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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.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 #include <linux/trace_events.h>
 39 
 40 #include "rcu.h"
 41 
 42 /* Forward declarations for tiny_plugin.h. */
 43 struct rcu_ctrlblk;
 44 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
 45 static void rcu_process_callbacks(struct softirq_action *unused);
 46 static void __call_rcu(struct rcu_head *head,
 47                        rcu_callback_t func,
 48                        struct rcu_ctrlblk *rcp);
 49 
 50 #include "tiny_plugin.h"
 51 
 52 #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
 53 
 54 /*
 55  * Test whether RCU thinks that the current CPU is idle.
 56  */
 57 bool notrace __rcu_is_watching(void)
 58 {
 59         return true;
 60 }
 61 EXPORT_SYMBOL(__rcu_is_watching);
 62 
 63 #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
 64 
 65 /*
 66  * Helper function for rcu_sched_qs() and rcu_bh_qs().
 67  * Also irqs are disabled to avoid confusion due to interrupt handlers
 68  * invoking call_rcu().
 69  */
 70 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 71 {
 72         RCU_TRACE(reset_cpu_stall_ticks(rcp));
 73         if (rcp->donetail != rcp->curtail) {
 74                 rcp->donetail = rcp->curtail;
 75                 return 1;
 76         }
 77 
 78         return 0;
 79 }
 80 
 81 /*
 82  * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 83  * are at it, given that any rcu quiescent state is also an rcu_bh
 84  * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 85  */
 86 void rcu_sched_qs(void)
 87 {
 88         unsigned long flags;
 89 
 90         local_irq_save(flags);
 91         if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 92             rcu_qsctr_help(&rcu_bh_ctrlblk))
 93                 raise_softirq(RCU_SOFTIRQ);
 94         local_irq_restore(flags);
 95 }
 96 
 97 /*
 98  * Record an rcu_bh quiescent state.
 99  */
100 void rcu_bh_qs(void)
101 {
102         unsigned long flags;
103 
104         local_irq_save(flags);
105         if (rcu_qsctr_help(&rcu_bh_ctrlblk))
106                 raise_softirq(RCU_SOFTIRQ);
107         local_irq_restore(flags);
108 }
109 
110 /*
111  * Check to see if the scheduling-clock interrupt came from an extended
112  * quiescent state, and, if so, tell RCU about it.  This function must
113  * be called from hardirq context.  It is normally called from the
114  * scheduling-clock interrupt.
115  */
116 void rcu_check_callbacks(int user)
117 {
118         RCU_TRACE(check_cpu_stalls());
119         if (user)
120                 rcu_sched_qs();
121         else if (!in_softirq())
122                 rcu_bh_qs();
123         if (user)
124                 rcu_note_voluntary_context_switch(current);
125 }
126 
127 /*
128  * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
129  * whose grace period has elapsed.
130  */
131 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
132 {
133         const char *rn = NULL;
134         struct rcu_head *next, *list;
135         unsigned long flags;
136         RCU_TRACE(int cb_count = 0);
137 
138         /* Move the ready-to-invoke callbacks to a local list. */
139         local_irq_save(flags);
140         if (rcp->donetail == &rcp->rcucblist) {
141                 /* No callbacks ready, so just leave. */
142                 local_irq_restore(flags);
143                 return;
144         }
145         RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
146         list = rcp->rcucblist;
147         rcp->rcucblist = *rcp->donetail;
148         *rcp->donetail = NULL;
149         if (rcp->curtail == rcp->donetail)
150                 rcp->curtail = &rcp->rcucblist;
151         rcp->donetail = &rcp->rcucblist;
152         local_irq_restore(flags);
153 
154         /* Invoke the callbacks on the local list. */
155         RCU_TRACE(rn = rcp->name);
156         while (list) {
157                 next = list->next;
158                 prefetch(next);
159                 debug_rcu_head_unqueue(list);
160                 local_bh_disable();
161                 __rcu_reclaim(rn, list);
162                 local_bh_enable();
163                 list = next;
164                 RCU_TRACE(cb_count++);
165         }
166         RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
167         RCU_TRACE(trace_rcu_batch_end(rcp->name,
168                                       cb_count, 0, need_resched(),
169                                       is_idle_task(current),
170                                       false));
171 }
172 
173 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
174 {
175         __rcu_process_callbacks(&rcu_sched_ctrlblk);
176         __rcu_process_callbacks(&rcu_bh_ctrlblk);
177 }
178 
179 /*
180  * Wait for a grace period to elapse.  But it is illegal to invoke
181  * synchronize_sched() from within an RCU read-side critical section.
182  * Therefore, any legal call to synchronize_sched() is a quiescent
183  * state, and so on a UP system, synchronize_sched() need do nothing.
184  * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
185  * benefits of doing might_sleep() to reduce latency.)
186  *
187  * Cool, huh?  (Due to Josh Triplett.)
188  */
189 void synchronize_sched(void)
190 {
191         RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
192                          lock_is_held(&rcu_lock_map) ||
193                          lock_is_held(&rcu_sched_lock_map),
194                          "Illegal synchronize_sched() in RCU read-side critical section");
195 }
196 EXPORT_SYMBOL_GPL(synchronize_sched);
197 
198 /*
199  * Helper function for call_rcu() and call_rcu_bh().
200  */
201 static void __call_rcu(struct rcu_head *head,
202                        rcu_callback_t func,
203                        struct rcu_ctrlblk *rcp)
204 {
205         unsigned long flags;
206 
207         debug_rcu_head_queue(head);
208         head->func = func;
209         head->next = NULL;
210 
211         local_irq_save(flags);
212         *rcp->curtail = head;
213         rcp->curtail = &head->next;
214         RCU_TRACE(rcp->qlen++);
215         local_irq_restore(flags);
216 
217         if (unlikely(is_idle_task(current))) {
218                 /* force scheduling for rcu_sched_qs() */
219                 resched_cpu(0);
220         }
221 }
222 
223 /*
224  * Post an RCU callback to be invoked after the end of an RCU-sched grace
225  * period.  But since we have but one CPU, that would be after any
226  * quiescent state.
227  */
228 void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
229 {
230         __call_rcu(head, func, &rcu_sched_ctrlblk);
231 }
232 EXPORT_SYMBOL_GPL(call_rcu_sched);
233 
234 /*
235  * Post an RCU bottom-half callback to be invoked after any subsequent
236  * quiescent state.
237  */
238 void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
239 {
240         __call_rcu(head, func, &rcu_bh_ctrlblk);
241 }
242 EXPORT_SYMBOL_GPL(call_rcu_bh);
243 
244 void __init rcu_init(void)
245 {
246         open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
247         RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
248         RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
249 
250         rcu_early_boot_tests();
251 }
252 

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