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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 | |
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 - | |
4ce5b903 | 23 | * Documentation/RCU |
9b1d82fa | 24 | */ |
9b1d82fa | 25 | #include <linux/moduleparam.h> |
4ce5b903 IM |
26 | #include <linux/completion.h> |
27 | #include <linux/interrupt.h> | |
9b1d82fa | 28 | #include <linux/notifier.h> |
4ce5b903 IM |
29 | #include <linux/rcupdate.h> |
30 | #include <linux/kernel.h> | |
31 | #include <linux/module.h> | |
9b1d82fa | 32 | #include <linux/mutex.h> |
4ce5b903 IM |
33 | #include <linux/sched.h> |
34 | #include <linux/types.h> | |
35 | #include <linux/init.h> | |
9b1d82fa | 36 | #include <linux/time.h> |
4ce5b903 | 37 | #include <linux/cpu.h> |
9b1d82fa PM |
38 | |
39 | /* Global control variables for rcupdate callback mechanism. */ | |
40 | struct rcu_ctrlblk { | |
41 | struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ | |
42 | struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ | |
43 | struct rcu_head **curtail; /* ->next pointer of last CB. */ | |
44 | }; | |
45 | ||
46 | /* Definition for rcupdate control block. */ | |
99652b54 PM |
47 | static struct rcu_ctrlblk rcu_sched_ctrlblk = { |
48 | .donetail = &rcu_sched_ctrlblk.rcucblist, | |
49 | .curtail = &rcu_sched_ctrlblk.rcucblist, | |
9b1d82fa | 50 | }; |
4ce5b903 | 51 | |
9b1d82fa | 52 | static struct rcu_ctrlblk rcu_bh_ctrlblk = { |
4ce5b903 IM |
53 | .donetail = &rcu_bh_ctrlblk.rcucblist, |
54 | .curtail = &rcu_bh_ctrlblk.rcucblist, | |
9b1d82fa PM |
55 | }; |
56 | ||
bbad9379 PM |
57 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
58 | int rcu_scheduler_active __read_mostly; | |
59 | EXPORT_SYMBOL_GPL(rcu_scheduler_active); | |
60 | #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */ | |
61 | ||
a57eb940 PM |
62 | /* Forward declarations for rcutiny_plugin.h. */ |
63 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); | |
64 | static void __call_rcu(struct rcu_head *head, | |
65 | void (*func)(struct rcu_head *rcu), | |
66 | struct rcu_ctrlblk *rcp); | |
67 | ||
68 | #include "rcutiny_plugin.h" | |
69 | ||
9b1d82fa PM |
70 | #ifdef CONFIG_NO_HZ |
71 | ||
72 | static long rcu_dynticks_nesting = 1; | |
73 | ||
74 | /* | |
75 | * Enter dynticks-idle mode, which is an extended quiescent state | |
76 | * if we have fully entered that mode (i.e., if the new value of | |
77 | * dynticks_nesting is zero). | |
78 | */ | |
79 | void rcu_enter_nohz(void) | |
80 | { | |
81 | if (--rcu_dynticks_nesting == 0) | |
82 | rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ | |
83 | } | |
84 | ||
85 | /* | |
86 | * Exit dynticks-idle mode, so that we are no longer in an extended | |
87 | * quiescent state. | |
88 | */ | |
89 | void rcu_exit_nohz(void) | |
90 | { | |
91 | rcu_dynticks_nesting++; | |
92 | } | |
93 | ||
94 | #endif /* #ifdef CONFIG_NO_HZ */ | |
95 | ||
96 | /* | |
97 | * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc(). | |
4ce5b903 IM |
98 | * Also disable irqs to avoid confusion due to interrupt handlers |
99 | * invoking call_rcu(). | |
9b1d82fa PM |
100 | */ |
101 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) | |
102 | { | |
103 | unsigned long flags; | |
104 | ||
105 | local_irq_save(flags); | |
106 | if (rcp->rcucblist != NULL && | |
