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1 : /* SPDX-License-Identifier: GPL-2.0 */ 2 : /* rwsem.h: R/W semaphores, public interface 3 : * 4 : * Written by David Howells (dhowells@redhat.com). 5 : * Derived from asm-i386/semaphore.h 6 : */ 7 : 8 : #ifndef _LINUX_RWSEM_H 9 : #define _LINUX_RWSEM_H 10 : 11 : #include <linux/linkage.h> 12 : 13 : #include <linux/types.h> 14 : #include <linux/list.h> 15 : #include <linux/spinlock.h> 16 : #include <linux/atomic.h> 17 : #include <linux/err.h> 18 : 19 : #ifdef CONFIG_DEBUG_LOCK_ALLOC 20 : # define __RWSEM_DEP_MAP_INIT(lockname) \ 21 : .dep_map = { \ 22 : .name = #lockname, \ 23 : .wait_type_inner = LD_WAIT_SLEEP, \ 24 : }, 25 : #else 26 : # define __RWSEM_DEP_MAP_INIT(lockname) 27 : #endif 28 : 29 : #ifndef CONFIG_PREEMPT_RT 30 : 31 : #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 32 : #include <linux/osq_lock.h> 33 : #endif 34 : 35 : /* 36 : * For an uncontended rwsem, count and owner are the only fields a task 37 : * needs to touch when acquiring the rwsem. So they are put next to each 38 : * other to increase the chance that they will share the same cacheline. 39 : * 40 : * In a contended rwsem, the owner is likely the most frequently accessed 41 : * field in the structure as the optimistic waiter that holds the osq lock 42 : * will spin on owner. For an embedded rwsem, other hot fields in the 43 : * containing structure should be moved further away from the rwsem to 44 : * reduce the chance that they will share the same cacheline causing 45 : * cacheline bouncing problem. 46 : */ 47 : struct rw_semaphore { 48 : atomic_long_t count; 49 : /* 50 : * Write owner or one of the read owners as well flags regarding 51 : * the current state of the rwsem. Can be used as a speculative 52 : * check to see if the write owner is running on the cpu. 53 : */ 54 : atomic_long_t owner; 55 : #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 56 : struct optimistic_spin_queue osq; /* spinner MCS lock */ 57 : #endif 58 : raw_spinlock_t wait_lock; 59 : struct list_head wait_list; 60 : #ifdef CONFIG_DEBUG_RWSEMS 61 : void *magic; 62 : #endif 63 : #ifdef CONFIG_DEBUG_LOCK_ALLOC 64 : struct lockdep_map dep_map; 65 : #endif 66 : }; 67 : 68 : /* In all implementations count != 0 means locked */ 69 : static inline int rwsem_is_locked(struct rw_semaphore *sem) 70 : { 71 44 : return atomic_long_read(&sem->count) != 0; 72 : } 73 : 74 : #define RWSEM_UNLOCKED_VALUE 0L 75 : #define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) 76 : 77 : /* Common initializer macros and functions */ 78 : 79 : #ifdef CONFIG_DEBUG_RWSEMS 80 : # define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, 81 : #else 82 : # define __RWSEM_DEBUG_INIT(lockname) 83 : #endif 84 : 85 : #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 86 : #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, 87 : #else 88 : #define __RWSEM_OPT_INIT(lockname) 89 : #endif 90 : 91 : #define __RWSEM_INITIALIZER(name) \ 92 : { __RWSEM_COUNT_INIT(name), \ 93 : .owner = ATOMIC_LONG_INIT(0), \ 94 : __RWSEM_OPT_INIT(name) \ 95 : .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ 96 : .wait_list = LIST_HEAD_INIT((name).wait_list), \ 97 : __RWSEM_DEBUG_INIT(name) \ 98 : __RWSEM_DEP_MAP_INIT(name) } 99 : 100 : #define DECLARE_RWSEM(name) \ 101 : struct rw_semaphore name = __RWSEM_INITIALIZER(name) 102 : 103 : extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 104 : struct lock_class_key *key); 105 : 106 : #define init_rwsem(sem) \ 107 : do { \ 108 : static struct lock_class_key __key; \ 109 : \ 110 : __init_rwsem((sem), #sem, &__key); \ 111 : } while (0) 112 : 113 : /* 114 : * This is the same regardless of which rwsem implementation that is being used. 115 : * It is just a heuristic meant to be called by somebody already holding the 116 : * rwsem to see if somebody from an incompatible type is wanting access to the 117 : * lock. 118 : */ 119 : static inline int rwsem_is_contended(struct rw_semaphore *sem) 120 : { 121 0 : return !list_empty(&sem->wait_list); 122 : } 123 : 124 : #else /* !CONFIG_PREEMPT_RT */ 125 : 126 : #include <linux/rwbase_rt.h> 127 : 128 : struct rw_semaphore { 129 : struct rwbase_rt rwbase; 130 : #ifdef CONFIG_DEBUG_LOCK_ALLOC 131 : struct lockdep_map dep_map; 132 : #endif 133 : }; 134 : 