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