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
23 int rcu_scheduler_active __read_mostly;
24 static LIST_HEAD(srcu_boot_list);
25 static bool srcu_init_done;
26
27 static 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
45 int __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 }
53 EXPORT_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 */
65 int init_srcu_struct(struct srcu_struct *ssp)
66 {
67 return init_srcu_struct_fields(ssp);
68 }
69 EXPORT_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 */
80 void 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 }
91 EXPORT_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 */
97 void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
98 {
99 int newval;
100
101 preempt_disable(); // Needed for PREEMPT_AUTO
102 newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1;
103 WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval);
104 preempt_enable();
105 if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task())
106 swake_up_one(&ssp->srcu_wq);
107 }
108 EXPORT_SYMBOL_GPL(__srcu_read_unlock);
109
110 /*
111 * Workqueue handler to drive one grace period and invoke any callbacks
112 * that become ready as a result. Single-CPU and !PREEMPTION operation
113 * means that we get away with murder on synchronization. ;-)
114 */
115 void srcu_drive_gp(struct work_struct *wp)
116 {
117 int idx;
118 struct rcu_head *lh;
119 struct rcu_head *rhp;
120 struct srcu_struct *ssp;
121
122 ssp = container_of(wp, struct srcu_struct, srcu_work);
123 preempt_disable(); // Needed for PREEMPT_AUTO
124 if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) {
125 return; /* Already running or nothing to do. */
126 preempt_enable();
127 }
128
129 /* Remove recently arrived callbacks and wait for readers. */
130 WRITE_ONCE(ssp->srcu_gp_running, true);
131 local_irq_disable();
132 lh = ssp->srcu_cb_head;
133 ssp->srcu_cb_head = NULL;
134 ssp->srcu_cb_tail = &ssp->srcu_cb_head;
135 local_irq_enable();
136 idx = (ssp->srcu_idx & 0x2) / 2;
137 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
138 WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */
139 preempt_enable();
140 swait_event_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]));
141 preempt_disable(); // Needed for PREEMPT_AUTO
142 WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */
143 WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1);
144 preempt_enable();
145
146 /* Invoke the callbacks we removed above. */
147 while (lh) {
148 rhp = lh;
149 lh = lh->next;
150 debug_rcu_head_callback(rhp);
151 local_bh_disable();
152 rhp->func(rhp);
153 local_bh_enable();
154 }
155
156 /*
157 * Enable rescheduling, and if there are more callbacks,
158 * reschedule ourselves. This can race with a call_srcu()
159 * at interrupt level, but the ->srcu_gp_running checks will
160 * straighten that out.
161 */
162 preempt_disable(); // Needed for PREEMPT_AUTO
163 WRITE_ONCE(ssp->srcu_gp_running, false);
164 idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max));
165 preempt_enable();
166 if (idx)
167 schedule_work(&ssp->srcu_work);
168 }
169 EXPORT_SYMBOL_GPL(srcu_drive_gp);
170
171 static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
172 {
173 unsigned long cookie;
174
175 preempt_disable(); // Needed for PREEMPT_AUTO
176 cookie = get_state_synchronize_srcu(ssp);
177 if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) {
178 preempt_enable();
179 return;
180 }
181 WRITE_ONCE(ssp->srcu_idx_max, cookie);
182 if (!READ_ONCE(ssp->srcu_gp_running)) {
183 if (likely(srcu_init_done))
184 schedule_work(&ssp->srcu_work);
185 else if (list_empty(&ssp->srcu_work.entry))
186 list_add(&ssp->srcu_work.entry, &srcu_boot_list);
187 }
188 preempt_enable();
189 }
190
191 /*
192 * Enqueue an SRCU callback on the specified srcu_struct structure,
193 * initiating grace-period processing if it is not already running.
194 */
195 void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
196 rcu_callback_t func)
197 {
198 unsigned long flags;
199
200 rhp->func = func;
201 rhp->next = NULL;
202 preempt_disable(); // Needed for PREEMPT_AUTO
203 local_irq_save(flags);
204 *ssp->srcu_cb_tail = rhp;
205 ssp->srcu_cb_tail = &rhp->next;
206 local_irq_restore(flags);
207 srcu_gp_start_if_needed(ssp);
208 preempt_enable();
209 }
210 EXPORT_SYMBOL_GPL(call_srcu);
211
212 /*
213 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
214 */
215 void synchronize_srcu(struct srcu_struct *ssp)
216 {
217 struct rcu_synchronize rs;
218
219 srcu_lock_sync(&ssp->dep_map);
220
221 RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
222 lock_is_held(&rcu_bh_lock_map) ||
223 lock_is_held(&rcu_lock_map) ||
224 lock_is_held(&rcu_sched_lock_map),
225 "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
226
227 if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
228 return;
229
230 might_sleep();
231 init_rcu_head_on_stack(&rs.head);
232 init_completion(&rs.completion);
233 call_srcu(ssp, &rs.head, wakeme_after_rcu);
234 wait_for_completion(&rs.completion);
235 destroy_rcu_head_on_stack(&rs.head);
236 }
237 EXPORT_SYMBOL_GPL(synchronize_srcu);
238
239 /*
240 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
241 */
242 unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
243 {
244 unsigned long ret;
245
246 barrier();
247 ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
248 barrier();
249 return ret;
250 }
251 EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
252
253 /*
254 * start_poll_synchronize_srcu - Provide cookie and start grace period
255 *
256 * The difference between this and get_state_synchronize_srcu() is that
257 * this function ensures that the poll_state_synchronize_srcu() will
258 * eventually return the value true.
259 */
260 unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
261 {
262 unsigned long ret;
263
264 preempt_disable(); // Needed for PREEMPT_AUTO
265 ret = get_state_synchronize_srcu(ssp);
266 srcu_gp_start_if_needed(ssp);
267 preempt_enable();
268 return ret;
269 }
270 EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
271
272 /*
273 * poll_state_synchronize_srcu - Has cookie's grace period ended?
274 */
275 bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
276 {
277 unsigned long cur_s = READ_ONCE(ssp->srcu_idx);
278
279 barrier();
280 return cookie == SRCU_GET_STATE_COMPLETED ||
281 ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);
282 }
283 EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
284
285 /* Lockdep diagnostics. */
286 void __init rcu_scheduler_starting(void)
287 {
288 rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
289 }
290
291 /*
292 * Queue work for srcu_struct structures with early boot callbacks.
293 * The work won't actually execute until the workqueue initialization
294 * phase that takes place after the scheduler starts.
295 */
296 void __init srcu_init(void)
297 {
298 struct srcu_struct *ssp;
299
300 srcu_init_done = true;
301 while (!list_empty(&srcu_boot_list)) {
302 ssp = list_first_entry(&srcu_boot_list,
303 struct srcu_struct, srcu_work.entry);
304 list_del_init(&ssp->srcu_work.entry);
305 schedule_work(&ssp->srcu_work);
306 }
307 }
308
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