1 #ifndef _LINUX_PERCPU_RWSEM_H
2 #define _LINUX_PERCPU_RWSEM_H
3
4 #include <linux/atomic.h>
5 #include <linux/rwsem.h>
6 #include <linux/percpu.h>
7 #include <linux/wait.h>
8 #include <linux/rcu_sync.h>
9 #include <linux/lockdep.h>
10
11 struct percpu_rw_semaphore {
12 struct rcu_sync rss;
13 unsigned int __percpu *read_count;
14 struct rw_semaphore rw_sem;
15 wait_queue_head_t writer;
16 int readers_block;
17 };
18
19 extern int __percpu_down_read(struct percpu_rw_semaphore *, int);
20 extern void __percpu_up_read(struct percpu_rw_semaphore *);
21
percpu_down_read(struct percpu_rw_semaphore * sem)22 static inline void percpu_down_read(struct percpu_rw_semaphore *sem)
23 {
24 might_sleep();
25
26 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 0, _RET_IP_);
27
28 preempt_disable();
29 /*
30 * We are in an RCU-sched read-side critical section, so the writer
31 * cannot both change sem->state from readers_fast and start checking
32 * counters while we are here. So if we see !sem->state, we know that
33 * the writer won't be checking until we're past the preempt_enable()
34 * and that one the synchronize_sched() is done, the writer will see
35 * anything we did within this RCU-sched read-size critical section.
36 */
37 __this_cpu_inc(*sem->read_count);
38 if (unlikely(!rcu_sync_is_idle(&sem->rss)))
39 __percpu_down_read(sem, false); /* Unconditional memory barrier */
40 preempt_enable();
41 /*
42 * The barrier() from preempt_enable() prevents the compiler from
43 * bleeding the critical section out.
44 */
45 }
46
percpu_down_read_trylock(struct percpu_rw_semaphore * sem)47 static inline int percpu_down_read_trylock(struct percpu_rw_semaphore *sem)
48 {
49 int ret = 1;
50
51 preempt_disable();
52 /*
53 * Same as in percpu_down_read().
54 */
55 __this_cpu_inc(*sem->read_count);
56 if (unlikely(!rcu_sync_is_idle(&sem->rss)))
57 ret = __percpu_down_read(sem, true); /* Unconditional memory barrier */
58 preempt_enable();
59 /*
60 * The barrier() from preempt_enable() prevents the compiler from
61 * bleeding the critical section out.
62 */
63
64 if (ret)
65 rwsem_acquire_read(&sem->rw_sem.dep_map, 0, 1, _RET_IP_);
66
67 return ret;
68 }
69
percpu_up_read(struct percpu_rw_semaphore * sem)70 static inline void percpu_up_read(struct percpu_rw_semaphore *sem)
71 {
72 /*
73 * The barrier() in preempt_disable() prevents the compiler from
74 * bleeding the critical section out.
75 */
76 preempt_disable();
77 /*
78 * Same as in percpu_down_read().
79 */
80 if (likely(rcu_sync_is_idle(&sem->rss)))
81 __this_cpu_dec(*sem->read_count);
82 else
83 __percpu_up_read(sem); /* Unconditional memory barrier */
84 preempt_enable();
85
86 rwsem_release(&sem->rw_sem.dep_map, 1, _RET_IP_);
87 }
88
89 extern void percpu_down_write(struct percpu_rw_semaphore *);
90 extern void percpu_up_write(struct percpu_rw_semaphore *);
91
92 extern int __percpu_init_rwsem(struct percpu_rw_semaphore *,
93 const char *, struct lock_class_key *);
94
95 extern void percpu_free_rwsem(struct percpu_rw_semaphore *);
96
97 #define percpu_init_rwsem(sem) \
98 ({ \
99 static struct lock_class_key rwsem_key; \
100 __percpu_init_rwsem(sem, #sem, &rwsem_key); \
101 })
102
103 #define percpu_rwsem_is_held(sem) lockdep_is_held(&(sem)->rw_sem)
104
percpu_rwsem_release(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)105 static inline void percpu_rwsem_release(struct percpu_rw_semaphore *sem,
106 bool read, unsigned long ip)
107 {
108 lock_release(&sem->rw_sem.dep_map, 1, ip);
109 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
110 if (!read)
111 sem->rw_sem.owner = NULL;
112 #endif
113 }
114
percpu_rwsem_acquire(struct percpu_rw_semaphore * sem,bool read,unsigned long ip)115 static inline void percpu_rwsem_acquire(struct percpu_rw_semaphore *sem,
116 bool read, unsigned long ip)
117 {
118 lock_acquire(&sem->rw_sem.dep_map, 0, 1, read, 1, NULL, ip);
119 }
120
121 #endif
122