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 = LLONG_MAX / 2;
58 /* Common code for rcu_idle_enter() and rcu_irq_exit(), see kernel/rcutree.c. */
59 static void rcu_idle_enter_common(void)
61 if (rcu_dynticks_nesting) {
62 RCU_TRACE(trace_rcu_dyntick("--=", rcu_dynticks_nesting));
65 RCU_TRACE(trace_rcu_dyntick("Start", rcu_dynticks_nesting));
66 if (!idle_cpu(smp_processor_id())) {
67 WARN_ON_ONCE(1); /* must be idle task! */
68 RCU_TRACE(trace_rcu_dyntick("Error on entry: not idle task",
69 rcu_dynticks_nesting));
70 ftrace_dump(DUMP_ALL);
72 rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */
76 * Enter idle, which is an extended quiescent state if we have fully
77 * entered that mode (i.e., if the new value of dynticks_nesting is zero).
79 void rcu_idle_enter(void)
83 local_irq_save(flags);
84 rcu_dynticks_nesting = 0;
85 rcu_idle_enter_common();
86 local_irq_restore(flags);
90 * Exit an interrupt handler towards idle.
92 void rcu_irq_exit(void)
96 local_irq_save(flags);
97 rcu_dynticks_nesting--;
98 WARN_ON_ONCE(rcu_dynticks_nesting < 0);
99 rcu_idle_enter_common();
100 local_irq_restore(flags);
103 /* Common code for rcu_idle_exit() and rcu_irq_enter(), see kernel/rcutree.c. */
104 static void rcu_idle_exit_common(long long oldval)
107 RCU_TRACE(trace_rcu_dyntick("++=", rcu_dynticks_nesting));
110 RCU_TRACE(trace_rcu_dyntick("End", oldval));
111 if (!idle_cpu(smp_processor_id())) {
112 WARN_ON_ONCE(1); /* must be idle task! */
113 RCU_TRACE(trace_rcu_dyntick("Error on exit: not idle task",
115 ftrace_dump(DUMP_ALL);
120 * Exit idle, so that we are no longer in an extended quiescent state.
122 void rcu_idle_exit(void)
127 local_irq_save(flags);
128 oldval = rcu_dynticks_nesting;
129 WARN_ON_ONCE(oldval != 0);
130 rcu_dynticks_nesting = LLONG_MAX / 2;
131 rcu_idle_exit_common(oldval);
132 local_irq_restore(flags);
136 * Enter an interrupt handler, moving away from idle.
138 void rcu_irq_enter(void)
143 local_irq_save(flags);
144 oldval = rcu_dynticks_nesting;
145 rcu_dynticks_nesting++;
146 WARN_ON_ONCE(rcu_dynticks_nesting == 0);
147 rcu_idle_exit_common(oldval);
148 local_irq_restore(flags);
151 #ifdef CONFIG_PROVE_RCU
154 * Test whether RCU thinks that the current CPU is idle.
156 int rcu_is_cpu_idle(void)
158 return !rcu_dynticks_nesting;
160 EXPORT_SYMBOL(rcu_is_cpu_idle);
162 #endif /* #ifdef CONFIG_PROVE_RCU */
165 * Test whether the current CPU was interrupted from idle. Nested
166 * interrupts don't count, we must be running at the first interrupt
169 int rcu_is_cpu_rrupt_from_idle(void)
171 return rcu_dynticks_nesting <= 0;
175 * Helper function for rcu_sched_qs() and rcu_bh_qs().
176 * Also irqs are disabled to avoid confusion due to interrupt handlers
177 * invoking call_rcu().
179 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
181 if (rcp->rcucblist != NULL &&
182 rcp->donetail != rcp->curtail) {
183 rcp->donetail = rcp->curtail;
191 * Record an rcu quiescent state. And an rcu_bh quiescent state while we
192 * are at it, given that any rcu quiescent state is also an rcu_bh
193 * quiescent state. Use "+" instead of "||" to defeat short circuiting.
