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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 | /* 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 | |
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(). |
98 | * Also disable irqs to avoid confusion due to interrupt handlers |
99 | * invoking call_rcu(). |
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); |
113 | |
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 | { |
124 | if (rcu_qsctr_help(&rcu_sched_ctrlblk) + |
125 | rcu_qsctr_help(&rcu_bh_ctrlblk)) |
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); |
151 | rcu_preempt_check_callbacks(); |
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 | { |
160 | struct rcu_head *next, *list; |
161 | unsigned long flags; |
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; |
174 | rcu_preempt_remove_callbacks(rcp); |
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); |
182 | debug_rcu_head_unqueue(list); |
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 | { |
193 | __rcu_process_callbacks(&rcu_sched_ctrlblk); |
194 | __rcu_process_callbacks(&rcu_bh_ctrlblk); |
195 | rcu_preempt_process_callbacks(); |
196 | } |
197 | |
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 | * |
208 | * But we want to make this a static inline later. The cond_resched() |
209 | * currently makes this problematic. |
210 | */ |
211 | void synchronize_sched(void) |
212 | { |
213 | cond_resched(); |
214 | } |
215 | EXPORT_SYMBOL_GPL(synchronize_sched); |
216 | |
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 | |
226 | debug_rcu_head_queue(head); |
227 | head->func = func; |
228 | head->next = NULL; |
229 | |
230 | local_irq_save(flags); |
231 | *rcp->curtail = head; |
232 | rcp->curtail = &head->next; |
233 | local_irq_restore(flags); |
234 | } |
235 | |
236 | /* |
237 | * Post an RCU callback to be invoked after the end of an RCU-sched grace |
238 | * period. But since we have but one CPU, that would be after any |
239 | * quiescent state. |
240 | */ |
241 | void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
242 | { |
243 | __call_rcu(head, func, &rcu_sched_ctrlblk); |
244 | } |
245 | EXPORT_SYMBOL_GPL(call_rcu_sched); |
246 | |
247 | /* |
248 | * Post an RCU bottom-half callback to be invoked after any subsequent |
249 | * quiescent state. |
250 | */ |
251 | void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) |
252 | { |
253 | __call_rcu(head, func, &rcu_bh_ctrlblk); |
254 | } |
255 | EXPORT_SYMBOL_GPL(call_rcu_bh); |
256 | |
257 | void rcu_barrier_bh(void) |
258 | { |
259 | struct rcu_synchronize rcu; |
260 | |
261 | init_rcu_head_on_stack(&rcu.head); |
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); |
267 | destroy_rcu_head_on_stack(&rcu.head); |
268 | } |
269 | EXPORT_SYMBOL_GPL(rcu_barrier_bh); |
270 | |
271 | void rcu_barrier_sched(void) |
272 | { |
273 | struct rcu_synchronize rcu; |
274 | |
275 | init_rcu_head_on_stack(&rcu.head); |
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); |
281 | destroy_rcu_head_on_stack(&rcu.head); |
282 | } |
283 | EXPORT_SYMBOL_GPL(rcu_barrier_sched); |
284 | |
285 | void __init rcu_init(void) |
286 | { |
287 | open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); |
288 | } |
289 |
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