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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 | * | |
18 | * Copyright (C) IBM Corporation, 2001 | |
19 | * | |
20 | * Author: Dipankar Sarma <dipankar@in.ibm.com> | |
21 | * | |
22 | * Based on the original work by Paul McKenney <paul.mckenney@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 | #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> | |
44 | ||
45 | /** | |
46 | * struct rcu_head - callback structure for use with RCU | |
47 | * @next: next update requests in a list | |
48 | * @func: actual update function to call after the grace period. | |
49 | */ | |
50 | struct rcu_head { | |
51 | struct rcu_head *next; | |
52 | void (*func)(struct rcu_head *head); | |
53 | }; | |
54 | ||
55 | #define RCU_HEAD_INIT(head) { .next = NULL, .func = NULL } | |
56 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT(head) | |
57 | #define INIT_RCU_HEAD(ptr) do { \ | |
58 | (ptr)->next = NULL; (ptr)->func = NULL; \ | |
59 | } while (0) | |
60 | ||
61 | ||
62 | ||
63 | /* Global control variables for rcupdate callback mechanism. */ | |
64 | struct rcu_ctrlblk { | |
65 | long cur; /* Current batch number. */ | |
66 | long completed; /* Number of the last completed batch */ | |
67 | int next_pending; /* Is the next batch already waiting? */ | |
68 | } ____cacheline_maxaligned_in_smp; | |
69 | ||
70 | /* Is batch a before batch b ? */ | |
71 | static inline int rcu_batch_before(long a, long b) | |
72 | { | |
73 | return (a - b) < 0; | |
74 | } | |
75 | ||
76 | /* Is batch a after batch b ? */ | |
77 | static inline int rcu_batch_after(long a, long b) | |
78 | { | |
79 | return (a - b) > 0; | |
80 | } | |
81 | ||
82 | /* | |
83 | * Per-CPU data for Read-Copy UPdate. | |
84 | * nxtlist - new callbacks are added here | |
85 | * curlist - current batch for which quiescent cycle started if any | |
86 | */ | |
87 | struct rcu_data { | |
88 | /* 1) quiescent state handling : */ | |
89 | long quiescbatch; /* Batch # for grace period */ | |
90 | int passed_quiesc; /* User-mode/idle loop etc. */ | |
91 | int qs_pending; /* core waits for quiesc state */ | |
92 | ||
93 | /* 2) batch handling */ | |
94 | long batch; /* Batch # for current RCU batch */ | |
95 | struct rcu_head *nxtlist; | |
96 | struct rcu_head **nxttail; | |
97 | struct rcu_head *curlist; | |
98 | struct rcu_head **curtail; | |
99 | struct rcu_head *donelist; | |
100 | struct rcu_head **donetail; | |
101 | int cpu; | |
102 | }; | |
103 | ||
104 | DECLARE_PER_CPU(struct rcu_data, rcu_data); | |
105 | DECLARE_PER_CPU(struct rcu_data, rcu_bh_data); | |
106 | extern struct rcu_ctrlblk rcu_ctrlblk; | |
107 | extern struct rcu_ctrlblk rcu_bh_ctrlblk; | |
108 | ||
109 | /* | |
110 | * Increment the quiescent state counter. | |
111 | * The counter is a bit degenerated: We do not need to know | |
112 | * how many quiescent states passed, just if there was at least | |
113 | * one since the start of the grace period. Thus just a flag. | |
114 | */ | |
115 | static inline void rcu_qsctr_inc(int cpu) | |
116 | { | |
117 | struct rcu_data *rdp = &per_cpu(rcu_data, cpu); | |
118 | rdp->passed_quiesc = 1; | |
119 | } | |
120 | static inline void rcu_bh_qsctr_inc(int cpu) | |
121 | { | |
122 | struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); | |
123 | rdp->passed_quiesc = 1; | |
124 | } | |
125 | ||
126 | static inline int __rcu_pending(struct rcu_ctrlblk *rcp, | |
127 | struct rcu_data *rdp) | |
128 | { | |
129 | /* This cpu has pending rcu entries and the grace period | |
130 | * for them has completed. | |
131 | */ | |
132 | if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) | |
133 | return 1; | |
134 | ||
135 | /* This cpu has no pending entries, but there are new entries */ | |
136 | if (!rdp->curlist && rdp->nxtlist) | |
137 | return 1; | |
138 | ||
139 | /* This cpu has finished callbacks to invoke */ | |
140 | if (rdp->donelist) | |
141 | return 1; | |
142 | ||
143 | /* The rcu core waits for a quiescent state from the cpu */ | |
144 | if (rdp->quiescbatch != rcp->cur || rdp->qs_pending) | |
145 | return 1; | |
146 | ||
147 | /* nothing to do */ | |
148 | return 0; | |
149 | } | |
150 | ||
151 | static inline int rcu_pending(int cpu) | |
152 | { | |
153 | return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) || | |
154 | __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)); | |
155 | } | |
156 | ||
157 | /** | |
158 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. | |
159 | * | |
160 | * When synchronize_kernel() is invoked on one CPU while other CPUs | |
161 | * are within RCU read-side critical sections, then the | |
162 | * synchronize_kernel() is guaranteed to block until after all the other | |
163 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked | |
