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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 - |
23 | * Documentation/RCU |
24 | */ |
25 | #include <linux/moduleparam.h> |
26 | #include <linux/completion.h> |
27 | #include <linux/interrupt.h> |
28 | #include <linux/notifier.h> |
29 | #include <linux/rcupdate.h> |
30 | #include <linux/kernel.h> |
31 | #include <linux/module.h> |
32 | #include <linux/mutex.h> |
33 | #include <linux/sched.h> |
34 | #include <linux/types.h> |
35 | #include <linux/init.h> |
36 | #include <linux/time.h> |
37 | #include <linux/cpu.h> |
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. */ |
47 | static struct rcu_ctrlblk rcu_sched_ctrlblk = { |
48 | .donetail = &rcu_sched_ctrlblk.rcucblist, |
49 | .curtail = &rcu_sched_ctrlblk.rcucblist, |
50 | }; |
51 | |
52 | static struct rcu_ctrlblk rcu_bh_ctrlblk = { |
53 | .donetail = &rcu_bh_ctrlblk.rcucblist, |
54 | .curtail = &rcu_bh_ctrlblk.rcucblist, |
55 | }; |
56 | |
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 | |
62 | #ifdef CONFIG_NO_HZ |
63 | |
64 | static long rcu_dynticks_nesting = 1; |
65 | |
66 | /* |
67 | * Enter dynticks-idle mode, which is an extended quiescent state |
68 | * if we have fully entered that mode (i.e., if the new value of |
69 | * dynticks_nesting is zero). |
70 | */ |
71 | void rcu_enter_nohz(void) |
72 | { |
73 | if (--rcu_dynticks_nesting == 0) |
74 | rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ |
75 | } |
76 | |
77 | /* |
78 | * Exit dynticks-idle mode, so that we are no longer in an extended |
79 | * quiescent state. |
80 | */ |
81 | void rcu_exit_nohz(void) |
82 | { |
83 | rcu_dynticks_nesting++; |
84 | } |
85 | |
86 | #endif /* #ifdef CONFIG_NO_HZ */ |
87 | |
88 | /* |
89 | * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc(). |
90 | * Also disable irqs to avoid confusion due to interrupt handlers |
91 | * invoking call_rcu(). |
92 | */ |
93 | static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) |
94 | { |
95 | unsigned long flags; |
96 | |
97 | local_irq_save(flags); |
98 | if (rcp->rcucblist != NULL && |
99 | rcp->donetail != rcp->curtail) { |
100 | rcp->donetail = rcp->curtail; |
101 | local_irq_restore(flags); |
102 | return 1; |
103 | } |
104 | local_irq_restore(flags); |
105 | |
106 | return 0; |
107 | } |
108 | |
109 | /* |
110 | * Record an rcu quiescent state. And an rcu_bh quiescent state while we |
111 | * are at it, given that any rcu quiescent state is also an rcu_bh |
112 | * quiescent state. Use "+" instead of "||" to defeat short circuiting. |
113 | */ |
114 | void rcu_sched_qs(int cpu) |
115 | { |
116 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
117 | rcu_qsctr_help(&rcu_bh_ctrlblk)) |
118 | raise_softirq(RCU_SOFTIRQ); |
119 | } |
120 | |
121 | /* |
122 | * Record an rcu_bh quiescent state. |
123 | */ |
124 | void rcu_bh_qs(int cpu) |
125 | { |
126 | if (rcu_qsctr_help(&rcu_bh_ctrlblk)) |
127 | raise_softirq(RCU_SOFTIRQ); |
128 | } |
129 | |
130 | /* |
131 | * Check to see if the scheduling-clock interrupt came from an extended |
132 | * quiescent state, and, if so, tell RCU about it. |
133 | */ |
134 | void rcu_check_callbacks(int cpu, int user) |
135 | { |
136 | if (user || |
137 | (idle_cpu(cpu) && |
138 | !in_softirq() && |
139 | hardirq_count() <= (1 << HARDIRQ_SHIFT))) |
140 | rcu_sched_qs(cpu); |
141 | else if (!in_softirq()) |
142 | rcu_bh_qs(cpu); |
143 | } |
144 | |
145 | /* |
146 | * Helper function for rcu_process_callbacks() that operates on the |
147 | * specified rcu_ctrlkblk structure. |
148 | */ |
149 | static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) |
150 | { |
151 | struct rcu_head *next, *list; |
152 | unsigned long flags; |
153 | |
154 | /* If no RCU callbacks ready to invoke, just return. */ |
155 | if (&rcp->rcucblist == rcp->donetail) |
156 | return; |
157 | |
158 | /* Move the ready-to-invoke callbacks to a local list. */ |
159 | local_irq_save(flags); |
160 | list = rcp->rcucblist; |
161 | rcp->rcucblist = *rcp->donetail; |
162 | *rcp->donetail = NULL; |
163 | if (rcp->curtail == rcp->donetail) |
164 | rcp->curtail = &rcp->rcucblist; |
