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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 unsigned long gp_seq; /* Grace-period counter. */
36};
37
38/* Definition for rcupdate control block. */
39static struct rcu_ctrlblk rcu_ctrlblk = {
40 .donetail = &rcu_ctrlblk.rcucblist,
41 .curtail = &rcu_ctrlblk.rcucblist,
42 .gp_seq = 0 - 300UL,
43};
44
45void rcu_barrier(void)
46{
47 wait_rcu_gp(call_rcu);
48}
49EXPORT_SYMBOL(rcu_barrier);
50
51/* Record an rcu quiescent state. */
52void rcu_qs(void)
53{
54 unsigned long flags;
55
56 local_irq_save(flags);
57 if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
58 rcu_ctrlblk.donetail = rcu_ctrlblk.curtail;
59 raise_softirq_irqoff(RCU_SOFTIRQ);
60 }
61 WRITE_ONCE(rcu_ctrlblk.gp_seq, rcu_ctrlblk.gp_seq + 1);
62 local_irq_restore(flags);
63}
64
65/*
66 * Check to see if the scheduling-clock interrupt came from an extended
67 * quiescent state, and, if so, tell RCU about it. This function must
68 * be called from hardirq context. It is normally called from the
69 * scheduling-clock interrupt.
70 */
71void rcu_sched_clock_irq(int user)
72{
73 if (user) {
74 rcu_qs();
75 } else if (rcu_ctrlblk.donetail != rcu_ctrlblk.curtail) {
76 set_tsk_need_resched(current);
77 set_preempt_need_resched();
78 }
79}
80
81/*
82 * Reclaim the specified callback, either by invoking it for non-kfree cases or
83 * freeing it directly (for kfree). Return true if kfreeing, false otherwise.
84 */
85static inline bool rcu_reclaim_tiny(struct rcu_head *head)
86{
87 rcu_callback_t f;
88 unsigned long offset = (unsigned long)head->func;
89
90 rcu_lock_acquire(&rcu_callback_map);
91 if (__is_kvfree_rcu_offset(offset)) {
92 trace_rcu_invoke_kvfree_callback("", head, offset);
93 kvfree((void *)head - offset);
94 rcu_lock_release(&rcu_callback_map);
95 return true;
96 }
97
98 trace_rcu_invoke_callback("", head);
99 f = head->func;
100 WRITE_ONCE(head->func, (rcu_callback_t)0L);
101 f(head);
102 rcu_lock_release(&rcu_callback_map);
103 return false;
104}
105
106/* Invoke the RCU callbacks whose grace period has elapsed. */
107static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused)
108{
109 struct rcu_head *next, *list;
110 unsigned long flags;
111
112 /* Move the ready-to-invoke callbacks to a local list. */
113 local_irq_save(flags);
114 if (rcu_ctrlblk.donetail == &rcu_ctrlblk.rcucblist) {
115 /* No callbacks ready, so just leave. */
116 local_irq_restore(flags);
117 return;
118 }
119 list = rcu_ctrlblk.rcucblist;
120 rcu_ctrlblk.rcucblist = *rcu_ctrlblk.donetail;
121 *rcu_ctrlblk.donetail = NULL;
122 if (rcu_ctrlblk.curtail == rcu_ctrlblk.donetail)
123 rcu_ctrlblk.curtail = &rcu_ctrlblk.rcucblist;
124 rcu_ctrlblk.donetail = &rcu_ctrlblk.rcucblist;
125 local_irq_restore(flags);
126
127 /* Invoke the callbacks on the local list. */
128 while (list) {
129 next = list->next;
130 prefetch(next);
131 debug_rcu_head_unqueue(list);
132 local_bh_disable();
133 rcu_reclaim_tiny(list);
134 local_bh_enable();
135 list = next;
136 }
137}
138
139/*
140 * Wait for a grace period to elapse. But it is illegal to invoke
141 * synchronize_rcu() from within an RCU read-side critical section.
142 * Therefore, any legal call to synchronize_rcu() is a quiescent
143 * state, and so on a UP system, synchronize_rcu() need do nothing.
144 * (But Lai Jiangshan points out the benefits of doing might_sleep()
145 * to reduce latency.)
146 *
147 * Cool, huh? (Due to Josh Triplett.)
148 */
149void synchronize_rcu(void)
150{
151 RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) ||
152 lock_is_held(&rcu_lock_map) ||
153 lock_is_held(&rcu_sched_lock_map),
154 "Illegal synchronize_rcu() in RCU read-side critical section");
155}
156EXPORT_SYMBOL_GPL(synchronize_rcu);
157
158/*
159 * Post an RCU callback to be invoked after the end of an RCU grace
160 * period. But since we have but one CPU, that would be after any
161 * quiescent state.
162 */
163void call_rcu(struct rcu_head *head, rcu_callback_t func)
164{
165 unsigned long flags;
166
167 debug_rcu_head_queue(head);
168 head->func = func;
169 head->next = NULL;
170
171 local_irq_save(flags);
172 *rcu_ctrlblk.curtail = head;
173 rcu_ctrlblk.curtail = &head->next;
174 local_irq_restore(flags);
175
176 if (unlikely(is_idle_task(current))) {
177 /* force scheduling for rcu_qs() */
178 resched_cpu(0);
179 }
180}
181EXPORT_SYMBOL_GPL(call_rcu);
182
183/*
184 * Return a grace-period-counter "cookie". For more information,
185 * see the Tree RCU header comment.
186 */
187unsigned long get_state_synchronize_rcu(void)
188{
189 return READ_ONCE(rcu_ctrlblk.gp_seq);
190}
191EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
192
193/*
194 * Return a grace-period-counter "cookie" and ensure that a future grace
195 * period completes. For more information, see the Tree RCU header comment.
196 */
197unsigned long start_poll_synchronize_rcu(void)
198{
199 unsigned long gp_seq = get_state_synchronize_rcu();
200
201 if (unlikely(is_idle_task(current))) {
202 /* force scheduling for rcu_qs() */
203 resched_cpu(0);
204 }
205 return gp_seq;
206}
207EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
208
209/*
210 * Return true if the grace period corresponding to oldstate has completed
211 * and false otherwise. For more information, see the Tree RCU header
212 * comment.
213 */
214bool poll_state_synchronize_rcu(unsigned long oldstate)
215{
216 return READ_ONCE(rcu_ctrlblk.gp_seq) != oldstate;
217}
218EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
219
220void __init rcu_init(void)
221{
222 open_softirq(RCU_SOFTIRQ, rcu_process_callbacks);
223 rcu_early_boot_tests();
224}