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1da177e4 LT |
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 | * | |
01c1c660 | 18 | * Copyright IBM Corporation, 2001 |
1da177e4 LT |
19 | * |
20 | * Author: Dipankar Sarma <dipankar@in.ibm.com> | |
21 | * | |
595182bc | 22 | * Based on the original work by Paul McKenney <paulmck@us.ibm.com> |
1da177e4 LT |
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 | ||
1da177e4 LT |
36 | #include <linux/cache.h> |
37 | #include <linux/spinlock.h> | |
38 | #include <linux/threads.h> | |
1da177e4 LT |
39 | #include <linux/cpumask.h> |
40 | #include <linux/seqlock.h> | |
851a67b8 | 41 | #include <linux/lockdep.h> |
4446a36f | 42 | #include <linux/completion.h> |
1da177e4 LT |
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 | ||
03b042bf PM |
54 | /* Exported common interfaces */ |
55 | extern void synchronize_rcu(void); | |
56 | extern void synchronize_rcu_bh(void); | |
57 | extern void rcu_barrier(void); | |
58 | extern void rcu_barrier_bh(void); | |
59 | extern void rcu_barrier_sched(void); | |
60 | extern void synchronize_sched_expedited(void); | |
61 | extern int sched_expedited_torture_stats(char *page); | |
62 | ||
63 | /* Internal to kernel */ | |
64 | extern void rcu_init(void); | |
65 | extern void rcu_scheduler_starting(void); | |
66 | extern int rcu_needs_cpu(int cpu); | |
a6826048 PM |
67 | extern int rcu_scheduler_active; |
68 | ||
c17ef453 | 69 | #if defined(CONFIG_TREE_RCU) |
64db4cff PM |
70 | #include <linux/rcutree.h> |
71 | #elif defined(CONFIG_PREEMPT_RCU) | |
e260be67 | 72 | #include <linux/rcupreempt.h> |
64db4cff PM |
73 | #else |
74 | #error "Unknown RCU implementation specified to kernel configuration" | |
75 | #endif /* #else #if defined(CONFIG_CLASSIC_RCU) */ | |
01c1c660 | 76 | |
8b6490e5 DS |
77 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
78 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT | |
1da177e4 LT |
79 | #define INIT_RCU_HEAD(ptr) do { \ |
80 | (ptr)->next = NULL; (ptr)->func = NULL; \ | |
81 | } while (0) | |
82 | ||
bc33f24b PM |
83 | #ifdef CONFIG_DEBUG_LOCK_ALLOC |
84 | extern struct lockdep_map rcu_lock_map; | |
85 | # define rcu_read_acquire() \ | |
86 | lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_) | |
87 | # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_) | |
88 | #else | |
89 | # define rcu_read_acquire() do { } while (0) | |
90 | # define rcu_read_release() do { } while (0) | |
91 | #endif | |
92 | ||
1da177e4 LT |
93 | /** |
94 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. | |
95 | * | |
9b06e818 | 96 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 97 | * are within RCU read-side critical sections, then the |
9b06e818 | 98 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
99 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
100 | * on one CPU while other CPUs are within RCU read-side critical | |
101 | * sections, invocation of the corresponding RCU callback is deferred | |
102 | * until after the all the other CPUs exit their critical sections. | |
103 | * | |
104 | * Note, however, that RCU callbacks are permitted to run concurrently | |
105 | * with RCU read-side critical sections. One way that this can happen | |
106 | * is via the following sequence of events: (1) CPU 0 enters an RCU | |
107 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
108 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
109 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
110 | * callback is invoked. This is legal, because the RCU read-side critical | |
111 | * section that was running concurrently with the call_rcu() (and which | |
112 | * therefore might be referencing something that the corresponding RCU | |
113 | * callback would free up) has completed before the corresponding | |
114 | * RCU callback is invoked. | |
115 | * | |
116 | * RCU read-side critical sections may be nested. Any deferred actions | |
117 | * will be deferred until the outermost RCU read-side critical section | |
118 | * completes. | |
119 | * | |
120 | * It is illegal to block while in an RCU read-side critical section. | |
121 | */ | |
bc33f24b PM |
