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9b1d82fa PM |
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 | |
87de1cfd PM |
15 | * along with this program; if not, you can access it online at |
16 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
9b1d82fa PM |
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 - | |
4ce5b903 | 23 | * Documentation/RCU |
9b1d82fa | 24 | */ |
4ce5b903 IM |
25 | #include <linux/completion.h> |
26 | #include <linux/interrupt.h> | |
9b1d82fa | 27 | #include <linux/notifier.h> |
f9411ebe | 28 | #include <linux/rcupdate_wait.h> |
4ce5b903 | 29 | #include <linux/kernel.h> |
9984de1a | 30 | #include <linux/export.h> |
9b1d82fa | 31 | #include <linux/mutex.h> |
4ce5b903 IM |
32 | #include <linux/sched.h> |
33 | #include <linux/types.h> | |
34 | #include <linux/init.h> | |
9b1d82fa | 35 | #include <linux/time.h> |
4ce5b903 | 36 | #include <linux/cpu.h> |
268bb0ce | 37 | #include <linux/prefetch.h> |
9b1d82fa | 38 | |
29c00b4a PM |
39 | #include "rcu.h" |
40 | ||
6d48152e PM |
41 | /* Global control variables for rcupdate callback mechanism. */ |
42 | struct 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. */ | |
49 | static struct rcu_ctrlblk rcu_sched_ctrlblk = { | |
50 | .donetail = &rcu_sched_ctrlblk.rcucblist, | |
51 | .curtail = &rcu_sched_ctrlblk.rcucblist, | |
52 | }; | |
53 | ||
54 | static struct rcu_ctrlblk rcu_bh_ctrlblk = { | |
55 | .donetail = &rcu_bh_ctrlblk.rcucblist, | |
56 | .curtail = &rcu_bh_ctrlblk.rcucblist, | |
57 | }; | |
a57eb940 | 58 | |
f9411ebe IM |
59 | void rcu_barrier_bh(void) |
60 | { | |
61 | wait_rcu_gp(call_rcu_bh); | |
62 | } | |
63 | EXPORT_SYMBOL(rcu_barrier_bh); | |
64 | ||
65 | void rcu_barrier_sched(void) | |
66 | { | |
67 | wait_rcu_gp(call_rcu_sched); | |
68 | } | |
69 | EXPORT_SYMBOL(rcu_barrier_sched); | |
70 | ||
9b1d82fa | 71 | /* |
b554d7de ED |
72 | * Helper function for rcu_sched_qs() and rcu_bh_qs(). |
73 | * Also irqs are disabled to avoid confusion due to interrupt handlers | |
4ce5b903 | 74 | * invoking call_rcu(). |
9b1d82fa PM |
75 | */ |
76 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) | |
77 | { | |
27153acb | 78 | if (rcp->donetail != rcp->curtail) { |
9b1d82fa | 79 | rcp->donetail = rcp->curtail; |
9b1d82fa PM |
80 | return 1; |
81 | } | |
4ce5b903 | 82 | |
9b1d82fa PM |
83 | return 0; |
84 | } | |
85 | ||
86 | /* | |
87 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we | |
88 | * are at it, given that any rcu quiescent state is also an rcu_bh | |
89 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. | |
90 | */ | |
284a8c93 | 91 | void rcu_sched_qs(void) |
9b1d82fa | 92 | { |
b554d7de ED |
93 | unsigned long flags; |
94 | ||
95 | local_irq_save(flags); | |
99652b54 PM |
96 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
97 | rcu_qsctr_help(&rcu_bh_ctrlblk)) | |
9dc5ad32 | 98 | raise_softirq(RCU_SOFTIRQ); |
b554d7de | 99 | local_irq_restore(flags); |
9b1d82fa PM |
100 | } |
101 | ||
102 | /* | |
103 | * Record an rcu_bh quiescent state. | |
104 | */ | |
284a8c93 | 105 | void rcu_bh_qs(void) |
9b1d82fa | 106 | { |
b554d7de ED |
107 | unsigned long flags; |
108 | ||
109 | local_irq_save(flags); | |
9b1d82fa | 110 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) |
9dc5ad32 | 111 | raise_softirq(RCU_SOFTIRQ); |
b554d7de | 112 | local_irq_restore(flags); |
9b1d82fa PM |
113 | } |
114 | ||
115 | /* | |
116 | * Check to see if the scheduling-clock interrupt came from an extended | |
9b2e4f18 PM |
117 | * quiescent state, and, if so, tell RCU about it. This function must |
118 | * be called from hardirq context. It is normally called from the | |
119 | * scheduling-clock interrupt. | |
9b1d82fa | 120 | */ |
c3377c2d | 121 | void rcu_check_callbacks(int user) |
9b1d82fa | 122 | { |
ca9558a3 | 123 | if (user) |
284a8c93 | 124 | rcu_sched_qs(); |
9b1d82fa | 125 | else if (!in_softirq()) |
284a8c93 | 126 | rcu_bh_qs(); |
8315f422 PM |
127 | if (user) |
128 | rcu_note_voluntary_context_switch(current); | |
9b1d82fa PM |
129 | } |
130 | ||
131 | /* | |
b2c0710c PM |
132 | * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure |
133 | * whose grace period has elapsed. | |
