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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 | 38 | |
24278d14 PM |
39 | /* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */ |
40 | static struct task_struct *rcu_kthread_task; | |
41 | static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq); | |
42 | static unsigned long have_rcu_kthread_work; | |
b2c0710c | 43 | |
a57eb940 | 44 | /* Forward declarations for rcutiny_plugin.h. */ |
24278d14 | 45 | struct rcu_ctrlblk; |
b554d7de | 46 | static void invoke_rcu_kthread(void); |
b2c0710c | 47 | static void rcu_process_callbacks(struct rcu_ctrlblk *rcp); |
24278d14 | 48 | static int rcu_kthread(void *arg); |
a57eb940 PM |
49 | static void __call_rcu(struct rcu_head *head, |
50 | void (*func)(struct rcu_head *rcu), | |
51 | struct rcu_ctrlblk *rcp); | |
52 | ||
53 | #include "rcutiny_plugin.h" | |
54 | ||
9b1d82fa PM |
55 | #ifdef CONFIG_NO_HZ |
56 | ||
57 | static long rcu_dynticks_nesting = 1; | |
58 | ||
59 | /* | |
60 | * Enter dynticks-idle mode, which is an extended quiescent state | |
61 | * if we have fully entered that mode (i.e., if the new value of | |
62 | * dynticks_nesting is zero). | |
63 | */ | |
64 | void rcu_enter_nohz(void) | |
65 | { | |
66 | if (--rcu_dynticks_nesting == 0) | |
67 | rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ | |
68 | } | |
69 | ||
70 | /* | |
71 | * Exit dynticks-idle mode, so that we are no longer in an extended | |
72 | * quiescent state. | |
73 | */ | |
74 | void rcu_exit_nohz(void) | |
75 | { | |
76 | rcu_dynticks_nesting++; | |
77 | } | |
78 | ||
79 | #endif /* #ifdef CONFIG_NO_HZ */ | |
80 | ||
81 | /* | |
b554d7de ED |
82 | * Helper function for rcu_sched_qs() and rcu_bh_qs(). |
83 | * Also irqs are disabled to avoid confusion due to interrupt handlers | |
4ce5b903 | 84 | * invoking call_rcu(). |
9b1d82fa PM |
85 | */ |
86 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) | |
87 | { | |
9b1d82fa PM |
88 | if (rcp->rcucblist != NULL && |
89 | rcp->donetail != rcp->curtail) { | |
90 | rcp->donetail = rcp->curtail; | |
9b1d82fa PM |
91 | return 1; |
92 | } | |
4ce5b903 | 93 | |
9b1d82fa PM |
94 | return 0; |
95 | } | |
96 | ||
b554d7de ED |
97 | /* |
98 | * Wake up rcu_kthread() to process callbacks now eligible for invocation | |
99 | * or to boost readers. | |
100 | */ | |
101 | static void invoke_rcu_kthread(void) | |
102 | { | |
103 | have_rcu_kthread_work = 1; | |
104 | wake_up(&rcu_kthread_wq); | |
105 | } | |
106 | ||
9b1d82fa PM |
107 | /* |
108 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we | |
109 | * are at it, given that any rcu quiescent state is also an rcu_bh | |
110 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. | |
111 | */ | |
112 | void rcu_sched_qs(int cpu) | |
113 | { | |
b554d7de ED |
114 | unsigned long flags; |
115 | ||
116 | local_irq_save(flags); | |
99652b54 PM |
117 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
118 | rcu_qsctr_help(&rcu_bh_ctrlblk)) | |
24278d14 | 119 | invoke_rcu_kthread(); |
b554d7de | 120 | local_irq_restore(flags); |
9b1d82fa PM |
121 | } |
122 | ||
123 | /* | |
124 | * Record an rcu_bh quiescent state. | |
125 | */ | |
126 | void rcu_bh_qs(int cpu) | |
127 | { | |
b554d7de ED |
128 | unsigned long flags; |
129 | ||
130 | local_irq_save(flags); | |
9b1d82fa | 131 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) |
24278d14 | 132 | invoke_rcu_kthread(); |