164 | * on one CPU while other CPUs are within RCU read-side critical | |
165 | * sections, invocation of the corresponding RCU callback is deferred | |
166 | * until after the all the other CPUs exit their critical sections. | |
167 | * | |
168 | * Note, however, that RCU callbacks are permitted to run concurrently | |
169 | * with RCU read-side critical sections. One way that this can happen | |
170 | * is via the following sequence of events: (1) CPU 0 enters an RCU | |
171 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
172 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
173 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
174 | * callback is invoked. This is legal, because the RCU read-side critical | |
175 | * section that was running concurrently with the call_rcu() (and which | |
176 | * therefore might be referencing something that the corresponding RCU | |
177 | * callback would free up) has completed before the corresponding | |
178 | * RCU callback is invoked. | |
179 | * | |
180 | * RCU read-side critical sections may be nested. Any deferred actions | |
181 | * will be deferred until the outermost RCU read-side critical section | |
182 | * completes. | |
183 | * | |
184 | * It is illegal to block while in an RCU read-side critical section. | |
185 | */ | |
186 | #define rcu_read_lock() preempt_disable() | |
187 | ||
188 | /** | |
189 | * rcu_read_unlock - marks the end of an RCU read-side critical section. | |
190 | * | |
191 | * See rcu_read_lock() for more information. | |
192 | */ | |
193 | #define rcu_read_unlock() preempt_enable() | |
194 | ||
195 | /* | |
196 | * So where is rcu_write_lock()? It does not exist, as there is no | |
197 | * way for writers to lock out RCU readers. This is a feature, not | |
198 | * a bug -- this property is what provides RCU's performance benefits. | |
199 | * Of course, writers must coordinate with each other. The normal | |
200 | * spinlock primitives work well for this, but any other technique may be | |
201 | * used as well. RCU does not care how the writers keep out of each | |
202 | * others' way, as long as they do so. | |
203 | */ | |
204 | ||
205 | /** | |
206 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section | |
207 | * | |
208 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
209 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks | |
210 | * consider completion of a softirq handler to be a quiescent state, | |
211 | * a process in RCU read-side critical section must be protected by | |
212 | * disabling softirqs. Read-side critical sections in interrupt context | |
213 | * can use just rcu_read_lock(). | |
214 | * | |
215 | */ | |
216 | #define rcu_read_lock_bh() local_bh_disable() | |
217 | ||
218 | /* | |
219 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
220 | * | |
221 | * See rcu_read_lock_bh() for more information. | |
222 | */ | |
223 | #define rcu_read_unlock_bh() local_bh_enable() | |
224 | ||
225 | /** | |
226 | * rcu_dereference - fetch an RCU-protected pointer in an | |
227 | * RCU read-side critical section. This pointer may later | |
228 | * be safely dereferenced. | |
229 | * | |
230 | * Inserts memory barriers on architectures that require them | |
231 | * (currently only the Alpha), and, more importantly, documents | |
232 | * exactly which pointers are protected by RCU. | |
233 | */ | |
234 | ||
235 | #define rcu_dereference(p) ({ \ | |
236 | typeof(p) _________p1 = p; \ | |
237 | smp_read_barrier_depends(); \ | |
238 | (_________p1); \ | |
239 | }) | |
240 | ||
241 | /** | |
242 | * rcu_assign_pointer - assign (publicize) a pointer to a newly | |
243 | * initialized structure that will be dereferenced by RCU read-side | |
244 | * critical sections. Returns the value assigned. | |
245 | * | |
246 | * Inserts memory barriers on architectures that require them | |
247 | * (pretty much all of them other than x86), and also prevents | |
248 | * the compiler from reordering the code that initializes the | |
249 | * structure after the pointer assignment. More importantly, this | |
250 | * call documents which pointers will be dereferenced by RCU read-side | |
251 | * code. | |
252 | */ | |
253 | ||
254 | #define rcu_assign_pointer(p, v) ({ \ | |
255 | smp_wmb(); \ | |
256 | (p) = (v); \ | |
257 | }) | |
258 | ||
259 | extern void rcu_init(void); | |
260 | extern void rcu_check_callbacks(int cpu, int user); | |
261 | extern void rcu_restart_cpu(int cpu); | |
262 | ||
263 | /* Exported interfaces */ | |
264 | extern void FASTCALL(call_rcu(struct rcu_head *head, | |
265 | void (*func)(struct rcu_head *head))); | |
266 | extern void FASTCALL(call_rcu_bh(struct rcu_head *head, | |
267 | void (*func)(struct rcu_head *head))); | |
268 | extern void synchronize_kernel(void); | |
269 | ||
270 | #endif /* __KERNEL__ */ | |
271 | #endif /* __LINUX_RCUPDATE_H */ |