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1 | /* |
2 | * Read-Copy Update mechanism for mutual exclusion |
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, 2001 |
19 | * |
20 | * Author: Dipankar Sarma <dipankar@in.ibm.com> |
21 | * |
22 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
23 | * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. |
24 | * Papers: |
25 | * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf |
26 | * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) |
27 | * |
28 | * For detailed explanation of Read-Copy Update mechanism see - |
29 | * http://lse.sourceforge.net/locking/rcupdate.html |
30 | * |
31 | */ |
32 | |
33 | #ifndef __LINUX_RCUPDATE_H |
34 | #define __LINUX_RCUPDATE_H |
35 | |
36 | #include <linux/cache.h> |
37 | #include <linux/spinlock.h> |
38 | #include <linux/threads.h> |
39 | #include <linux/cpumask.h> |
40 | #include <linux/seqlock.h> |
41 | #include <linux/lockdep.h> |
42 | #include <linux/completion.h> |
43 | |
44 | /** |
45 | * struct rcu_head - callback structure for use with RCU |
46 | * @next: next update requests in a list |
47 | * @func: actual update function to call after the grace period. |
48 | */ |
49 | struct rcu_head { |
50 | struct rcu_head *next; |
51 | void (*func)(struct rcu_head *head); |
52 | }; |
53 | |
54 | /* Exported common interfaces */ |
55 | #ifdef CONFIG_TREE_PREEMPT_RCU |
56 | extern void synchronize_rcu(void); |
57 | #else /* #ifdef CONFIG_TREE_PREEMPT_RCU */ |
58 | #define synchronize_rcu synchronize_sched |
59 | #endif /* #else #ifdef CONFIG_TREE_PREEMPT_RCU */ |
60 | extern void synchronize_rcu_bh(void); |
61 | extern void synchronize_sched(void); |
62 | extern void rcu_barrier(void); |
63 | extern void rcu_barrier_bh(void); |
64 | extern void rcu_barrier_sched(void); |
65 | extern void synchronize_sched_expedited(void); |
66 | extern int sched_expedited_torture_stats(char *page); |
67 | |
68 | /* Internal to kernel */ |
69 | extern void rcu_init(void); |
70 | extern void rcu_scheduler_starting(void); |
71 | extern int rcu_needs_cpu(int cpu); |
72 | extern int rcu_scheduler_active; |
73 | |
74 | #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU) |
75 | #include <linux/rcutree.h> |
76 | #else |
77 | #error "Unknown RCU implementation specified to kernel configuration" |
78 | #endif |
79 | |
80 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
81 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT |
82 | #define INIT_RCU_HEAD(ptr) do { \ |
83 | (ptr)->next = NULL; (ptr)->func = NULL; \ |
84 | } while (0) |
85 | |
86 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
87 | extern struct lockdep_map rcu_lock_map; |
88 | # define rcu_read_acquire() \ |
89 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) |
90 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) |
91 | #else |
92 | # define rcu_read_acquire() do { } while (0) |
93 | # define rcu_read_release() do { } while (0) |
94 | #endif |
95 | |
96 | /** |
97 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. |
98 | * |
99 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
100 | * are within RCU read-side critical sections, then the |
101 | * synchronize_rcu() is guaranteed to block until after all the other |
102 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
103 | * on one CPU while other CPUs are within RCU read-side critical |
104 | * sections, invocation of the corresponding RCU callback is deferred |
105 | * until after the all the other CPUs exit their critical sections. |
106 | * |
107 | * Note, however, that RCU callbacks are permitted to run concurrently |
108 | * with RCU read-side critical sections. One way that this can happen |
109 | * is via the following sequence of events: (1) CPU 0 enters an RCU |
110 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register |
111 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, |
112 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU |
113 | * callback is invoked. This is legal, because the RCU read-side critical |
114 | * section that was running concurrently with the call_rcu() (and which |
115 | * therefore might be referencing something that the corresponding RCU |
116 | * callback would free up) has completed before the corresponding |
117 | * RCU callback is invoked. |
118 | * |
119 | * RCU read-side critical sections may be nested. Any deferred actions |
120 | * will be deferred until the outermost RCU read-side critical section |
121 | * completes. |
122 | * |
123 | * It is illegal to block while in an RCU read-side critical section. |
124 | */ |
125 | static inline void rcu_read_lock(void) |
126 | { |
127 | __rcu_read_lock(); |
128 | __acquire(RCU); |
129 | rcu_read_acquire(); |
130 | } |
131 | |
132 | /* |
133 | * So where is rcu_write_lock()? It does not exist, as there is no |
134 | * way for writers to lock out RCU readers. This is a feature, not |
135 | * a bug -- this property is what provides RCU's performance benefits. |
136 | * Of course, writers must coordinate with each other. The normal |
137 | * spinlock primitives work well for this, but any other technique may be |
138 | * used as well. RCU does not care how the writers keep out of each |
139 | * others' way, as long as they do so. |
140 | */ |
141 | |
142 | /** |
143 | * rcu_read_unlock - marks the end of an RCU read-side critical section. |
144 | * |
145 | * See rcu_read_lock() for more information. |
146 | */ |
147 | static inline void rcu_read_unlock(void) |
148 | { |
149 | rcu_read_release(); |
150 | __release(RCU); |
151 | __rcu_read_unlock(); |
152 | } |
153 | |
154 | /** |
155 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section |
156 | * |