122 | static inline void rcu_read_lock(void) |
123 | { | |
124 | __rcu_read_lock(); | |
125 | __acquire(RCU); | |
126 | rcu_read_acquire(); | |
127 | } | |
1da177e4 LT |
128 | |
129 | /** | |
130 | * rcu_read_unlock - marks the end of an RCU read-side critical section. | |
131 | * | |
132 | * See rcu_read_lock() for more information. | |
133 | */ | |
1da177e4 LT |
134 | |
135 | /* | |
136 | * So where is rcu_write_lock()? It does not exist, as there is no | |
137 | * way for writers to lock out RCU readers. This is a feature, not | |
138 | * a bug -- this property is what provides RCU's performance benefits. | |
139 | * Of course, writers must coordinate with each other. The normal | |
140 | * spinlock primitives work well for this, but any other technique may be | |
141 | * used as well. RCU does not care how the writers keep out of each | |
142 | * others' way, as long as they do so. | |
143 | */ | |
bc33f24b PM |
144 | static inline void rcu_read_unlock(void) |
145 | { | |
146 | rcu_read_release(); | |
147 | __release(RCU); | |
148 | __rcu_read_unlock(); | |
149 | } | |
1da177e4 LT |
150 | |
151 | /** | |
152 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section | |
153 | * | |
154 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
155 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks | |
156 | * consider completion of a softirq handler to be a quiescent state, | |
157 | * a process in RCU read-side critical section must be protected by | |
158 | * disabling softirqs. Read-side critical sections in interrupt context | |
159 | * can use just rcu_read_lock(). | |
160 | * | |
161 | */ | |
bc33f24b PM |
162 | static inline void rcu_read_lock_bh(void) |
163 | { | |
164 | __rcu_read_lock_bh(); | |
165 | __acquire(RCU_BH); | |
166 | rcu_read_acquire(); | |
167 | } | |
1da177e4 LT |
168 | |
169 | /* | |
170 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
171 | * | |
172 | * See rcu_read_lock_bh() for more information. | |
173 | */ | |
bc33f24b PM |
174 | static inline void rcu_read_unlock_bh(void) |
175 | { | |
176 | rcu_read_release(); | |
177 | __release(RCU_BH); | |
178 | __rcu_read_unlock_bh(); | |
179 | } | |
1da177e4 | 180 | |
1c50b728 MD |
181 | /** |
182 | * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section | |
183 | * | |
184 | * Should be used with either | |
185 | * - synchronize_sched() | |
186 | * or | |
187 | * - call_rcu_sched() and rcu_barrier_sched() | |
188 | * on the write-side to insure proper synchronization. | |
189 | */ | |
d6714c22 PM |
190 | static inline void rcu_read_lock_sched(void) |
191 | { | |
192 | preempt_disable(); | |
bc33f24b PM |
193 | __acquire(RCU_SCHED); |
194 | rcu_read_acquire(); | |
d6714c22 PM |
195 | } |
196 | static inline void rcu_read_lock_sched_notrace(void) | |
197 | { | |
198 | preempt_disable_notrace(); | |
bc33f24b PM |
199 | __acquire(RCU_SCHED); |
200 | rcu_read_acquire(); | |
d6714c22 | 201 | } |
1c50b728 MD |
202 | |
203 | /* | |
204 | * rcu_read_unlock_sched - marks the end of a RCU-classic critical section | |
205 | * | |
206 | * See rcu_read_lock_sched for more information. | |
207 | */ | |
d6714c22 PM |
208 | static inline void rcu_read_unlock_sched(void) |
209 | { | |
bc33f24b PM |
210 | rcu_read_release(); |
211 | __release(RCU_SCHED); | |
d6714c22 PM |
212 | preempt_enable(); |
213 | } | |
214 | static inline void rcu_read_unlock_sched_notrace(void) | |
215 | { | |
bc33f24b PM |
216 | rcu_read_release(); |
217 | __release(RCU_SCHED); | |
d6714c22 PM |
218 | preempt_enable_notrace(); |
219 | } | |
1c50b728 MD |
220 | |
221 | ||
1da177e4 LT |
222 | /** |
223 | * rcu_dereference - fetch an RCU-protected pointer in an | |
224 | * RCU read-side critical section. This pointer may later | |
225 | * be safely dereferenced. | |
226 | * | |
227 | * Inserts memory barriers on architectures that require them | |
228 | * (currently only the Alpha), and, more importantly, documents | |
229 | * exactly which pointers are protected by RCU. | |
230 | */ | |
231 | ||
232 | #define rcu_dereference(p) ({ \ | |
97b43032 | 233 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
1da177e4 LT |
234 | smp_read_barrier_depends(); \ |
235 | (_________p1); \ | |
