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