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