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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 | ||
36 | #ifdef __KERNEL__ | |
37 | ||
38 | #include <linux/cache.h> | |
39 | #include <linux/spinlock.h> | |
40 | #include <linux/threads.h> | |
41 | #include <linux/percpu.h> | |
42 | #include <linux/cpumask.h> | |
43 | #include <linux/seqlock.h> | |
851a67b8 | 44 | #include <linux/lockdep.h> |
1da177e4 LT |
45 | |
46 | /** | |
47 | * struct rcu_head - callback structure for use with RCU | |
48 | * @next: next update requests in a list | |
49 | * @func: actual update function to call after the grace period. | |
50 | */ | |
51 | struct rcu_head { | |
52 | struct rcu_head *next; | |
53 | void (*func)(struct rcu_head *head); | |
54 | }; | |
55 | ||
e260be67 | 56 | #ifdef CONFIG_CLASSIC_RCU |
01c1c660 | 57 | #include <linux/rcuclassic.h> |
e260be67 PM |
58 | #else /* #ifdef CONFIG_CLASSIC_RCU */ |
59 | #include <linux/rcupreempt.h> | |
60 | #endif /* #else #ifdef CONFIG_CLASSIC_RCU */ | |
01c1c660 | 61 | |
8b6490e5 DS |
62 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
63 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT | |
1da177e4 LT |
64 | #define INIT_RCU_HEAD(ptr) do { \ |
65 | (ptr)->next = NULL; (ptr)->func = NULL; \ | |
66 | } while (0) | |
67 | ||
1da177e4 LT |
68 | /** |
69 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. | |
70 | * | |
9b06e818 | 71 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 72 | * are within RCU read-side critical sections, then the |
9b06e818 | 73 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
74 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
75 | * on one CPU while other CPUs are within RCU read-side critical | |
76 | * sections, invocation of the corresponding RCU callback is deferred | |
77 | * until after the all the other CPUs exit their critical sections. | |
78 | * | |
79 | * Note, however, that RCU callbacks are permitted to run concurrently | |
80 | * with RCU read-side critical sections. One way that this can happen | |
81 | * is via the following sequence of events: (1) CPU 0 enters an RCU | |
82 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
83 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
84 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
85 | * callback is invoked. This is legal, because the RCU read-side critical | |
86 | * section that was running concurrently with the call_rcu() (and which | |
87 | * therefore might be referencing something that the corresponding RCU | |
88 | * callback would free up) has completed before the corresponding | |
89 | * RCU callback is invoked. | |
90 | * | |
91 | * RCU read-side critical sections may be nested. Any deferred actions | |
92 | * will be deferred until the outermost RCU read-side critical section | |
93 | * completes. | |
94 | * | |
95 | * It is illegal to block while in an RCU read-side critical section. | |
96 | */ | |
01c1c660 | 97 | #define rcu_read_lock() __rcu_read_lock() |
1da177e4 LT |
98 | |
99 | /** | |
100 | * rcu_read_unlock - marks the end of an RCU read-side critical section. | |
101 | * | |
102 | * See rcu_read_lock() for more information. | |
103 | */ | |
1da177e4 LT |
104 | |
105 | /* | |
106 | * So where is rcu_write_lock()? It does not exist, as there is no | |
107 | * way for writers to lock out RCU readers. This is a feature, not | |
108 | * a bug -- this property is what provides RCU's performance benefits. | |
109 | * Of course, writers must coordinate with each other. The normal | |
110 | * spinlock primitives work well for this, but any other technique may be | |
111 | * used as well. RCU does not care how the writers keep out of each | |
112 | * others' way, as long as they do so. | |
113 | */ | |
01c1c660 | 114 | #define rcu_read_unlock() __rcu_read_unlock() |
1da177e4 LT |
115 | |
116 | /** | |
117 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section | |
118 | * | |
119 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
120 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks | |
121 | * consider completion of a softirq handler to be a quiescent state, | |
122 | * a process in RCU read-side critical section must be protected by | |
123 | * disabling softirqs. Read-side critical sections in interrupt context | |
124 | * can use just rcu_read_lock(). | |
125 | * | |
126 | */ | |
01c1c660 | 127 | #define rcu_read_lock_bh() __rcu_read_lock_bh() |
1da177e4 LT |
128 | |
129 | /* | |
130 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
131 | * | |
132 | * See rcu_read_lock_bh() for more information. | |
133 | */ | |
01c1c660 | 134 | #define rcu_read_unlock_bh() __rcu_read_unlock_bh() |
1da177e4 | 135 | |
97b43032 PM |
136 | /* |
137 | * Prevent the compiler from merging or refetching accesses. The compiler | |
138 | * is also forbidden from reordering successive instances of ACCESS_ONCE(), | |
139 | * but only when the compiler is aware of some particular ordering. One way | |
140 | * to make the compiler aware of ordering is to put the two invocations of | |
141 | * ACCESS_ONCE() in different C statements. | |
142 | * | |
143 | * This macro does absolutely -nothing- to prevent the CPU from reordering, | |
