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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 | ||
b2c0710c PM |
62 | /* Controls for rcu_cbs() kthread, replacing RCU_SOFTIRQ used previously. */ |
63 | static struct task_struct *rcu_cbs_task; | |
64 | static DECLARE_WAIT_QUEUE_HEAD(rcu_cbs_wq); | |
65 | static unsigned long have_rcu_cbs; | |
66 | static void invoke_rcu_cbs(void); | |
67 | ||
a57eb940 | 68 | /* Forward declarations for rcutiny_plugin.h. */ |
b2c0710c PM |
69 | static void rcu_process_callbacks(struct rcu_ctrlblk *rcp); |
70 | static int rcu_cbs(void *arg); | |
a57eb940 PM |
71 | static void __call_rcu(struct rcu_head *head, |
72 | void (*func)(struct rcu_head *rcu), | |
73 | struct rcu_ctrlblk *rcp); | |
74 | ||
75 | #include "rcutiny_plugin.h" | |
76 | ||
9b1d82fa PM |
77 | #ifdef CONFIG_NO_HZ |
78 | ||
79 | static long rcu_dynticks_nesting = 1; | |
80 | ||
81 | /* | |
82 | * Enter dynticks-idle mode, which is an extended quiescent state | |
83 | * if we have fully entered that mode (i.e., if the new value of | |
84 | * dynticks_nesting is zero). | |
85 | */ | |
86 | void rcu_enter_nohz(void) | |
87 | { | |
88 | if (--rcu_dynticks_nesting == 0) | |
89 | rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ | |
90 | } | |
91 | ||
92 | /* | |
93 | * Exit dynticks-idle mode, so that we are no longer in an extended | |
94 | * quiescent state. | |
95 | */ | |
96 | void rcu_exit_nohz(void) | |
97 | { | |
98 | rcu_dynticks_nesting++; | |
99 | } | |
100 | ||
101 | #endif /* #ifdef CONFIG_NO_HZ */ | |
102 | ||
103 | /* | |
104 | * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc(). | |
4ce5b903 IM |
105 | * Also disable irqs to avoid confusion due to interrupt handlers |
106 | * invoking call_rcu(). | |
9b1d82fa PM |
107 | */ |
108 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) | |
109 | { | |
110 | unsigned long flags; | |
111 | ||
112 | local_irq_save(flags); | |
113 | if (rcp->rcucblist != NULL && | |
114 | rcp->donetail != rcp->curtail) { | |
115 | rcp->donetail = rcp->curtail; | |
116 | local_irq_restore(flags); | |
117 | return 1; | |
118 | } | |
119 | local_irq_restore(flags); | |
4ce5b903 | 120 | |
9b1d82fa PM |
121 | return 0; |
122 | } | |
123 | ||
124 | /* | |
125 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we | |
126 | * are at it, given that any rcu quiescent state is also an rcu_bh | |
127 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. | |
128 | */ | |
129 | void rcu_sched_qs(int cpu) | |
130 | { | |
99652b54 PM |
131 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
132 | rcu_qsctr_help(&rcu_bh_ctrlblk)) | |
b2c0710c | 133 | invoke_rcu_cbs(); |
9b1d82fa PM |
134 | } |
135 | ||
136 | /* | |
137 | * Record an rcu_bh quiescent state. | |
138 | */ | |
139 | void rcu_bh_qs(int cpu) | |
140 | { | |
141 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) | |
b2c0710c | 142 | invoke_rcu_cbs(); |
9b1d82fa PM |
143 | } |
144 | ||
145 | /* | |
146 | * Check to see if the scheduling-clock interrupt came from an extended | |
147 | * quiescent state, and, if so, tell RCU about it. | |
148 | */ | |
149 | void rcu_check_callbacks(int cpu, int user) | |
150 | { | |
151 | if (user || | |
152 | (idle_cpu(cpu) && | |
153 | !in_softirq() && | |
154 | hardirq_count() <= (1 << HARDIRQ_SHIFT))) | |
