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