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1// SPDX-License-Identifier: GPL-2.0+
2/*
3 * Sleepable Read-Copy Update mechanism for mutual exclusion,
4 * tiny version for non-preemptible single-CPU use.
5 *
6 * Copyright (C) IBM Corporation, 2017
7 *
8 * Author: Paul McKenney <paulmck@linux.ibm.com>
9 */
10
11#include <linux/export.h>
12#include <linux/mutex.h>
13#include <linux/preempt.h>
14#include <linux/rcupdate_wait.h>
15#include <linux/sched.h>
16#include <linux/delay.h>
17#include <linux/srcu.h>
18
19#include <linux/rcu_node_tree.h>
20#include "rcu_segcblist.h"
21#include "rcu.h"
22
23int rcu_scheduler_active __read_mostly;
24static LIST_HEAD(srcu_boot_list);
25static bool srcu_init_done;
26
27static int init_srcu_struct_fields(struct srcu_struct *ssp)
28{
29 ssp->srcu_lock_nesting[0] = 0;
30 ssp->srcu_lock_nesting[1] = 0;
31 init_swait_queue_head(&ssp->srcu_wq);
32 ssp->srcu_cb_head = NULL;
33 ssp->srcu_cb_tail = &ssp->srcu_cb_head;
34 ssp->srcu_gp_running = false;
35 ssp->srcu_gp_waiting = false;
36 ssp->srcu_idx = 0;
37 INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
38 INIT_LIST_HEAD(&ssp->srcu_work.entry);
39 return 0;
40}
41
42#ifdef CONFIG_DEBUG_LOCK_ALLOC
43
44int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
45 struct lock_class_key *key)
46{
47 /* Don't re-initialize a lock while it is held. */
48 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
49 lockdep_init_map(&ssp->dep_map, name, key, 0);
50 return init_srcu_struct_fields(ssp);
51}
52EXPORT_SYMBOL_GPL(__init_srcu_struct);
53
54#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
55
56/*
57 * init_srcu_struct - initialize a sleep-RCU structure
58 * @ssp: structure to initialize.
59 *
60 * Must invoke this on a given srcu_struct before passing that srcu_struct
61 * to any other function. Each srcu_struct represents a separate domain
62 * of SRCU protection.
63 */
64int init_srcu_struct(struct srcu_struct *ssp)
65{
66 return init_srcu_struct_fields(ssp);
67}
68EXPORT_SYMBOL_GPL(init_srcu_struct);
69
70#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
71
72/*
73 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
74 * @ssp: structure to clean up.
75 *
76 * Must invoke this after you are finished using a given srcu_struct that
77 * was initialized via init_srcu_struct(), else you leak memory.
78 */
79void cleanup_srcu_struct(struct srcu_struct *ssp)
80{
81 WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
82 flush_work(&ssp->srcu_work);
83 WARN_ON(ssp->srcu_gp_running);
84 WARN_ON(ssp->srcu_gp_waiting);
85 WARN_ON(ssp->srcu_cb_head);
86 WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
87}
88EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
89
90/*
91 * Removes the count for the old reader from the appropriate element of
92 * the srcu_struct.
93 */
94void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
95{
96 int newval = ssp->srcu_lock_nesting[idx] - 1;
97
98 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
99 if (!newval && READ_ONCE(ssp->srcu_gp_waiting))
100 swake_up_one(&ssp->srcu_wq);
101}
102EXPORT_SYMBOL_GPL(__srcu_read_unlock);
103
104/*
105 * Workqueue handler to drive one grace period and invoke any callbacks
106 * that become ready as a result. Single-CPU and !PREEMPT operation
107 * means that we get away with murder on synchronization. ;-)
108 */
109void srcu_drive_gp(struct work_struct *wp)
110{
111 int idx;
112 struct rcu_head *lh;
113 struct rcu_head *rhp;
114 struct srcu_struct *ssp;
115
116 ssp = container_of(wp, struct srcu_struct, srcu_work);
117 if (ssp->srcu_gp_running || !READ_ONCE(ssp->srcu_cb_head))
118 return; /* Already running or nothing to do. */
119
120 /* Remove recently arrived callbacks and wait for readers. */
121 WRITE_ONCE(ssp->srcu_gp_running, true);
122 local_irq_disable();
123 lh = ssp->srcu_cb_head;
124 ssp->srcu_cb_head = NULL;
125 ssp->srcu_cb_tail = &ssp->srcu_cb_head;
126 local_irq_enable();
127 idx = ssp->srcu_idx;
128 WRITE_ONCE(ssp->srcu_idx, !ssp->srcu_idx);
129 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
130 swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
131 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
132
133 /* Invoke the callbacks we removed above. */
134 while (lh) {
135 rhp = lh;
136 lh = lh->next;
137 local_bh_disable();
138 rhp->func(rhp);
139 local_bh_enable();
140 }
141
142 /*
143 * Enable rescheduling, and if there are more callbacks,
144 * reschedule ourselves. This can race with a call_srcu()
145 * at interrupt level, but the ->srcu_gp_running checks will
146 * straighten that out.
