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, write to the Free Software
16 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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/moduleparam.h>
26 #include <linux/completion.h>
27 #include <linux/interrupt.h>
28 #include <linux/notifier.h>
29 #include <linux/rcupdate.h>
30 #include <linux/kernel.h>
31 #include <linux/module.h>
32 #include <linux/mutex.h>
33 #include <linux/sched.h>
34 #include <linux/types.h>
35 #include <linux/init.h>
36 #include <linux/time.h>
37 #include <linux/cpu.h>
39 /* Global control variables for rcupdate callback mechanism. */
41 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
42 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
43 struct rcu_head **curtail; /* ->next pointer of last CB. */
46 /* Definition for rcupdate control block. */
47 static struct rcu_ctrlblk rcu_sched_ctrlblk = {
48 .donetail = &rcu_sched_ctrlblk.rcucblist,
49 .curtail = &rcu_sched_ctrlblk.rcucblist,
52 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
53 .donetail = &rcu_bh_ctrlblk.rcucblist,
54 .curtail = &rcu_bh_ctrlblk.rcucblist,
59 static long rcu_dynticks_nesting = 1;
62 * Enter dynticks-idle mode, which is an extended quiescent state
63 * if we have fully entered that mode (i.e., if the new value of
64 * dynticks_nesting is zero).
66 void rcu_enter_nohz(void)
68 if (--rcu_dynticks_nesting == 0)
69 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
73 * Exit dynticks-idle mode, so that we are no longer in an extended
76 void rcu_exit_nohz(void)
78 rcu_dynticks_nesting++;
81 #endif /* #ifdef CONFIG_NO_HZ */
84 * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
85 * Also disable irqs to avoid confusion due to interrupt handlers
86 * invoking call_rcu().
88 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
92 local_irq_save(flags);
93 if (rcp->rcucblist != NULL &&
94 rcp->donetail != rcp->curtail) {
95 rcp->donetail = rcp->curtail;
96 local_irq_restore(flags);
99 local_irq_restore(flags);
105 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
106 * are at it, given that any rcu quiescent state is also an rcu_bh
107 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
109 void rcu_sched_qs(int cpu)
111 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
112 rcu_qsctr_help(&rcu_bh_ctrlblk))
113 raise_softirq(RCU_SOFTIRQ);
117 * Record an rcu_bh quiescent state.
119 void rcu_bh_qs(int cpu)
121 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
122 raise_softirq(RCU_SOFTIRQ);
126 * Check to see if the scheduling-clock interrupt came from an extended
127 * quiescent state, and, if so, tell RCU about it.
129 void rcu_check_callbacks(int cpu, int user)
134 hardirq_count() <= (1 << HARDIRQ_SHIFT)))
136 else if (!in_softirq())
141 * Helper function for rcu_process_callbacks() that operates on the
142 * specified rcu_ctrlkblk structure.
144 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
146 struct rcu_head *next, *list;
149 /* If no RCU callbacks ready to invoke, just return. */
150 if (&rcp->rcucblist == rcp->donetail)
153 /* Move the ready-to-invoke callbacks to a local list. */
154 local_irq_save(flags);
155 list = rcp->rcucblist;
156 rcp->rcucblist = *rcp->donetail;
157 *rcp->donetail = NULL;
158 if (rcp->curtail == rcp->donetail)
159 rcp->curtail = &rcp->rcucblist;
160 rcp->donetail = &rcp->rcucblist;
161 local_irq_restore(flags);
163 /* Invoke the callbacks on the local list. */
173 * Invoke any callbacks whose grace period has completed.
175 static void rcu_process_callbacks(struct softirq_action *unused)
177 __rcu_process_callbacks(&rcu_sched_ctrlblk);
178 __rcu_process_callbacks(&rcu_bh_ctrlblk);
182 * Wait for a grace period to elapse. But it is illegal to invoke
183 * synchronize_sched() from within an RCU read-side critical section.
184 * Therefore, any legal call to synchronize_sched() is a quiescent
185 * state, and so on a UP system, synchronize_sched() need do nothing.
186 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
187 * benefits of doing might_sleep() to reduce latency.)
189 * Cool, huh? (Due to Josh Triplett.)
191 * But we want to make this a static inline later. The cond_resched()
192 * currently makes this problematic.
194 void synchronize_sched(void)
198 EXPORT_SYMBOL_GPL(synchronize_sched);
201 * Helper function for call_rcu() and call_rcu_bh().
203 static void __call_rcu(struct rcu_head *head,
204 void (*func)(struct rcu_head *rcu),
205 struct rcu_ctrlblk *rcp)
212 local_irq_save(flags);
213 *rcp->curtail = head;
214 rcp->curtail = &head->next;
215 local_irq_restore(flags);
219 * Post an RCU callback to be invoked after the end of an RCU grace
220 * period. But since we have but one CPU, that would be after any
223 void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
225 __call_rcu(head, func, &rcu_sched_ctrlblk);
227 EXPORT_SYMBOL_GPL(call_rcu);
230 * Post an RCU bottom-half callback to be invoked after any subsequent
233 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
235 __call_rcu(head, func, &rcu_bh_ctrlblk);
237 EXPORT_SYMBOL_GPL(call_rcu_bh);
239 void rcu_barrier(void)
241 struct rcu_synchronize rcu;
243 init_completion(&rcu.completion);
244 /* Will wake me after RCU finished. */
245 call_rcu(&rcu.head, wakeme_after_rcu);
247 wait_for_completion(&rcu.completion);
249 EXPORT_SYMBOL_GPL(rcu_barrier);
251 void rcu_barrier_bh(void)
253 struct rcu_synchronize rcu;
255 init_completion(&rcu.completion);
256 /* Will wake me after RCU finished. */
257 call_rcu_bh(&rcu.head, wakeme_after_rcu);
259 wait_for_completion(&rcu.completion);
261 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
263 void rcu_barrier_sched(void)
265 struct rcu_synchronize rcu;
267 init_completion(&rcu.completion);
268 /* Will wake me after RCU finished. */
269 call_rcu_sched(&rcu.head, wakeme_after_rcu);
271 wait_for_completion(&rcu.completion);
273 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
275 void __init rcu_init(void)
277 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);