Line data Source code
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 : extern void synchronize_rcu_bh(void);
56 : extern void synchronize_sched(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 :
66 : #if defined(CONFIG_TREE_RCU) || defined(CONFIG_TREE_PREEMPT_RCU)
67 : #include <linux/rcutree.h>
68 : #elif defined(CONFIG_TINY_RCU)
69 : #include <linux/rcutiny.h>
70 : #else
71 : #error "Unknown RCU implementation specified to kernel configuration"
72 : #endif
73 :
74 : #define RCU_HEAD_INIT { .next = NULL, .func = NULL }
75 : #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT
76 : #define INIT_RCU_HEAD(ptr) do { \
77 : (ptr)->next = NULL; (ptr)->func = NULL; \
78 : } while (0)
79 :
80 : #ifdef CONFIG_DEBUG_LOCK_ALLOC
81 : extern struct lockdep_map rcu_lock_map;
82 : # define rcu_read_acquire() \
83 : lock_acquire(&rcu_lock_map, 0, 0, 2, 1, NULL, _THIS_IP_)
84 : # define rcu_read_release() lock_release(&rcu_lock_map, 1, _THIS_IP_)
85 : #else
86 : # define rcu_read_acquire() do { } while (0)
87 : # define rcu_read_release() do { } while (0)
88 : #endif
89 :
90 : /**
91 : * rcu_read_lock - mark the beginning of an RCU read-side critical section.
92 : *
93 : * When synchronize_rcu() is invoked on one CPU while other CPUs
94 : * are within RCU read-side critical sections, then the
95 : * synchronize_rcu() is guaranteed to block until after all the other
96 : * CPUs exit their critical sections. Similarly, if call_rcu() is invoked
97 : * on one CPU while other CPUs are within RCU read-side critical
98 : * sections, invocation of the corresponding RCU callback is deferred
99 : * until after the all the other CPUs exit their critical sections.
100 : *
101 : * Note, however, that RCU callbacks are permitted to run concurrently
102 : * with RCU read-side critical sections. One way that this can happen
103 : * is via the following sequence of events: (1) CPU 0 enters an RCU
104 : * read-side critical section, (2) CPU 1 invokes call_rcu() to register
105 : * an RCU callback, (3) CPU 0 exits the RCU read-side critical section,
106 : * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU
107 : * callback is invoked. This is legal, because the RCU read-side critical
108 : * section that was running concurrently with the call_rcu() (and which
109 : * therefore might be referencing something that the corresponding RCU
110 : * callback would free up) has completed before the corresponding
111 : * RCU callback is invoked.
112 : *
113 : * RCU read-side critical sections may be nested. Any deferred actions
114 : * will be deferred until the outermost RCU read-side critical section
115 : * completes.
116 : *
117 : * It is illegal to block while in an RCU read-side critical section.
118 : */
119 : static inline void rcu_read_lock(void)
120 : {
121 16 : __rcu_read_lock();
122 : __acquire(RCU);
123 8 : rcu_read_acquire();
124 : }
125 :
126 : /*
127 : * So where is rcu_write_lock()? It does not exist, as there is no
128 : * way for writers to lock out RCU readers. This is a feature, not
129 : * a bug -- this property is what provides RCU's performance benefits.
130 : * Of course, writers must coordinate with each other. The normal
131 : * spinlock primitives work well for this, but any other technique may be
132 : * used as well. RCU does not care how the writers keep out of each
133 : * others' way, as long as they do so.
134 : */
135 :
136 : /**
137 : * rcu_read_unlock - marks the end of an RCU read-side critical section.
138 : *
139 : * See rcu_read_lock() for more information.
140 : */
141 : static inline void rcu_read_unlock(void)
142 : {
143 : rcu_read_release();
144 : __release(RCU);
145 : __rcu_read_unlock();
146 : }
147 :
148 : /**
149 : * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section
150 : *
151 : * This is equivalent of rcu_read_lock(), but to be used when updates
152 : * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks
153 : * consider completion of a softirq handler to be a quiescent state,
154 : * a process in RCU read-side critical section must be protected by
155 : * disabling softirqs. Read-side critical sections in interrupt context
156 : * can use just rcu_read_lock().
157 : *
158 : */
159 : static inline void rcu_read_lock_bh(void)
160 : {
161 : __rcu_read_lock_bh();
162 : __acquire(RCU_BH);
163 : rcu_read_acquire();
164 : }
165 :
166 : /*
167 : * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section
168 : *
169 : * See rcu_read_lock_bh() for more information.
