Line data Source code
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 :
47 14110 : static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
48 : {
49 14110 : might_sleep();
50 :
51 14110 : rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
52 :
53 14110 : 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 14110 : if (likely(rcu_sync_is_idle(&sem->rss)))
63 12083 : this_cpu_inc(*sem->read_count);
64 : else
65 2027 : __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 14110 : preempt_enable();
71 14110 : }
72 :
73 11856 : static inline bool percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
74 : {
75 11856 : bool ret = true;
76 :
77 11856 : preempt_disable();
78 : /*
79 : * Same as in percpu_down_read().
80 : */
81 11856 : if (likely(rcu_sync_is_idle(&sem->rss)))
82 11855 : this_cpu_inc(*sem->read_count);
83 : else
84 0 : ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
85 11855 : preempt_enable();
86 : /*
87 : * The barrier() from preempt_enable() prevents the compiler from
88 : * bleeding the critical section out.
89 : */
90 :
91 11855 : if (ret)
92 11855 : rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
93 :
94 11856 : return ret;
95 : }
96 :
97 25966 : static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
98 : {
99 25966 : rwsem_release(&sem->dep_map, _RET_IP_);
100 :
101 25966 : preempt_disable();
102 : /*
103 : * Same as in percpu_down_read().
104 : */
105 25966 : if (likely(rcu_sync_is_idle(&sem->rss))) {
106 23939 : this_cpu_dec(*sem->read_count);
107 : } else {
108 : /*
109 : * slowpath; reader will only ever wake a single blocked
110 : * writer.
111 : */
112 2027 : 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 2027 : this_cpu_dec(*sem->read_count);
119 2027 : rcuwait_wake_up(&sem->writer);
120 : }
121 25966 : preempt_enable();
122 25966 : }
123 :
124 : extern void percpu_down_write(struct percpu_rw_semaphore *);
125 : extern void percpu_up_write(struct percpu_rw_semaphore *);
126 :
127 : extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
128 : const char *, struct lock_class_key *);
129 :
130 : extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
131 :
132 : #define percpu_init_rwsem(sem) \
133 : ({ \
134 : static struct lock_class_key rwsem_key; \
135 : __percpu_init_rwsem(sem, #sem, &rwsem_key); \
136 : })
137 :
138 : #define percpu_rwsem_is_held(sem) lockdep_is_held(sem)
139 : #define percpu_rwsem_assert_held(sem) lockdep_assert_held(sem)
140 :
141 0 : static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
142 : bool read, unsigned long ip)
143 : {
144 0 : lock_release(&sem->dep_map, ip);
145 : }
146 :
147 0 : static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
148 : bool read, unsigned long ip)
149 : {
150 0 : lock_acquire(&sem->dep_map, 0, 1, read, 1, NULL, ip);
151 0 : }
152 :
153 : #endif
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