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 -
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>
39 #ifdef CONFIG_RCU_TRACE
40 #include <trace/events/rcu.h>
41 #endif /* #else #ifdef CONFIG_RCU_TRACE */
45 /* Forward declarations for rcutiny_plugin.h. */
47 static void invoke_rcu_callbacks(void);
48 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
49 static void rcu_process_callbacks(struct softirq_action *unused);
50 static void __call_rcu(struct rcu_head *head,
51 void (*func)(struct rcu_head *rcu),
52 struct rcu_ctrlblk *rcp);
54 #include "rcutiny_plugin.h"
56 static long long rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
58 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
59 static void rcu_idle_enter_common(long long oldval)
61 if (rcu_dynticks_nesting) {
62 RCU_TRACE(trace_rcu_dyntick("--=",
63 oldval, rcu_dynticks_nesting));
66 RCU_TRACE(trace_rcu_dyntick("Start", oldval, rcu_dynticks_nesting));
67 if (!idle_cpu(smp_processor_id())) {
68 struct task_struct *idle = idle_task(smp_processor_id());
70 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
71 oldval, rcu_dynticks_nesting));
72 ftrace_dump(DUMP_ALL);
73 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
74 current->pid, current->comm,
75 idle->pid, idle->comm); /* must be idle task! */
77 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
81 * Enter idle, which is an extended quiescent state if we have fully
82 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
84 void rcu_idle_enter(void)
89 local_irq_save(flags);
90 oldval = rcu_dynticks_nesting;
91 rcu_dynticks_nesting = 0;
92 rcu_idle_enter_common(oldval);
93 local_irq_restore(flags);
97 * Exit an interrupt handler towards idle.
99 void rcu_irq_exit(void)
104 local_irq_save(flags);
105 oldval = rcu_dynticks_nesting;
106 rcu_dynticks_nesting--;
107 WARN_ON_ONCE(rcu_dynticks_nesting < 0);
108 rcu_idle_enter_common(oldval);
109 local_irq_restore(flags);
112 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
113 static void rcu_idle_exit_common(long long oldval)
116 RCU_TRACE(trace_rcu_dyntick("++=",
117 oldval, rcu_dynticks_nesting));
120 RCU_TRACE(trace_rcu_dyntick("End", oldval, rcu_dynticks_nesting));
121 if (!idle_cpu(smp_processor_id())) {
122 struct task_struct *idle = idle_task(smp_processor_id());
124 RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
125 oldval, rcu_dynticks_nesting));
126 ftrace_dump(DUMP_ALL);
127 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
128 current->pid, current->comm,
129 idle->pid, idle->comm); /* must be idle task! */
134 * Exit idle, so that we are no longer in an extended quiescent state.
136 void rcu_idle_exit(void)
141 local_irq_save(flags);
142 oldval = rcu_dynticks_nesting;
143 WARN_ON_ONCE(oldval != 0);
144 rcu_dynticks_nesting = DYNTICK_TASK_NESTING;
145 rcu_idle_exit_common(oldval);
146 local_irq_restore(flags);
150 * Enter an interrupt handler, moving away from idle.
152 void rcu_irq_enter(void)
157 local_irq_save(flags);
158 oldval = rcu_dynticks_nesting;
159 rcu_dynticks_nesting++;
160 WARN_ON_ONCE(rcu_dynticks_nesting == 0);
161 rcu_idle_exit_common(oldval);
162 local_irq_restore(flags);
165 #ifdef CONFIG_PROVE_RCU
168 * Test whether RCU thinks that the current CPU is idle.
170 int rcu_is_cpu_idle(void)
172 return !rcu_dynticks_nesting;
174 EXPORT_SYMBOL(rcu_is_cpu_idle);
176 #endif /* #ifdef CONFIG_PROVE_RCU */
179 * Test whether the current CPU was interrupted from idle. Nested
180 * interrupts don't count, we must be running at the first interrupt
183 int rcu_is_cpu_rrupt_from_idle(void)
185 return rcu_dynticks_nesting <= 0;
189 * Helper function for rcu_sched_qs() and rcu_bh_qs().