165 | rcp->donetail = &rcp->rcucblist; |
166 | local_irq_restore(flags); |
167 | |
168 | /* Invoke the callbacks on the local list. */ |
169 | while (list) { |
170 | next = list->next; |
171 | prefetch(next); |
172 | debug_rcu_head_unqueue(list); |
173 | list->func(list); |
174 | list = next; |
175 | } |
176 | } |
177 | |
178 | /* |
179 | * Invoke any callbacks whose grace period has completed. |
180 | */ |
181 | static void rcu_process_callbacks(struct softirq_action *unused) |
182 | { |
183 | __rcu_process_callbacks(&rcu_sched_ctrlblk); |
184 | __rcu_process_callbacks(&rcu_bh_ctrlblk); |
185 | } |
186 | |
187 | /* |
188 | * Wait for a grace period to elapse. But it is illegal to invoke |
189 | * synchronize_sched() from within an RCU read-side critical section. |
190 | * Therefore, any legal call to synchronize_sched() is a quiescent |
191 | * state, and so on a UP system, synchronize_sched() need do nothing. |
192 | * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the |
193 | * benefits of doing might_sleep() to reduce latency.) |
194 | * |
195 | * Cool, huh? (Due to Josh Triplett.) |
196 | * |
197 | * But we want to make this a static inline later. The cond_resched() |
198 | * currently makes this problematic. |
199 | */ |
200 | void synchronize_sched(void) |
201 | { |
202 | cond_resched(); |
203 | } |
204 | EXPORT_SYMBOL_GPL(synchronize_sched); |
205 | |
206 | /* |
207 | * Helper function for call_rcu() and call_rcu_bh(). |
208 | */ |
209 | static void __call_rcu(struct rcu_head *head, |
210 | void (*func)(struct rcu_head *rcu), |
211 | struct rcu_ctrlblk *rcp) |
212 | { |
213 | unsigned long flags; |
214 | |
215 | debug_rcu_head_queue(head); |
216 | head->func = func; |
217 | head->next = NULL; |
218 | |
219 | local_irq_save(flags); |
220 | *rcp->curtail = head; |
221 | rcp->curtail = &head->next; |
222 | local_irq_restore(flags); |
223 | } |
224 | |
225 | /* |
226 | * Post an RCU callback to be invoked after the end of an RCU grace |
227 | * period. But since we have but one CPU, that would be after any |
228 | * quiescent state. |
229 | */ |
230 | void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
231 | { |
232 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
233 | } |
234 | EXPORT_SYMBOL_GPL(call_rcu); |
235 | |
236 | /* |
237 | * Post an RCU bottom-half callback to be invoked after any subsequent |
238 | * quiescent state. |
239 | */ |
240 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
241 | { |
242 | __call_rcu(head, func, &rcu_bh_ctrlblk); |
243 | } |
244 | EXPORT_SYMBOL_GPL(call_rcu_bh); |
245 | |
246 | void rcu_barrier(void) |
247 | { |
248 | struct rcu_synchronize rcu; |
249 | |
250 | init_rcu_head_on_stack(&rcu.head); |
251 | init_completion(&rcu.completion); |
252 | /* Will wake me after RCU finished. */ |
253 | call_rcu(&rcu.head, wakeme_after_rcu); |
254 | /* Wait for it. */ |
255 | wait_for_completion(&rcu.completion); |
256 | destroy_rcu_head_on_stack(&rcu.head); |
257 | } |
258 | EXPORT_SYMBOL_GPL(rcu_barrier); |
259 | |
260 | void rcu_barrier_bh(void) |
261 | { |
262 | struct rcu_synchronize rcu; |
263 | |
264 | init_rcu_head_on_stack(&rcu.head); |
265 | init_completion(&rcu.completion); |
266 | /* Will wake me after RCU finished. */ |
267 | call_rcu_bh(&rcu.head, wakeme_after_rcu); |
268 | /* Wait for it. */ |
269 | wait_for_completion(&rcu.completion); |
270 | destroy_rcu_head_on_stack(&rcu.head); |
271 | } |
272 | EXPORT_SYMBOL_GPL(rcu_barrier_bh); |
273 | |
274 | void rcu_barrier_sched(void) |
275 | { |
276 | struct rcu_synchronize rcu; |
277 | |
278 | init_rcu_head_on_stack(&rcu.head); |
279 | init_completion(&rcu.completion); |
280 | /* Will wake me after RCU finished. */ |
281 | call_rcu_sched(&rcu.head, wakeme_after_rcu); |
282 | /* Wait for it. */ |
283 | wait_for_completion(&rcu.completion); |
284 | destroy_rcu_head_on_stack(&rcu.head); |
285 | } |
286 | EXPORT_SYMBOL_GPL(rcu_barrier_sched); |
287 | |
288 | void __init rcu_init(void) |
289 | { |
290 | open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); |
291 | } |
292 | |
293 | #include "rcutiny_plugin.h" |
294 |
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