]>
Commit | Line | Data |
---|---|---|
cc44ca84 ON |
1 | /* |
2 | * RCU-based infrastructure for lightweight reader-writer locking | |
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, you can access it online at | |
16 | * http://www.gnu.org/licenses/gpl-2.0.html. | |
17 | * | |
18 | * Copyright (c) 2015, Red Hat, Inc. | |
19 | * | |
20 | * Author: Oleg Nesterov <oleg@redhat.com> | |
21 | */ | |
22 | ||
23 | #include <linux/rcu_sync.h> | |
24 | #include <linux/sched.h> | |
25 | ||
3a518b76 ON |
26 | #ifdef CONFIG_PROVE_RCU |
27 | #define __INIT_HELD(func) .held = func, | |
28 | #else | |
29 | #define __INIT_HELD(func) | |
30 | #endif | |
31 | ||
82e8c565 ON |
32 | static const struct { |
33 | void (*sync)(void); | |
34 | void (*call)(struct rcu_head *, void (*)(struct rcu_head *)); | |
07899a6e | 35 | void (*wait)(void); |
3a518b76 ON |
36 | #ifdef CONFIG_PROVE_RCU |
37 | int (*held)(void); | |
38 | #endif | |
82e8c565 ON |
39 | } gp_ops[] = { |
40 | [RCU_SYNC] = { | |
41 | .sync = synchronize_rcu, | |
42 | .call = call_rcu, | |
07899a6e | 43 | .wait = rcu_barrier, |
3a518b76 | 44 | __INIT_HELD(rcu_read_lock_held) |
82e8c565 ON |
45 | }, |
46 | [RCU_SCHED_SYNC] = { | |
47 | .sync = synchronize_sched, | |
48 | .call = call_rcu_sched, | |
07899a6e | 49 | .wait = rcu_barrier_sched, |
3a518b76 | 50 | __INIT_HELD(rcu_read_lock_sched_held) |
82e8c565 ON |
51 | }, |
52 | [RCU_BH_SYNC] = { | |
53 | .sync = synchronize_rcu_bh, | |
54 | .call = call_rcu_bh, | |
07899a6e | 55 | .wait = rcu_barrier_bh, |
3a518b76 | 56 | __INIT_HELD(rcu_read_lock_bh_held) |
82e8c565 ON |
57 | }, |
58 | }; | |
59 | ||
cc44ca84 ON |
60 | enum { GP_IDLE = 0, GP_PENDING, GP_PASSED }; |
61 | enum { CB_IDLE = 0, CB_PENDING, CB_REPLAY }; | |
62 | ||
63 | #define rss_lock gp_wait.lock | |
64 | ||
3a518b76 | 65 | #ifdef CONFIG_PROVE_RCU |
4bace734 | 66 | void rcu_sync_lockdep_assert(struct rcu_sync *rsp) |
3a518b76 | 67 | { |
4bace734 ON |
68 | RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(), |
69 | "suspicious rcu_sync_is_idle() usage"); | |
3a518b76 | 70 | } |
80127a39 PZ |
71 | |
72 | EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert); | |
3a518b76 ON |
73 | #endif |
74 | ||
cc44ca84 ON |
75 | /** |
76 | * rcu_sync_init() - Initialize an rcu_sync structure | |
77 | * @rsp: Pointer to rcu_sync structure to be initialized | |
78 | * @type: Flavor of RCU with which to synchronize rcu_sync structure | |
79 | */ | |
80 | void rcu_sync_init(struct rcu_sync *rsp, enum rcu_sync_type type) | |
81 | { | |
82 | memset(rsp, 0, sizeof(*rsp)); | |
83 | init_waitqueue_head(&rsp->gp_wait); | |
82e8c565 | 84 | rsp->gp_type = type; |
cc44ca84 ON |
85 | } |
86 | ||
3942a9bd | 87 | /** |
27fdb35f PM |
88 | * rcu_sync_enter_start - Force readers onto slow path for multiple updates |
89 | * @rsp: Pointer to rcu_sync structure to use for synchronization | |
90 | * | |
3942a9bd PZ |
91 | * Must be called after rcu_sync_init() and before first use. |
92 | * | |
93 | * Ensures rcu_sync_is_idle() returns false and rcu_sync_{enter,exit}() | |
