1 /* SPDX-License-Identifier: GPL-2.0 */ 2 /* rwsem.h: R/W semaphores, public interface 3 * 4 * Written by David Howells ([email protected]). 5 * Derived from asm-i386/semaphore.h 6 */ 7 8 #ifndef _LINUX_RWSEM_H 9 #define _LINUX_RWSEM_H 10 11 #include <linux/linkage.h> 12 13 #include <linux/types.h> 14 #include <linux/kernel.h> 15 #include <linux/list.h> 16 #include <linux/spinlock.h> 17 #include <linux/atomic.h> 18 #include <linux/err.h> 19 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 20 #include <linux/osq_lock.h> 21 #endif 22 23 struct rw_semaphore; 24 25 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK 26 #include <linux/rwsem-spinlock.h> /* use a generic implementation */ 27 #define __RWSEM_INIT_COUNT(name) .count = RWSEM_UNLOCKED_VALUE 28 #else 29 /* All arch specific implementations share the same struct */ 30 struct rw_semaphore { 31 atomic_long_t count; 32 struct list_head wait_list; 33 raw_spinlock_t wait_lock; 34 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 35 struct optimistic_spin_queue osq; /* spinner MCS lock */ 36 /* 37 * Write owner. Used as a speculative check to see 38 * if the owner is running on the cpu. 39 */ 40 struct task_struct *owner; 41 #endif 42 #ifdef CONFIG_DEBUG_LOCK_ALLOC 43 struct lockdep_map dep_map; 44 #endif 45 }; 46 47 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); 48 extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem); 49 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); 50 extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem); 51 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); 52 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); 53 54 /* Include the arch specific part */ 55 #include <asm/rwsem.h> 56 57 /* In all implementations count != 0 means locked */ 58 static inline int rwsem_is_locked(struct rw_semaphore *sem) 59 { 60 return atomic_long_read(&sem->count) != 0; 61 } 62 63 #define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) 64 #endif 65 66 /* Common initializer macros and functions */ 67 68 #ifdef CONFIG_DEBUG_LOCK_ALLOC 69 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } 70 #else 71 # define __RWSEM_DEP_MAP_INIT(lockname) 72 #endif 73 74 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 75 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL 76 #else 77 #define __RWSEM_OPT_INIT(lockname) 78 #endif 79 80 #define __RWSEM_INITIALIZER(name) \ 81 { __RWSEM_INIT_COUNT(name), \ 82 .wait_list = LIST_HEAD_INIT((name).wait_list), \ 83 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ 84 __RWSEM_OPT_INIT(name) \ 85 __RWSEM_DEP_MAP_INIT(name) } 86 87 #define DECLARE_RWSEM(name) \ 88 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 89 90 extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 91 struct lock_class_key *key); 92 93 #define init_rwsem(sem) \ 94 do { \ 95 static struct lock_class_key __key; \ 96 \ 97 __init_rwsem((sem), #sem, &__key); \ 98 } while (0) 99 100 /* 101 * This is the same regardless of which rwsem implementation that is being used. 102 * It is just a heuristic meant to be called by somebody alreadying holding the 103 * rwsem to see if somebody from an incompatible type is wanting access to the 104 * lock. 105 */ 106 static inline int rwsem_is_contended(struct rw_semaphore *sem) 107 { 108 return !list_empty(&sem->wait_list); 109 } 110 111 /* 112 * lock for reading 113 */ 114 extern void down_read(struct rw_semaphore *sem); 115 extern int __must_check down_read_killable(struct rw_semaphore *sem); 116 117 /* 118 * trylock for reading -- returns 1 if successful, 0 if contention 119 */ 120 extern int down_read_trylock(struct rw_semaphore *sem); 121 122 /* 123 * lock for writing 124 */ 125 extern void down_write(struct rw_semaphore *sem); 126 extern int __must_check down_write_killable(struct rw_semaphore *sem); 127 128 /* 129 * trylock for writing -- returns 1 if successful, 0 if contention 130 */ 131 extern int down_write_trylock(struct rw_semaphore *sem); 132 133 /* 134 * release a read lock 135 */ 136 extern void up_read(struct rw_semaphore *sem); 137 138 /* 139 * release a write lock 140 */ 141 extern void up_write(struct rw_semaphore *sem); 142 143 /* 144 * downgrade write lock to read lock 145 */ 146 extern void downgrade_write(struct rw_semaphore *sem); 147 148 #ifdef CONFIG_DEBUG_LOCK_ALLOC 149 /* 150 * nested locking. NOTE: rwsems are not allowed to recurse 151 * (which occurs if the same task tries to acquire the same 152 * lock instance multiple times), but multiple locks of the 153 * same lock class might be taken, if the order of the locks 154 * is always the same. This ordering rule can be expressed 155 * to lockdep via the _nested() APIs, but enumerating the 156 * subclasses that are used. (If the nesting relationship is 157 * static then another method for expressing nested locking is 158 * the explicit definition of lock class keys and the use of 159 * lockdep_set_class() at lock initialization time. 160 * See Documentation/locking/lockdep-design.txt for more details.) 161 */ 162 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 163 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 164 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); 165 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); 166 167 # define down_write_nest_lock(sem, nest_lock) \ 168 do { \ 169 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ 170 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ 171 } while (0); 172 173 /* 174 * Take/release a lock when not the owner will release it. 175 * 176 * [ This API should be avoided as much as possible - the 177 * proper abstraction for this case is completions. ] 178 */ 179 extern void down_read_non_owner(struct rw_semaphore *sem); 180 extern void up_read_non_owner(struct rw_semaphore *sem); 181 #else 182 # define down_read_nested(sem, subclass) down_read(sem) 183 # define down_write_nest_lock(sem, nest_lock) down_write(sem) 184 # define down_write_nested(sem, subclass) down_write(sem) 185 # define down_write_killable_nested(sem, subclass) down_write_killable(sem) 186 # define down_read_non_owner(sem) down_read(sem) 187 # define up_read_non_owner(sem) up_read(sem) 188 #endif 189 190 #endif /* _LINUX_RWSEM_H */ 191