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