Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / kernel / rcutiny.c
blob0c343b9a46d565cde538f153894010748f1c924d
1 /*
2 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
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.
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.
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.
18 * Copyright IBM Corporation, 2008
20 * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
22 * For detailed explanation of Read-Copy Update mechanism see -
23 * Documentation/RCU
25 #include <linux/moduleparam.h>
26 #include <linux/completion.h>
27 #include <linux/interrupt.h>
28 #include <linux/notifier.h>
29 #include <linux/rcupdate.h>
30 #include <linux/kernel.h>
31 #include <linux/module.h>
32 #include <linux/mutex.h>
33 #include <linux/sched.h>
34 #include <linux/types.h>
35 #include <linux/init.h>
36 #include <linux/time.h>
37 #include <linux/cpu.h>
39 /* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */
40 static struct task_struct *rcu_kthread_task;
41 static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq);
42 static unsigned long have_rcu_kthread_work;
43 static void invoke_rcu_kthread(void);
45 /* Forward declarations for rcutiny_plugin.h. */
46 struct rcu_ctrlblk;
47 static void rcu_process_callbacks(struct rcu_ctrlblk *rcp);
48 static int rcu_kthread(void *arg);
49 static void __call_rcu(struct rcu_head *head,
50 void (*func)(struct rcu_head *rcu),
51 struct rcu_ctrlblk *rcp);
53 #include "rcutiny_plugin.h"
55 #ifdef CONFIG_NO_HZ
57 static long rcu_dynticks_nesting = 1;
60 * Enter dynticks-idle mode, which is an extended quiescent state
61 * if we have fully entered that mode (i.e., if the new value of
62 * dynticks_nesting is zero).
64 void rcu_enter_nohz(void)
66 if (--rcu_dynticks_nesting == 0)
67 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
71 * Exit dynticks-idle mode, so that we are no longer in an extended
72 * quiescent state.
74 void rcu_exit_nohz(void)
76 rcu_dynticks_nesting++;
79 #endif /* #ifdef CONFIG_NO_HZ */
82 * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc().
83 * Also disable irqs to avoid confusion due to interrupt handlers
84 * invoking call_rcu().
86 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
88 unsigned long flags;
90 local_irq_save(flags);
91 if (rcp->rcucblist != NULL &&
92 rcp->donetail != rcp->curtail) {
93 rcp->donetail = rcp->curtail;
94 local_irq_restore(flags);
95 return 1;
97 local_irq_restore(flags);
99 return 0;
103 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
104 * are at it, given that any rcu quiescent state is also an rcu_bh
105 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
107 void rcu_sched_qs(int cpu)
109 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
110 rcu_qsctr_help(&rcu_bh_ctrlblk))
111 invoke_rcu_kthread();
115 * Record an rcu_bh quiescent state.
117 void rcu_bh_qs(int cpu)
119 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
120 invoke_rcu_kthread();
124 * Check to see if the scheduling-clock interrupt came from an extended
125 * quiescent state, and, if so, tell RCU about it.
127 void rcu_check_callbacks(int cpu, int user)
129 if (user ||
130 (idle_cpu(cpu) &&
131 !in_softirq() &&
132 hardirq_count() <= (1 << HARDIRQ_SHIFT)))
133 rcu_sched_qs(cpu);
134 else if (!in_softirq())
135 rcu_bh_qs(cpu);
136 rcu_preempt_check_callbacks();
140 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
141 * whose grace period has elapsed.
143 static void rcu_process_callbacks(struct rcu_ctrlblk *rcp)
145 struct rcu_head *next, *list;
146 unsigned long flags;
147 RCU_TRACE(int cb_count = 0);
149 /* If no RCU callbacks ready to invoke, just return. */
150 if (&rcp->rcucblist == rcp->donetail)
151 return;
153 /* Move the ready-to-invoke callbacks to a local list. */
154 local_irq_save(flags);
155 list = rcp->rcucblist;
156 rcp->rcucblist = *rcp->donetail;
157 *rcp->donetail = NULL;
158 if (rcp->curtail == rcp->donetail)
159 rcp->curtail = &rcp->rcucblist;
160 rcu_preempt_remove_callbacks(rcp);
161 rcp->donetail = &rcp->rcucblist;
162 local_irq_restore(flags);
164 /* Invoke the callbacks on the local list. */
165 while (list) {
166 next = list->next;
167 prefetch(next);
168 debug_rcu_head_unqueue(list);
169 local_bh_disable();
170 list->func(list);
171 local_bh_enable();
172 list = next;
173 RCU_TRACE(cb_count++);
175 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
179 * This kthread invokes RCU callbacks whose grace periods have
180 * elapsed. It is awakened as needed, and takes the place of the
181 * RCU_SOFTIRQ that was used previously for this purpose.
