projects/linux·blob v4.13 · refs

243 lines · 6.3 KiB

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, you can access it online at
16 * http://www.gnu.org/licenses/gpl-2.0.html.
17 *
18 * Copyright IBM Corporation, 2008
19 *
20 * Author: Paul E. McKenney <[email protected]>
21 *
22 * For detailed explanation of Read-Copy Update mechanism see -
23 * Documentation/RCU
24 */
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
39#include "rcu.h"
40
41/* Global control variables for rcupdate callback mechanism. */
42struct rcu_ctrlblk {
43 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
44 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
45 struct rcu_head **curtail; /* ->next pointer of last CB. */
46};
47
48/* Definition for rcupdate control block. */
49static struct rcu_ctrlblk rcu_sched_ctrlblk = {
50 .donetail = &rcu_sched_ctrlblk.rcucblist,
51 .curtail = &rcu_sched_ctrlblk.rcucblist,
52};
53
54static struct rcu_ctrlblk rcu_bh_ctrlblk = {
55 .donetail = &rcu_bh_ctrlblk.rcucblist,
56 .curtail = &rcu_bh_ctrlblk.rcucblist,
57};
58
59#include "tiny_plugin.h"
60
61void rcu_barrier_bh(void)
62{
63 wait_rcu_gp(call_rcu_bh);
64}
65EXPORT_SYMBOL(rcu_barrier_bh);
66
67void rcu_barrier_sched(void)
68{
69 wait_rcu_gp(call_rcu_sched);
70}
71EXPORT_SYMBOL(rcu_barrier_sched);
72
73/*
74 * Helper function for rcu_sched_qs() and rcu_bh_qs().
75 * Also irqs are disabled to avoid confusion due to interrupt handlers
76 * invoking call_rcu().
77 */
78static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
79{
80 if (rcp->donetail != rcp->curtail) {
81 rcp->donetail = rcp->curtail;
82 return 1;
83 }
84
85 return 0;
86}
87
88/*
89 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
90 * are at it, given that any rcu quiescent state is also an rcu_bh
91 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
92 */
93void rcu_sched_qs(void)
94{
95 unsigned long flags;
96
97 local_irq_save(flags);
98 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
99 rcu_qsctr_help(&rcu_bh_ctrlblk))
100 raise_softirq(RCU_SOFTIRQ);
101 local_irq_restore(flags);
102}
103
104/*
105 * Record an rcu_bh quiescent state.
106 */
107void rcu_bh_qs(void)
108{
109 unsigned long flags;
110
111 local_irq_save(flags);
112 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
113 raise_softirq(RCU_SOFTIRQ);
114 local_irq_restore(flags);
115}
116
117/*
118 * Check to see if the scheduling-clock interrupt came from an extended
119 * quiescent state, and, if so, tell RCU about it. This function must
120 * be called from hardirq context. It is normally called from the
121 * scheduling-clock interrupt.
122 */
123void rcu_check_callbacks(int user)
124{
125 if (user)
126 rcu_sched_qs();
127 else if (!in_softirq())
128 rcu_bh_qs();
129 if (user)
130 rcu_note_voluntary_context_switch(current);
131}
132
133/*
134 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
135 * whose grace period has elapsed.
136 */
137static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
138{
139 struct rcu_head *next, *list;
140 unsigned long flags;
141
142 /* Move the ready-to-invoke callbacks to a local list. */
143 local_irq_save(flags);
144 if (rcp->donetail == &rcp->rcucblist) {
145 /* No callbacks ready, so just leave. */
146 local_irq_restore(flags);
147 return;
148 }
149 list = rcp->rcucblist;
150 rcp->rcucblist = *rcp->donetail;
151 *rcp->donetail = NULL;
152 if (rcp->curtail == rcp->donetail)
153 rcp->curtail = &rcp->rcucblist;
154 rcp->donetail = &rcp->rcucblist;
155 local_irq_restore(flags);
156
157 /* Invoke the callbacks on the local list. */
158 while (list) {
159 next = list->next;
160 prefetch(next);
161 debug_rcu_head_unqueue(list);
162 local_bh_disable();
163 __rcu_reclaim("", list);
164 local_bh_enable();
165 list = next;
166 }
167}
168
169static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
170{
171 __rcu_process_callbacks(&rcu_sched_ctrlblk);
172 __rcu_process_callbacks(&rcu_bh_ctrlblk);
173}
174
175/*
176 * Wait for a grace period to elapse. But it is illegal to invoke
177 * synchronize_sched() from within an RCU read-side critical section.
178 * Therefore, any legal call to synchronize_sched() is a quiescent
179 * state, and so on a UP system, synchronize_sched() need do nothing.
180 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
181 * benefits of doing might_sleep() to reduce latency.)
182 *
183 * Cool, huh? (Due to Josh Triplett.)
184 */
185void synchronize_sched(void)
186{
187 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
188 lock_is_held(&rcu_lock_map) ||
189 lock_is_held(&rcu_sched_lock_map),
190 "Illegal synchronize_sched() in RCU read-side critical section");
191}
192EXPORT_SYMBOL_GPL(synchronize_sched);
193
194/*
195 * Helper function for call_rcu() and call_rcu_bh().
196 */
197static void __call_rcu(struct rcu_head *head,
198 rcu_callback_t func,
199 struct rcu_ctrlblk *rcp)
200{
201 unsigned long flags;
202
203 debug_rcu_head_queue(head);
204 head->func = func;
205 head->next = NULL;
206
207 local_irq_save(flags);
208 *rcp->curtail = head;
209 rcp->curtail = &head->next;
210 local_irq_restore(flags);
211
212 if (unlikely(is_idle_task(current))) {
213 /* force scheduling for rcu_sched_qs() */
214 resched_cpu(0);
215 }
216}
217
218/*
219 * Post an RCU callback to be invoked after the end of an RCU-sched grace
220 * period. But since we have but one CPU, that would be after any
221 * quiescent state.
222 */
223void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
224{
225 __call_rcu(head, func, &rcu_sched_ctrlblk);
226}
227EXPORT_SYMBOL_GPL(call_rcu_sched);
228
229/*
230 * Post an RCU bottom-half callback to be invoked after any subsequent
231 * quiescent state.
232 */
233void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
234{
235 __call_rcu(head, func, &rcu_bh_ctrlblk);
236}
237EXPORT_SYMBOL_GPL(call_rcu_bh);
238
239void __init rcu_init(void)
240{
241 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
242 rcu_early_boot_tests();
243}