155 | rcu_sched_qs(cpu); | |
156 | else if (!in_softirq()) | |
157 | rcu_bh_qs(cpu); | |
a57eb940 | 158 | rcu_preempt_check_callbacks(); |
9b1d82fa PM |
159 | } |
160 | ||
161 | /* | |
b2c0710c PM |
162 | * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure |
163 | * whose grace period has elapsed. | |
9b1d82fa | 164 | */ |
b2c0710c | 165 | static void rcu_process_callbacks(struct rcu_ctrlblk *rcp) |
9b1d82fa | 166 | { |
9b1d82fa | 167 | struct rcu_head *next, *list; |
4ce5b903 | 168 | unsigned long flags; |
9b1d82fa PM |
169 | |
170 | /* If no RCU callbacks ready to invoke, just return. */ | |
171 | if (&rcp->rcucblist == rcp->donetail) | |
172 | return; | |
173 | ||
174 | /* Move the ready-to-invoke callbacks to a local list. */ | |
175 | local_irq_save(flags); | |
176 | list = rcp->rcucblist; | |
177 | rcp->rcucblist = *rcp->donetail; | |
178 | *rcp->donetail = NULL; | |
179 | if (rcp->curtail == rcp->donetail) | |
180 | rcp->curtail = &rcp->rcucblist; | |
a57eb940 | 181 | rcu_preempt_remove_callbacks(rcp); |
9b1d82fa PM |
182 | rcp->donetail = &rcp->rcucblist; |
183 | local_irq_restore(flags); | |
184 | ||
185 | /* Invoke the callbacks on the local list. */ | |
186 | while (list) { | |
187 | next = list->next; | |
188 | prefetch(next); | |
551d55a9 | 189 | debug_rcu_head_unqueue(list); |
b2c0710c | 190 | local_bh_disable(); |
9b1d82fa | 191 | list->func(list); |
b2c0710c | 192 | local_bh_enable(); |
9b1d82fa PM |
193 | list = next; |
194 | } | |
195 | } | |
196 | ||
197 | /* | |
b2c0710c PM |
198 | * This kthread invokes RCU callbacks whose grace periods have |
199 | * elapsed. It is awakened as needed, and takes the place of the | |
200 | * RCU_SOFTIRQ that was used previously for this purpose. | |
201 | * This is a kthread, but it is never stopped, at least not until | |
202 | * the system goes down. | |
203 | */ | |
204 | static int rcu_cbs(void *arg) | |
205 | { | |
206 | unsigned long work; | |
207 | unsigned long flags; | |
208 | ||
209 | for (;;) { | |
210 | wait_event(rcu_cbs_wq, have_rcu_cbs != 0); | |
211 | local_irq_save(flags); | |
212 | work = have_rcu_cbs; | |
213 | have_rcu_cbs = 0; | |
214 | local_irq_restore(flags); | |
215 | if (work) { | |
216 | rcu_process_callbacks(&rcu_sched_ctrlblk); | |
217 | rcu_process_callbacks(&rcu_bh_ctrlblk); | |
218 | rcu_preempt_process_callbacks(); | |
219 | } | |
220 | } | |
221 | ||
222 | return 0; /* Not reached, but needed to shut gcc up. */ | |
223 | } | |
224 | ||
225 | /* | |
226 | * Wake up rcu_cbs() to process callbacks now eligible for invocation. | |
9b1d82fa | 227 | */ |
b2c0710c | 228 | static void invoke_rcu_cbs(void) |
9b1d82fa | 229 | { |
b2c0710c PM |
230 | unsigned long flags; |
231 | ||
232 | local_irq_save(flags); | |
233 | have_rcu_cbs = 1; | |
234 | wake_up(&rcu_cbs_wq); | |
235 | local_irq_restore(flags); | |
9b1d82fa PM |
236 | } |
237 | ||
9b1d82fa PM |
238 | /* |
239 | * Wait for a grace period to elapse. But it is illegal to invoke | |
240 | * synchronize_sched() from within an RCU read-side critical section. | |
241 | * Therefore, any legal call to synchronize_sched() is a quiescent | |
242 | * state, and so on a UP system, synchronize_sched() need do nothing. | |
243 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the | |
