2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2 of the License, or
7 * (at your option) any later version.
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
18 * Copyright IBM Corporation, 2008
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
22 * For detailed explanation of Read-Copy Update mechanism see -
25 #include <linux/completion.h>
26 #include <linux/interrupt.h>
27 #include <linux/notifier.h>
28 #include <linux/rcupdate_wait.h>
29 #include <linux/kernel.h>
30 #include <linux/export.h>
31 #include <linux/mutex.h>
32 #include <linux/sched.h>
33 #include <linux/types.h>
34 #include <linux/init.h>
35 #include <linux/time.h>
36 #include <linux/cpu.h>
37 #include <linux/prefetch.h>
38 #include <linux/trace_events.h>
42 /* Forward declarations for tiny_plugin.h. */
44 static void __call_rcu(struct rcu_head *head,
46 struct rcu_ctrlblk *rcp);
48 #include "tiny_plugin.h"
50 void rcu_barrier_bh(void)
52 wait_rcu_gp(call_rcu_bh);
54 EXPORT_SYMBOL(rcu_barrier_bh);
56 void rcu_barrier_sched(void)
58 wait_rcu_gp(call_rcu_sched);
60 EXPORT_SYMBOL(rcu_barrier_sched);
62 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
65 * Test whether RCU thinks that the current CPU is idle.
67 bool notrace __rcu_is_watching(void)
71 EXPORT_SYMBOL(__rcu_is_watching);
73 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
76 * Helper function for rcu_sched_qs() and rcu_bh_qs().
77 * Also irqs are disabled to avoid confusion due to interrupt handlers
78 * invoking call_rcu().
80 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
82 RCU_TRACE(reset_cpu_stall_ticks(rcp);)
83 if (rcp->donetail != rcp->curtail) {
84 rcp->donetail = rcp->curtail;
92 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
93 * are at it, given that any rcu quiescent state is also an rcu_bh
94 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
96 void rcu_sched_qs(void)
100 local_irq_save(flags);
101 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
102 rcu_qsctr_help(&rcu_bh_ctrlblk))
103 raise_softirq(RCU_SOFTIRQ);
104 local_irq_restore(flags);
108 * Record an rcu_bh quiescent state.
114 local_irq_save(flags);
115 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
116 raise_softirq(RCU_SOFTIRQ);
117 local_irq_restore(flags);
121 * Check to see if the scheduling-clock interrupt came from an extended
122 * quiescent state, and, if so, tell RCU about it. This function must
123 * be called from hardirq context. It is normally called from the
124 * scheduling-clock interrupt.
126 void rcu_check_callbacks(int user)
128 RCU_TRACE(check_cpu_stalls();)
131 else if (!in_softirq())
134 rcu_note_voluntary_context_switch(current);
138 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
139 * whose grace period has elapsed.
141 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
143 const char *rn = NULL;
144 struct rcu_head *next, *list;
146 RCU_TRACE(int cb_count = 0;)
148 /* Move the ready-to-invoke callbacks to a local list. */
149 local_irq_save(flags);
150 if (rcp->donetail == &rcp->rcucblist) {
151 /* No callbacks ready, so just leave. */
152 local_irq_restore(flags);
155 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1);)
156 list = rcp->rcucblist;
157 rcp->rcucblist = *rcp->donetail;
158 *rcp->donetail = NULL;
159 if (rcp->curtail == rcp->donetail)
160 rcp->curtail = &rcp->rcucblist;
161 rcp->donetail = &rcp->rcucblist;
162 local_irq_restore(flags);
164 /* Invoke the callbacks on the local list. */
165 RCU_TRACE(rn = rcp->name;)
169 debug_rcu_head_unqueue(list);
171 __rcu_reclaim(rn, list);
174 RCU_TRACE(cb_count++;)
176 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count);)
177 RCU_TRACE(trace_rcu_batch_end(rcp->name,
178 cb_count, 0, need_resched(),
179 is_idle_task(current),
183 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
185 __rcu_process_callbacks(&rcu_sched_ctrlblk);
186 __rcu_process_callbacks(&rcu_bh_ctrlblk);
190 * Wait for a grace period to elapse. But it is illegal to invoke
191 * synchronize_sched() from within an RCU read-side critical section.
192 * Therefore, any legal call to synchronize_sched() is a quiescent
193 * state, and so on a UP system, synchronize_sched() need do nothing.
194 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
195 * benefits of doing might_sleep() to reduce latency.)
197 * Cool, huh? (Due to Josh Triplett.)
199 void synchronize_sched(void)
201 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
202 lock_is_held(&rcu_lock_map) ||
203 lock_is_held(&rcu_sched_lock_map),
204 "Illegal synchronize_sched() in RCU read-side critical section");
206 EXPORT_SYMBOL_GPL(synchronize_sched);
209 * Helper function for call_rcu() and call_rcu_bh().
211 static void __call_rcu(struct rcu_head *head,
213 struct rcu_ctrlblk *rcp)
217 debug_rcu_head_queue(head);
221 local_irq_save(flags);
222 *rcp->curtail = head;
223 rcp->curtail = &head->next;
224 RCU_TRACE(rcp->qlen++;)
225 local_irq_restore(flags);
227 if (unlikely(is_idle_task(current))) {
228 /* force scheduling for rcu_sched_qs() */
234 * Post an RCU callback to be invoked after the end of an RCU-sched grace
235 * period. But since we have but one CPU, that would be after any
238 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
240 __call_rcu(head, func, &rcu_sched_ctrlblk);
242 EXPORT_SYMBOL_GPL(call_rcu_sched);
245 * Post an RCU bottom-half callback to be invoked after any subsequent
248 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
250 __call_rcu(head, func, &rcu_bh_ctrlblk);
252 EXPORT_SYMBOL_GPL(call_rcu_bh);
254 void __init rcu_init(void)
256 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
257 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk);)
258 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk);)
260 rcu_early_boot_tests();