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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 ssp->srcu_idx_max = 0;
38 INIT_WORK(&ssp->srcu_work, srcu_drive_gp);
39 INIT_LIST_HEAD(&ssp->srcu_work.entry);
40 return 0;
41}
42
43#ifdef CONFIG_DEBUG_LOCK_ALLOC
44
45int __init_srcu_struct(struct srcu_struct *ssp, const char *name,
46 struct lock_class_key *key)
47{
48 /* Don't re-initialize a lock while it is held. */
49 debug_check_no_locks_freed((void *)ssp, sizeof(*ssp));
50 lockdep_init_map(&ssp->dep_map, name, key, 0);
51 return init_srcu_struct_fields(ssp);
52}
53EXPORT_SYMBOL_GPL(__init_srcu_struct);
54
55#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
56
57/*
58 * init_srcu_struct - initialize a sleep-RCU structure
59 * @ssp: structure to initialize.
60 *
61 * Must invoke this on a given srcu_struct before passing that srcu_struct
62 * to any other function. Each srcu_struct represents a separate domain
63 * of SRCU protection.
64 */
65int init_srcu_struct(struct srcu_struct *ssp)
66{
67 return init_srcu_struct_fields(ssp);
68}
69EXPORT_SYMBOL_GPL(init_srcu_struct);
70
71#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
72
73/*
74 * cleanup_srcu_struct - deconstruct a sleep-RCU structure
75 * @ssp: structure to clean up.
76 *
77 * Must invoke this after you are finished using a given srcu_struct that
78 * was initialized via init_srcu_struct(), else you leak memory.
79 */
80void cleanup_srcu_struct(struct srcu_struct *ssp)
81{
82 WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]);
83 flush_work(&ssp->srcu_work);
84 WARN_ON(ssp->srcu_gp_running);
85 WARN_ON(ssp->srcu_gp_waiting);
86 WARN_ON(ssp->srcu_cb_head);
87 WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail);
88 WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max);
89 WARN_ON(ssp->srcu_idx & 0x1);
90}
91EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
92
93/*
94 * Removes the count for the old reader from the appropriate element of
95 * the srcu_struct.
96 */
97void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
98{
99 int newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
100
101 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
102 if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task())
103 swake_up_one(&ssp->srcu_wq);
104}
105EXPORT_SYMBOL_GPL(__srcu_read_unlock);
106
107/*
108 * Workqueue handler to drive one grace period and invoke any callbacks
109 * that become ready as a result. Single-CPU and !PREEMPTION operation
110 * means that we get away with murder on synchronization. ;-)
111 */
112void srcu_drive_gp(struct work_struct *wp)
113{
114 int idx;
115 struct rcu_head *lh;
116 struct rcu_head *rhp;
117 struct srcu_struct *ssp;
118
119 ssp = container_of(wp, struct srcu_struct, srcu_work);
120 if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
121 return; /* Already running or nothing to do. */
122
123 /* Remove recently arrived callbacks and wait for readers. */
124 WRITE_ONCE(ssp->srcu_gp_running, true);
125 local_irq_disable();
126 lh = ssp->srcu_cb_head;
127 ssp->srcu_cb_head = NULL;
128 ssp->srcu_cb_tail = &ssp->srcu_cb_head;
129 local_irq_enable();
130 idx = (ssp->srcu_idx & 0x2) / 2;
131 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
132 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
133 swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
134 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
135 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
136
137 /* Invoke the callbacks we removed above. */
138 while (lh) {
139 rhp = lh;
140 lh = lh->next;
141 local_bh_disable();
142 rhp->func(rhp);
143 local_bh_enable();
144 }
145
146 /*
147 * Enable rescheduling, and if there are more callbacks,
148 * reschedule ourselves. This can race with a call_srcu()
149 * at interrupt level, but the ->srcu_gp_running checks will
150 * straighten that out.
151 */
152 WRITE_ONCE(ssp->srcu_gp_running, false);
153 if (ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
154 schedule_work(&ssp->srcu_work);
155}
156EXPORT_SYMBOL_GPL(srcu_drive_gp);
157
158static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
159{
160 unsigned long cookie;
161
162 cookie = get_state_synchronize_srcu(ssp);
163 if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
164 return;
165 WRITE_ONCE(ssp->srcu_idx_max, cookie);
166 if (!READ_ONCE(ssp->srcu_gp_running)) {
167 if (likely(srcu_init_done))
168 schedule_work(&ssp->srcu_work);
169 else if (list_empty(&ssp->srcu_work.entry))
170 list_add(&ssp->srcu_work.entry, &srcu_boot_list);
171 }
172}
173
174/*
175 * Enqueue an SRCU callback on the specified srcu_struct structure,
176 * initiating grace-period processing if it is not already running.
177 */
178void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
179 rcu_callback_t func)
180{
181 unsigned long flags;
182
183 rhp->func = func;
184 rhp->next = NULL;
185 local_irq_save(flags);
186 *ssp->srcu_cb_tail = rhp;
187 ssp->srcu_cb_tail = &rhp->next;
188 local_irq_restore(flags);
189 srcu_gp_start_if_needed(ssp);
190}
191EXPORT_SYMBOL_GPL(call_srcu);
192
193/*
194 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
195 */
196void synchronize_srcu(struct srcu_struct *ssp)
197{
198 struct rcu_synchronize rs;
199
200 RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
201 lock_is_held(&rcu_bh_lock_map) ||
202 lock_is_held(&rcu_lock_map) ||
203 lock_is_held(&rcu_sched_lock_map),
204 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
205
206 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
207 return;
208
209 might_sleep();
210 init_rcu_head_on_stack(&rs.head);
211 init_completion(&rs.completion);
212 call_srcu(ssp, &rs.head, wakeme_after_rcu);
213 wait_for_completion(&rs.completion);
214 destroy_rcu_head_on_stack(&rs.head);
215}
216EXPORT_SYMBOL_GPL(synchronize_srcu);
217
218/*
219 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
220 */
221unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
222{
223 unsigned long ret;
224
225 barrier();
226 ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
227 barrier();
228 return ret;
229}
230EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
231
232/*
233 * start_poll_synchronize_srcu - Provide cookie and start grace period
234 *
235 * The difference between this and get_state_synchronize_srcu() is that
236 * this function ensures that the poll_state_synchronize_srcu() will
237 * eventually return the value true.
238 */
239unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
240{
241 unsigned long ret = get_state_synchronize_srcu(ssp);
242
243 srcu_gp_start_if_needed(ssp);
244 return ret;
245}
246EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
247
248/*
249 * poll_state_synchronize_srcu - Has cookie's grace period ended?
250 */
251bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
252{
253 unsigned long cur_s = READ_ONCE(ssp->srcu_idx);
254
255 barrier();
256 return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);
257}
258EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
259
260/* Lockdep diagnostics. */
261void __init rcu_scheduler_starting(void)
262{
263 rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
264}
265
266/*
267 * Queue work for srcu_struct structures with early boot callbacks.
268 * The work won't actually execute until the workqueue initialization
269 * phase that takes place after the scheduler starts.
270 */
271void __init srcu_init(void)
272{
273 struct srcu_struct *ssp;
274
275 srcu_init_done = true;
276 while (!list_empty(&srcu_boot_list)) {
277 ssp = list_first_entry(&srcu_boot_list,
278 struct srcu_struct, srcu_work.entry);
279 list_del_init(&ssp->srcu_work.entry);
280 schedule_work(&ssp->srcu_work);
281 }
282}
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}