144 | * merging, or refetching absolutely anything at any time. | |
145 | */ | |
146 | #define ACCESS_ONCE(x) (*(volatile typeof(x) *)&(x)) | |
147 | ||
1da177e4 LT |
148 | /** |
149 | * rcu_dereference - fetch an RCU-protected pointer in an | |
150 | * RCU read-side critical section. This pointer may later | |
151 | * be safely dereferenced. | |
152 | * | |
153 | * Inserts memory barriers on architectures that require them | |
154 | * (currently only the Alpha), and, more importantly, documents | |
155 | * exactly which pointers are protected by RCU. | |
156 | */ | |
157 | ||
158 | #define rcu_dereference(p) ({ \ | |
97b43032 | 159 | typeof(p) _________p1 = ACCESS_ONCE(p); \ |
1da177e4 LT |
160 | smp_read_barrier_depends(); \ |
161 | (_________p1); \ | |
162 | }) | |
163 | ||
164 | /** | |
165 | * rcu_assign_pointer - assign (publicize) a pointer to a newly | |
166 | * initialized structure that will be dereferenced by RCU read-side | |
167 | * critical sections. Returns the value assigned. | |
168 | * | |
169 | * Inserts memory barriers on architectures that require them | |
170 | * (pretty much all of them other than x86), and also prevents | |
171 | * the compiler from reordering the code that initializes the | |
172 | * structure after the pointer assignment. More importantly, this | |
173 | * call documents which pointers will be dereferenced by RCU read-side | |
174 | * code. | |
175 | */ | |
176 | ||
d99c4f6b PM |
177 | #define rcu_assign_pointer(p, v) \ |
178 | ({ \ | |
179 | if (!__builtin_constant_p(v) || \ | |
180 | ((v) != NULL)) \ | |
181 | smp_wmb(); \ | |
182 | (p) = (v); \ | |
183 | }) | |
1da177e4 | 184 | |
9b06e818 PM |
185 | /** |
186 | * synchronize_sched - block until all CPUs have exited any non-preemptive | |
187 | * kernel code sequences. | |
188 | * | |
189 | * This means that all preempt_disable code sequences, including NMI and | |
190 | * hardware-interrupt handlers, in progress on entry will have completed | |
191 | * before this primitive returns. However, this does not guarantee that | |
bb3b9cf1 PM |
192 | * softirq handlers will have completed, since in some kernels, these |
193 | * handlers can run in process context, and can block. | |
9b06e818 | 194 | * |
d83015b8 | 195 | * This primitive provides the guarantees made by the (now removed) |
9b06e818 PM |
196 | * synchronize_kernel() API. In contrast, synchronize_rcu() only |
197 | * guarantees that rcu_read_lock() sections will have completed. | |
bb3b9cf1 PM |
198 | * In "classic RCU", these two guarantees happen to be one and |
199 | * the same, but can differ in realtime RCU implementations. | |
9b06e818 | 200 | */ |
01c1c660 PM |
201 | #define synchronize_sched() __synchronize_sched() |
202 | ||
203 | /** | |
204 | * call_rcu - Queue an RCU callback for invocation after a grace period. | |
205 | * @head: structure to be used for queueing the RCU updates. | |
206 | * @func: actual update function to be invoked after the grace period | |
207 | * | |
208 | * The update function will be invoked some time after a full grace | |
209 | * period elapses, in other words after all currently executing RCU | |
210 | * read-side critical sections have completed. RCU read-side critical | |
211 | * sections are delimited by rcu_read_lock() and rcu_read_unlock(), | |
212 | * and may be nested. | |
213 | */ | |
214 | extern void call_rcu(struct rcu_head *head, | |
215 | void (*func)(struct rcu_head *head)); | |
216 | ||
217 | /** | |
218 | * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. | |
219 | * @head: structure to be used for queueing the RCU updates. | |
220 | * @func: actual update function to be invoked after the grace period | |
221 | * | |
222 | * The update function will be invoked some time after a full grace | |
223 | * period elapses, in other words after all currently executing RCU | |
224 | * read-side critical sections have completed. call_rcu_bh() assumes | |
225 | * that the read-side critical sections end on completion of a softirq | |
226 | * handler. This means that read-side critical sections in process | |
227 | * context must not be interrupted by softirqs. This interface is to be | |
228 | * used when most of the read-side critical sections are in softirq context. | |
229 | * RCU read-side critical sections are delimited by : | |
230 | * - rcu_read_lock() and rcu_read_unlock(), if in interrupt context. | |
231 | * OR | |
232 | * - rcu_read_lock_bh() and rcu_read_unlock_bh(), if in process context. | |
233 | * These may be nested. | |
234 | */ | |
235 | extern void call_rcu_bh(struct rcu_head *head, | |
236 | void (*func)(struct rcu_head *head)); | |
237 | ||
238 | /* Exported common interfaces */ | |
239 | extern void synchronize_rcu(void); | |
240 | extern void rcu_barrier(void); | |
e260be67 PM |
241 | extern long rcu_batches_completed(void); |
242 | extern long rcu_batches_completed_bh(void); | |
9b06e818 | 243 | |
01c1c660 | 244 | /* Internal to kernel */ |
1da177e4 | 245 | extern void rcu_init(void); |
e260be67 | 246 | extern int rcu_needs_cpu(int cpu); |
1da177e4 | 247 | |
1da177e4 LT |
248 | #endif /* __KERNEL__ */ |
249 | #endif /* __LINUX_RCUPDATE_H */ |