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 __rcu_process_callbacks(struct rcu_ctrlblk
*rcp
);
48 static void rcu_process_callbacks(struct softirq_action
*unused
);
49 static void __call_rcu(struct rcu_head
*head
,
50 void (*func
)(struct rcu_head
*rcu
),
51 struct rcu_ctrlblk
*rcp
);
53 static long long rcu_dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
55 #include "rcutiny_plugin.h"
57 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
58 static void rcu_idle_enter_common(long long newval
)
61 RCU_TRACE(trace_rcu_dyntick("--=",
62 rcu_dynticks_nesting
, newval
));
63 rcu_dynticks_nesting
= newval
;
66 RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting
, newval
));
67 if (!is_idle_task(current
)) {
68 struct task_struct
*idle
= idle_task(smp_processor_id());
70 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
71 rcu_dynticks_nesting
, newval
));
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) */
79 rcu_dynticks_nesting
= newval
;
83 * Enter idle, which is an extended quiescent state if we have fully
84 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
86 void rcu_idle_enter(void)
91 local_irq_save(flags
);
92 WARN_ON_ONCE((rcu_dynticks_nesting
& DYNTICK_TASK_NEST_MASK
) == 0);
93 if ((rcu_dynticks_nesting
& DYNTICK_TASK_NEST_MASK
) ==
94 DYNTICK_TASK_NEST_VALUE
)
97 newval
= rcu_dynticks_nesting
- DYNTICK_TASK_NEST_VALUE
;
98 rcu_idle_enter_common(newval
);
99 local_irq_restore(flags
);
101 EXPORT_SYMBOL_GPL(rcu_idle_enter
);
104 * Exit an interrupt handler towards idle.
106 void rcu_irq_exit(void)
111 local_irq_save(flags
);
112 newval
= rcu_dynticks_nesting
- 1;
113 WARN_ON_ONCE(newval
< 0);
114 rcu_idle_enter_common(newval
);
115 local_irq_restore(flags
);
117 EXPORT_SYMBOL_GPL(rcu_irq_exit
);
119 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
120 static void rcu_idle_exit_common(long long oldval
)
123 RCU_TRACE(trace_rcu_dyntick("++=",
124 oldval
, rcu_dynticks_nesting
));
127 RCU_TRACE(trace_rcu_dyntick("End", oldval
, rcu_dynticks_nesting
));
128 if (!is_idle_task(current
)) {
129 struct task_struct
*idle
= idle_task(smp_processor_id());
131 RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
132 oldval
, rcu_dynticks_nesting
));
133 ftrace_dump(DUMP_ALL
);
134 WARN_ONCE(1, "Current pid: %d comm: %s / Idle pid: %d comm: %s",
135 current
->pid
, current
->comm
,
136 idle
->pid
, idle
->comm
); /* must be idle task! */
141 * Exit idle, so that we are no longer in an extended quiescent state.
143 void rcu_idle_exit(void)
148 local_irq_save(flags
);
149 oldval
= rcu_dynticks_nesting
;
150 WARN_ON_ONCE(rcu_dynticks_nesting
< 0);
151 if (rcu_dynticks_nesting
& DYNTICK_TASK_NEST_MASK
)
152 rcu_dynticks_nesting
+= DYNTICK_TASK_NEST_VALUE
;
154 rcu_dynticks_nesting
= DYNTICK_TASK_EXIT_IDLE
;
155 rcu_idle_exit_common(oldval
);
156 local_irq_restore(flags
);
158 EXPORT_SYMBOL_GPL(rcu_idle_exit
);
161 * Enter an interrupt handler, moving away from idle.
163 void rcu_irq_enter(void)
168 local_irq_save(flags
);
169 oldval
= rcu_dynticks_nesting
;
170 rcu_dynticks_nesting
++;
171 WARN_ON_ONCE(rcu_dynticks_nesting
== 0);
172 rcu_idle_exit_common(oldval
);
173 local_irq_restore(flags
);
175 EXPORT_SYMBOL_GPL(rcu_irq_enter
);
177 #ifdef CONFIG_DEBUG_LOCK_ALLOC
180 * Test whether RCU thinks that the current CPU is idle.
182 int rcu_is_cpu_idle(void)
184 return !rcu_dynticks_nesting
;
186 EXPORT_SYMBOL(rcu_is_cpu_idle
);
188 #endif /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
191 * Test whether the current CPU was interrupted from idle. Nested
192 * interrupts don't count, we must be running at the first interrupt
195 static int rcu_is_cpu_rrupt_from_idle(void)
197 return rcu_dynticks_nesting
<= 1;
201 * Helper function for rcu_sched_qs() and rcu_bh_qs().
202 * Also irqs are disabled to avoid confusion due to interrupt handlers
203 * invoking call_rcu().
205 static int rcu_qsctr_help(struct rcu_ctrlblk
*rcp
)
207 RCU_TRACE(reset_cpu_stall_ticks(rcp
));
208 if (rcp
->rcucblist
!= NULL
&&
209 rcp
->donetail
!= rcp
->curtail
) {
210 rcp
->donetail
= rcp
->curtail
;
218 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
219 * are at it, given that any rcu quiescent state is also an rcu_bh
220 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
222 void rcu_sched_qs(int cpu
)
226 local_irq_save(flags
);
227 if (rcu_qsctr_help(&rcu_sched_ctrlblk
) +
228 rcu_qsctr_help(&rcu_bh_ctrlblk
))
229 raise_softirq(RCU_SOFTIRQ
);
230 local_irq_restore(flags
);
234 * Record an rcu_bh quiescent state.