190 * Also irqs are disabled to avoid confusion due to interrupt handlers
191 * invoking call_rcu().
193 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
195 if (rcp->rcucblist != NULL &&
196 rcp->donetail != rcp->curtail) {
197 rcp->donetail = rcp->curtail;
205 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
206 * are at it, given that any rcu quiescent state is also an rcu_bh
207 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
209 void rcu_sched_qs(int cpu)
213 local_irq_save(flags);
214 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
215 rcu_qsctr_help(&rcu_bh_ctrlblk))
216 invoke_rcu_callbacks();
217 local_irq_restore(flags);
221 * Record an rcu_bh quiescent state.
223 void rcu_bh_qs(int cpu)
227 local_irq_save(flags);
228 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
229 invoke_rcu_callbacks();
230 local_irq_restore(flags);
234 * Check to see if the scheduling-clock interrupt came from an extended
235 * quiescent state, and, if so, tell RCU about it. This function must
236 * be called from hardirq context. It is normally called from the
237 * scheduling-clock interrupt.
239 void rcu_check_callbacks(int cpu, int user)
241 if (user || rcu_is_cpu_rrupt_from_idle())
243 else if (!in_softirq())
245 rcu_preempt_check_callbacks();
249 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
250 * whose grace period has elapsed.
252 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
255 struct rcu_head *next, *list;
257 RCU_TRACE(int cb_count = 0);
259 /* If no RCU callbacks ready to invoke, just return. */
260 if (&rcp->rcucblist == rcp->donetail) {
261 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
262 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0));
266 /* Move the ready-to-invoke callbacks to a local list. */
267 local_irq_save(flags);
268 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
269 list = rcp->rcucblist;
270 rcp->rcucblist = *rcp->donetail;
271 *rcp->donetail = NULL;
272 if (rcp->curtail == rcp->donetail)
273 rcp->curtail = &rcp->rcucblist;
274 rcu_preempt_remove_callbacks(rcp);
275 rcp->donetail = &rcp->rcucblist;
276 local_irq_restore(flags);
278 /* Invoke the callbacks on the local list. */
279 RCU_TRACE(rn = rcp->name);
283 debug_rcu_head_unqueue(list);
285 __rcu_reclaim(rn, list);
288 RCU_TRACE(cb_count++);
290 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
291 RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));
294 static void rcu_process_callbacks(struct softirq_action *unused)
296 __rcu_process_callbacks(&rcu_sched_ctrlblk);
297 __rcu_process_callbacks(&rcu_bh_ctrlblk);
298 rcu_preempt_process_callbacks();
302 * Wait for a grace period to elapse. But it is illegal to invoke
303 * synchronize_sched() from within an RCU read-side critical section.
304 * Therefore, any legal call to synchronize_sched() is a quiescent
305 * state, and so on a UP system, synchronize_sched() need do nothing.
306 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
307 * benefits of doing might_sleep() to reduce latency.)
309 * Cool, huh? (Due to Josh Triplett.)
311 * But we want to make this a static inline later. The cond_resched()
312 * currently makes this problematic.
314 void synchronize_sched(void)
318 EXPORT_SYMBOL_GPL(synchronize_sched);
321 * Helper function for call_rcu() and call_rcu_bh().
323 static void __call_rcu(struct rcu_head *head,
324 void (*func)(struct rcu_head *rcu),
325 struct rcu_ctrlblk *rcp)
329 debug_rcu_head_queue(head);
333 local_irq_save(flags);
334 *rcp->curtail = head;
335 rcp->curtail = &head->next;
336 RCU_TRACE(rcp->qlen++);
337 local_irq_restore(flags);
341 * Post an RCU callback to be invoked after the end of an RCU-sched grace
342 * period. But since we have but one CPU, that would be after any
345 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
347 __call_rcu(head, func, &rcu_sched_ctrlblk);
349 EXPORT_SYMBOL_GPL(call_rcu_sched);
352 * Post an RCU bottom-half callback to be invoked after any subsequent
355 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
357 __call_rcu(head, func, &rcu_bh_ctrlblk);
359 EXPORT_SYMBOL_GPL(call_rcu_bh);