182 * This is a kthread, but it is never stopped, at least not until
183 * the system goes down.
185 static int rcu_kthread(void *arg)
187 unsigned long work;
188 unsigned long morework;
189 unsigned long flags;
191 for (;;) {
192 wait_event_interruptible(rcu_kthread_wq,
193 have_rcu_kthread_work != 0);
194 morework = rcu_boost();
195 local_irq_save(flags);
196 work = have_rcu_kthread_work;
197 have_rcu_kthread_work = morework;
198 local_irq_restore(flags);
199 if (work) {
200 rcu_process_callbacks(&rcu_sched_ctrlblk);
201 rcu_process_callbacks(&rcu_bh_ctrlblk);
202 rcu_preempt_process_callbacks();
204 schedule_timeout_interruptible(1); /* Leave CPU for others. */
207 return 0; /* Not reached, but needed to shut gcc up. */
211 * Wake up rcu_kthread() to process callbacks now eligible for invocation
212 * or to boost readers.
214 static void invoke_rcu_kthread(void)
216 unsigned long flags;
218 local_irq_save(flags);
219 have_rcu_kthread_work = 1;
220 wake_up(&rcu_kthread_wq);
221 local_irq_restore(flags);
225 * Wait for a grace period to elapse. But it is illegal to invoke
226 * synchronize_sched() from within an RCU read-side critical section.
227 * Therefore, any legal call to synchronize_sched() is a quiescent
228 * state, and so on a UP system, synchronize_sched() need do nothing.
229 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
230 * benefits of doing might_sleep() to reduce latency.)
232 * Cool, huh? (Due to Josh Triplett.)
234 * But we want to make this a static inline later. The cond_resched()
235 * currently makes this problematic.
237 void synchronize_sched(void)
239 cond_resched();
241 EXPORT_SYMBOL_GPL(synchronize_sched);
244 * Helper function for call_rcu() and call_rcu_bh().
246 static void __call_rcu(struct rcu_head *head,
247 void (*func)(struct rcu_head *rcu),
248 struct rcu_ctrlblk *rcp)
250 unsigned long flags;
252 debug_rcu_head_queue(head);
253 head->func = func;
254 head->next = NULL;
256 local_irq_save(flags);
257 *rcp->curtail = head;
258 rcp->curtail = &head->next;
259 RCU_TRACE(rcp->qlen++);
260 local_irq_restore(flags);
264 * Post an RCU callback to be invoked after the end of an RCU-sched grace
265 * period. But since we have but one CPU, that would be after any
266 * quiescent state.
268 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
270 __call_rcu(head, func, &rcu_sched_ctrlblk);
272 EXPORT_SYMBOL_GPL(call_rcu_sched);
275 * Post an RCU bottom-half callback to be invoked after any subsequent
276 * quiescent state.
278 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
280 __call_rcu(head, func, &rcu_bh_ctrlblk);
282 EXPORT_SYMBOL_GPL(call_rcu_bh);
284 void rcu_barrier_bh(void)
286 struct rcu_synchronize rcu;
288 init_rcu_head_on_stack(&rcu.head);
289 init_completion(&rcu.completion);
290 /* Will wake me after RCU finished. */
291 call_rcu_bh(&rcu.head, wakeme_after_rcu);
292 /* Wait for it. */
293 wait_for_completion(&rcu.completion);
294 destroy_rcu_head_on_stack(&rcu.head);
296 EXPORT_SYMBOL_GPL(rcu_barrier_bh);
298 void rcu_barrier_sched(void)
300 struct rcu_synchronize rcu;
302 init_rcu_head_on_stack(&rcu.head);
303 init_completion(&rcu.completion);
304 /* Will wake me after RCU finished. */
305 call_rcu_sched(&rcu.head, wakeme_after_rcu);
306 /* Wait for it. */
307 wait_for_completion(&rcu.completion);
308 destroy_rcu_head_on_stack(&rcu.head);
310 EXPORT_SYMBOL_GPL(rcu_barrier_sched);
313 * Spawn the kthread that invokes RCU callbacks.
315 static int __init rcu_spawn_kthreads(void)
317 struct sched_param sp;
319 rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread");
320 sp.sched_priority = RCU_BOOST_PRIO;
321 sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp);
322 return 0;
324 early_initcall(rcu_spawn_kthreads);