236 void rcu_bh_qs(int cpu
)
240 local_irq_save(flags
);
241 if (rcu_qsctr_help(&rcu_bh_ctrlblk
))
242 raise_softirq(RCU_SOFTIRQ
);
243 local_irq_restore(flags
);
247 * Check to see if the scheduling-clock interrupt came from an extended
248 * quiescent state, and, if so, tell RCU about it. This function must
249 * be called from hardirq context. It is normally called from the
250 * scheduling-clock interrupt.
252 void rcu_check_callbacks(int cpu
, int user
)
254 RCU_TRACE(check_cpu_stalls());
255 if (user
|| rcu_is_cpu_rrupt_from_idle())
257 else if (!in_softirq())
262 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
263 * whose grace period has elapsed.
265 static void __rcu_process_callbacks(struct rcu_ctrlblk
*rcp
)
268 struct rcu_head
*next
, *list
;
270 RCU_TRACE(int cb_count
= 0);
272 /* If no RCU callbacks ready to invoke, just return. */
273 if (&rcp
->rcucblist
== rcp
->donetail
) {
274 RCU_TRACE(trace_rcu_batch_start(rcp
->name
, 0, 0, -1));
275 RCU_TRACE(trace_rcu_batch_end(rcp
->name
, 0,
276 ACCESS_ONCE(rcp
->rcucblist
),
278 is_idle_task(current
),
283 /* Move the ready-to-invoke callbacks to a local list. */
284 local_irq_save(flags
);
285 RCU_TRACE(trace_rcu_batch_start(rcp
->name
, 0, rcp
->qlen
, -1));
286 list
= rcp
->rcucblist
;
287 rcp
->rcucblist
= *rcp
->donetail
;
288 *rcp
->donetail
= NULL
;
289 if (rcp
->curtail
== rcp
->donetail
)
290 rcp
->curtail
= &rcp
->rcucblist
;
291 rcp
->donetail
= &rcp
->rcucblist
;
292 local_irq_restore(flags
);
294 /* Invoke the callbacks on the local list. */
295 RCU_TRACE(rn
= rcp
->name
);
299 debug_rcu_head_unqueue(list
);
301 __rcu_reclaim(rn
, list
);
304 RCU_TRACE(cb_count
++);
306 RCU_TRACE(rcu_trace_sub_qlen(rcp
, cb_count
));
307 RCU_TRACE(trace_rcu_batch_end(rcp
->name
, cb_count
, 0, need_resched(),
308 is_idle_task(current
),
312 static void rcu_process_callbacks(struct softirq_action
*unused
)
314 __rcu_process_callbacks(&rcu_sched_ctrlblk
);
315 __rcu_process_callbacks(&rcu_bh_ctrlblk
);
319 * Wait for a grace period to elapse. But it is illegal to invoke
320 * synchronize_sched() from within an RCU read-side critical section.
321 * Therefore, any legal call to synchronize_sched() is a quiescent
322 * state, and so on a UP system, synchronize_sched() need do nothing.
323 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
324 * benefits of doing might_sleep() to reduce latency.)
326 * Cool, huh? (Due to Josh Triplett.)
328 * But we want to make this a static inline later. The cond_resched()
329 * currently makes this problematic.
331 void synchronize_sched(void)
333 rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map
) &&
334 !lock_is_held(&rcu_lock_map
) &&
335 !lock_is_held(&rcu_sched_lock_map
),
336 "Illegal synchronize_sched() in RCU read-side critical section");
339 EXPORT_SYMBOL_GPL(synchronize_sched
);
342 * Helper function for call_rcu() and call_rcu_bh().
344 static void __call_rcu(struct rcu_head
*head
,
345 void (*func
)(struct rcu_head
*rcu
),
346 struct rcu_ctrlblk
*rcp
)
350 debug_rcu_head_queue(head
);
354 local_irq_save(flags
);
355 *rcp
->curtail
= head
;
356 rcp
->curtail
= &head
->next
;
357 RCU_TRACE(rcp
->qlen
++);
358 local_irq_restore(flags
);
362 * Post an RCU callback to be invoked after the end of an RCU-sched grace
363 * period. But since we have but one CPU, that would be after any
366 void call_rcu_sched(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
368 __call_rcu(head
, func
, &rcu_sched_ctrlblk
);
370 EXPORT_SYMBOL_GPL(call_rcu_sched
);
373 * Post an RCU bottom-half callback to be invoked after any subsequent
376 void call_rcu_bh(struct rcu_head
*head
, void (*func
)(struct rcu_head
*rcu
))
378 __call_rcu(head
, func
, &rcu_bh_ctrlblk
);
380 EXPORT_SYMBOL_GPL(call_rcu_bh
);
384 open_softirq(RCU_SOFTIRQ
, rcu_process_callbacks
);
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