236 | }) | |
237 | ||
238 | /** | |
239 | * rcu_assign_pointer - assign (publicize) a pointer to a newly | |
240 | * initialized structure that will be dereferenced by RCU read-side | |
241 | * critical sections. Returns the value assigned. | |
242 | * | |
243 | * Inserts memory barriers on architectures that require them | |
244 | * (pretty much all of them other than x86), and also prevents | |
245 | * the compiler from reordering the code that initializes the | |
246 | * structure after the pointer assignment. More importantly, this | |
247 | * call documents which pointers will be dereferenced by RCU read-side | |
248 | * code. | |
249 | */ | |
250 | ||
d99c4f6b PM |
251 | #define rcu_assign_pointer(p, v) \ |
252 | ({ \ | |
253 | if (!__builtin_constant_p(v) || \ | |
254 | ((v) != NULL)) \ | |
255 | smp_wmb(); \ | |
256 | (p) = (v); \ | |
257 | }) | |
1da177e4 | 258 | |
4446a36f PM |
259 | /* Infrastructure to implement the synchronize_() primitives. */ |
260 | ||
261 | struct rcu_synchronize { | |
262 | struct rcu_head head; | |
263 | struct completion completion; | |
264 | }; | |
265 | ||
266 | extern void wakeme_after_rcu(struct rcu_head *head); | |
267 | ||
9b06e818 PM |
268 | /** |
269 | * synchronize_sched - block until all CPUs have exited any non-preemptive | |
270 | * kernel code sequences. | |
271 | * | |
272 | * This means that all preempt_disable code sequences, including NMI and | |
273 | * hardware-interrupt handlers, in progress on entry will have completed | |
274 | * before this primitive returns. However, this does not guarantee that | |
bb3b9cf1 PM |
275 | * softirq handlers will have completed, since in some kernels, these |
276 | * handlers can run in process context, and can block. | |
9b06e818 | 277 | * |
d83015b8 | 278 | * This primitive provides the guarantees made by the (now removed) |
9b06e818 PM |
279 | * synchronize_kernel() API. In contrast, synchronize_rcu() only |
280 | * guarantees that rcu_read_lock() sections will have completed. | |
bb3b9cf1 PM |
281 | * In "classic RCU", these two guarantees happen to be one and |
282 | * the same, but can differ in realtime RCU implementations. | |
9b06e818 | 283 | */ |
01c1c660 PM |
284 | #define synchronize_sched() __synchronize_sched() |
285 | ||
286 | /** | |
287 | * call_rcu - Queue an RCU callback for invocation after a grace period. | |
288 | * @head: structure to be used for queueing the RCU updates. | |
289 | * @func: actual update function to be invoked after the grace period | |
290 | * | |
291 | * The update function will be invoked some time after a full grace | |
292 | * period elapses, in other words after all currently executing RCU | |
293 | * read-side critical sections have completed. RCU read-side critical | |
294 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
295 | * and may be nested. | |
296 | */ | |
297 | extern void call_rcu(struct rcu_head *head, | |
298 | void (*func)(struct rcu_head *head)); | |
299 | ||
300 | /** | |
301 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. | |
302 | * @head: structure to be used for queueing the RCU updates. | |
303 | * @func: actual update function to be invoked after the grace period | |
304 | * | |
305 | * The update function will be invoked some time after a full grace | |
306 | * period elapses, in other words after all currently executing RCU | |
307 | * read-side critical sections have completed. call_rcu_bh() assumes | |
308 | * that the read-side critical sections end on completion of a softirq | |
309 | * handler. This means that read-side critical sections in process | |
310 | * context must not be interrupted by softirqs. This interface is to be | |
311 | * used when most of the read-side critical sections are in softirq context. | |
312 | * RCU read-side critical sections are delimited by : | |
313 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
314 | * OR | |
315 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
316 | * These may be nested. | |
317 | */ | |
318 | extern void call_rcu_bh(struct rcu_head *head, | |
319 | void (*func)(struct rcu_head *head)); | |
320 | ||
1da177e4 | 321 | #endif /* __LINUX_RCUPDATE_H */ |