9b1d82fa | 134 | */ |
965a002b | 135 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) |
9b1d82fa | 136 | { |
9b1d82fa | 137 | struct rcu_head *next, *list; |
4ce5b903 | 138 | unsigned long flags; |
9b1d82fa | 139 | |
9b1d82fa PM |
140 | /* Move the ready-to-invoke callbacks to a local list. */ |
141 | local_irq_save(flags); | |
6e91f8cb PM |
142 | if (rcp->donetail == &rcp->rcucblist) { |
143 | /* No callbacks ready, so just leave. */ | |
144 | local_irq_restore(flags); | |
145 | return; | |
146 | } | |
9b1d82fa PM |
147 | list = rcp->rcucblist; |
148 | rcp->rcucblist = *rcp->donetail; | |
149 | *rcp->donetail = NULL; | |
150 | if (rcp->curtail == rcp->donetail) | |
151 | rcp->curtail = &rcp->rcucblist; | |
152 | rcp->donetail = &rcp->rcucblist; | |
153 | local_irq_restore(flags); | |
154 | ||
155 | /* Invoke the callbacks on the local list. */ | |
156 | while (list) { | |
157 | next = list->next; | |
158 | prefetch(next); | |
551d55a9 | 159 | debug_rcu_head_unqueue(list); |
b2c0710c | 160 | local_bh_disable(); |
6d48152e | 161 | __rcu_reclaim("", list); |
b2c0710c | 162 | local_bh_enable(); |
9b1d82fa PM |
163 | list = next; |
164 | } | |
165 | } | |
166 | ||
0766f788 | 167 | static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) |
b2c0710c | 168 | { |
965a002b PM |
169 | __rcu_process_callbacks(&rcu_sched_ctrlblk); |
170 | __rcu_process_callbacks(&rcu_bh_ctrlblk); | |
b2c0710c PM |
171 | } |
172 | ||
9b1d82fa PM |
173 | /* |
174 | * Wait for a grace period to elapse. But it is illegal to invoke | |
175 | * synchronize_sched() from within an RCU read-side critical section. | |
176 | * Therefore, any legal call to synchronize_sched() is a quiescent | |
177 | * state, and so on a UP system, synchronize_sched() need do nothing. | |
178 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the | |
179 | * benefits of doing might_sleep() to reduce latency.) | |
180 | * | |
181 | * Cool, huh? (Due to Josh Triplett.) | |
9b1d82fa PM |
182 | */ |
183 | void synchronize_sched(void) | |
184 | { | |
f78f5b90 PM |
185 | RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || |
186 | lock_is_held(&rcu_lock_map) || | |
187 | lock_is_held(&rcu_sched_lock_map), | |
188 | "Illegal synchronize_sched() in RCU read-side critical section"); | |
9b1d82fa PM |
189 | } |
190 | EXPORT_SYMBOL_GPL(synchronize_sched); | |
191 | ||
9b1d82fa PM |
192 | /* |
193 | * Helper function for call_rcu() and call_rcu_bh(). | |
194 | */ | |
195 | static void __call_rcu(struct rcu_head *head, | |
b6a4ae76 | 196 | rcu_callback_t func, |
9b1d82fa PM |
197 | struct rcu_ctrlblk *rcp) |
198 | { | |
199 | unsigned long flags; | |
200 | ||
551d55a9 | 201 | debug_rcu_head_queue(head); |
9b1d82fa PM |
202 | head->func = func; |
203 | head->next = NULL; | |
4ce5b903 | 204 | |
9b1d82fa PM |
205 | local_irq_save(flags); |
206 | *rcp->curtail = head; | |
207 | rcp->curtail = &head->next; | |
208 | local_irq_restore(flags); | |
5f6130fa LJ |
209 | |
210 | if (unlikely(is_idle_task(current))) { | |
211 | /* force scheduling for rcu_sched_qs() */ | |
212 | resched_cpu(0); | |
213 | } | |
9b1d82fa PM |
214 | } |
215 | ||
216 | /* | |
a57eb940 | 217 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
9b1d82fa PM |
218 | * period. But since we have but one CPU, that would be after any |
219 | * quiescent state. | |
220 | */ | |
b6a4ae76 | 221 | void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) |
9b1d82fa | 222 | { |
99652b54 | 223 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
9b1d82fa | 224 | } |
a57eb940 | 225 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
9b1d82fa PM |
226 | |
227 | /* | |
228 | * Post an RCU bottom-half callback to be invoked after any subsequent | |
229 | * quiescent state. | |
230 | */ | |
b6a4ae76 | 231 | void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) |
9b1d82fa PM |
232 | { |
233 | __call_rcu(head, func, &rcu_bh_ctrlblk); | |
234 | } | |
235 | EXPORT_SYMBOL_GPL(call_rcu_bh); | |
9dc5ad32 | 236 | |
aa23c6fb | 237 | void __init rcu_init(void) |
9dc5ad32 PM |
238 | { |
239 | open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); | |
aa23c6fb | 240 | rcu_early_boot_tests(); |
9dc5ad32 | 241 | } |