projects/linux·blob v4.0 · refs

295 lines · 7.6 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/ftrace_event.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/*
53 * Enter idle, which is an extended quiescent state if we have fully
54 * entered that mode.
55 */
56void rcu_idle_enter(void)
57{
58}
59EXPORT_SYMBOL_GPL(rcu_idle_enter);
60
61/*
62 * Exit an interrupt handler towards idle.
63 */
64void rcu_irq_exit(void)
65{
66}
67EXPORT_SYMBOL_GPL(rcu_irq_exit);
68
69/*
70 * Exit idle, so that we are no longer in an extended quiescent state.
71 */
72void rcu_idle_exit(void)
73{
74}
75EXPORT_SYMBOL_GPL(rcu_idle_exit);
76
77/*
78 * Enter an interrupt handler, moving away from idle.
79 */
80void rcu_irq_enter(void)
81{
82}
83EXPORT_SYMBOL_GPL(rcu_irq_enter);
84
85#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
86
87/*
88 * Test whether RCU thinks that the current CPU is idle.
89 */
90bool notrace __rcu_is_watching(void)
91{
92 return true;
93}
94EXPORT_SYMBOL(__rcu_is_watching);
95
96#endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
97
98/*
99 * Helper function for rcu_sched_qs() and rcu_bh_qs().
100 * Also irqs are disabled to avoid confusion due to interrupt handlers
101 * invoking call_rcu().
102 */
103static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
104{
105 RCU_TRACE(reset_cpu_stall_ticks(rcp));
106 if (rcp->rcucblist != NULL &&
107 rcp->donetail != rcp->curtail) {
108 rcp->donetail = rcp->curtail;
109 return 1;
110 }
111
112 return 0;
113}
114
115/*
116 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
117 * are at it, given that any rcu quiescent state is also an rcu_bh
118 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
119 */
120void rcu_sched_qs(void)
121{
122 unsigned long flags;
123
124 local_irq_save(flags);
125 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
126 rcu_qsctr_help(&rcu_bh_ctrlblk))
127 raise_softirq(RCU_SOFTIRQ);
128 local_irq_restore(flags);
129}
130
131/*
132 * Record an rcu_bh quiescent state.
133 */
134void rcu_bh_qs(void)
135{
136 unsigned long flags;
137
138 local_irq_save(flags);
139 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
140 raise_softirq(RCU_SOFTIRQ);
141 local_irq_restore(flags);
142}
143
144/*
145 * Check to see if the scheduling-clock interrupt came from an extended
146 * quiescent state, and, if so, tell RCU about it. This function must
147 * be called from hardirq context. It is normally called from the
148 * scheduling-clock interrupt.
149 */
150void rcu_check_callbacks(int user)
151{
152 RCU_TRACE(check_cpu_stalls());
153 if (user)
154 rcu_sched_qs();
155 else if (!in_softirq())
156 rcu_bh_qs();
157 if (user)
158 rcu_note_voluntary_context_switch(current);
159}
160
161/*
162 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
163 * whose grace period has elapsed.
164 */
165static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
166{
167 const char *rn = NULL;
168 struct rcu_head *next, *list;
169 unsigned long flags;
170 RCU_TRACE(int cb_count = 0);
171
172 /* If no RCU callbacks ready to invoke, just return. */
173 if (&rcp->rcucblist == rcp->donetail) {
174 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, 0, -1));
175 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0,
176 !!ACCESS_ONCE(rcp->rcucblist),
177 need_resched(),
178 is_idle_task(current),
179 false));
180 return;
181 }
182
183 /* Move the ready-to-invoke callbacks to a local list. */
184 local_irq_save(flags);
185 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
186 list = rcp->rcucblist;
187 rcp->rcucblist = *rcp->donetail;
188 *rcp->donetail = NULL;
189 if (rcp->curtail == rcp->donetail)
190 rcp->curtail = &rcp->rcucblist;
191 rcp->donetail = &rcp->rcucblist;
192 local_irq_restore(flags);
193
194 /* Invoke the callbacks on the local list. */
195 RCU_TRACE(rn = rcp->name);
196 while (list) {
197 next = list->next;
198 prefetch(next);
199 debug_rcu_head_unqueue(list);
200 local_bh_disable();
201 __rcu_reclaim(rn, list);
202 local_bh_enable();
203 list = next;
204 RCU_TRACE(cb_count++);
205 }
206 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
207 RCU_TRACE(trace_rcu_batch_end(rcp->name,
208 cb_count, 0, need_resched(),
209 is_idle_task(current),
210 false));
211}
212
213static void rcu_process_callbacks(struct softirq_action *unused)
214{
215 __rcu_process_callbacks(&rcu_sched_ctrlblk);
216 __rcu_process_callbacks(&rcu_bh_ctrlblk);
217}
218
219/*
220 * Wait for a grace period to elapse. But it is illegal to invoke
221 * synchronize_sched() from within an RCU read-side critical section.
222 * Therefore, any legal call to synchronize_sched() is a quiescent
223 * state, and so on a UP system, synchronize_sched() need do nothing.
224 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
225 * benefits of doing might_sleep() to reduce latency.)
226 *
227 * Cool, huh? (Due to Josh Triplett.)
228 *
229 * But we want to make this a static inline later. The cond_resched()
230 * currently makes this problematic.
231 */
232void synchronize_sched(void)
233{
234 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
235 !lock_is_held(&rcu_lock_map) &&
236 !lock_is_held(&rcu_sched_lock_map),
237 "Illegal synchronize_sched() in RCU read-side critical section");
238 cond_resched();
239}
240EXPORT_SYMBOL_GPL(synchronize_sched);
241
242/*
243 * Helper function for call_rcu() and call_rcu_bh().
244 */
245static void __call_rcu(struct rcu_head *head,
246 void (*func)(struct rcu_head *rcu),
247 struct rcu_ctrlblk *rcp)
248{
249 unsigned long flags;
250
251 debug_rcu_head_queue(head);
252 head->func = func;
253 head->next = NULL;
254
255 local_irq_save(flags);
256 *rcp->curtail = head;
257 rcp->curtail = &head->next;
258 RCU_TRACE(rcp->qlen++);
259 local_irq_restore(flags);
260
261 if (unlikely(is_idle_task(current))) {
262 /* force scheduling for rcu_sched_qs() */
263 resched_cpu(0);
264 }
265}
266
267/*
268 * Post an RCU callback to be invoked after the end of an RCU-sched grace
269 * period. But since we have but one CPU, that would be after any
270 * quiescent state.
271 */
272void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
273{
274 __call_rcu(head, func, &rcu_sched_ctrlblk);
275}
276EXPORT_SYMBOL_GPL(call_rcu_sched);
277
278/*
279 * Post an RCU bottom-half callback to be invoked after any subsequent
280 * quiescent state.
281 */
282void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
283{
284 __call_rcu(head, func, &rcu_bh_ctrlblk);
285}
286EXPORT_SYMBOL_GPL(call_rcu_bh);
287
288void __init rcu_init(void)
289{
290 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
291 RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
292 RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
293
294 rcu_early_boot_tests();
295}