1// SPDX-License-Identifier: GPL-2.0-only
2/*
3 * PREEMPT_RT substitution for spin/rw_locks
4 *
5 * spinlocks and rwlocks on RT are based on rtmutexes, with a few twists to
6 * resemble the non RT semantics:
7 *
8 * - Contrary to plain rtmutexes, spinlocks and rwlocks are state
9 *   preserving. The task state is saved before blocking on the underlying
10 *   rtmutex, and restored when the lock has been acquired. Regular wakeups
11 *   during that time are redirected to the saved state so no wake up is
12 *   missed.
13 *
14 * - Non RT spin/rwlocks disable preemption and eventually interrupts.
15 *   Disabling preemption has the side effect of disabling migration and
16 *   preventing RCU grace periods.
17 *
18 *   The RT substitutions explicitly disable migration and take
19 *   rcu_read_lock() across the lock held section.
20 */
21#include <linux/spinlock.h>
22#include <linux/export.h>
23
24#define RT_MUTEX_BUILD_SPINLOCKS
25#include "rtmutex.c"
26
27/*
28 * __might_resched() skips the state check as rtlocks are state
29 * preserving. Take RCU nesting into account as spin/read/write_lock() can
30 * legitimately nest into an RCU read side critical section.
31 */
32#define RTLOCK_RESCHED_OFFSETS						\
33	(rcu_preempt_depth() << MIGHT_RESCHED_RCU_SHIFT)
34
35#define rtlock_might_resched()						\
36	__might_resched(__FILE__, __LINE__, RTLOCK_RESCHED_OFFSETS)
37
38static __always_inline void rtlock_lock(struct rt_mutex_base *rtm)
39{
40	lockdep_assert(!current->pi_blocked_on);
41
42	if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
43		rtlock_slowlock(rtm);
44}
45
46static __always_inline void __rt_spin_lock(spinlock_t *lock)
47{
48	rtlock_might_resched();
49	rtlock_lock(&lock->lock);
50	rcu_read_lock();
51	migrate_disable();
52}
53
54void __sched rt_spin_lock(spinlock_t *lock)
55{
56	spin_acquire(&lock->dep_map, 0, 0, _RET_IP_);
57	__rt_spin_lock(lock);
58}
59EXPORT_SYMBOL(rt_spin_lock);
60
61#ifdef CONFIG_DEBUG_LOCK_ALLOC
62void __sched rt_spin_lock_nested(spinlock_t *lock, int subclass)
63{
64	spin_acquire(&lock->dep_map, subclass, 0, _RET_IP_);
65	__rt_spin_lock(lock);
66}
67EXPORT_SYMBOL(rt_spin_lock_nested);
68
69void __sched rt_spin_lock_nest_lock(spinlock_t *lock,
70				    struct lockdep_map *nest_lock)
71{
72	spin_acquire_nest(&lock->dep_map, 0, 0, nest_lock, _RET_IP_);
73	__rt_spin_lock(lock);
74}
75EXPORT_SYMBOL(rt_spin_lock_nest_lock);
76#endif
77
78void __sched rt_spin_unlock(spinlock_t *lock)
79{
80	spin_release(&lock->dep_map, _RET_IP_);
81	migrate_enable();
82	rcu_read_unlock();
83
84	if (unlikely(!rt_mutex_cmpxchg_release(&lock->lock, current, NULL)))
85		rt_mutex_slowunlock(&lock->lock);
86}
87EXPORT_SYMBOL(rt_spin_unlock);
88
89/*
90 * Wait for the lock to get unlocked: instead of polling for an unlock
91 * (like raw spinlocks do), lock and unlock, to force the kernel to
92 * schedule if there's contention:
93 */
94void __sched rt_spin_lock_unlock(spinlock_t *lock)
95{
96	spin_lock(lock);
97	spin_unlock(lock);
98}
99EXPORT_SYMBOL(rt_spin_lock_unlock);
100
101static __always_inline int __rt_spin_trylock(spinlock_t *lock)
102{
103	int ret = 1;
104
105	if (unlikely(!rt_mutex_cmpxchg_acquire(&lock->lock, NULL, current)))
106		ret = rt_mutex_slowtrylock(&lock->lock);
107
108	if (ret) {
109		spin_acquire(&lock->dep_map, 0, 1, _RET_IP_);
110		rcu_read_lock();
111		migrate_disable();
112	}
113	return ret;
114}
115
116int __sched rt_spin_trylock(spinlock_t *lock)
117{
118	return __rt_spin_trylock(lock);
119}
120EXPORT_SYMBOL(rt_spin_trylock);
121
122int __sched rt_spin_trylock_bh(spinlock_t *lock)
123{
124	int ret;
125
126	local_bh_disable();
127	ret = __rt_spin_trylock(lock);
128	if (!ret)
129		local_bh_enable();
130	return ret;
131}
132EXPORT_SYMBOL(rt_spin_trylock_bh);
133
134#ifdef CONFIG_DEBUG_LOCK_ALLOC
135void __rt_spin_lock_init(spinlock_t *lock, const char *name,
136			 struct lock_class_key *key, bool percpu)
137{
138	u8 type = percpu ? LD_LOCK_PERCPU : LD_LOCK_NORMAL;
139
