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_wait.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
 39#include "rcu.h"
 40
 41/* Global control variables for rcupdate callback mechanism. */
 42struct rcu_ctrlblk {
 43	struct rcu_head *rcucblist;	/* List of pending callbacks (CBs). */
 44	struct rcu_head **donetail;	/* ->next pointer of last "done" CB. */
 45	struct rcu_head **curtail;	/* ->next pointer of last CB. */
 46};
 47
 48/* Definition for rcupdate control block. */
 49static struct rcu_ctrlblk rcu_sched_ctrlblk = {
 50	.donetail	= &rcu_sched_ctrlblk.rcucblist,
 51	.curtail	= &rcu_sched_ctrlblk.rcucblist,
 52};
 53
 54static struct rcu_ctrlblk rcu_bh_ctrlblk = {
 55	.donetail	= &rcu_bh_ctrlblk.rcucblist,
 56	.curtail	= &rcu_bh_ctrlblk.rcucblist,
 57};
 58
 59void rcu_barrier_bh(void)
 60{
 61	wait_rcu_gp(call_rcu_bh);
 62}
 63EXPORT_SYMBOL(rcu_barrier_bh);
 64
 65void rcu_barrier_sched(void)
 66{
 67	wait_rcu_gp(call_rcu_sched);
 68}
 69EXPORT_SYMBOL(rcu_barrier_sched);
 70
 71/*
 72 * Helper function for rcu_sched_qs() and rcu_bh_qs().
 73 * Also irqs are disabled to avoid confusion due to interrupt handlers
 74 * invoking call_rcu().
 75 */
 76static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 77{
 78	if (rcp->donetail != rcp->curtail) {
 79		rcp->donetail = rcp->curtail;
 80		return 1;
 81	}
 82
 83	return 0;
 84}
 85
 86/*
 87 * Record an rcu quiescent state.  And an rcu_bh quiescent state while we
 88 * are at it, given that any rcu quiescent state is also an rcu_bh
 89 * quiescent state.  Use "+" instead of "||" to defeat short circuiting.
 90 */
 91void rcu_sched_qs(void)
 92{
 93	unsigned long flags;
 94
 95	local_irq_save(flags);
 96	if (rcu_qsctr_help(&rcu_sched_ctrlblk) +
 97	    rcu_qsctr_help(&rcu_bh_ctrlblk))
 98		raise_softirq(RCU_SOFTIRQ);
 99	local_irq_restore(flags);
100}
101
102/*
103 * Record an rcu_bh quiescent state.
104 */
105void rcu_bh_qs(void)
106{
107	unsigned long flags;
108
109	local_irq_save(flags);
110	if (rcu_qsctr_help(&rcu_bh_ctrlblk))
111		raise_softirq(RCU_SOFTIRQ);
112	local_irq_restore(flags);
113}
114
115/*
116 * Check to see if the scheduling-clock interrupt came from an extended
117 * quiescent state, and, if so, tell RCU about it.  This function must
118 * be called from hardirq context.  It is normally called from the
119 * scheduling-clock interrupt.
120 */
121void rcu_check_callbacks(int user)
122{
123	if (user)
124		rcu_sched_qs();
125	else if (!in_softirq())
126		rcu_bh_qs();
127	if (user)
128		rcu_note_voluntary_context_switch(current);
129}
130
131/*
132 * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure
133 * whose grace period has elapsed.
134 */
135static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp)
136{
137	struct rcu_head *next, *list;
138	unsigned long flags;
139
140	/* Move the ready-to-invoke callbacks to a local list. */
141	local_irq_save(flags);
142	if (rcp->donetail == &rcp->rcucblist) {
143		/* No callbacks ready, so just leave. */
144		local_irq_restore(flags);
145		return;
146	}
147	list = rcp->rcucblist;
148	rcp->rcucblist = *rcp->donetail;
149	*rcp->donetail = NULL;
150	if (rcp->curtail == rcp->donetail)
151		rcp->curtail = &rcp->rcucblist;
152	rcp->donetail = &rcp->rcucblist;
153	local_irq_restore(flags);
154
155	/* Invoke the callbacks on the local list. */
156	while (list) {
157		next = list->next;
158		prefetch(next);
159		debug_rcu_head_unqueue(list);
160		local_bh_disable();
161		__rcu_reclaim("", list);
162		local_bh_enable();
163		list = next;
164	}
165}
166
167static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
168{
169	__rcu_process_callbacks(&rcu_sched_ctrlblk);
170	__rcu_process_callbacks(&rcu_bh_ctrlblk);
171}
172
173/*
174 * Wait for a grace period to elapse.  But it is illegal to invoke
175 * synchronize_sched() from within an RCU read-side critical section.
176 * Therefore, any legal call to synchronize_sched() is a quiescent
177 * state, and so on a UP system, synchronize_sched() need do nothing.
178 * Ditto for synchronize_rcu_bh().  (But Lai Jiangshan points out the
179 * benefits of doing might_sleep() to reduce latency.)
180 *
181 * Cool, huh?  (Due to Josh Triplett.)
182 */
183void synchronize_sched(void)
184{
185	RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
186			 lock_is_held(&rcu_lock_map) ||
187			 lock_is_held(&rcu_sched_lock_map),
188			 "Illegal synchronize_sched() in RCU read-side critical section");
189}
190EXPORT_SYMBOL_GPL(synchronize_sched);
191
192/*
193 * Helper function for call_rcu() and call_rcu_bh().
194 */
195static void __call_rcu(struct rcu_head *head,
196		       rcu_callback_t func,
197		       struct rcu_ctrlblk *rcp)
198{
199	unsigned long flags;
200
201	debug_rcu_head_queue(head);
202	head->func = func;
203	head->next = NULL;
204
205	local_irq_save(flags);
206	*rcp->curtail = head;
207	rcp->curtail = &head->next;
208	local_irq_restore(flags);
209
210	if (unlikely(is_idle_task(current))) {
211		/* force scheduling for rcu_sched_qs() */
212		resched_cpu(0);
213	}
214}
215
216/*
217 * Post an RCU callback to be invoked after the end of an RCU-sched grace
218 * period.  But since we have but one CPU, that would be after any
219 * quiescent state.
220 */
221void call_rcu_sched(struct rcu_head *head, rcu_callback_t func)
222{
223	__call_rcu(head, func, &rcu_sched_ctrlblk);
224}
225EXPORT_SYMBOL_GPL(call_rcu_sched);
226
227/*
228 * Post an RCU bottom-half callback to be invoked after any subsequent
229 * quiescent state.
230 */
231void call_rcu_bh(struct rcu_head *head, rcu_callback_t func)
232{
233	__call_rcu(head, func, &rcu_bh_ctrlblk);
234}
235EXPORT_SYMBOL_GPL(call_rcu_bh);
236
237void __init rcu_init(void)
238{
239	open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
240	rcu_early_boot_tests();
241}