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Linux/kernel/rcu/tiny.c

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  1 /*
  2  * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
  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 IBM Corporation, 2008
 19  *
 20  * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
 21  *
 22  * For detailed explanation of Read-Copy Update mechanism see -
 23  *              Documentation/RCU
 24  */
 25 #include <linux/completion.h>
 26 #include <linux/interrupt.h>
 27 #include <linux/notifier.h>
 28 #include <linux/rcupdate_wait.h>
 29 #include <linux/kernel.h>
 30 #include <linux/export.h>
 31 #include <linux/mutex.h>
 32 #include <linux/sched.h>
 33 #include <linux/types.h>
 34 #include <linux/init.h>
 35 #include <linux/time.h>
 36 #include <linux/cpu.h>
 37 #include <linux/prefetch.h>
 38 
 39 #include "rcu.h"
 40 
 41 /* Global control variables for rcupdate callback mechanism. */
 42 struct rcu_ctrlblk {
 43         struct rcu_head *rcucblist;     /* List of pending callbacks (CBs). */
 44         struct rcu_head **donetail;     /* ->next pointer of last "done" CB. */
 45         struct rcu_head **curtail;      /* ->next pointer of last CB. */
 46 };
 47 
 48 /* Definition for rcupdate control block. */
 49 static struct rcu_ctrlblk rcu_sched_ctrlblk = {
 50         .donetail       = &rcu_sched_ctrlblk.rcucblist,
 51         .curtail        = &rcu_sched_ctrlblk.rcucblist,
 52 };
 53 
 54 static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 55         .donetail       = &rcu_bh_ctrlblk.rcucblist,
 56         .curtail        = &rcu_bh_ctrlblk.rcucblist,
 57 };
 58 
 59 void rcu_barrier_bh(void)
 60 {
 61         wait_rcu_gp(call_rcu_bh);
 62 }
 63 EXPORT_SYMBOL(rcu_barrier_bh);
 64 
 65 void rcu_barrier_sched(void)
 66 {
 67         wait_rcu_gp(call_rcu_sched);
 68 }
 69 EXPORT_SYMBOL(rcu_barrier_sched);
 70 
 71 /*
 72  * Helper function for rcu_sched_qs() and rcu_bh_qs().
 73  * Also irqs are disabled to avoid confusion due to interrupt handlers
 74  * invoking call_rcu().
 75  */
 76 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 77 {
 78         if (rcp->donetail != rcp->curtail) {
 79                 rcp->donetail = rcp->curtail;
 80                 return 1;
 81         }
 82 
 83         return 0;
 84 }
 85 
 86 /*
 87  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 88  * are at it, given that any rcu quiescent state is also an rcu_bh
 89  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 90  */
 91 void rcu_sched_qs(void)
 92 {
 93         unsigned long flags;
 94 
 95         local_irq_save(flags);
 96         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 97             rcu_qsctr_help(&rcu_bh_ctrlblk))
 98                 raise_softirq(RCU_SOFTIRQ);
 99         local_irq_restore(flags);
100 }
101 
102 /*
103  * Record an rcu_bh quiescent state.
104  */
105 void rcu_bh_qs(void)
106 {
107         unsigned long flags;
108 
109         local_irq_save(flags);
110         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
111                 raise_softirq(RCU_SOFTIRQ);
112         local_irq_restore(flags);
113 }
114 
115 /*
116  * Check to see if the scheduling-clock interrupt came from an extended
117  * quiescent state, and, if so, tell RCU about it.  This function must
118  * be called from hardirq context.  It is normally called from the
119  * scheduling-clock interrupt.
120  */
121 void rcu_check_callbacks(int user)
122 {
123         if (user)
124                 rcu_sched_qs();
125         else if (!in_softirq())
126                 rcu_bh_qs();
127         if (user)
128                 rcu_note_voluntary_context_switch(current);
129 }
130 
131 /*
132  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
133  * whose grace period has elapsed.
134  */
135 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
136 {
137         struct rcu_head *next, *list;
138         unsigned long flags;
139 
140         /* Move the ready-to-invoke callbacks to a local list. */
141         local_irq_save(flags);
142         if (rcp->donetail == &rcp->rcucblist) {
143                 /* No callbacks ready, so just leave. */
144                 local_irq_restore(flags);
145                 return;
146         }
147         list = rcp->rcucblist;
148         rcp->rcucblist = *rcp->donetail;
149         *rcp->donetail = NULL;
150         if (rcp->curtail == rcp->donetail)
151                 rcp->curtail = &rcp->rcucblist;
152         rcp->donetail = &rcp->rcucblist;
153         local_irq_restore(flags);
154 
155         /* Invoke the callbacks on the local list. */
156         while (list) {
157                 next = list->next;
158                 prefetch(next);
159                 debug_rcu_head_unqueue(list);
160                 local_bh_disable();
161                 __rcu_reclaim("", list);
162                 local_bh_enable();
163                 list = next;
164         }
165 }
166 
167 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
168 {
169         __rcu_process_callbacks(&rcu_sched_ctrlblk);
170         __rcu_process_callbacks(&rcu_bh_ctrlblk);
171 }
172 
173 /*
174  * Wait for a grace period to elapse.  But it is illegal to invoke
175  * synchronize_sched() from within an RCU read-side critical section.
176  * Therefore, any legal call to synchronize_sched() is a quiescent
177  * state, and so on a UP system, synchronize_sched() need do nothing.
178  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
179  * benefits of doing might_sleep() to reduce latency.)
180  *
181  * Cool, huh?  (Due to Josh Triplett.)
182  */
183 void synchronize_sched(void)
184 {
185         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
186                          lock_is_held(&rcu_lock_map) ||
187                          lock_is_held(&rcu_sched_lock_map),
188                          "Illegal synchronize_sched() in RCU read-side critical section");
189 }
190 EXPORT_SYMBOL_GPL(synchronize_sched);
191 
192 /*
193  * Helper function for call_rcu() and call_rcu_bh().
194  */
195 static void __call_rcu(struct rcu_head *head,
196                        rcu_callback_t func,
197                        struct rcu_ctrlblk *rcp)
198 {
199         unsigned long flags;
200 
201         debug_rcu_head_queue(head);
202         head->func = func;
203         head->next = NULL;
204 
205         local_irq_save(flags);
206         *rcp->curtail = head;
207         rcp->curtail = &head->next;
208         local_irq_restore(flags);
209 
210         if (unlikely(is_idle_task(current))) {
211                 /* force scheduling for rcu_sched_qs() */
212                 resched_cpu(0);
213         }
214 }
215 
216 /*
217  * Post an RCU callback to be invoked after the end of an RCU-sched grace
218  * period.  But since we have but one CPU, that would be after any
219  * quiescent state.
220  */
221 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
222 {
223         __call_rcu(head, func, &rcu_sched_ctrlblk);
224 }
225 EXPORT_SYMBOL_GPL(call_rcu_sched);
226 
227 /*
228  * Post an RCU bottom-half callback to be invoked after any subsequent
229  * quiescent state.
230  */
231 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
232 {
233         __call_rcu(head, func, &rcu_bh_ctrlblk);
234 }
235 EXPORT_SYMBOL_GPL(call_rcu_bh);
236 
237 void __init rcu_init(void)
238 {
239         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
240         rcu_early_boot_tests();
241 }
242 

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