140	debug_check_no_locks_freed((void *)lock, sizeof(*lock));
141	lockdep_init_map_type(&lock->dep_map, name, key, 0, LD_WAIT_CONFIG,
142			      LD_WAIT_INV, type);
143}
144EXPORT_SYMBOL(__rt_spin_lock_init);
145#endif
146
147/*
148 * RT-specific reader/writer locks
149 */
150#define rwbase_set_and_save_current_state(state)	\
151	current_save_and_set_rtlock_wait_state()
152
153#define rwbase_restore_current_state()			\
154	current_restore_rtlock_saved_state()
155
156static __always_inline int
157rwbase_rtmutex_lock_state(struct rt_mutex_base *rtm, unsigned int state)
158{
159	if (unlikely(!rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
160		rtlock_slowlock(rtm);
161	return 0;
162}
163
164static __always_inline int
165rwbase_rtmutex_slowlock_locked(struct rt_mutex_base *rtm, unsigned int state)
166{
167	rtlock_slowlock_locked(rtm);
168	return 0;
169}
170
171static __always_inline void rwbase_rtmutex_unlock(struct rt_mutex_base *rtm)
172{
173	if (likely(rt_mutex_cmpxchg_acquire(rtm, current, NULL)))
174		return;
175
176	rt_mutex_slowunlock(rtm);
177}
178
179static __always_inline int  rwbase_rtmutex_trylock(struct rt_mutex_base *rtm)
180{
181	if (likely(rt_mutex_cmpxchg_acquire(rtm, NULL, current)))
182		return 1;
183
184	return rt_mutex_slowtrylock(rtm);
185}
186
187#define rwbase_signal_pending_state(state, current)	(0)
188
189#define rwbase_pre_schedule()
190
191#define rwbase_schedule()				\
192	schedule_rtlock()
193
194#define rwbase_post_schedule()
195
196#include "rwbase_rt.c"
197/*
198 * The common functions which get wrapped into the rwlock API.
199 */
200int __sched rt_read_trylock(rwlock_t *rwlock)
201{
202	int ret;
203
204	ret = rwbase_read_trylock(&rwlock->rwbase);
205	if (ret) {
206		rwlock_acquire_read(&rwlock->dep_map, 0, 1, _RET_IP_);
207		rcu_read_lock();
208		migrate_disable();
209	}
210	return ret;
211}
212EXPORT_SYMBOL(rt_read_trylock);
213
214int __sched rt_write_trylock(rwlock_t *rwlock)
215{
216	int ret;
217
218	ret = rwbase_write_trylock(&rwlock->rwbase);
219	if (ret) {
220		rwlock_acquire(&rwlock->dep_map, 0, 1, _RET_IP_);
221		rcu_read_lock();
222		migrate_disable();
223	}
224	return ret;
225}
226EXPORT_SYMBOL(rt_write_trylock);
227
228void __sched rt_read_lock(rwlock_t *rwlock)
229{
230	rtlock_might_resched();
231	rwlock_acquire_read(&rwlock->dep_map, 0, 0, _RET_IP_);
232	rwbase_read_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
233	rcu_read_lock();
234	migrate_disable();
235}
236EXPORT_SYMBOL(rt_read_lock);
237
238void __sched rt_write_lock(rwlock_t *rwlock)
239{
240	rtlock_might_resched();
241	rwlock_acquire(&rwlock->dep_map, 0, 0, _RET_IP_);
242	rwbase_write_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
243	rcu_read_lock();
244	migrate_disable();
245}
246EXPORT_SYMBOL(rt_write_lock);
247
248#ifdef CONFIG_DEBUG_LOCK_ALLOC
249void __sched rt_write_lock_nested(rwlock_t *rwlock, int subclass)
250{
251	rtlock_might_resched();
252	rwlock_acquire(&rwlock->dep_map, subclass, 0, _RET_IP_);
253	rwbase_write_lock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
254	rcu_read_lock();
255	migrate_disable();
256}
257EXPORT_SYMBOL(rt_write_lock_nested);
258#endif
259
260void __sched rt_read_unlock(rwlock_t *rwlock)
261{
262	rwlock_release(&rwlock->dep_map, _RET_IP_);
263	migrate_enable();
264	rcu_read_unlock();
265	rwbase_read_unlock(&rwlock->rwbase, TASK_RTLOCK_WAIT);
266}
267EXPORT_SYMBOL(rt_read_unlock);
268
269void __sched rt_write_unlock(rwlock_t *rwlock)
270{
271	rwlock_release(&rwlock->dep_map, _RET_IP_);
272	rcu_read_unlock();
273	migrate_enable();
274	rwbase_write_unlock(&rwlock->rwbase);
275}
276EXPORT_SYMBOL(rt_write_unlock);
277
278#ifdef CONFIG_DEBUG_LOCK_ALLOC
279void __rt_rwlock_init(rwlock_t *rwlock, const char *name,
280		      struct lock_class_key *key)
281{
282	debug_check_no_locks_freed((void *)rwlock, sizeof(*rwlock));
283	lockdep_init_map_wait(&rwlock->dep_map, name, key, 0, LD_WAIT_CONFIG);
284}
285EXPORT_SYMBOL(__rt_rwlock_init);
286#endif
287