244 | * benefits of doing might_sleep() to reduce latency.) | |
245 | * | |
246 | * Cool, huh? (Due to Josh Triplett.) | |
247 | * | |
da848c47 PM |
248 | * But we want to make this a static inline later. The cond_resched() |
249 | * currently makes this problematic. | |
9b1d82fa PM |
250 | */ |
251 | void synchronize_sched(void) | |
252 | { | |
253 | cond_resched(); | |
254 | } | |
255 | EXPORT_SYMBOL_GPL(synchronize_sched); | |
256 | ||
9b1d82fa PM |
257 | /* |
258 | * Helper function for call_rcu() and call_rcu_bh(). | |
259 | */ | |
260 | static void __call_rcu(struct rcu_head *head, | |
261 | void (*func)(struct rcu_head *rcu), | |
262 | struct rcu_ctrlblk *rcp) | |
263 | { | |
264 | unsigned long flags; | |
265 | ||
551d55a9 | 266 | debug_rcu_head_queue(head); |
9b1d82fa PM |
267 | head->func = func; |
268 | head->next = NULL; | |
4ce5b903 | 269 | |
9b1d82fa PM |
270 | local_irq_save(flags); |
271 | *rcp->curtail = head; | |
272 | rcp->curtail = &head->next; | |
273 | local_irq_restore(flags); | |
274 | } | |
275 | ||
276 | /* | |
a57eb940 | 277 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
9b1d82fa PM |
278 | * period. But since we have but one CPU, that would be after any |
279 | * quiescent state. | |
280 | */ | |
a57eb940 | 281 | void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
9b1d82fa | 282 | { |
99652b54 | 283 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
9b1d82fa | 284 | } |
a57eb940 | 285 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
9b1d82fa PM |
286 | |
287 | /* | |
288 | * Post an RCU bottom-half callback to be invoked after any subsequent | |
289 | * quiescent state. | |
290 | */ | |
4ce5b903 | 291 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
9b1d82fa PM |
292 | { |
293 | __call_rcu(head, func, &rcu_bh_ctrlblk); | |
294 | } | |
295 | EXPORT_SYMBOL_GPL(call_rcu_bh); | |
296 | ||
9b1d82fa PM |
297 | void rcu_barrier_bh(void) |
298 | { | |
299 | struct rcu_synchronize rcu; | |
300 | ||
72d5a9f7 | 301 | init_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
302 | init_completion(&rcu.completion); |
303 | /* Will wake me after RCU finished. */ | |
304 | call_rcu_bh(&rcu.head, wakeme_after_rcu); | |
305 | /* Wait for it. */ | |
306 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 307 | destroy_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
308 | } |
309 | EXPORT_SYMBOL_GPL(rcu_barrier_bh); | |
310 | ||
311 | void rcu_barrier_sched(void) | |
312 | { | |
313 | struct rcu_synchronize rcu; | |
314 | ||
72d5a9f7 | 315 | init_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
316 | init_completion(&rcu.completion); |
317 | /* Will wake me after RCU finished. */ | |
318 | call_rcu_sched(&rcu.head, wakeme_after_rcu); | |
319 | /* Wait for it. */ | |
320 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 321 | destroy_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
322 | } |
323 | EXPORT_SYMBOL_GPL(rcu_barrier_sched); | |
324 | ||
b2c0710c PM |
325 | /* |
326 | * Spawn the kthread that invokes RCU callbacks. | |
327 | */ | |
328 | static int __init rcu_spawn_kthreads(void) | |
9b1d82fa | 329 | { |
b2c0710c PM |
330 | rcu_cbs_task = kthread_run(rcu_cbs, NULL, "rcu_cbs"); |
331 | return 0; | |
9b1d82fa | 332 | } |
b2c0710c | 333 | early_initcall(rcu_spawn_kthreads); |