170 : */
171 : static inline void rcu_read_unlock_bh(void)
172 : {
173 : rcu_read_release();
174 : __release(RCU_BH);
175 : __rcu_read_unlock_bh();
176 : }
177 :
178 : /**
179 : * rcu_read_lock_sched - mark the beginning of a RCU-classic critical section
180 : *
181 : * Should be used with either
182 : * - synchronize_sched()
183 : * or
184 : * - call_rcu_sched() and rcu_barrier_sched()
185 : * on the write-side to insure proper synchronization.
186 : */
187 : static inline void rcu_read_lock_sched(void)
188 : {
189 : preempt_disable();
190 : __acquire(RCU_SCHED);
191 : rcu_read_acquire();
192 : }
193 :
194 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
195 : static inline notrace void rcu_read_lock_sched_notrace(void)
196 : {
197 : preempt_disable_notrace();
198 : __acquire(RCU_SCHED);
199 : }
200 :
201 : /*
202 : * rcu_read_unlock_sched - marks the end of a RCU-classic critical section
203 : *
204 : * See rcu_read_lock_sched for more information.
205 : */
206 : static inline void rcu_read_unlock_sched(void)
207 : {
208 : rcu_read_release();
209 : __release(RCU_SCHED);
210 : preempt_enable();
211 : }
212 :
213 : /* Used by lockdep and tracing: cannot be traced, cannot call lockdep. */
214 : static inline notrace void rcu_read_unlock_sched_notrace(void)
215 : {
216 : __release(RCU_SCHED);
217 : preempt_enable_notrace();
218 : }
219 :
220 :
221 : /**
222 : * rcu_dereference - fetch an RCU-protected pointer in an
223 : * RCU read-side critical section. This pointer may later
224 : * be safely dereferenced.
225 : *
226 : * Inserts memory barriers on architectures that require them
227 : * (currently only the Alpha), and, more importantly, documents
228 : * exactly which pointers are protected by RCU.
229 : */
230 :
231 : #define rcu_dereference(p) ({ \
232 : typeof(p) _________p1 = ACCESS_ONCE(p); \
233 : smp_read_barrier_depends(); \
234 : (_________p1); \
235 : })
236 :
237 : /**
238 : * rcu_assign_pointer - assign (publicize) a pointer to a newly
239 : * initialized structure that will be dereferenced by RCU read-side
240 : * critical sections. Returns the value assigned.
241 : *
242 : * Inserts memory barriers on architectures that require them
243 : * (pretty much all of them other than x86), and also prevents
244 : * the compiler from reordering the code that initializes the
245 : * structure after the pointer assignment. More importantly, this
246 : * call documents which pointers will be dereferenced by RCU read-side
247 : * code.
248 : */
249 :
250 : #define rcu_assign_pointer(p, v) \
251 : ({ \
252 : if (!__builtin_constant_p(v) || \
253 : ((v) != NULL)) \
254 : smp_wmb(); \
255 : (p) = (v); \
256 : })
257 :
258 : /* Infrastructure to implement the synchronize_() primitives. */
259 :
260 : struct rcu_synchronize {
261 : struct rcu_head head;
262 : struct completion completion;
263 : };
264 :
265 : extern void wakeme_after_rcu(struct rcu_head *head);
266 :
267 : /**
268 : * call_rcu - Queue an RCU callback for invocation after a grace period.
269 : * @head: structure to be used for queueing the RCU updates.
270 : * @func: actual update function to be invoked after the grace period
271 : *
272 : * The update function will be invoked some time after a full grace
273 : * period elapses, in other words after all currently executing RCU
274 : * read-side critical sections have completed. RCU read-side critical
275 : * sections are delimited by rcu_read_lock() and rcu_read_unlock(),
276 : * and may be nested.
277 : */
278 : extern void call_rcu(struct rcu_head *head,
279 : void (*func)(struct rcu_head *head));
280 :
281 : /**
282 : * call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
283 : * @head: structure to be used for queueing the RCU updates.
284 : * @func: actual update function to be invoked after the grace period
285 : *
286 : * The update function will be invoked some time after a full grace
287 : * period elapses, in other words after all currently executing RCU
288 : * read-side critical sections have completed. call_rcu_bh() assumes
289 : * that the read-side critical sections end on completion of a softirq
290 : * handler. This means that read-side critical sections in process
291 : * context must not be interrupted by softirqs. This interface is to be
292 : * used when most of the read-side critical sections are in softirq context.
293 : * RCU read-side critical sections are delimited by :
294 : * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context.
295 : * OR
296 : * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context.
297 : * These may be nested.
298 : */
299 : extern void call_rcu_bh(struct rcu_head *head,
300 : void (*func)(struct rcu_head *head));
301 :
302 : #endif /* __LINUX_RCUPDATE_H */
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