b554d7de | 133 | local_irq_restore(flags); |
9b1d82fa PM |
134 | } |
135 | ||
136 | /* | |
137 | * Check to see if the scheduling-clock interrupt came from an extended | |
138 | * quiescent state, and, if so, tell RCU about it. | |
139 | */ | |
140 | void rcu_check_callbacks(int cpu, int user) | |
141 | { | |
142 | if (user || | |
143 | (idle_cpu(cpu) && | |
144 | !in_softirq() && | |
145 | hardirq_count() <= (1 << HARDIRQ_SHIFT))) | |
146 | rcu_sched_qs(cpu); | |
147 | else if (!in_softirq()) | |
148 | rcu_bh_qs(cpu); | |
a57eb940 | 149 | rcu_preempt_check_callbacks(); |
9b1d82fa PM |
150 | } |
151 | ||
152 | /* | |
b2c0710c PM |
153 | * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure |
154 | * whose grace period has elapsed. | |
9b1d82fa | 155 | */ |
b2c0710c | 156 | static void rcu_process_callbacks(struct rcu_ctrlblk *rcp) |
9b1d82fa | 157 | { |
9b1d82fa | 158 | struct rcu_head *next, *list; |
4ce5b903 | 159 | unsigned long flags; |
9e571a82 | 160 | RCU_TRACE(int cb_count = 0); |
9b1d82fa PM |
161 | |
162 | /* If no RCU callbacks ready to invoke, just return. */ | |
163 | if (&rcp->rcucblist == rcp->donetail) | |
164 | return; | |
165 | ||
166 | /* Move the ready-to-invoke callbacks to a local list. */ | |
167 | local_irq_save(flags); | |
168 | list = rcp->rcucblist; | |
169 | rcp->rcucblist = *rcp->donetail; | |
170 | *rcp->donetail = NULL; | |
171 | if (rcp->curtail == rcp->donetail) | |
172 | rcp->curtail = &rcp->rcucblist; | |
a57eb940 | 173 | rcu_preempt_remove_callbacks(rcp); |
9b1d82fa PM |
174 | rcp->donetail = &rcp->rcucblist; |
175 | local_irq_restore(flags); | |
176 | ||
177 | /* Invoke the callbacks on the local list. */ | |
178 | while (list) { | |
179 | next = list->next; | |
180 | prefetch(next); | |
551d55a9 | 181 | debug_rcu_head_unqueue(list); |
b2c0710c | 182 | local_bh_disable(); |
9ab1544e | 183 | __rcu_reclaim(list); |
b2c0710c | 184 | local_bh_enable(); |
9b1d82fa | 185 | list = next; |
9e571a82 | 186 | RCU_TRACE(cb_count++); |
9b1d82fa | 187 | } |
9e571a82 | 188 | RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); |
9b1d82fa PM |
189 | } |
190 | ||
191 | /* | |
b2c0710c PM |
192 | * This kthread invokes RCU callbacks whose grace periods have |
193 | * elapsed. It is awakened as needed, and takes the place of the | |
194 | * RCU_SOFTIRQ that was used previously for this purpose. | |
195 | * This is a kthread, but it is never stopped, at least not until | |
196 | * the system goes down. | |
197 | */ | |
24278d14 | 198 | static int rcu_kthread(void *arg) |
b2c0710c PM |
199 | { |
200 | unsigned long work; | |
24278d14 | 201 | unsigned long morework; |
b2c0710c PM |
202 | unsigned long flags; |
203 | ||
204 | for (;;) { | |
b24efdfd PM |
205 | wait_event_interruptible(rcu_kthread_wq, |
206 | have_rcu_kthread_work != 0); | |
24278d14 | 207 | morework = rcu_boost(); |
b2c0710c | 208 | local_irq_save(flags); |
24278d14 PM |
209 | work = have_rcu_kthread_work; |
210 | have_rcu_kthread_work = morework; | |
b2c0710c PM |
211 | local_irq_restore(flags); |
212 | if (work) { | |
213 | rcu_process_callbacks(&rcu_sched_ctrlblk); | |
214 | rcu_process_callbacks(&rcu_bh_ctrlblk); | |
215 | rcu_preempt_process_callbacks(); | |
216 | } | |
24278d14 | 217 | schedule_timeout_interruptible(1); /* Leave CPU for others. */ |
b2c0710c PM |
218 | } |
219 | ||
220 | return 0; /* Not reached, but needed to shut gcc up. */ | |
221 | } | |
222 | ||
