projects/linux·blob v5.0 · refs

171 lines · 4.7 KiB

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 <[email protected]>
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_ctrlblk = {
50 .donetail = &rcu_ctrlblk.rcucblist,
51 .curtail = &rcu_ctrlblk.rcucblist,
52};
53
54void rcu_barrier(void)
55{
56 wait_rcu_gp(call_rcu);
57}
58EXPORT_SYMBOL(rcu_barrier);
59
60/* Record an rcu quiescent state. */
61void rcu_qs(void)
62{
63 unsigned long flags;
64
65 local_irq_save(flags);
66 if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
67 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
68 raise_softirq(RCU_SOFTIRQ);
69 }
70 local_irq_restore(flags);
71}
72
73/*
74 * Check to see if the scheduling-clock interrupt came from an extended
75 * quiescent state, and, if so, tell RCU about it. This function must
76 * be called from hardirq context. It is normally called from the
77 * scheduling-clock interrupt.
78 */
79void rcu_check_callbacks(int user)
80{
81 if (user) {
82 rcu_qs();
83 } else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
84 set_tsk_need_resched(current);
85 set_preempt_need_resched();
86 }
87}
88
89/* Invoke the RCU callbacks whose grace period has elapsed. */
90static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
91{
92 struct rcu_head *next, *list;
93 unsigned long flags;
94
95 /* Move the ready-to-invoke callbacks to a local list. */
96 local_irq_save(flags);
97 if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
98 /* No callbacks ready, so just leave. */
99 local_irq_restore(flags);
100 return;
101 }
102 list = rcu_ctrlblk.rcucblist;
103 rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
104 *rcu_ctrlblk.donetail = NULL;
105 if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
106 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
107 rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
108 local_irq_restore(flags);
109
110 /* Invoke the callbacks on the local list. */
111 while (list) {
112 next = list->next;
113 prefetch(next);
114 debug_rcu_head_unqueue(list);
115 local_bh_disable();
116 __rcu_reclaim("", list);
117 local_bh_enable();
118 list = next;
119 }
120}
121
122/*
123 * Wait for a grace period to elapse. But it is illegal to invoke
124 * synchronize_rcu() from within an RCU read-side critical section.
125 * Therefore, any legal call to synchronize_rcu() is a quiescent
126 * state, and so on a UP system, synchronize_rcu() need do nothing.
127 * (But Lai Jiangshan points out the benefits of doing might_sleep()
128 * to reduce latency.)
129 *
130 * Cool, huh? (Due to Josh Triplett.)
131 */
132void synchronize_rcu(void)
133{
134 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
135 lock_is_held(&rcu_lock_map) ||
136 lock_is_held(&rcu_sched_lock_map),
137 "Illegal synchronize_rcu() in RCU read-side critical section");
138}
139EXPORT_SYMBOL_GPL(synchronize_rcu);
140
141/*
142 * Post an RCU callback to be invoked after the end of an RCU grace
143 * period. But since we have but one CPU, that would be after any
144 * quiescent state.
145 */
146void call_rcu(struct rcu_head *head, rcu_callback_t func)
147{
148 unsigned long flags;
149
150 debug_rcu_head_queue(head);
151 head->func = func;
152 head->next = NULL;
153
154 local_irq_save(flags);
155 *rcu_ctrlblk.curtail = head;
156 rcu_ctrlblk.curtail = &head->next;
157 local_irq_restore(flags);
158
159 if (unlikely(is_idle_task(current))) {
160 /* force scheduling for rcu_qs() */
161 resched_cpu(0);
162 }
163}
164EXPORT_SYMBOL_GPL(call_rcu);
165
166void __init rcu_init(void)
167{
168 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
169 rcu_early_boot_tests();
170 srcu_init();
171}