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1/*
2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
3 *
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.
8 *
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.
13 *
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.
17 *
18 * Copyright IBM Corporation, 2008
19 *
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
21 *
22 * For detailed explanation of Read-Copy Update mechanism see -
23 * Documentation/RCU
24 */
25
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>
39
40/* Global control variables for rcupdate callback mechanism. */
41struct rcu_ctrlblk {
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. */
45};
46
47/* Definition for rcupdate control block. */
48static struct rcu_ctrlblk rcu_ctrlblk = {
49 .rcucblist = NULL,
50 .donetail = &rcu_ctrlblk.rcucblist,
51 .curtail = &rcu_ctrlblk.rcucblist,
52};
53static struct rcu_ctrlblk rcu_bh_ctrlblk = {
54 .rcucblist = NULL,
55 .donetail = &rcu_bh_ctrlblk.rcucblist,
56 .curtail = &rcu_bh_ctrlblk.rcucblist,
57};
58
59#ifdef CONFIG_NO_HZ
60
61static long rcu_dynticks_nesting = 1;
62
63/*
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).
67 */
68void rcu_enter_nohz(void)
69{
70 if (--rcu_dynticks_nesting == 0)
71 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
72}
73
74/*
75 * Exit dynticks-idle mode, so that we are no longer in an extended
76 * quiescent state.
77 */
78void rcu_exit_nohz(void)
79{
80 rcu_dynticks_nesting++;
81}
82
83#endif /* #ifdef CONFIG_NO_HZ */
84
85/*
86 * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
87 * Also disable irqs to avoid confusion due to interrupt handlers invoking
88 * call_rcu().
89 */
90static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
91{
92 unsigned long flags;
93
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);
99 return 1;
100 }
101 local_irq_restore(flags);
102 return 0;
103}
104
105/*
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.
109 */
110void rcu_sched_qs(int cpu)
111{
112 if (rcu_qsctr_help(&rcu_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk))
113 raise_softirq(RCU_SOFTIRQ);
114}
115
116/*
117 * Record an rcu_bh quiescent state.
118 */
119void rcu_bh_qs(int cpu)
120{
121 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
122 raise_softirq(RCU_SOFTIRQ);
123}
124
125/*
126 * Check to see if the scheduling-clock interrupt came from an extended
127 * quiescent state, and, if so, tell RCU about it.
128 */
129void rcu_check_callbacks(int cpu, int user)
130{
131 if (user ||
132 (idle_cpu(cpu) &&
133 !in_softirq() &&
134 hardirq_count() <= (1 << HARDIRQ_SHIFT)))
135 rcu_sched_qs(cpu);
136 else if (!in_softirq())
137 rcu_bh_qs(cpu);
138}
139
140/*
141 * Helper function for rcu_process_callbacks() that operates on the
142 * specified rcu_ctrlkblk structure.
143 */
144static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
145{
146 unsigned long flags;
147 struct rcu_head *next, *list;
148
149 /* If no RCU callbacks ready to invoke, just return. */
150 if (&rcp->rcucblist == rcp->donetail)
151 return;
152
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);
162
163 /* Invoke the callbacks on the local list. */
164 while (list) {
165 next = list->next;
166 prefetch(next);
167 list->func(list);
168 list = next;
169 }
170}
171
172/*
173 * Invoke any callbacks whose grace period has completed.
174 */
175static void rcu_process_callbacks(struct softirq_action *unused)
176{
177 __rcu_process_callbacks(&rcu_ctrlblk);
178 __rcu_process_callbacks(&rcu_bh_ctrlblk);
179}
180
181/*
182 * Null function to handle CPU being onlined. Longer term, we want to
183 * make TINY_RCU avoid using rcupdate.c, but later...
184 */
185int rcu_cpu_notify(struct notifier_block *self,
186 unsigned long action, void *hcpu)
187{
188 return NOTIFY_OK;
189}
190
191/*
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.)
198 *
199 * Cool, huh? (Due to Josh Triplett.)
200 *
201 * But we want to make this a static inline later.
202 */
203void synchronize_sched(void)
204{
205 cond_resched();
206}
207EXPORT_SYMBOL_GPL(synchronize_sched);
208
209void synchronize_rcu_bh(void)
210{
211 synchronize_sched();
212}
213EXPORT_SYMBOL_GPL(synchronize_rcu_bh);
214
215/*
216 * Helper function for call_rcu() and call_rcu_bh().
217 */
218static void __call_rcu(struct rcu_head *head,
219 void (*func)(struct rcu_head *rcu),
220 struct rcu_ctrlblk *rcp)
221{
222 unsigned long flags;
223
224 head->func = func;
225 head->next = NULL;
226 local_irq_save(flags);
227 *rcp->curtail = head;
228 rcp->curtail = &head->next;
229 local_irq_restore(flags);
230}
231
232/*
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
235 * quiescent state.
236 */
237void call_rcu(struct rcu_head *head,
238 void (*func)(struct rcu_head *rcu))
239{
240 __call_rcu(head, func, &rcu_ctrlblk);
241}
242EXPORT_SYMBOL_GPL(call_rcu);
243
244/*
245 * Post an RCU bottom-half callback to be invoked after any subsequent
246 * quiescent state.
247 */
248void call_rcu_bh(struct rcu_head *head,
249 void (*func)(struct rcu_head *rcu))
250{
251 __call_rcu(head, func, &rcu_bh_ctrlblk);
252}
253EXPORT_SYMBOL_GPL(call_rcu_bh);
254
255void rcu_barrier(void)
256{
257 struct rcu_synchronize rcu;
258
259 init_completion(&rcu.completion);
260 /* Will wake me after RCU finished. */
261 call_rcu(&rcu.head, wakeme_after_rcu);
262 /* Wait for it. */
263 wait_for_completion(&rcu.completion);
264}
265EXPORT_SYMBOL_GPL(rcu_barrier);
266
267void rcu_barrier_bh(void)
268{
269 struct rcu_synchronize rcu;
270
271 init_completion(&rcu.completion);
272 /* Will wake me after RCU finished. */
273 call_rcu_bh(&rcu.head, wakeme_after_rcu);
274 /* Wait for it. */
275 wait_for_completion(&rcu.completion);
276}
277EXPORT_SYMBOL_GPL(rcu_barrier_bh);
278
279void rcu_barrier_sched(void)
280{
281 struct rcu_synchronize rcu;
282
283 init_completion(&rcu.completion);
284 /* Will wake me after RCU finished. */
285 call_rcu_sched(&rcu.head, wakeme_after_rcu);
286 /* Wait for it. */
287 wait_for_completion(&rcu.completion);
288}
289EXPORT_SYMBOL_GPL(rcu_barrier_sched);
290
291void __rcu_init(void)
292{
293 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
294}