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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 | ||
8b6490e5 DS |
55 | #define RCU_HEAD_INIT { .next = NULL, .func = NULL } |
56 | #define RCU_HEAD(head) struct rcu_head head = RCU_HEAD_INIT | |
1da177e4 LT |
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? */ | |
69a0b315 ON |
68 | |
69 | spinlock_t lock ____cacheline_internodealigned_in_smp; | |
70 | cpumask_t cpumask; /* CPUs that need to switch in order */ | |
71 | /* for current batch to proceed. */ | |
22fc6ecc | 72 | } ____cacheline_internodealigned_in_smp; |
1da177e4 LT |
73 | |
74 | /* Is batch a before batch b ? */ | |
75 | static inline int rcu_batch_before(long a, long b) | |
76 | { | |
77 | return (a - b) < 0; | |
78 | } | |
79 | ||
80 | /* Is batch a after batch b ? */ | |
81 | static inline int rcu_batch_after(long a, long b) | |
82 | { | |
83 | return (a - b) > 0; | |
84 | } | |
85 | ||
86 | /* | |
87 | * Per-CPU data for Read-Copy UPdate. | |
88 | * nxtlist - new callbacks are added here | |
89 | * curlist - current batch for which quiescent cycle started if any | |
90 | */ | |
91 | struct rcu_data { | |
92 | /* 1) quiescent state handling : */ | |
93 | long quiescbatch; /* Batch # for grace period */ | |
94 | int passed_quiesc; /* User-mode/idle loop etc. */ | |
95 | int qs_pending; /* core waits for quiesc state */ | |
96 | ||
97 | /* 2) batch handling */ | |
98 | long batch; /* Batch # for current RCU batch */ | |
99 | struct rcu_head *nxtlist; | |
100 | struct rcu_head **nxttail; | |
21a1ea9e | 101 | long qlen; /* # of queued callbacks */ |
1da177e4 LT |
102 | struct rcu_head *curlist; |
103 | struct rcu_head **curtail; | |
104 | struct rcu_head *donelist; | |
105 | struct rcu_head **donetail; | |
21a1ea9e | 106 | long blimit; /* Upper limit on a processed batch */ |
1da177e4 | 107 | int cpu; |
ab4720ec | 108 | struct rcu_head barrier; |
21a1ea9e DS |
109 | #ifdef CONFIG_SMP |
110 | long last_rs_qlen; /* qlen during the last resched */ | |
111 | #endif | |
1da177e4 LT |
112 | }; |
113 | ||
114 | DECLARE_PER_CPU(struct rcu_data, rcu_data); | |
115 | DECLARE_PER_CPU(struct rcu_data, rcu_bh_data); | |
116 | extern struct rcu_ctrlblk rcu_ctrlblk; | |
117 | extern struct rcu_ctrlblk rcu_bh_ctrlblk; | |
118 | ||
119 | /* | |
120 | * Increment the quiescent state counter. | |
121 | * The counter is a bit degenerated: We do not need to know | |
122 | * how many quiescent states passed, just if there was at least | |
123 | * one since the start of the grace period. Thus just a flag. | |
124 | */ | |
125 | static inline void rcu_qsctr_inc(int cpu) | |
126 | { | |
127 | struct rcu_data *rdp = &per_cpu(rcu_data, cpu); | |
128 | rdp->passed_quiesc = 1; | |
129 | } | |
130 | static inline void rcu_bh_qsctr_inc(int cpu) | |
131 | { | |
132 | struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); | |
133 | rdp->passed_quiesc = 1; | |
134 | } | |
135 | ||
67751777 | 136 | extern int rcu_pending(int cpu); |
1da177e4 LT |
137 | |
138 | /** | |
139 | * rcu_read_lock - mark the beginning of an RCU read-side critical section. | |
140 | * | |
9b06e818 | 141 | * When synchronize_rcu() is invoked on one CPU while other CPUs |
1da177e4 | 142 | * are within RCU read-side critical sections, then the |
9b06e818 | 143 | * synchronize_rcu() is guaranteed to block until after all the other |
1da177e4 LT |
144 | * CPUs exit their critical sections. Similarly, if call_rcu() is invoked |
145 | * on one CPU while other CPUs are within RCU read-side critical | |
146 | * sections, invocation of the corresponding RCU callback is deferred | |
147 | * until after the all the other CPUs exit their critical sections. | |
148 | * | |
149 | * Note, however, that RCU callbacks are permitted to run concurrently | |
150 | * with RCU read-side critical sections. One way that this can happen | |
151 | * is via the following sequence of events: (1) CPU 0 enters an RCU | |
152 | * read-side critical section, (2) CPU 1 invokes call_rcu() to register | |
153 | * an RCU callback, (3) CPU 0 exits the RCU read-side critical section, | |
154 | * (4) CPU 2 enters a RCU read-side critical section, (5) the RCU | |
155 | * callback is invoked. This is legal, because the RCU read-side critical | |
156 | * section that was running concurrently with the call_rcu() (and which | |
157 | * therefore might be referencing something that the corresponding RCU | |
158 | * callback would free up) has completed before the corresponding | |
159 | * RCU callback is invoked. | |
160 | * | |
161 | * RCU read-side critical sections may be nested. Any deferred actions | |
162 | * will be deferred until the outermost RCU read-side critical section | |
163 | * completes. | |
164 | * | |
165 | * It is illegal to block while in an RCU read-side critical section. | |
