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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. */
29struct 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. */
36static struct rcu_ctrlblk rcu_ctrlblk = {
37 .donetail = &rcu_ctrlblk.rcucblist,
38 .curtail = &rcu_ctrlblk.rcucblist,
39};
40
41void rcu_barrier(void)
42{
43 wait_rcu_gp(call_rcu);
44}
45EXPORT_SYMBOL(rcu_barrier);
46
47/* Record an rcu quiescent state. */
48void 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 */
66void 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. */
77static __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 */
119void 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}
126EXPORT_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 */
133void 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}
151EXPORT_SYMBOL_GPL(call_rcu);
152
153void __init rcu_init(void)
154{
155 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
156 rcu_early_boot_tests();
157 srcu_init();
158}
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#include <linux/slab.h>
26#include <linux/mm.h>
27
28#include "rcu.h"
29
30/* Global control variables for rcupdate callback mechanism. */
31struct rcu_ctrlblk {
32 struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */
33 struct rcu_head **donetail; /* ->next pointer of last "done" CB. */
34 struct rcu_head **curtail; /* ->next pointer of last CB. */
35};
36
37/* Definition for rcupdate control block. */
38static struct rcu_ctrlblk rcu_ctrlblk = {
39 .donetail = &rcu_ctrlblk.rcucblist,
40 .curtail = &rcu_ctrlblk.rcucblist,
41};
42
43void rcu_barrier(void)
44{
45 wait_rcu_gp(call_rcu);
46}
47EXPORT_SYMBOL(rcu_barrier);
48
49/* Record an rcu quiescent state. */
50void rcu_qs(void)
51{
52 unsigned long flags;
53
54 local_irq_save(flags);
55 if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
56 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
57 raise_softirq_irqoff(RCU_SOFTIRQ);
58 }
59 local_irq_restore(flags);
60}
61
62/*
63 * Check to see if the scheduling-clock interrupt came from an extended
64 * quiescent state, and, if so, tell RCU about it. This function must
65 * be called from hardirq context. It is normally called from the
66 * scheduling-clock interrupt.
67 */
68void rcu_sched_clock_irq(int user)
69{
70 if (user) {
71 rcu_qs();
72 } else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
73 set_tsk_need_resched(current);
74 set_preempt_need_resched();
75 }
76}
77
78/*
79 * Reclaim the specified callback, either by invoking it for non-kfree cases or
80 * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
81 */
82static inline bool rcu_reclaim_tiny(struct rcu_head *head)
83{
84 rcu_callback_t f;
85 unsigned long offset = (unsigned long)head->func;
86
87 rcu_lock_acquire(&rcu_callback_map);
88 if (__is_kvfree_rcu_offset(offset)) {
89 trace_rcu_invoke_kvfree_callback("", head, offset);
90 kvfree((void *)head - offset);
91 rcu_lock_release(&rcu_callback_map);
92 return true;
93 }
94
95 trace_rcu_invoke_callback("", head);
96 f = head->func;
97 WRITE_ONCE(head->func, (rcu_callback_t)0L);
98 f(head);
99 rcu_lock_release(&rcu_callback_map);
100 return false;
101}
102
103/* Invoke the RCU callbacks whose grace period has elapsed. */
104static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
105{
106 struct rcu_head *next, *list;
107 unsigned long flags;
108
109 /* Move the ready-to-invoke callbacks to a local list. */
110 local_irq_save(flags);
111 if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
112 /* No callbacks ready, so just leave. */
113 local_irq_restore(flags);
114 return;
115 }
116 list = rcu_ctrlblk.rcucblist;
117 rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
118 *rcu_ctrlblk.donetail = NULL;
119 if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
120 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
121 rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
122 local_irq_restore(flags);
123
124 /* Invoke the callbacks on the local list. */
125 while (list) {
126 next = list->next;
127 prefetch(next);
128 debug_rcu_head_unqueue(list);
129 local_bh_disable();
130 rcu_reclaim_tiny(list);
131 local_bh_enable();
132 list = next;
133 }
134}
135
136/*
137 * Wait for a grace period to elapse. But it is illegal to invoke
138 * synchronize_rcu() from within an RCU read-side critical section.
139 * Therefore, any legal call to synchronize_rcu() is a quiescent
140 * state, and so on a UP system, synchronize_rcu() need do nothing.
141 * (But Lai Jiangshan points out the benefits of doing might_sleep()
142 * to reduce latency.)
143 *
144 * Cool, huh? (Due to Josh Triplett.)
145 */
146void synchronize_rcu(void)
147{
148 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
149 lock_is_held(&rcu_lock_map) ||
150 lock_is_held(&rcu_sched_lock_map),
151 "Illegal synchronize_rcu() in RCU read-side critical section");
152}
153EXPORT_SYMBOL_GPL(synchronize_rcu);
154
155/*
156 * Post an RCU callback to be invoked after the end of an RCU grace
157 * period. But since we have but one CPU, that would be after any
158 * quiescent state.
159 */
160void call_rcu(struct rcu_head *head, rcu_callback_t func)
161{
162 unsigned long flags;
163
164 debug_rcu_head_queue(head);
165 head->func = func;
166 head->next = NULL;
167
168 local_irq_save(flags);
169 *rcu_ctrlblk.curtail = head;
170 rcu_ctrlblk.curtail = &head->next;
171 local_irq_restore(flags);
172
173 if (unlikely(is_idle_task(current))) {
174 /* force scheduling for rcu_qs() */
175 resched_cpu(0);
176 }
177}
178EXPORT_SYMBOL_GPL(call_rcu);
179
180void __init rcu_init(void)
181{
182 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
183 rcu_early_boot_tests();
184 srcu_init();
185}