147 */
148 WRITE_ONCE(ssp->srcu_gp_running, false);
149 if (READ_ONCE(ssp->srcu_cb_head))
150 schedule_work(&ssp->srcu_work);
151}
152EXPORT_SYMBOL_GPL(srcu_drive_gp);
153
154/*
155 * Enqueue an SRCU callback on the specified srcu_struct structure,
156 * initiating grace-period processing if it is not already running.
157 */
158void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
159 rcu_callback_t func)
160{
161 unsigned long flags;
162
163 rhp->func = func;
164 rhp->next = NULL;
165 local_irq_save(flags);
166 *ssp->srcu_cb_tail = rhp;
167 ssp->srcu_cb_tail = &rhp->next;
168 local_irq_restore(flags);
169 if (!READ_ONCE(ssp->srcu_gp_running)) {
170 if (likely(srcu_init_done))
171 schedule_work(&ssp->srcu_work);
172 else if (list_empty(&ssp->srcu_work.entry))
173 list_add(&ssp->srcu_work.entry, &srcu_boot_list);
174 }
175}
176EXPORT_SYMBOL_GPL(call_srcu);
177
178/*
179 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
180 */
181void synchronize_srcu(struct srcu_struct *ssp)
182{
183 struct rcu_synchronize rs;
184
185 init_rcu_head_on_stack(&rs.head);
186 init_completion(&rs.completion);
187 call_srcu(ssp, &rs.head, wakeme_after_rcu);
188 wait_for_completion(&rs.completion);
189 destroy_rcu_head_on_stack(&rs.head);
190}
191EXPORT_SYMBOL_GPL(synchronize_srcu);
192
193/* Lockdep diagnostics. */
194void __init rcu_scheduler_starting(void)
195{
196 rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
197}
198
199/*
200 * Queue work for srcu_struct structures with early boot callbacks.
201 * The work won't actually execute until the workqueue initialization
202 * phase that takes place after the scheduler starts.
203 */
204void __init srcu_init(void)
205{
206 struct srcu_struct *ssp;
207
208 srcu_init_done = true;
209 while (!list_empty(&srcu_boot_list)) {
210 ssp = list_first_entry(&srcu_boot_list,
211 struct srcu_struct, srcu_work.entry);
212 list_del_init(&ssp->srcu_work.entry);
213 schedule_work(&ssp->srcu_work);
214 }
215}
1/*
2 * Sleepable Read-Copy Update mechanism for mutual exclusion,
3 * tiny version for non-preemptible single-CPU use.
4 *
5 * This program is free software; you can redistribute it and/or modify
6 * it under the terms of the GNU General Public License as published by
7 * the Free Software Foundation; either version 2 of the License, or
8 * (at your option) any later version.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program; if not, you can access it online at
17 * http://www.gnu.org/licenses/gpl-2.0.html.
18 *
19 * Copyright (C) IBM Corporation, 2017
20 *
21 * Author: Paul McKenney <paulmck@us.ibm.com>
22 */
23
24#include <linux/export.h>
25#include <linux/mutex.h>
26#include <linux/preempt.h>
27#include <linux/rcupdate_wait.h>
28#include <linux/sched.h>
29#include <linux/delay.h>
30#include <linux/srcu.h>
31
32#include <linux/rcu_node_tree.h>
33#include "rcu_segcblist.h"
34#include "rcu.h"
35
36int rcu_scheduler_active __read_mostly;
37
38static int init_srcu_struct_fields(struct srcu_struct *sp)
39{
40 sp->srcu_lock_nesting[0] = 0;
41 sp->srcu_lock_nesting[1] = 0;
42 init_swait_queue_head(&sp->srcu_wq);
43 sp->srcu_cb_head = NULL;
44 sp->srcu_cb_tail = &sp->srcu_cb_head;
45 sp->srcu_gp_running = false;
46 sp->srcu_gp_waiting = false;
47 sp->srcu_idx = 0;
48 INIT_WORK(&sp->srcu_work, srcu_drive_gp);
49 return 0;
50}
51
52#ifdef CONFIG_DEBUG_LOCK_ALLOC
53
54int __init_srcu_struct(struct srcu_struct *sp, const char *name,
55 struct lock_class_key *key)
56{
57 /* Don't re-initialize a lock while it is held. */
58 debug_check_no_locks_freed((void *)sp, sizeof(*sp));
59 lockdep_init_map(&sp->dep_map, name, key, 0);
60 return init_srcu_struct_fields(sp);
61}
62EXPORT_SYMBOL_GPL(__init_srcu_struct);
63
64#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
65
66/*
67 * init_srcu_struct - initialize a sleep-RCU structure
68 * @sp: structure to initialize.
69 *
70 * Must invoke this on a given srcu_struct before passing that srcu_struct
71 * to any other function. Each srcu_struct represents a separate domain
72 * of SRCU protection.