157 | * This is equivalent of rcu_read_lock(), but to be used when updates |
158 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks |
159 | * consider completion of a softirq handler to be a quiescent state, |
160 | * a process in RCU read-side critical section must be protected by |
161 | * disabling softirqs. Read-side critical sections in interrupt context |
162 | * can use just rcu_read_lock(). |
163 | * |
164 | */ |
165 | static inline void rcu_read_lock_bh(void) |
166 | { |
167 | __rcu_read_lock_bh(); |
168 | __acquire(RCU_BH); |
169 | rcu_read_acquire(); |
170 | } |
171 | |
172 | /* |
173 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section |
174 | * |
175 | * See rcu_read_lock_bh() for more information. |
176 | */ |
177 | static inline void rcu_read_unlock_bh(void) |
178 | { |
179 | rcu_read_release(); |
180 | __release(RCU_BH); |
181 | __rcu_read_unlock_bh(); |
182 | } |
183 | |
184 | /** |
185 | * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section |
186 | * |
187 | * Should be used with either |
188 | * - synchronize_sched() |
189 | * or |
190 | * - call_rcu_sched() and rcu_barrier_sched() |
191 | * on the write-side to insure proper synchronization. |
192 | */ |
193 | static inline void rcu_read_lock_sched(void) |
194 | { |
195 | preempt_disable(); |
196 | __acquire(RCU_SCHED); |
197 | rcu_read_acquire(); |
198 | } |
199 | |
200 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
201 | static inline notrace void rcu_read_lock_sched_notrace(void) |
202 | { |
203 | preempt_disable_notrace(); |
204 | __acquire(RCU_SCHED); |
205 | } |
206 | |
207 | /* |
208 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section |
209 | * |
210 | * See rcu_read_lock_sched for more information. |
211 | */ |
212 | static inline void rcu_read_unlock_sched(void) |
213 | { |
214 | rcu_read_release(); |
215 | __release(RCU_SCHED); |
216 | preempt_enable(); |
217 | } |
218 | |
219 | /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */ |
220 | static inline notrace void rcu_read_unlock_sched_notrace(void) |
221 | { |
222 | __release(RCU_SCHED); |
223 | preempt_enable_notrace(); |
224 | } |
225 | |
226 | |
227 | /** |
228 | * rcu_dereference - fetch an RCU-protected pointer in an |
229 | * RCU read-side critical section. This pointer may later |
230 | * be safely dereferenced. |
231 | * |
232 | * Inserts memory barriers on architectures that require them |
233 | * (currently only the Alpha), and, more importantly, documents |
234 | * exactly which pointers are protected by RCU. |
235 | */ |
236 | |
237 | #define rcu_dereference(p) ({ \ |
238 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
239 | smp_read_barrier_depends(); \ |
240 | (_________p1); \ |
241 | }) |
242 | |
243 | /** |
244 | * rcu_assign_pointer - assign (publicize) a pointer to a newly |
245 | * initialized structure that will be dereferenced by RCU read-side |
246 | * critical sections. Returns the value assigned. |
247 | * |
248 | * Inserts memory barriers on architectures that require them |
249 | * (pretty much all of them other than x86), and also prevents |
250 | * the compiler from reordering the code that initializes the |
251 | * structure after the pointer assignment. More importantly, this |
252 | * call documents which pointers will be dereferenced by RCU read-side |
253 | * code. |
254 | */ |
255 | |
256 | #define rcu_assign_pointer(p, v) \ |
257 | ({ \ |
258 | if (!__builtin_constant_p(v) || \ |
259 | ((v) != NULL)) \ |
260 | smp_wmb(); \ |
261 | (p) = (v); \ |
262 | }) |
263 | |
264 | /* Infrastructure to implement the synchronize_() primitives. */ |
265 | |
266 | struct rcu_synchronize { |
267 | struct rcu_head head; |
268 | struct completion completion; |
269 | }; |
270 | |
271 | extern void wakeme_after_rcu(struct rcu_head *head); |
272 | |
273 | /** |
274 | * call_rcu - Queue an RCU callback for invocation after a grace period. |
275 | * @head: structure to be used for queueing the RCU updates. |
276 | * @func: actual update function to be invoked after the grace period |
277 | * |
278 | * The update function will be invoked some time after a full grace |
279 | * period elapses, in other words after all currently executing RCU |
280 | * read-side critical sections have completed. RCU read-side critical |
281 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), |
282 | * and may be nested. |
283 | */ |
284 | extern void call_rcu(struct rcu_head *head, |
285 | void (*func)(struct rcu_head *head)); |
286 | |
287 | /** |
288 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. |
289 | * @head: structure to be used for queueing the RCU updates. |
290 | * @func: actual update function to be invoked after the grace period |
291 | * |
292 | * The update function will be invoked some time after a full grace |
293 | * period elapses, in other words after all currently executing RCU |
294 | * read-side critical sections have completed. call_rcu_bh() assumes |
295 | * that the read-side critical sections end on completion of a softirq |
296 | * handler. This means that read-side critical sections in process |
297 | * context must not be interrupted by softirqs. This interface is to be |
298 | * used when most of the read-side critical sections are in softirq context. |
299 | * RCU read-side critical sections are delimited by : |
300 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. |
301 | * OR |
302 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. |
303 | * These may be nested. |
304 | */ |
305 | extern void call_rcu_bh(struct rcu_head *head, |
306 | void (*func)(struct rcu_head *head)); |
307 | |
308 | #endif /* __LINUX_RCUPDATE_H */ |
309 |
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