107 | rcp->donetail != rcp->curtail) { | |
108 | rcp->donetail = rcp->curtail; | |
109 | local_irq_restore(flags); | |
110 | return 1; | |
111 | } | |
112 | local_irq_restore(flags); | |
4ce5b903 | 113 | |
9b1d82fa PM |
114 | return 0; |
115 | } | |
116 | ||
117 | /* | |
118 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we | |
119 | * are at it, given that any rcu quiescent state is also an rcu_bh | |
120 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. | |
121 | */ | |
122 | void rcu_sched_qs(int cpu) | |
123 | { | |
99652b54 PM |
124 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
125 | rcu_qsctr_help(&rcu_bh_ctrlblk)) | |
9b1d82fa PM |
126 | raise_softirq(RCU_SOFTIRQ); |
127 | } | |
128 | ||
129 | /* | |
130 | * Record an rcu_bh quiescent state. | |
131 | */ | |
132 | void rcu_bh_qs(int cpu) | |
133 | { | |
134 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) | |
135 | raise_softirq(RCU_SOFTIRQ); | |
136 | } | |
137 | ||
138 | /* | |
139 | * Check to see if the scheduling-clock interrupt came from an extended | |
140 | * quiescent state, and, if so, tell RCU about it. | |
141 | */ | |
142 | void rcu_check_callbacks(int cpu, int user) | |
143 | { | |
144 | if (user || | |
145 | (idle_cpu(cpu) && | |
146 | !in_softirq() && | |
147 | hardirq_count() <= (1 << HARDIRQ_SHIFT))) | |
148 | rcu_sched_qs(cpu); | |
149 | else if (!in_softirq()) | |
150 | rcu_bh_qs(cpu); | |
a57eb940 | 151 | rcu_preempt_check_callbacks(); |
9b1d82fa PM |
152 | } |
153 | ||
154 | /* | |
155 | * Helper function for rcu_process_callbacks() that operates on the | |
156 | * specified rcu_ctrlkblk structure. | |
157 | */ | |
158 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) | |
159 | { | |
9b1d82fa | 160 | struct rcu_head *next, *list; |
4ce5b903 | 161 | unsigned long flags; |
9b1d82fa PM |
162 | |
163 | /* If no RCU callbacks ready to invoke, just return. */ | |
164 | if (&rcp->rcucblist == rcp->donetail) | |
165 | return; | |
166 | ||
167 | /* Move the ready-to-invoke callbacks to a local list. */ | |
168 | local_irq_save(flags); | |
169 | list = rcp->rcucblist; | |
170 | rcp->rcucblist = *rcp->donetail; | |
171 | *rcp->donetail = NULL; | |
172 | if (rcp->curtail == rcp->donetail) | |
173 | rcp->curtail = &rcp->rcucblist; | |
a57eb940 | 174 | rcu_preempt_remove_callbacks(rcp); |
9b1d82fa PM |
175 | rcp->donetail = &rcp->rcucblist; |
176 | local_irq_restore(flags); | |
177 | ||
178 | /* Invoke the callbacks on the local list. */ | |
179 | while (list) { | |
180 | next = list->next; | |
181 | prefetch(next); | |
551d55a9 | 182 | debug_rcu_head_unqueue(list); |
9b1d82fa PM |
183 | list->func(list); |
184 | list = next; | |
185 | } | |
186 | } | |
187 | ||
188 | /* | |
189 | * Invoke any callbacks whose grace period has completed. | |
190 | */ | |
191 | static void rcu_process_callbacks(struct softirq_action *unused) | |
192 | { | |
99652b54 | 193 | __rcu_process_callbacks(&rcu_sched_ctrlblk); |
9b1d82fa | 194 | __rcu_process_callbacks(&rcu_bh_ctrlblk); |
a57eb940 | 195 | rcu_preempt_process_callbacks(); |
9b1d82fa PM |
196 | } |
197 | ||
9b1d82fa PM |
198 | /* |
199 | * Wait for a grace period to elapse. But it is illegal to invoke | |
200 | * synchronize_sched() from within an RCU read-side critical section. | |
