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