projects/linux·blob v4.3 · refs

255 lines · 6.8 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.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>
39
40#include "rcu.h"
41
42/* Forward declarations for tiny_plugin.h. */
43struct rcu_ctrlblk;
44static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
45static void rcu_process_callbacks(struct softirq_action *unused);
46static void __call_rcu(struct rcu_head *head,
47 void (*func)(struct rcu_head *rcu),
48 struct rcu_ctrlblk *rcp);
49
50#include "tiny_plugin.h"
51
52#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
53
54/*
55 * Test whether RCU thinks that the current CPU is idle.
56 */
57bool notrace __rcu_is_watching(void)
58{
59 return true;
60}
61EXPORT_SYMBOL(__rcu_is_watching);
62
63#endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
64
65/*
66 * Helper function for rcu_sched_qs() and rcu_bh_qs().
67 * Also irqs are disabled to avoid confusion due to interrupt handlers
68 * invoking call_rcu().
69 */
70static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
71{
72 RCU_TRACE(reset_cpu_stall_ticks(rcp));
73 if (rcp->donetail != rcp->curtail) {
74 rcp->donetail = rcp->curtail;
75 return 1;
76 }
77
78 return 0;
79}
80
81/*
82 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
83 * are at it, given that any rcu quiescent state is also an rcu_bh
84 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
85 */
86void rcu_sched_qs(void)
87{
88 unsigned long flags;
89
90 local_irq_save(flags);
91 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
92 rcu_qsctr_help(&rcu_bh_ctrlblk))
93 raise_softirq(RCU_SOFTIRQ);
94 local_irq_restore(flags);
95}
96
97/*
98 * Record an rcu_bh quiescent state.
99 */
100void rcu_bh_qs(void)
101{
102 unsigned long flags;
103
104 local_irq_save(flags);
105 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
106 raise_softirq(RCU_SOFTIRQ);
107 local_irq_restore(flags);
108}
109
110/*
111 * Check to see if the scheduling-clock interrupt came from an extended
112 * quiescent state, and, if so, tell RCU about it. This function must
113 * be called from hardirq context. It is normally called from the
114 * scheduling-clock interrupt.
115 */
116void rcu_check_callbacks(int user)
117{
118 RCU_TRACE(check_cpu_stalls());
119 if (user)
120 rcu_sched_qs();
121 else if (!in_softirq())
122 rcu_bh_qs();
123 if (user)
124 rcu_note_voluntary_context_switch(current);
125}
126
127/*
128 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
129 * whose grace period has elapsed.
130 */
131static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
132{
133 const char *rn = NULL;
134 struct rcu_head *next, *list;
135 unsigned long flags;
136 RCU_TRACE(int cb_count = 0);
137
138 /* Move the ready-to-invoke callbacks to a local list. */
139 local_irq_save(flags);
140 if (rcp->donetail == &rcp->rcucblist) {
141 /* No callbacks ready, so just leave. */
142 local_irq_restore(flags);
143 return;
144 }
145 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
146 list = rcp->rcucblist;
147 rcp->rcucblist = *rcp->donetail;
148 *rcp->donetail = NULL;
149 if (rcp->curtail == rcp->donetail)
150 rcp->curtail = &rcp->rcucblist;
151 rcp->donetail = &rcp->rcucblist;
152 local_irq_restore(flags);
153
154 /* Invoke the callbacks on the local list. */
155 RCU_TRACE(rn = rcp->name);
156 while (list) {
157 next = list->next;
158 prefetch(next);
159 debug_rcu_head_unqueue(list);
160 local_bh_disable();
161 __rcu_reclaim(rn, list);
162 local_bh_enable();
163 list = next;
164 RCU_TRACE(cb_count++);
165 }
166 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
167 RCU_TRACE(trace_rcu_batch_end(rcp->name,
168 cb_count, 0, need_resched(),
169 is_idle_task(current),
170 false));
171}
172
173static void rcu_process_callbacks(struct softirq_action *unused)
174{
175 __rcu_process_callbacks(&rcu_sched_ctrlblk);
176 __rcu_process_callbacks(&rcu_bh_ctrlblk);
177}
178
179/*
180 * Wait for a grace period to elapse. But it is illegal to invoke
181 * synchronize_sched() from within an RCU read-side critical section.
182 * Therefore, any legal call to synchronize_sched() is a quiescent
183 * state, and so on a UP system, synchronize_sched() need do nothing.
184 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
185 * benefits of doing might_sleep() to reduce latency.)
186 *
187 * Cool, huh? (Due to Josh Triplett.)
188 *
189 * But we want to make this a static inline later. The cond_resched()
190 * currently makes this problematic.
191 */
192void synchronize_sched(void)
193{
194 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
195 lock_is_held(&rcu_lock_map) ||
196 lock_is_held(&rcu_sched_lock_map),
197 "Illegal synchronize_sched() in RCU read-side critical section");
198 cond_resched();
199}
200EXPORT_SYMBOL_GPL(synchronize_sched);
201
202/*
203 * Helper function for call_rcu() and call_rcu_bh().
204 */
205static void __call_rcu(struct rcu_head *head,
206 void (*func)(struct rcu_head *rcu),
207 struct rcu_ctrlblk *rcp)
208{
209 unsigned long flags;
210
211 debug_rcu_head_queue(head);
212 head->func = func;
213 head->next = NULL;
214
215 local_irq_save(flags);
216 *rcp->curtail = head;
217 rcp->curtail = &head->next;
218 RCU_TRACE(rcp->qlen++);
219 local_irq_restore(flags);
220
221 if (unlikely(is_idle_task(current))) {
222 /* force scheduling for rcu_sched_qs() */
223 resched_cpu(0);
224 }
225}
226
227/*
228 * Post an RCU callback to be invoked after the end of an RCU-sched grace
229 * period. But since we have but one CPU, that would be after any
230 * quiescent state.
231 */
232void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
233{
234 __call_rcu(head, func, &rcu_sched_ctrlblk);
235}
236EXPORT_SYMBOL_GPL(call_rcu_sched);
237
238/*
239 * Post an RCU bottom-half callback to be invoked after any subsequent
240 * quiescent state.
241 */
242void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
243{
244 __call_rcu(head, func, &rcu_bh_ctrlblk);
245}
246EXPORT_SYMBOL_GPL(call_rcu_bh);
247
248void __init rcu_init(void)
249{
250 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
251 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
252 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
253
254 rcu_early_boot_tests();
255}