94 | * pairs turn into NO-OPs. | |
95 | */ | |
96 | void rcu_sync_enter_start(struct rcu_sync *rsp) | |
97 | { | |
98 | rsp->gp_count++; | |
99 | rsp->gp_state = GP_PASSED; | |
100 | } | |
101 | ||
cc44ca84 ON |
102 | /** |
103 | * rcu_sync_enter() - Force readers onto slowpath | |
104 | * @rsp: Pointer to rcu_sync structure to use for synchronization | |
105 | * | |
106 | * This function is used by updaters who need readers to make use of | |
107 | * a slowpath during the update. After this function returns, all | |
108 | * subsequent calls to rcu_sync_is_idle() will return false, which | |
109 | * tells readers to stay off their fastpaths. A later call to | |
110 | * rcu_sync_exit() re-enables reader slowpaths. | |
111 | * | |
112 | * When called in isolation, rcu_sync_enter() must wait for a grace | |
113 | * period, however, closely spaced calls to rcu_sync_enter() can | |
114 | * optimize away the grace-period wait via a state machine implemented | |
115 | * by rcu_sync_enter(), rcu_sync_exit(), and rcu_sync_func(). | |
116 | */ | |
117 | void rcu_sync_enter(struct rcu_sync *rsp) | |
118 | { | |
119 | bool need_wait, need_sync; | |
120 | ||
121 | spin_lock_irq(&rsp->rss_lock); | |
122 | need_wait = rsp->gp_count++; | |
123 | need_sync = rsp->gp_state == GP_IDLE; | |
124 | if (need_sync) | |
125 | rsp->gp_state = GP_PENDING; | |
126 | spin_unlock_irq(&rsp->rss_lock); | |
127 | ||
128 | BUG_ON(need_wait && need_sync); | |
129 | ||
130 | if (need_sync) { | |
82e8c565 | 131 | gp_ops[rsp->gp_type].sync(); |
cc44ca84 ON |
132 | rsp->gp_state = GP_PASSED; |
133 | wake_up_all(&rsp->gp_wait); | |
134 | } else if (need_wait) { | |
135 | wait_event(rsp->gp_wait, rsp->gp_state == GP_PASSED); | |
136 | } else { | |
137 | /* | |
138 | * Possible when there's a pending CB from a rcu_sync_exit(). | |
139 | * Nobody has yet been allowed the 'fast' path and thus we can | |
140 | * avoid doing any sync(). The callback will get 'dropped'. | |
141 | */ | |
142 | BUG_ON(rsp->gp_state != GP_PASSED); | |
143 | } | |
144 | } | |
145 | ||
146 | /** | |
147 | * rcu_sync_func() - Callback function managing reader access to fastpath | |
27fdb35f | 148 | * @rhp: Pointer to rcu_head in rcu_sync structure to use for synchronization |
cc44ca84 ON |
149 | * |
150 | * This function is passed to one of the call_rcu() functions by | |
151 | * rcu_sync_exit(), so that it is invoked after a grace period following the | |
152 | * that invocation of rcu_sync_exit(). It takes action based on events that | |
153 | * have taken place in the meantime, so that closely spaced rcu_sync_enter() | |
154 | * and rcu_sync_exit() pairs need not wait for a grace period. | |
155 | * | |
156 | * If another rcu_sync_enter() is invoked before the grace period | |
157 | * ended, reset state to allow the next rcu_sync_exit() to let the | |
158 | * readers back onto their fastpaths (after a grace period). If both | |
159 | * another rcu_sync_enter() and its matching rcu_sync_exit() are invoked | |
160 | * before the grace period ended, re-invoke call_rcu() on behalf of that | |
