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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// 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 !PREEMPTION 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}