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 <paulmck@linux.ibm.com>
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
26 #include "rcu.h"
27
28 /* Global control variables for rcupdate callback mechanism. */
29 struct rcu_ctrlblk {
30 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
31 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
32 struct rcu_head **curtail; /* ->next pointer of last CB. */
33 };
34
35 /* Definition for rcupdate control block. */
36 static struct rcu_ctrlblk rcu_ctrlblk = {
37 .donetail = &rcu_ctrlblk.rcucblist,
38 .curtail = &rcu_ctrlblk.rcucblist,
39 };
40
rcu_barrier(void)41 void rcu_barrier(void)
42 {
43 wait_rcu_gp(call_rcu);
44 }
45 EXPORT_SYMBOL(rcu_barrier);
46
47 /* Record an rcu quiescent state. */
rcu_qs(void)48 void rcu_qs(void)
49 {
50 unsigned long flags;
51
52 local_irq_save(flags);
53 if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
54 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
55 raise_softirq_irqoff(RCU_SOFTIRQ);
56 }
57 local_irq_restore(flags);
58 }
59
60 /*
61 * Check to see if the scheduling-clock interrupt came from an extended
62 * quiescent state, and, if so, tell RCU about it. This function must
63 * be called from hardirq context. It is normally called from the
64 * scheduling-clock interrupt.
65 */
rcu_sched_clock_irq(int user)66 void rcu_sched_clock_irq(int user)
67 {
68 if (user) {
69 rcu_qs();
70 } else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
71 set_tsk_need_resched(current);
72 set_preempt_need_resched();
73 }
74 }
75
76 /* Invoke the RCU callbacks whose grace period has elapsed. */
rcu_process_callbacks(struct softirq_action * unused)77 static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
78 {
79 struct rcu_head *next, *list;
80 unsigned long flags;
81
82 /* Move the ready-to-invoke callbacks to a local list. */
83 local_irq_save(flags);
84 if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
85 /* No callbacks ready, so just leave. */
86 local_irq_restore(flags);
87 return;
88 }
89 list = rcu_ctrlblk.rcucblist;
90 rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
91 *rcu_ctrlblk.donetail = NULL;
92 if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
93 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
94 rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
95 local_irq_restore(flags);
96
97 /* Invoke the callbacks on the local list. */
98 while (list) {
99 next = list->next;
100 prefetch(next);
101 debug_rcu_head_unqueue(list);
102 local_bh_disable();
103 __rcu_reclaim("", list);
104 local_bh_enable();
105 list = next;
106 }
107 }
108
109 /*
110 * Wait for a grace period to elapse. But it is illegal to invoke
111 * synchronize_rcu() from within an RCU read-side critical section.
112 * Therefore, any legal call to synchronize_rcu() is a quiescent
113 * state, and so on a UP system, synchronize_rcu() need do nothing.
114 * (But Lai Jiangshan points out the benefits of doing might_sleep()
115 * to reduce latency.)
116 *
117 * Cool, huh? (Due to Josh Triplett.)
118 */
synchronize_rcu(void)119 void synchronize_rcu(void)
120 {
121 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
122 lock_is_held(&rcu_lock_map) ||
123 lock_is_held(&rcu_sched_lock_map),
124 "Illegal synchronize_rcu() in RCU read-side critical section");
125 }
126 EXPORT_SYMBOL_GPL(synchronize_rcu);
127
128 /*
129 * Post an RCU callback to be invoked after the end of an RCU grace
130 * period. But since we have but one CPU, that would be after any
131 * quiescent state.
132 */
call_rcu(struct rcu_head * head,rcu_callback_t func)133 void call_rcu(struct rcu_head *head, rcu_callback_t func)
134 {
135 unsigned long flags;
136
137 debug_rcu_head_queue(head);
138 head->func = func;
139 head->next = NULL;
140
141 local_irq_save(flags);
142 *rcu_ctrlblk.curtail = head;
143 rcu_ctrlblk.curtail = &head->next;
144 local_irq_restore(flags);
145
146 if (unlikely(is_idle_task(current))) {
147 /* force scheduling for rcu_qs() */
148 resched_cpu(0);
149 }
150 }
151 EXPORT_SYMBOL_GPL(call_rcu);
152
rcu_init(void)153 void __init rcu_init(void)
154 {
155 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
156 rcu_early_boot_tests();
157 srcu_init();
158 }
159