1 /* SPDX-License-Identifier: GPL-2.0 */
2 #ifndef _LINUX_PERCPU_RWSEM_H
3 #define _LINUX_PERCPU_RWSEM_H
4
5 #include <linux/atomic.h>
6 #include <linux/percpu.h>
7 #include <linux/rcuwait.h>
8 #include <linux/wait.h>
9 #include <linux/rcu_sync.h>
10 #include <linux/lockdep.h>
11
12 struct percpu_rw_semaphore {
13 struct rcu_sync rss;
14 unsigned int __percpu *read_count;
15 struct rcuwait writer;
16 wait_queue_head_t waiters;
17 atomic_t block;
18 #ifdef CONFIG_DEBUG_LOCK_ALLOC
19 struct lockdep_map dep_map;
20 #endif
21 };
22
23 #ifdef CONFIG_DEBUG_LOCK_ALLOC
24 #define __PERCPU_RWSEM_DEP_MAP_INIT(lockname) .dep_map = { .name = #lockname },
25 #else
26 #define __PERCPU_RWSEM_DEP_MAP_INIT(lockname)
27 #endif
28
29 #define __DEFINE_PERCPU_RWSEM(name, is_static) \
30 static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
31 is_static struct percpu_rw_semaphore name = { \
32 .rss = __RCU_SYNC_INITIALIZER(name.rss), \
33 .read_count = &__percpu_rwsem_rc_##name, \
34 .writer = __RCUWAIT_INITIALIZER(name.writer), \
35 .waiters = __WAIT_QUEUE_HEAD_INITIALIZER(name.waiters), \
36 .block = ATOMIC_INIT(0), \
37 __PERCPU_RWSEM_DEP_MAP_INIT(name) \
38 }
39
40 #define DEFINE_PERCPU_RWSEM(name) \
41 __DEFINE_PERCPU_RWSEM(name, /* not static */)
42 #define DEFINE_STATIC_PERCPU_RWSEM(name) \
43 __DEFINE_PERCPU_RWSEM(name, static)
44
45 extern bool __percpu_down_read(struct percpu_rw_semaphore *, bool);
46
percpu_down_read(struct percpu_rw_semaphore * sem)47 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
48 {
49 might_sleep();
50
51 rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
52
53 preempt_disable();
54 /*
55 * We are in an RCU-sched read-side critical section, so the writer
56 * cannot both change sem->state from readers_fast and start checking
57 * counters while we are here. So if we see !sem->state, we know that
58 * the writer won't be checking until we're past the preempt_enable()
59 * and that once the synchronize_rcu() is done, the writer will see
60 * anything we did within this RCU-sched read-size critical section.
61 */
62 if (likely(rcu_sync_is_idle(&sem->rss)))
63 this_cpu_inc(*sem->read_count);
64 else
65 __percpu_down_read(sem, false); /* Unconditional memory barrier */
66 /*
67 * The preempt_enable() prevents the compiler from
68 * bleeding the critical section out.
69 */
70 preempt_enable();
71 }
72
percpu_down_read_trylock(struct percpu_rw_semaphore * sem)73 static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
74 {
75 bool ret = true;
76
77 preempt_disable();
78 /*
79 * Same as in percpu_down_read().
80 */
81 if (likely(rcu_sync_is_idle(&sem->rss)))
82 this_cpu_inc(*sem->read_count);
83 else
84 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
85 preempt_enable();
86 /*
87 * The barrier() from preempt_enable() prevents the compiler from
88 * bleeding the critical section out.
89 */
90
91 if (ret)
92 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
93
94 return ret;
95 }
96
percpu_up_read(struct percpu_rw_semaphore * sem)97 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
98 {
99 rwsem_release(&sem->dep_map, _RET_IP_);
100
101 preempt_disable();
102 /*
103 * Same as in percpu_down_read().
104 */
105 if (likely(rcu_sync_is_idle(&sem->rss))) {
106 this_cpu_dec(*sem->read_count);
107 } else {
108 /*
109 * slowpath; reader will only ever wake a single blocked
110 * writer.
111 */
112 smp_mb(); /* B matches C */
113 /*
114 * In other words, if they see our decrement (presumably to
115 * aggregate zero, as that is the only time it matters) they
116 * will also see our critical section.
117 */
118 this_cpu_dec(*sem->read_count);
119 rcuwait_wake_up(&sem->writer);
120 }
121 preempt_enable();
122 }
123
124 extern bool percpu_is_read_locked(struct percpu_rw_semaphore *);
125 extern void percpu_down_write(struct percpu_rw_semaphore *);
126 extern void percpu_up_write(struct percpu_rw_semaphore *);
127
percpu_is_write_locked(struct percpu_rw_semaphore * sem)128 static inline bool percpu_is_write_locked(struct percpu_rw_semaphore *sem)
129 {
130 return atomic_read(&sem->block);
131 }
132
133 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
134 const char *, struct lock_class_key *);
135
136 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
137
138 #define percpu_init_rwsem(sem) \
139 ({ \
140 static struct lock_class_key rwsem_key; \
141 __percpu_init_rwsem(sem, #sem, &rwsem_key); \
142 })
143
144 #define percpu_rwsem_is_held(sem) lockdep_is_held(sem)
145 #define percpu_rwsem_assert_held(sem) lockdep_assert_held(sem)
146
percpu_rwsem_release(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)147 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
148 bool read, unsigned long ip)
149 {
150 lock_release(&sem->dep_map, ip);
151 }
152
percpu_rwsem_acquire(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)153 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
154 bool read, unsigned long ip)
155 {
156 lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
157 }
158
159 #endif
160