161 | * rcu_sync_exit(). Otherwise, set all state back to idle so that readers | |
162 | * can again use their fastpaths. | |
163 | */ | |
27fdb35f | 164 | static void rcu_sync_func(struct rcu_head *rhp) |
cc44ca84 | 165 | { |
27fdb35f | 166 | struct rcu_sync *rsp = container_of(rhp, struct rcu_sync, cb_head); |
cc44ca84 ON |
167 | unsigned long flags; |
168 | ||
169 | BUG_ON(rsp->gp_state != GP_PASSED); | |
170 | BUG_ON(rsp->cb_state == CB_IDLE); | |
171 | ||
172 | spin_lock_irqsave(&rsp->rss_lock, flags); | |
173 | if (rsp->gp_count) { | |
174 | /* | |
175 | * A new rcu_sync_begin() has happened; drop the callback. | |
176 | */ | |
177 | rsp->cb_state = CB_IDLE; | |
178 | } else if (rsp->cb_state == CB_REPLAY) { | |
179 | /* | |
180 | * A new rcu_sync_exit() has happened; requeue the callback | |
181 | * to catch a later GP. | |
182 | */ | |
183 | rsp->cb_state = CB_PENDING; | |
82e8c565 | 184 | gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func); |
cc44ca84 ON |
185 | } else { |
186 | /* | |
187 | * We're at least a GP after rcu_sync_exit(); eveybody will now | |
188 | * have observed the write side critical section. Let 'em rip!. | |
189 | */ | |
190 | rsp->cb_state = CB_IDLE; | |
191 | rsp->gp_state = GP_IDLE; | |
192 | } | |
193 | spin_unlock_irqrestore(&rsp->rss_lock, flags); | |
194 | } | |
195 | ||
196 | /** | |
197 | * rcu_sync_exit() - Allow readers back onto fast patch after grace period | |
198 | * @rsp: Pointer to rcu_sync structure to use for synchronization | |
199 | * | |
200 | * This function is used by updaters who have completed, and can therefore | |
201 | * now allow readers to make use of their fastpaths after a grace period | |
202 | * has elapsed. After this grace period has completed, all subsequent | |
203 | * calls to rcu_sync_is_idle() will return true, which tells readers that | |
204 | * they can once again use their fastpaths. | |
205 | */ | |
206 | void rcu_sync_exit(struct rcu_sync *rsp) | |
207 | { | |
208 | spin_lock_irq(&rsp->rss_lock); | |
209 | if (!--rsp->gp_count) { | |
210 | if (rsp->cb_state == CB_IDLE) { | |
211 | rsp->cb_state = CB_PENDING; | |
82e8c565 | 212 | gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func); |
cc44ca84 ON |
213 | } else if (rsp->cb_state == CB_PENDING) { |
214 | rsp->cb_state = CB_REPLAY; | |
215 | } | |
216 | } | |
217 | spin_unlock_irq(&rsp->rss_lock); | |
218 | } | |
07899a6e ON |
219 | |
220 | /** | |
221 | * rcu_sync_dtor() - Clean up an rcu_sync structure | |
222 | * @rsp: Pointer to rcu_sync structure to be cleaned up | |
223 | */ | |
224 | void rcu_sync_dtor(struct rcu_sync *rsp) | |
225 | { | |
226 | int cb_state; | |
227 | ||
228 | BUG_ON(rsp->gp_count); | |
229 | ||
230 | spin_lock_irq(&rsp->rss_lock); | |
231 | if (rsp->cb_state == CB_REPLAY) | |
232 | rsp->cb_state = CB_PENDING; | |
233 | cb_state = rsp->cb_state; | |
234 | spin_unlock_irq(&rsp->rss_lock); | |
235 | ||
236 | if (cb_state != CB_IDLE) { | |
237 | gp_ops[rsp->gp_type].wait(); | |
238 | BUG_ON(rsp->cb_state != CB_IDLE); | |
239 | } | |
240 | } |