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/rwsem.h>
7 #include <linux/percpu.h>
8 #include <linux/rcuwait.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 rw_semaphore rw_sem; /* slowpath */
16 struct rcuwait writer; /* blocked writer */
17 int readers_block;
18 };
19
20 #define DEFINE_STATIC_PERCPU_RWSEM(name) \
21 static DEFINE_PER_CPU(unsigned int, __percpu_rwsem_rc_##name); \
22 static struct percpu_rw_semaphore name = { \
23 .rss = __RCU_SYNC_INITIALIZER(name.rss, RCU_SCHED_SYNC), \
24 .read_count = &__percpu_rwsem_rc_##name, \
25 .rw_sem = __RWSEM_INITIALIZER(name.rw_sem), \
26 .writer = __RCUWAIT_INITIALIZER(name.writer), \
27 }
28
29 extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
30 extern void __percpu_up_read(struct percpu_rw_semaphore *);
31
percpu_down_read_preempt_disable(struct percpu_rw_semaphore * sem)32 static inline void percpu_down_read_preempt_disable(struct percpu_rw_semaphore *sem)
33 {
34 might_sleep();
35
36 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
37
38 preempt_disable();
39 /*
40 * We are in an RCU-sched read-side critical section, so the writer
41 * cannot both change sem->state from readers_fast and start checking
42 * counters while we are here. So if we see !sem->state, we know that
43 * the writer won't be checking until we're past the preempt_enable()
44 * and that one the synchronize_sched() is done, the writer will see
45 * anything we did within this RCU-sched read-size critical section.
46 */
47 __this_cpu_inc(*sem->read_count);
48 if (unlikely(!rcu_sync_is_idle(&sem->rss)))
49 __percpu_down_read(sem, false); /* Unconditional memory barrier */
50 barrier();
51 /*
52 * The barrier() prevents the compiler from
53 * bleeding the critical section out.
54 */
55 }
56
percpu_down_read(struct percpu_rw_semaphore * sem)57 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
58 {
59 percpu_down_read_preempt_disable(sem);
60 preempt_enable();
61 }
62
percpu_down_read_trylock(struct percpu_rw_semaphore * sem)63 static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
64 {
65 int ret = 1;
66
67 preempt_disable();
68 /*
69 * Same as in percpu_down_read().
70 */
71 __this_cpu_inc(*sem->read_count);
72 if (unlikely(!rcu_sync_is_idle(&sem->rss)))
73 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
74 preempt_enable();
75 /*
76 * The barrier() from preempt_enable() prevents the compiler from
77 * bleeding the critical section out.
78 */
79
80 if (ret)
81 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
82
83 return ret;
84 }
85
percpu_up_read_preempt_enable(struct percpu_rw_semaphore * sem)86 static inline void percpu_up_read_preempt_enable(struct percpu_rw_semaphore *sem)
87 {
88 /*
89 * The barrier() prevents the compiler from
90 * bleeding the critical section out.
91 */
92 barrier();
93 /*
94 * Same as in percpu_down_read().
95 */
96 if (likely(rcu_sync_is_idle(&sem->rss)))
97 __this_cpu_dec(*sem->read_count);
98 else
99 __percpu_up_read(sem); /* Unconditional memory barrier */
100 preempt_enable();
101
102 rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
103 }
104
percpu_up_read(struct percpu_rw_semaphore * sem)105 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
106 {
107 preempt_disable();
108 percpu_up_read_preempt_enable(sem);
109 }
110
111 extern void percpu_down_write(struct percpu_rw_semaphore *);
112 extern void percpu_up_write(struct percpu_rw_semaphore *);
113
114 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
115 const char *, struct lock_class_key *);
116
117 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
118
119 #define percpu_init_rwsem(sem) \
120 ({ \
121 static struct lock_class_key rwsem_key; \
122 __percpu_init_rwsem(sem, #sem, &rwsem_key); \
123 })
124
125 #define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
126
127 #define percpu_rwsem_assert_held(sem) \
128 lockdep_assert_held(&(sem)->rw_sem)
129
percpu_rwsem_release(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)130 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
131 bool read, unsigned long ip)
132 {
133 lock_release(&sem->rw_sem.dep_map, 1, ip);
134 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
135 if (!read)
136 sem->rw_sem.owner = RWSEM_OWNER_UNKNOWN;
137 #endif
138 }
139
percpu_rwsem_acquire(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)140 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
141 bool read, unsigned long ip)
142 {
143 lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
144 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
145 if (!read)
146 sem->rw_sem.owner = current;
147 #endif
148 }
149
150 #endif
151