9b1d82fa PM |
223 | /* |
224 | * Wait for a grace period to elapse. But it is illegal to invoke | |
225 | * synchronize_sched() from within an RCU read-side critical section. | |
226 | * Therefore, any legal call to synchronize_sched() is a quiescent | |
227 | * state, and so on a UP system, synchronize_sched() need do nothing. | |
228 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the | |
229 | * benefits of doing might_sleep() to reduce latency.) | |
230 | * | |
231 | * Cool, huh? (Due to Josh Triplett.) | |
232 | * | |
da848c47 PM |
233 | * But we want to make this a static inline later. The cond_resched() |
234 | * currently makes this problematic. | |
9b1d82fa PM |
235 | */ |
236 | void synchronize_sched(void) | |
237 | { | |
238 | cond_resched(); | |
239 | } | |
240 | EXPORT_SYMBOL_GPL(synchronize_sched); | |
241 | ||
9b1d82fa PM |
242 | /* |
243 | * Helper function for call_rcu() and call_rcu_bh(). | |
244 | */ | |
245 | static 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 | ||
551d55a9 | 251 | debug_rcu_head_queue(head); |
9b1d82fa PM |
252 | head->func = func; |
253 | head->next = NULL; | |
4ce5b903 | 254 | |
9b1d82fa PM |
255 | local_irq_save(flags); |
256 | *rcp->curtail = head; | |
257 | rcp->curtail = &head->next; | |
9e571a82 | 258 | RCU_TRACE(rcp->qlen++); |
9b1d82fa PM |
259 | local_irq_restore(flags); |
260 | } | |
261 | ||
262 | /* | |
a57eb940 | 263 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
9b1d82fa PM |
264 | * period. But since we have but one CPU, that would be after any |
265 | * quiescent state. | |
266 | */ | |
a57eb940 | 267 | void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
9b1d82fa | 268 | { |
99652b54 | 269 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
9b1d82fa | 270 | } |
a57eb940 | 271 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
9b1d82fa PM |
272 | |
273 | /* | |
274 | * Post an RCU bottom-half callback to be invoked after any subsequent | |
275 | * quiescent state. | |
276 | */ | |
4ce5b903 | 277 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
9b1d82fa PM |
278 | { |
279 | __call_rcu(head, func, &rcu_bh_ctrlblk); | |
280 | } | |
281 | EXPORT_SYMBOL_GPL(call_rcu_bh); | |
282 | ||
9b1d82fa PM |
283 | void rcu_barrier_bh(void) |
284 | { | |
285 | struct rcu_synchronize rcu; | |
286 | ||
72d5a9f7 | 287 | init_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
288 | init_completion(&rcu.completion); |
289 | /* Will wake me after RCU finished. */ | |
290 | call_rcu_bh(&rcu.head, wakeme_after_rcu); | |
291 | /* Wait for it. */ | |
292 | wait_for_completion(&rcu.completion); | |
72d5a9f7 | 293 | destroy_rcu_head_on_stack(&rcu.head); |
9b1d82fa PM |
294 | } |
295 | EXPORT_SYMBOL_GPL(rcu_barrier_bh); | |
296 | ||
297 | void rcu_barrier_sched(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_sched(&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_sched); | |
310 | ||
b2c0710c PM |
311 | /* |
312 | * Spawn the kthread that invokes RCU callbacks. | |
313 | */ | |
314 | static int __init rcu_spawn_kthreads(void) | |
9b1d82fa | 315 | { |
24278d14 PM |
316 | struct sched_param sp; |
317 | ||
318 | rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread"); | |
319 | sp.sched_priority = RCU_BOOST_PRIO; | |
320 | sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp); | |
b2c0710c | 321 | return 0; |
9b1d82fa | 322 | } |
b2c0710c | 323 | early_initcall(rcu_spawn_kthreads); |