projects/linux·blob v5.7 · refs

184 lines · 4.8 KiB

1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition.
4 *
5 * Copyright IBM Corporation, 2008
6 *
7 * Author: Paul E. McKenney <[email protected]>
8 *
9 * For detailed explanation of Read-Copy Update mechanism see -
10 * Documentation/RCU
11 */
12#include <linux/completion.h>
13#include <linux/interrupt.h>
14#include <linux/notifier.h>
15#include <linux/rcupdate_wait.h>
16#include <linux/kernel.h>
17#include <linux/export.h>
18#include <linux/mutex.h>
19#include <linux/sched.h>
20#include <linux/types.h>
21#include <linux/init.h>
22#include <linux/time.h>
23#include <linux/cpu.h>
24#include <linux/prefetch.h>
25#include <linux/slab.h>
26
27#include "rcu.h"
28
29/* Global control variables for rcupdate callback mechanism. */
30struct rcu_ctrlblk {
31 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
32 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
33 struct rcu_head **curtail; /* ->next pointer of last CB. */
34};
35
36/* Definition for rcupdate control block. */
37static struct rcu_ctrlblk rcu_ctrlblk = {
38 .donetail = &rcu_ctrlblk.rcucblist,
39 .curtail = &rcu_ctrlblk.rcucblist,
40};
41
42void rcu_barrier(void)
43{
44 wait_rcu_gp(call_rcu);
45}
46EXPORT_SYMBOL(rcu_barrier);
47
48/* Record an rcu quiescent state. */
49void rcu_qs(void)
50{
51 unsigned long flags;
52
53 local_irq_save(flags);
54 if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
55 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
56 raise_softirq_irqoff(RCU_SOFTIRQ);
57 }
58 local_irq_restore(flags);
59}
60
61/*
62 * Check to see if the scheduling-clock interrupt came from an extended
63 * quiescent state, and, if so, tell RCU about it. This function must
64 * be called from hardirq context. It is normally called from the
65 * scheduling-clock interrupt.
66 */
67void rcu_sched_clock_irq(int user)
68{
69 if (user) {
70 rcu_qs();
71 } else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
72 set_tsk_need_resched(current);
73 set_preempt_need_resched();
74 }
75}
76
77/*
78 * Reclaim the specified callback, either by invoking it for non-kfree cases or
79 * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
80 */
81static inline bool rcu_reclaim_tiny(struct rcu_head *head)
82{
83 rcu_callback_t f;
84 unsigned long offset = (unsigned long)head->func;
85
86 rcu_lock_acquire(&rcu_callback_map);
87 if (__is_kfree_rcu_offset(offset)) {
88 trace_rcu_invoke_kfree_callback("", head, offset);
89 kfree((void *)head - offset);
90 rcu_lock_release(&rcu_callback_map);
91 return true;
92 }
93
94 trace_rcu_invoke_callback("", head);
95 f = head->func;
96 WRITE_ONCE(head->func, (rcu_callback_t)0L);
97 f(head);
98 rcu_lock_release(&rcu_callback_map);
99 return false;
100}
101
102/* Invoke the RCU callbacks whose grace period has elapsed. */
103static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
104{
105 struct rcu_head *next, *list;
106 unsigned long flags;
107
108 /* Move the ready-to-invoke callbacks to a local list. */
109 local_irq_save(flags);
110 if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
111 /* No callbacks ready, so just leave. */
112 local_irq_restore(flags);
113 return;
114 }
115 list = rcu_ctrlblk.rcucblist;
116 rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
117 *rcu_ctrlblk.donetail = NULL;
118 if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
119 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
120 rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
121 local_irq_restore(flags);
122
123 /* Invoke the callbacks on the local list. */
124 while (list) {
125 next = list->next;
126 prefetch(next);
127 debug_rcu_head_unqueue(list);
128 local_bh_disable();
129 rcu_reclaim_tiny(list);
130 local_bh_enable();
131 list = next;
132 }
133}
134
135/*
136 * Wait for a grace period to elapse. But it is illegal to invoke
137 * synchronize_rcu() from within an RCU read-side critical section.
138 * Therefore, any legal call to synchronize_rcu() is a quiescent
139 * state, and so on a UP system, synchronize_rcu() need do nothing.
140 * (But Lai Jiangshan points out the benefits of doing might_sleep()
141 * to reduce latency.)
142 *
143 * Cool, huh? (Due to Josh Triplett.)
144 */
145void synchronize_rcu(void)
146{
147 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
148 lock_is_held(&rcu_lock_map) ||
149 lock_is_held(&rcu_sched_lock_map),
150 "Illegal synchronize_rcu() in RCU read-side critical section");
151}
152EXPORT_SYMBOL_GPL(synchronize_rcu);
153
154/*
155 * Post an RCU callback to be invoked after the end of an RCU grace
156 * period. But since we have but one CPU, that would be after any
157 * quiescent state.
158 */
159void call_rcu(struct rcu_head *head, rcu_callback_t func)
160{
161 unsigned long flags;
162
163 debug_rcu_head_queue(head);
164 head->func = func;
165 head->next = NULL;
166
167 local_irq_save(flags);
168 *rcu_ctrlblk.curtail = head;
169 rcu_ctrlblk.curtail = &head->next;
170 local_irq_restore(flags);
171
172 if (unlikely(is_idle_task(current))) {
173 /* force scheduling for rcu_qs() */
174 resched_cpu(0);
175 }
176}
177EXPORT_SYMBOL_GPL(call_rcu);
178
179void __init rcu_init(void)
180{
181 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
182 rcu_early_boot_tests();
183 srcu_init();
184}