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/ftrace_event.h>
39
40#include "rcu.h"
41
42/* Forward declarations for tiny_plugin.h. */
43struct rcu_ctrlblk;
44static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp);
45static void rcu_process_callbacks(struct softirq_action *unused);
46static void __call_rcu(struct rcu_head *head,
47		       void (*func)(struct rcu_head *rcu),
48		       struct rcu_ctrlblk *rcp);
49
50#include "tiny_plugin.h"
51
52/*
53 * Enter idle, which is an extended quiescent state if we have fully
54 * entered that mode.
55 */
56void rcu_idle_enter(void)
57{
58}
59EXPORT_SYMBOL_GPL(rcu_idle_enter);
60
61/*
62 * Exit an interrupt handler towards idle.
63 */
64void rcu_irq_exit(void)
65{
66}
67EXPORT_SYMBOL_GPL(rcu_irq_exit);
68
69/*
70 * Exit idle, so that we are no longer in an extended quiescent state.
71 */
72void rcu_idle_exit(void)
73{
74}
75EXPORT_SYMBOL_GPL(rcu_idle_exit);
76
77/*
78 * Enter an interrupt handler, moving away from idle.
79 */
80void rcu_irq_enter(void)
81{
82}
83EXPORT_SYMBOL_GPL(rcu_irq_enter);
84
85#if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE)
86
87/*
88 * Test whether RCU thinks that the current CPU is idle.
89 */
90bool notrace __rcu_is_watching(void)
91{
92	return true;
93}
94EXPORT_SYMBOL(__rcu_is_watching);
95
96#endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */
97
98/*
99 * Helper function for rcu_sched_qs() and rcu_bh_qs().
100 * Also irqs are disabled to avoid confusion due to interrupt handlers
101 * invoking call_rcu().
102 */
103static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
104{
105	RCU_TRACE(reset_cpu_stall_ticks(rcp));
106	if (rcp->donetail != rcp->curtail) {
107		rcp->donetail = rcp->curtail;
108		return 1;
109	}
110
111	return 0;
112}
113
114/*
115 * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
116 * are at it, given that any rcu quiescent state is also an rcu_bh
117 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
118 */
119void rcu_sched_qs(void)
120{
121	unsigned long flags;
122
123	local_irq_save(flags);
124	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
125	    rcu_qsctr_help(&rcu_bh_ctrlblk))
126		raise_softirq(RCU_SOFTIRQ);
127	local_irq_restore(flags);
128}
129
130/*
131 * Record an rcu_bh quiescent state.
132 */
133void rcu_bh_qs(void)
134{
135	unsigned long flags;
136
137	local_irq_save(flags);
138	if (rcu_qsctr_help(&rcu_bh_ctrlblk))
139		raise_softirq(RCU_SOFTIRQ);
140	local_irq_restore(flags);
141}
142
143/*
144 * Check to see if the scheduling-clock interrupt came from an extended
145 * quiescent state, and, if so, tell RCU about it.  This function must
146 * be called from hardirq context.  It is normally called from the
147 * scheduling-clock interrupt.
148 */
149void rcu_check_callbacks(int user)
150{
151	RCU_TRACE(check_cpu_stalls());
152	if (user)
153		rcu_sched_qs();
154	else if (!in_softirq())
155		rcu_bh_qs();
156	if (user)
157		rcu_note_voluntary_context_switch(current);
158}
159
160/*
161 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
162 * whose grace period has elapsed.
163 */
164static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
165{
166	const char *rn = NULL;
167	struct rcu_head *next, *list;
168	unsigned long flags;
169	RCU_TRACE(int cb_count = 0);
170
171	/* Move the ready-to-invoke callbacks to a local list. */
172	local_irq_save(flags);
173	if (rcp->donetail == &rcp->rcucblist) {
174		/* No callbacks ready, so just leave. */
175		local_irq_restore(flags);
176		return;
177	}
178	RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1));
179	list = rcp->rcucblist;
180	rcp->rcucblist = *rcp->donetail;
181	*rcp->donetail = NULL;
182	if (rcp->curtail == rcp->donetail)
183		rcp->curtail = &rcp->rcucblist;
184	rcp->donetail = &rcp->rcucblist;
185	local_irq_restore(flags);
186
187	/* Invoke the callbacks on the local list. */
188	RCU_TRACE(rn = rcp->name);
189	while (list) {
190		next = list->next;
191		prefetch(next);
192		debug_rcu_head_unqueue(list);
193		local_bh_disable();
194		__rcu_reclaim(rn, list);
195		local_bh_enable();
196		list = next;
197		RCU_TRACE(cb_count++);
198	}
199	RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count));
200	RCU_TRACE(trace_rcu_batch_end(rcp->name,
201				      cb_count, 0, need_resched(),
202				      is_idle_task(current),
203				      false));
204}
205
206static void rcu_process_callbacks(struct softirq_action *unused)
207{
208	__rcu_process_callbacks(&rcu_sched_ctrlblk);
209	__rcu_process_callbacks(&rcu_bh_ctrlblk);
210}
211
212/*
213 * Wait for a grace period to elapse.  But it is illegal to invoke
214 * synchronize_sched() from within an RCU read-side critical section.
215 * Therefore, any legal call to synchronize_sched() is a quiescent
216 * state, and so on a UP system, synchronize_sched() need do nothing.
217 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
218 * benefits of doing might_sleep() to reduce latency.)
219 *
220 * Cool, huh?  (Due to Josh Triplett.)
221 *
222 * But we want to make this a static inline later.  The cond_resched()
223 * currently makes this problematic.
224 */
225void synchronize_sched(void)
226{
227	rcu_lockdep_assert(!lock_is_held(&rcu_bh_lock_map) &&
228			   !lock_is_held(&rcu_lock_map) &&
229			   !lock_is_held(&rcu_sched_lock_map),
230			   "Illegal synchronize_sched() in RCU read-side critical section");
231	cond_resched();
232}
233EXPORT_SYMBOL_GPL(synchronize_sched);
234
235/*
236 * Helper function for call_rcu() and call_rcu_bh().
237 */
238static void __call_rcu(struct rcu_head *head,
239		       void (*func)(struct rcu_head *rcu),
240		       struct rcu_ctrlblk *rcp)
241{
242	unsigned long flags;
243
244	debug_rcu_head_queue(head);
245	head->func = func;
246	head->next = NULL;
247
248	local_irq_save(flags);
249	*rcp->curtail = head;
250	rcp->curtail = &head->next;
251	RCU_TRACE(rcp->qlen++);
252	local_irq_restore(flags);
253
254	if (unlikely(is_idle_task(current))) {
255		/* force scheduling for rcu_sched_qs() */
256		resched_cpu(0);
257	}
258}
259
260/*
261 * Post an RCU callback to be invoked after the end of an RCU-sched grace
262 * period.  But since we have but one CPU, that would be after any
263 * quiescent state.
264 */
265void call_rcu_sched(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
266{
267	__call_rcu(head, func, &rcu_sched_ctrlblk);
268}
269EXPORT_SYMBOL_GPL(call_rcu_sched);
270
271/*
272 * Post an RCU bottom-half callback to be invoked after any subsequent
273 * quiescent state.
274 */
275void call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu))
276{
277	__call_rcu(head, func, &rcu_bh_ctrlblk);
278}
279EXPORT_SYMBOL_GPL(call_rcu_bh);
280
281void __init rcu_init(void)
282{
283	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
284	RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk));
285	RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk));
286
287	rcu_early_boot_tests();
288}
289