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