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		debug_rcu_head_callback(rhp);
142		local_bh_disable();
143		rhp->func(rhp);
144		local_bh_enable();
145	}
146
147	/*
148	 * Enable rescheduling, and if there are more callbacks,
149	 * reschedule ourselves.  This can race with a call_srcu()
150	 * at interrupt level, but the ->srcu_gp_running checks will
151	 * straighten that out.
152	 */
153	WRITE_ONCE(ssp->srcu_gp_running, false);
154	if (ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)))
155		schedule_work(&ssp->srcu_work);
156}
157EXPORT_SYMBOL_GPL(srcu_drive_gp);
158
159static void srcu_gp_start_if_needed(struct srcu_struct *ssp)
160{
161	unsigned long cookie;
162
163	cookie = get_state_synchronize_srcu(ssp);
164	if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie))
165		return;
166	WRITE_ONCE(ssp->srcu_idx_max, cookie);
167	if (!READ_ONCE(ssp->srcu_gp_running)) {
168		if (likely(srcu_init_done))
169			schedule_work(&ssp->srcu_work);
170		else if (list_empty(&ssp->srcu_work.entry))
171			list_add(&ssp->srcu_work.entry, &srcu_boot_list);
172	}
173}
174
175/*
176 * Enqueue an SRCU callback on the specified srcu_struct structure,
177 * initiating grace-period processing if it is not already running.
178 */
179void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp,
180	       rcu_callback_t func)
181{
182	unsigned long flags;
183
184	rhp->func = func;
185	rhp->next = NULL;
186	local_irq_save(flags);
187	*ssp->srcu_cb_tail = rhp;
188	ssp->srcu_cb_tail = &rhp->next;
189	local_irq_restore(flags);
190	srcu_gp_start_if_needed(ssp);
191}
192EXPORT_SYMBOL_GPL(call_srcu);
193
194/*
195 * synchronize_srcu - wait for prior SRCU read-side critical-section completion
196 */
197void synchronize_srcu(struct srcu_struct *ssp)
198{
199	struct rcu_synchronize rs;
200
201	srcu_lock_sync(&ssp->dep_map);
202
203	RCU_LOCKDEP_WARN(lockdep_is_held(ssp) ||
204			lock_is_held(&rcu_bh_lock_map) ||
205			lock_is_held(&rcu_lock_map) ||
206			lock_is_held(&rcu_sched_lock_map),
207			"Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
208
209	if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE)
210		return;
211
212	might_sleep();
213	init_rcu_head_on_stack(&rs.head);
214	init_completion(&rs.completion);
215	call_srcu(ssp, &rs.head, wakeme_after_rcu);
216	wait_for_completion(&rs.completion);
217	destroy_rcu_head_on_stack(&rs.head);
218}
219EXPORT_SYMBOL_GPL(synchronize_srcu);
220
221/*
222 * get_state_synchronize_srcu - Provide an end-of-grace-period cookie
223 */
224unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp)
225{
226	unsigned long ret;
227
228	barrier();
229	ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1;
230	barrier();
231	return ret;
232}
233EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
234
235/*
236 * start_poll_synchronize_srcu - Provide cookie and start grace period
237 *
238 * The difference between this and get_state_synchronize_srcu() is that
239 * this function ensures that the poll_state_synchronize_srcu() will
240 * eventually return the value true.
241 */
242unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp)
243{
244	unsigned long ret = get_state_synchronize_srcu(ssp);
245
246	srcu_gp_start_if_needed(ssp);
247	return ret;
248}
249EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
250
251/*
252 * poll_state_synchronize_srcu - Has cookie's grace period ended?
253 */
254bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie)
255{
256	unsigned long cur_s = READ_ONCE(ssp->srcu_idx);
257
258	barrier();
259	return ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);
260}
261EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
262
263/* Lockdep diagnostics.  */
264void __init rcu_scheduler_starting(void)
265{
266	rcu_scheduler_active = RCU_SCHEDULER_RUNNING;
267}
268
269/*
270 * Queue work for srcu_struct structures with early boot callbacks.
271 * The work won't actually execute until the workqueue initialization
272 * phase that takes place after the scheduler starts.
273 */
274void __init srcu_init(void)
275{
276	struct srcu_struct *ssp;
277
278	srcu_init_done = true;
279	while (!list_empty(&srcu_boot_list)) {
280		ssp = list_first_entry(&srcu_boot_list,
281				      struct srcu_struct, srcu_work.entry);
282		list_del_init(&ssp->srcu_work.entry);
283		schedule_work(&ssp->srcu_work);
284	}
285}
286