73 */
74int init_srcu_struct(struct srcu_struct *sp)
75{
76 return init_srcu_struct_fields(sp);
77}
78EXPORT_SYMBOL_GPL(init_srcu_struct);
79
80#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
81
82/*
83 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
84 * @sp: structure to clean up.
85 *
86 * Must invoke this after you are finished using a given srcu_struct that
87 * was initialized via init_srcu_struct(), else you leak memory.
88 */
89void cleanup_srcu_struct(struct srcu_struct *sp)
90{
91 WARN_ON(sp->srcu_lock_nesting[0] || sp->srcu_lock_nesting[1]);
92 flush_work(&sp->srcu_work);
93 WARN_ON(sp->srcu_gp_running);
94 WARN_ON(sp->srcu_gp_waiting);
95 WARN_ON(sp->srcu_cb_head);
96 WARN_ON(&sp->srcu_cb_head != sp->srcu_cb_tail);
97}
98EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
99
100/*
101 * Removes the count for the old reader from the appropriate element of
102 * the srcu_struct.
103 */
104void __srcu_read_unlock(struct srcu_struct *sp, int idx)
105{
106 int newval = sp->srcu_lock_nesting[idx] - 1;
107
108 WRITE_ONCE(sp->srcu_lock_nesting[idx], newval);
109 if (!newval && READ_ONCE(sp->srcu_gp_waiting))
110 swake_up(&sp->srcu_wq);
111}
112EXPORT_SYMBOL_GPL(__srcu_read_unlock);
113
114/*
115 * Workqueue handler to drive one grace period and invoke any callbacks
116 * that become ready as a result. Single-CPU and !PREEMPT operation
117 * means that we get away with murder on synchronization. ;-)
118 */
119void srcu_drive_gp(struct work_struct *wp)
120{
121 int idx;
122 struct rcu_head *lh;
123 struct rcu_head *rhp;
124 struct srcu_struct *sp;
125
126 sp = container_of(wp, struct srcu_struct, srcu_work);
127 if (sp->srcu_gp_running || !READ_ONCE(sp->srcu_cb_head))
128 return; /* Already running or nothing to do. */
129
130 /* Remove recently arrived callbacks and wait for readers. */
131 WRITE_ONCE(sp->srcu_gp_running, true);
132 local_irq_disable();
133 lh = sp->srcu_cb_head;
134 sp->srcu_cb_head = NULL;
135 sp->srcu_cb_tail = &sp->srcu_cb_head;
136 local_irq_enable();
137 idx = sp->srcu_idx;
138 WRITE_ONCE(sp->srcu_idx, !sp->srcu_idx);
139 WRITE_ONCE(sp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
140 swait_event(sp->srcu_wq, !READ_ONCE(sp->srcu_lock_nesting[idx]));
141 WRITE_ONCE(sp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
142
143 /* Invoke the callbacks we removed above. */
144 while (lh) {
145 rhp = lh;
146 lh = lh->next;
147 local_bh_disable();
148 rhp->func(rhp);
149 local_bh_enable();
150 }
151
152 /*
153 * Enable rescheduling, and if there are more callbacks,
154 * reschedule ourselves. This can race with a call_srcu()
155 * at interrupt level, but the ->srcu_gp_running checks will
156 * straighten that out.
157 */
158 WRITE_ONCE(sp->srcu_gp_running, false);
159 if (READ_ONCE(sp->srcu_cb_head))
160 schedule_work(&sp->srcu_work);
161}
162EXPORT_SYMBOL_GPL(srcu_drive_gp);
163
164/*
165 * Enqueue an SRCU callback on the specified srcu_struct structure,
166 * initiating grace-period processing if it is not already running.
167 */
168void call_srcu(struct srcu_struct *sp, struct rcu_head *rhp,
169 rcu_callback_t func)
170{
171 unsigned long flags;
172
173 rhp->func = func;
174 rhp->next = NULL;
175 local_irq_save(flags);
176 *sp->srcu_cb_tail = rhp;
177 sp->srcu_cb_tail = &rhp->next;
178 local_irq_restore(flags);
179 if (!READ_ONCE(sp->srcu_gp_running))
180 schedule_work(&sp->srcu_work);
181}
182EXPORT_SYMBOL_GPL(call_srcu);
183
184/*
185 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
186 */
187void synchronize_srcu(struct srcu_struct *sp)
188{
189 struct rcu_synchronize rs;
190
191 init_rcu_head_on_stack(&rs.head);
192 init_completion(&rs.completion);
193 call_srcu(sp, &rs.head, wakeme_after_rcu);
194 wait_for_completion(&rs.completion);
195 destroy_rcu_head_on_stack(&rs.head);
196}
197EXPORT_SYMBOL_GPL(synchronize_srcu);
198
199/* Lockdep diagnostics. */
200void __init rcu_scheduler_starting(void)
201{
202 rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
203}