McKenneya858af22012-01-16 13:29:10 -08002137}
2138
2139#endif /* #else #ifdef CONFIG_RCU_FAST_NO_HZ */
2140
2141/* Initiate the stall-info list. */
2142static void print_cpu_stall_info_begin(void)
2143{
2144 printk(KERN_CONT "\n");
2145}
2146
2147/*
2148 * Print out diagnostic information for the specified stalled CPU.
2149 *
2150 * If the specified CPU is aware of the current RCU grace period
2151 * (flavor specified by rsp), then print the number of scheduling
2152 * clock interrupts the CPU has taken during the time that it has
2153 * been aware. Otherwise, print the number of RCU grace periods
2154 * that this CPU is ignorant of, for example, "1" if the CPU was
2155 * aware of the previous grace period.
2156 *
2157 * Also print out idle and (if CONFIG_RCU_FAST_NO_HZ) idle-entry info.
2158 */
2159static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
2160{
2161 char fast_no_hz[72];
2162 struct rcu_data *rdp = per_cpu_ptr(rsp->rda, cpu);
2163 struct rcu_dynticks *rdtp = rdp->dynticks;
2164 char *ticks_title;
2165 unsigned long ticks_value;
2166
2167 if (rsp->gpnum == rdp->gpnum) {
2168 ticks_title = "ticks this GP";
2169 ticks_value = rdp->ticks_this_gp;
2170 } else {
2171 ticks_title = "GPs behind";
2172 ticks_value = rsp->gpnum - rdp->gpnum;
2173 }
2174 print_cpu_stall_fast_no_hz(fast_no_hz, cpu);
2175 printk(KERN_ERR "\t%d: (%lu %s) idle=%03x/%llx/%d %s\n",
2176 cpu, ticks_value, ticks_title,
2177 atomic_read(&rdtp->dynticks) & 0xfff,
2178 rdtp->dynticks_nesting, rdtp->dynticks_nmi_nesting,
2179 fast_no_hz);
2180}
2181
2182/* Terminate the stall-info list. */
2183static void print_cpu_stall_info_end(void)
2184{
2185 printk(KERN_ERR "\t");
2186}
2187
2188/* Zero ->ticks_this_gp for all flavors of RCU. */
2189static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2190{
2191 rdp->ticks_this_gp = 0;
2192}
2193
2194/* Increment ->ticks_this_gp for all flavors of RCU. */
2195static void increment_cpu_stall_ticks(void)
2196{
2197 __get_cpu_var(rcu_sched_data).ticks_this_gp++;
2198 __get_cpu_var(rcu_bh_data).ticks_this_gp++;
2199#ifdef CONFIG_TREE_PREEMPT_RCU
2200 __get_cpu_var(rcu_preempt_data).ticks_this_gp++;
2201#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU */
2202}
2203
2204#else /* #ifdef CONFIG_RCU_CPU_STALL_INFO */
2205
2206static void print_cpu_stall_info_begin(void)
2207{
2208 printk(KERN_CONT " {");
2209}
2210
2211static void print_cpu_stall_info(struct rcu_state *rsp, int cpu)
2212{
2213 printk(KERN_CONT " %d", cpu);
2214}
2215
2216static void print_cpu_stall_info_end(void)
2217{
2218 printk(KERN_CONT "} ");
2219}
2220
2221static void zero_cpu_stall_ticks(struct rcu_data *rdp)
2222{
2223}
2224
2225static void increment_cpu_stall_ticks(void)
2226{
2227}
2228
2229#endif /* #else #ifdef CONFIG_RCU_CPU_STALL_INFO */