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 -
26 #include <linux/types.h>
27 #include <linux/kernel.h>
28 #include <linux/init.h>
29 #include <linux/rcupdate.h>
30 #include <linux/interrupt.h>
31 #include <linux/sched.h>
32 #include <linux/module.h>
33 #include <linux/completion.h>
34 #include <linux/moduleparam.h>
35 #include <linux/notifier.h>
36 #include <linux/cpu.h>
37 #include <linux/mutex.h>
38 #include <linux/time.h>
40 /* Global control variables for rcupdate callback mechanism. */
42 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
43 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
44 struct rcu_head **curtail; /* ->next pointer of last CB. */
47 /* Definition for rcupdate control block. */
48 static struct rcu_ctrlblk rcu_ctrlblk = {
50 .donetail = &rcu_ctrlblk.rcucblist,
51 .curtail = &rcu_ctrlblk.rcucblist,
53 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
55 .donetail = &rcu_bh_ctrlblk.rcucblist,
56 .curtail = &rcu_bh_ctrlblk.rcucblist,
61 static long rcu_dynticks_nesting = 1;
64 * Enter dynticks-idle mode, which is an extended quiescent state
65 * if we have fully entered that mode (i.e., if the new value of
66 * dynticks_nesting is zero).
68 void rcu_enter_nohz(void)
70 if (--rcu_dynticks_nesting == 0)
71 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
75 * Exit dynticks-idle mode, so that we are no longer in an extended
78 void rcu_exit_nohz(void)
80 rcu_dynticks_nesting++;
83 #endif /* #ifdef CONFIG_NO_HZ */
86 * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
87 * Also disable irqs to avoid confusion due to interrupt handlers invoking
90 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
94 local_irq_save(flags);
95 if (rcp->rcucblist != NULL &&
96 rcp->donetail != rcp->curtail) {
97 rcp->donetail = rcp->curtail;
98 local_irq_restore(flags);
101 local_irq_restore(flags);
106 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
107 * are at it, given that any rcu quiescent state is also an rcu_bh
108 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
110 void rcu_sched_qs(int cpu)
112 if (rcu_qsctr_help(&rcu_ctrlblk) + 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)
147 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_ctrlblk);
178 __rcu_process_callbacks(&rcu_bh_ctrlblk);
182 * Null function to handle CPU being onlined. Longer term, we want to
183 * make TINY_RCU avoid using rcupdate.c, but later...
185 int rcu_cpu_notify(struct notifier_block *self,
186 unsigned long action, void *hcpu)
192 * Wait for a grace period to elapse. But it is illegal to invoke
193 * synchronize_sched() from within an RCU read-side critical section.
194 * Therefore, any legal call to synchronize_sched() is a quiescent
195 * state, and so on a UP system, synchronize_sched() need do nothing.
196 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
197 * benefits of doing might_sleep() to reduce latency.)
199 * Cool, huh? (Due to Josh Triplett.)
201 * But we want to make this a static inline later.
203 void synchronize_sched(void)
207 EXPORT_SYMBOL_GPL(synchronize_sched);
209 void synchronize_rcu_bh(void)
213 EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
216 * Helper function for call_rcu() and call_rcu_bh().
218 static void __call_rcu(struct rcu_head *head,
219 void (*func)(struct rcu_head *rcu),
220 struct rcu_ctrlblk *rcp)
226 local_irq_save(flags);
227 *rcp->curtail = head;
228 rcp->curtail = &head->next;
229 local_irq_restore(flags);
233 * Post an RCU callback to be invoked after the end of an RCU grace
234 * period. But since we have but one CPU, that would be after any
237 void call_rcu(struct rcu_head *head,
238 void (*func)(struct rcu_head *rcu))
240 __call_rcu(head, func, &rcu_ctrlblk);
242 EXPORT_SYMBOL_GPL(call_rcu);
245 * Post an RCU bottom-half callback to be invoked after any subsequent
248 void call_rcu_bh(struct rcu_head *head,
249 void (*func)(struct rcu_head *rcu))
251 __call_rcu(head, func, &rcu_bh_ctrlblk);
253 EXPORT_SYMBOL_GPL(call_rcu_bh);
255 void rcu_barrier(void)
257 struct rcu_synchronize rcu;
259 init_completion(&rcu.completion);
260 /* Will wake me after RCU finished. */
261 call_rcu(&rcu.head, wakeme_after_rcu);
263 wait_for_completion(&rcu.completion);
265 EXPORT_SYMBOL_GPL(rcu_barrier);
267 void rcu_barrier_bh(void)
269 struct rcu_synchronize rcu;
271 init_completion(&rcu.completion);
272 /* Will wake me after RCU finished. */
273 call_rcu_bh(&rcu.head, wakeme_after_rcu);
275 wait_for_completion(&rcu.completion);
277 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
279 void rcu_barrier_sched(void)
281 struct rcu_synchronize rcu;
283 init_completion(&rcu.completion);
284 /* Will wake me after RCU finished. */
285 call_rcu_sched(&rcu.head, wakeme_after_rcu);
287 wait_for_completion(&rcu.completion);
289 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
291 void __rcu_init(void)
293 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);