195 void rcu_sched_qs(int cpu)
199 local_irq_save(flags);
200 if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
201 rcu_qsctr_help(&rcu_bh_ctrlblk))
202 invoke_rcu_callbacks();
203 local_irq_restore(flags);
207 * Record an rcu_bh quiescent state.
209 void rcu_bh_qs(int cpu)
213 local_irq_save(flags);
214 if (rcu_qsctr_help(&rcu_bh_ctrlblk))
215 invoke_rcu_callbacks();
216 local_irq_restore(flags);
220 * Check to see if the scheduling-clock interrupt came from an extended
221 * quiescent state, and, if so, tell RCU about it. This function must
222 * be called from hardirq context. It is normally called from the
223 * scheduling-clock interrupt.
225 void rcu_check_callbacks(int cpu, int user)
227 if (user || rcu_is_cpu_rrupt_from_idle())
229 else if (!in_softirq())
231 rcu_preempt_check_callbacks();
235 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
236 * whose grace period has elapsed.
238 static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
241 struct rcu_head *next, *list;
243 RCU_TRACE(int cb_count = 0);
245 /* If no RCU callbacks ready to invoke, just return. */
246 if (&rcp->rcucblist == rcp->donetail) {
247 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
248 RCU_TRACE(trace_rcu_batch_end(rcp->name, 0));
252 /* Move the ready-to-invoke callbacks to a local list. */
253 local_irq_save(flags);
254 RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, -1));
255 list = rcp->rcucblist;
256 rcp->rcucblist = *rcp->donetail;
257 *rcp->donetail = NULL;
258 if (rcp->curtail == rcp->donetail)
259 rcp->curtail = &rcp->rcucblist;
260 rcu_preempt_remove_callbacks(rcp);
261 rcp->donetail = &rcp->rcucblist;
262 local_irq_restore(flags);
264 /* Invoke the callbacks on the local list. */
265 RCU_TRACE(rn = rcp->name);
269 debug_rcu_head_unqueue(list);
271 __rcu_reclaim(rn, list);
274 RCU_TRACE(cb_count++);
276 RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
277 RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count));
280 static void rcu_process_callbacks(struct softirq_action *unused)
282 __rcu_process_callbacks(&rcu_sched_ctrlblk);
283 __rcu_process_callbacks(&rcu_bh_ctrlblk);
284 rcu_preempt_process_callbacks();
288 * Wait for a grace period to elapse. But it is illegal to invoke
289 * synchronize_sched() from within an RCU read-side critical section.
290 * Therefore, any legal call to synchronize_sched() is a quiescent
291 * state, and so on a UP system, synchronize_sched() need do nothing.
292 * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the
293 * benefits of doing might_sleep() to reduce latency.)
295 * Cool, huh? (Due to Josh Triplett.)
297 * But we want to make this a static inline later. The cond_resched()
298 * currently makes this problematic.
300 void synchronize_sched(void)
304 EXPORT_SYMBOL_GPL(synchronize_sched);
307 * Helper function for call_rcu() and call_rcu_bh().
309 static void __call_rcu(struct rcu_head *head,
310 void (*func)(struct rcu_head *rcu),
311 struct rcu_ctrlblk *rcp)
315 debug_rcu_head_queue(head);
319 local_irq_save(flags);
320 *rcp->curtail = head;
321 rcp->curtail = &head->next;
322 RCU_TRACE(rcp->qlen++);
323 local_irq_restore(flags);
327 * Post an RCU callback to be invoked after the end of an RCU-sched grace
328 * period. But since we have but one CPU, that would be after any
331 void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
333 __call_rcu(head, func, &rcu_sched_ctrlblk);
335 EXPORT_SYMBOL_GPL(call_rcu_sched);
338 * Post an RCU bottom-half callback to be invoked after any subsequent
341 void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
343 __call_rcu(head, func, &rcu_bh_ctrlblk);
345 EXPORT_SYMBOL_GPL(call_rcu_bh);