201 | * Therefore, any legal call to synchronize_sched() is a quiescent | |
202 | * state, and so on a UP system, synchronize_sched() need do nothing. | |
203 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the | |
204 | * benefits of doing might_sleep() to reduce latency.) | |
205 | * | |
206 | * Cool, huh? (Due to Josh Triplett.) | |
207 | * | |
da848c47 PM |
208 | * But we want to make this a static inline later. The cond_resched() |
209 | * currently makes this problematic. | |
9b1d82fa PM |
210 | */ |
211 | void synchronize_sched(void) | |
212 | { | |
213 | cond_resched(); | |
214 | } | |
215 | EXPORT_SYMBOL_GPL(synchronize_sched); | |
216 | ||
9b1d82fa PM |
217 | /* |
218 | * Helper function for call_rcu() and call_rcu_bh(). | |
219 | */ | |
220 | static void __call_rcu(struct rcu_head *head, | |
221 | void (*func)(struct rcu_head *rcu), | |
222 | struct rcu_ctrlblk *rcp) | |
223 | { | |
224 | unsigned long flags; | |
225 | ||
551d55a9 | 226 | debug_rcu_head_queue(head); |
9b1d82fa PM |
227 | head->func = func; |
228 | head->next = NULL; | |
4ce5b903 | 229 | |
9b1d82fa PM |
230 | local_irq_save(flags); |
231 | *rcp->curtail = head; | |
232 | rcp->curtail = &head->next; | |
233 | local_irq_restore(flags); | |
234 | } | |
235 | ||
236 | /* | |
a57eb940 | 237 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
9b1d82fa PM |
238 | * period. But since we have but one CPU, that would be after any |
239 | * quiescent state. | |
240 | */ | |
a57eb940 | 241 | void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
9b1d82fa | 242 | { |
99652b54 | 243 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
9b1d82fa | 244 | } |
a57eb940 | 245 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
9b1d82fa PM |
246 | |
247 | /* | |
248 | * Post an RCU bottom-half callback to be invoked after any subsequent | |
249 | * quiescent state. | |
250 | */ | |
4ce5b903 | 251 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
9b1d82fa PM |
252 | { |
253 | __call_rcu(head, func, &rcu_bh_ctrlblk); | |
254 | } | |
255 | EXPORT_SYMBOL_GPL(call_rcu_bh); | |
256 | ||
9b1d82fa PM |
257 | void rcu_barrier_bh(void) |
258 | { | |
259 | struct rcu_synchronize rcu; | |
260 | ||
72d5a9f7 | 261 | init_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
262 | init_completion(&rcu.completion); |
263 | /* Will wake me after RCU finished. */ | |
264 | call_rcu_bh(&rcu.head, wakeme_after_rcu); | |
265 | /* Wait for it. */ | |
266 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 267 | destroy_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
268 | } |
269 | EXPORT_SYMBOL_GPL(rcu_barrier_bh); | |
270 | ||
271 | void rcu_barrier_sched(void) | |
272 | { | |
273 | struct rcu_synchronize rcu; | |
274 | ||
72d5a9f7 | 275 | init_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
276 | init_completion(&rcu.completion); |
277 | /* Will wake me after RCU finished. */ | |
278 | call_rcu_sched(&rcu.head, wakeme_after_rcu); | |
279 | /* Wait for it. */ | |
280 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 281 | destroy_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
282 | } |
283 | EXPORT_SYMBOL_GPL(rcu_barrier_sched); | |
284 | ||
9f680ab4 | 285 | void __init rcu_init(void) |
9b1d82fa PM |
286 | { |
287 | open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); | |
288 | } |