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