135 : #define __RWSEM_INITIALIZER(name) \ 136 : { \ 137 : .rwbase = __RWBASE_INITIALIZER(name), \ 138 : __RWSEM_DEP_MAP_INIT(name) \ 139 : } 140 : 141 : #define DECLARE_RWSEM(lockname) \ 142 : struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) 143 : 144 : extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name, 145 : struct lock_class_key *key); 146 : 147 : #define init_rwsem(sem) \ 148 : do { \ 149 : static struct lock_class_key __key; \ 150 : \ 151 : __init_rwsem((sem), #sem, &__key); \ 152 : } while (0) 153 : 154 : static __always_inline int rwsem_is_locked(struct rw_semaphore *sem) 155 : { 156 : return rw_base_is_locked(&sem->rwbase); 157 : } 158 : 159 : static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) 160 : { 161 : return rw_base_is_contended(&sem->rwbase); 162 : } 163 : 164 : #endif /* CONFIG_PREEMPT_RT */ 165 : 166 : /* 167 : * The functions below are the same for all rwsem implementations including 168 : * the RT specific variant. 169 : */ 170 : 171 : /* 172 : * lock for reading 173 : */ 174 : extern void down_read(struct rw_semaphore *sem); 175 : extern int __must_check down_read_interruptible(struct rw_semaphore *sem); 176 : extern int __must_check down_read_killable(struct rw_semaphore *sem); 177 : 178 : /* 179 : * trylock for reading -- returns 1 if successful, 0 if contention 180 : */ 181 : extern int down_read_trylock(struct rw_semaphore *sem); 182 : 183 : /* 184 : * lock for writing 185 : */ 186 : extern void down_write(struct rw_semaphore *sem); 187 : extern int __must_check down_write_killable(struct rw_semaphore *sem); 188 : 189 : /* 190 : * trylock for writing -- returns 1 if successful, 0 if contention 191 : */ 192 : extern int down_write_trylock(struct rw_semaphore *sem); 193 : 194 : /* 195 : * release a read lock 196 : */ 197 : extern void up_read(struct rw_semaphore *sem); 198 : 199 : /* 200 : * release a write lock 201 : */ 202 : extern void up_write(struct rw_semaphore *sem); 203 : 204 : /* 205 : * downgrade write lock to read lock 206 : */ 207 : extern void downgrade_write(struct rw_semaphore *sem); 208 : 209 : #ifdef CONFIG_DEBUG_LOCK_ALLOC 210 : /* 211 : * nested locking. NOTE: rwsems are not allowed to recurse 212 : * (which occurs if the same task tries to acquire the same 213 : * lock instance multiple times), but multiple locks of the 214 : * same lock class might be taken, if the order of the locks 215 : * is always the same. This ordering rule can be expressed 216 : * to lockdep via the _nested() APIs, but enumerating the 217 : * subclasses that are used. (If the nesting relationship is 218 : * static then another method for expressing nested locking is 219 : * the explicit definition of lock class keys and the use of 220 : * lockdep_set_class() at lock initialization time. 221 : * See Documentation/locking/lockdep-design.rst for more details.) 222 : */ 223 : extern void down_read_nested(struct rw_semaphore *sem, int subclass); 224 : extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); 225 : extern void down_write_nested(struct rw_semaphore *sem, int subclass); 226 : extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); 227 : extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); 228 : 229 : # define down_write_nest_lock(sem, nest_lock) \ 230 : do { \ 231 : typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ 232 : _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ 233 : } while (0) 234 : 235 : /* 236 : * Take/release a lock when not the owner will release it. 237 : * 238 : * [ This API should be avoided as much as possible - the 239 : * proper abstraction for this case is completions. ] 240 : */ 241 : extern void down_read_non_owner(struct rw_semaphore *sem); 242 : extern void up_read_non_owner(struct rw_semaphore *sem); 243 : #else 244 : # define down_read_nested(sem, subclass) down_read(sem) 245 : # define down_read_killable_nested(sem, subclass) down_read_killable(sem) 246 : # define down_write_nest_lock(sem, nest_lock) down_write(sem) 247 : # define down_write_nested(sem, subclass) down_write(sem) 248 : # define down_write_killable_nested(sem, subclass) down_write_killable(sem) 249 : # define down_read_non_owner(sem) down_read(sem) 250 : # define up_read_non_owner(sem) up_read(sem) 251 : #endif 252 : 253 : #endif /* _LINUX_RWSEM_H */
