~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

TOMOYO Linux Cross Reference
Linux/kernel/rcu/sync.c

Version: ~ [ linux-4.16-rc1 ] ~ [ linux-4.15.2 ] ~ [ linux-4.14.18 ] ~ [ linux-4.13.16 ] ~ [ linux-4.12.14 ] ~ [ linux-4.11.12 ] ~ [ linux-4.10.17 ] ~ [ linux-4.9.80 ] ~ [ linux-4.8.17 ] ~ [ linux-4.7.10 ] ~ [ linux-4.6.7 ] ~ [ linux-4.5.7 ] ~ [ linux-4.4.115 ] ~ [ linux-4.3.6 ] ~ [ linux-4.2.8 ] ~ [ linux-4.1.49 ] ~ [ linux-4.0.9 ] ~ [ linux-3.19.8 ] ~ [ linux-3.18.94 ] ~ [ linux-3.17.8 ] ~ [ linux-3.16.53 ] ~ [ linux-3.15.10 ] ~ [ linux-3.14.79 ] ~ [ linux-3.13.11 ] ~ [ linux-3.12.74 ] ~ [ linux-3.11.10 ] ~ [ linux-3.10.108 ] ~ [ linux-3.9.11 ] ~ [ linux-3.8.13 ] ~ [ linux-3.7.10 ] ~ [ linux-3.6.11 ] ~ [ linux-3.5.7 ] ~ [ linux-3.4.113 ] ~ [ linux-3.3.8 ] ~ [ linux-3.2.98 ] ~ [ linux-3.1.10 ] ~ [ linux-3.0.101 ] ~ [ linux-2.6.39.4 ] ~ [ linux-2.6.38.8 ] ~ [ linux-2.6.37.6 ] ~ [ linux-2.6.36.4 ] ~ [ linux-2.6.35.14 ] ~ [ linux-2.6.34.15 ] ~ [ linux-2.6.33.20 ] ~ [ linux-2.6.32.71 ] ~ [ linux-2.6.27.62 ] ~ [ linux-2.6.0 ] ~ [ linux-2.4.37.11 ] ~ [ unix-v6-master ] ~ [ ccs-tools-1.8.5 ] ~ [ policy-sample ] ~
Architecture: ~ [ i386 ] ~ [ alpha ] ~ [ m68k ] ~ [ mips ] ~ [ ppc ] ~ [ sparc ] ~ [ sparc64 ] ~

  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 
 26 #ifdef CONFIG_PROVE_RCU
 27 #define __INIT_HELD(func)       .held = func,
 28 #else
 29 #define __INIT_HELD(func)
 30 #endif
 31 
 32 static const struct {
 33         void (*sync)(void);
 34         void (*call)(struct rcu_head *, void (*)(struct rcu_head *));
 35         void (*wait)(void);
 36 #ifdef CONFIG_PROVE_RCU
 37         int  (*held)(void);
 38 #endif
 39 } gp_ops[] = {
 40         [RCU_SYNC] = {
 41                 .sync = synchronize_rcu,
 42                 .call = call_rcu,
 43                 .wait = rcu_barrier,
 44                 __INIT_HELD(rcu_read_lock_held)
 45         },
 46         [RCU_SCHED_SYNC] = {
 47                 .sync = synchronize_sched,
 48                 .call = call_rcu_sched,
 49                 .wait = rcu_barrier_sched,
 50                 __INIT_HELD(rcu_read_lock_sched_held)
 51         },
 52         [RCU_BH_SYNC] = {
 53                 .sync = synchronize_rcu_bh,
 54                 .call = call_rcu_bh,
 55                 .wait = rcu_barrier_bh,
 56                 __INIT_HELD(rcu_read_lock_bh_held)
 57         },
 58 };
 59 
 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 
 65 #ifdef CONFIG_PROVE_RCU
 66 void rcu_sync_lockdep_assert(struct rcu_sync *rsp)
 67 {
 68         RCU_LOCKDEP_WARN(!gp_ops[rsp->gp_type].held(),
 69                          "suspicious rcu_sync_is_idle() usage");
 70 }
 71 
 72 EXPORT_SYMBOL_GPL(rcu_sync_lockdep_assert);
 73 #endif
 74 
 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);
 84         rsp->gp_type = type;
 85 }
 86 
 87 /**
 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  *
 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 
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) {
131                 gp_ops[rsp->gp_type].sync();
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
148  * @rhp: Pointer to rcu_head in rcu_sync structure to use for synchronization
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  */
164 static void rcu_sync_func(struct rcu_head *rhp)
165 {
166         struct rcu_sync *rsp = container_of(rhp, struct rcu_sync, cb_head);
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;
184                 gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
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;
212                         gp_ops[rsp->gp_type].call(&rsp->cb_head, rcu_sync_func);
213                 } else if (rsp->cb_state == CB_PENDING) {
214                         rsp->cb_state = CB_REPLAY;
215                 }
216         }
217         spin_unlock_irq(&rsp->rss_lock);
218 }
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 }
241 

~ [ source navigation ] ~ [ diff markup ] ~ [ identifier search ] ~

kernel.org | git.kernel.org | LWN.net | Project Home | Wiki (Japanese) | Wiki (English) | SVN repository | Mail admin

Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.

osdn.jp