166 | */ | |
167 | #define rcu_read_lock() preempt_disable() | |
168 | ||
169 | /** | |
170 | * rcu_read_unlock - marks the end of an RCU read-side critical section. | |
171 | * | |
172 | * See rcu_read_lock() for more information. | |
173 | */ | |
174 | #define rcu_read_unlock() preempt_enable() | |
175 | ||
176 | /* | |
177 | * So where is rcu_write_lock()? It does not exist, as there is no | |
178 | * way for writers to lock out RCU readers. This is a feature, not | |
179 | * a bug -- this property is what provides RCU's performance benefits. | |
180 | * Of course, writers must coordinate with each other. The normal | |
181 | * spinlock primitives work well for this, but any other technique may be | |
182 | * used as well. RCU does not care how the writers keep out of each | |
183 | * others' way, as long as they do so. | |
184 | */ | |
185 | ||
186 | /** | |
187 | * rcu_read_lock_bh - mark the beginning of a softirq-only RCU critical section | |
188 | * | |
189 | * This is equivalent of rcu_read_lock(), but to be used when updates | |
190 | * are being done using call_rcu_bh(). Since call_rcu_bh() callbacks | |
191 | * consider completion of a softirq handler to be a quiescent state, | |
192 | * a process in RCU read-side critical section must be protected by | |
193 | * disabling softirqs. Read-side critical sections in interrupt context | |
194 | * can use just rcu_read_lock(). | |
195 | * | |
196 | */ | |
197 | #define rcu_read_lock_bh() local_bh_disable() | |
198 | ||
199 | /* | |
200 | * rcu_read_unlock_bh - marks the end of a softirq-only RCU critical section | |
201 | * | |
202 | * See rcu_read_lock_bh() for more information. | |
203 | */ | |
204 | #define rcu_read_unlock_bh() local_bh_enable() | |
205 | ||
206 | /** | |
207 | * rcu_dereference - fetch an RCU-protected pointer in an | |
208 | * RCU read-side critical section. This pointer may later | |
209 | * be safely dereferenced. | |
210 | * | |
211 | * Inserts memory barriers on architectures that require them | |
212 | * (currently only the Alpha), and, more importantly, documents | |
213 | * exactly which pointers are protected by RCU. | |
214 | */ | |
215 | ||
216 | #define rcu_dereference(p) ({ \ | |
217 | typeof(p) _________p1 = p; \ | |
218 | smp_read_barrier_depends(); \ | |
219 | (_________p1); \ | |
220 | }) | |
221 | ||
222 | /** | |
223 | * rcu_assign_pointer - assign (publicize) a pointer to a newly | |
224 | * initialized structure that will be dereferenced by RCU read-side | |
225 | * critical sections. Returns the value assigned. | |
226 | * | |
227 | * Inserts memory barriers on architectures that require them | |
228 | * (pretty much all of them other than x86), and also prevents | |
229 | * the compiler from reordering the code that initializes the | |
230 | * structure after the pointer assignment. More importantly, this | |
231 | * call documents which pointers will be dereferenced by RCU read-side | |
232 | * code. | |
233 | */ | |
234 | ||
235 | #define rcu_assign_pointer(p, v) ({ \ | |
236 | smp_wmb(); \ | |
237 | (p) = (v); \ | |
238 | }) | |
239 | ||
9b06e818 PM |
240 | /** |
241 | * synchronize_sched - block until all CPUs have exited any non-preemptive | |
242 | * kernel code sequences. | |
243 | * | |
244 | * This means that all preempt_disable code sequences, including NMI and | |
245 | * hardware-interrupt handlers, in progress on entry will have completed | |
246 | * before this primitive returns. However, this does not guarantee that | |
bb3b9cf1 PM |
247 | * softirq handlers will have completed, since in some kernels, these |
248 | * handlers can run in process context, and can block. | |
9b06e818 PM |
249 | * |
250 | * This primitive provides the guarantees made by the (deprecated) | |
251 | * synchronize_kernel() API. In contrast, synchronize_rcu() only | |
252 | * guarantees that rcu_read_lock() sections will have completed. | |
bb3b9cf1 PM |
253 | * In "classic RCU", these two guarantees happen to be one and |
254 | * the same, but can differ in realtime RCU implementations. | |
9b06e818 PM |
255 | */ |
256 | #define synchronize_sched() synchronize_rcu() | |
257 | ||
1da177e4 LT |
258 | extern void rcu_init(void); |
259 | extern void rcu_check_callbacks(int cpu, int user); | |
260 | extern void rcu_restart_cpu(int cpu); | |
a241ec65 | 261 | extern long rcu_batches_completed(void); |
1da177e4 LT |
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))); | |
9b06e818 PM |
268 | extern __deprecated_for_modules void synchronize_kernel(void); |
269 | extern void synchronize_rcu(void); | |
270 | void synchronize_idle(void); | |
ab4720ec | 271 | extern void rcu_barrier(void); |
1da177e4 LT |
272 | |
273 | #endif /* __KERNEL__ */ | |
274 | #endif /* __LINUX_RCUPDATE_H */ |