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 #include <linux/cleanup.h> 19 20 #ifdef CONFIG_DEBUG_LOCK_ALLOC 21 # define __RWSEM_DEP_MAP_INIT(lockname) \ 22 .dep_map = { \ 23 .name = #lockname, \ 24 .wait_type_inner = LD_WAIT_SLEEP, \ 25 }, 26 #else 27 # define __RWSEM_DEP_MAP_INIT(lockname) 28 #endif 29 30 #ifndef CONFIG_PREEMPT_RT 31 32 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 33 #include <linux/osq_lock.h> 34 #endif 35 36 /* 37 * For an uncontended rwsem, count and owner are the only fields a task 38 * needs to touch when acquiring the rwsem. So they are put next to each 39 * other to increase the chance that they will share the same cacheline. 40 * 41 * In a contended rwsem, the owner is likely the most frequently accessed 42 * field in the structure as the optimistic waiter that holds the osq lock 43 * will spin on owner. For an embedded rwsem, other hot fields in the 44 * containing structure should be moved further away from the rwsem to 45 * reduce the chance that they will share the same cacheline causing 46 * cacheline bouncing problem. 47 */ 48 struct rw_semaphore { 49 atomic_long_t count; 50 /* 51 * Write owner or one of the read owners as well flags regarding 52 * the current state of the rwsem. Can be used as a speculative 53 * check to see if the write owner is running on the cpu. 54 */ 55 atomic_long_t owner; 56 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 57 struct optimistic_spin_queue osq; /* spinner MCS lock */ 58 #endif 59 raw_spinlock_t wait_lock; 60 struct list_head wait_list; 61 #ifdef CONFIG_DEBUG_RWSEMS 62 void *magic; 63 #endif 64 #ifdef CONFIG_DEBUG_LOCK_ALLOC 65 struct lockdep_map dep_map; 66 #endif 67 }; 68 69 #define RWSEM_UNLOCKED_VALUE 0UL 70 #define RWSEM_WRITER_LOCKED (1UL << 0) 71 #define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) 72 rwsem_is_locked(struct rw_semaphore * sem)73 static inline int rwsem_is_locked(struct rw_semaphore *sem) 74 { 75 return atomic_long_read(&sem->count) != RWSEM_UNLOCKED_VALUE; 76 } 77 rwsem_assert_held_nolockdep(const struct rw_semaphore * sem)78 static inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem) 79 { 80 WARN_ON(atomic_long_read(&sem->count) == RWSEM_UNLOCKED_VALUE); 81 } 82 rwsem_assert_held_write_nolockdep(const struct rw_semaphore * sem)83 static inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem) 84 { 85 WARN_ON(!(atomic_long_read(&sem->count) & RWSEM_WRITER_LOCKED)); 86 } 87 88 /* Common initializer macros and functions */ 89 90 #ifdef CONFIG_DEBUG_RWSEMS 91 # define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, 92 #else 93 # define __RWSEM_DEBUG_INIT(lockname) 94 #endif 95 96 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 97 #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, 98 #else 99 #define __RWSEM_OPT_INIT(lockname) 100 #endif 101 102 #define __RWSEM_INITIALIZER(name) \ 103 { __RWSEM_COUNT_INIT(name), \ 104 .owner = ATOMIC_LONG_INIT(0), \ 105 __RWSEM_OPT_INIT(name) \ 106 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ 107 .wait_list = LIST_HEAD_INIT((name).wait_list), \ 108 __RWSEM_DEBUG_INIT(name) \ 109 __RWSEM_DEP_MAP_INIT(name) } 110 111 #define DECLARE_RWSEM(name) \ 112 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 113 114 extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 115 struct lock_class_key *key); 116 117 #define init_rwsem(sem) \ 118 do { \ 119 static struct lock_class_key __key; \ 120 \ 121 __init_rwsem((sem), #sem, &__key); \ 122 } while (0) 123 124 /* 125 * This is the same regardless of which rwsem implementation that is being used. 126 * It is just a heuristic meant to be called by somebody already holding the 127 * rwsem to see if somebody from an incompatible type is wanting access to the 128 * lock. 129 */ rwsem_is_contended(struct rw_semaphore * sem)130 static inline int rwsem_is_contended(struct rw_semaphore *sem) 131 { 132 return !list_empty(&sem->wait_list); 133 } 134 135 #else /* !CONFIG_PREEMPT_RT */ 136 137 #include <linux/rwbase_rt.h> 138 139 struct rw_semaphore { 140 struct rwbase_rt rwbase; 141 #ifdef CONFIG_DEBUG_LOCK_ALLOC 142 struct lockdep_map dep_map; 143 #endif 144 }; 145 146 #define __RWSEM_INITIALIZER(name) \ 147 { \ 148 .rwbase = __RWBASE_INITIALIZER(name), \ 149 __RWSEM_DEP_MAP_INIT(name) \ 150 } 151 152 #define DECLARE_RWSEM(lockname) \ 153 struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) 154 155 extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name, 156 struct lock_class_key *key); 157 158 #define init_rwsem(sem) \ 159 do { \ 160 static struct lock_class_key __key; \ 161 \ 162 __init_rwsem((sem), #sem, &__key); \ 163 } while (0) 164 rwsem_is_locked(const struct rw_semaphore * sem)165 static __always_inline int rwsem_is_locked(const struct rw_semaphore *sem) 166 { 167 return rw_base_is_locked(&sem->rwbase); 168 } 169 rwsem_assert_held_nolockdep(const struct rw_semaphore * sem)170 static __always_inline void rwsem_assert_held_nolockdep(const struct rw_semaphore *sem) 171 { 172 WARN_ON(!rwsem_is_locked(sem)); 173 } 174 rwsem_assert_held_write_nolockdep(const struct rw_semaphore * sem)175 static __always_inline void rwsem_assert_held_write_nolockdep(const struct rw_semaphore *sem) 176 { 177 WARN_ON(!rw_base_is_write_locked(&sem->rwbase)); 178 } 179 rwsem_is_contended(struct rw_semaphore * sem)180 static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) 181 { 182 return rw_base_is_contended(&sem->rwbase); 183 } 184 185 #endif /* CONFIG_PREEMPT_RT */ 186 187 /* 188 * The functions below are the same for all rwsem implementations including 189 * the RT specific variant. 190 */ 191 rwsem_assert_held(const struct rw_semaphore * sem)192 static inline void rwsem_assert_held(const struct rw_semaphore *sem) 193 { 194 if (IS_ENABLED(CONFIG_LOCKDEP)) 195 lockdep_assert_held(sem); 196 else 197 rwsem_assert_held_nolockdep(sem); 198 } 199 rwsem_assert_held_write(const struct rw_semaphore * sem)200 static inline void rwsem_assert_held_write(const struct rw_semaphore *sem) 201 { 202 if (IS_ENABLED(CONFIG_LOCKDEP)) 203 lockdep_assert_held_write(sem); 204 else 205 rwsem_assert_held_write_nolockdep(sem); 206 } 207 208 /* 209 * lock for reading 210 */ 211 extern void down_read(struct rw_semaphore *sem); 212 extern int __must_check down_read_interruptible(struct rw_semaphore *sem); 213 extern int __must_check down_read_killable(struct rw_semaphore *sem); 214 215 /* 216 * trylock for reading -- returns 1 if successful, 0 if contention 217 */ 218 extern int down_read_trylock(struct rw_semaphore *sem); 219 220 /* 221 * lock for writing 222 */ 223 extern void down_write(struct rw_semaphore *sem); 224 extern int __must_check down_write_killable(struct rw_semaphore *sem); 225 226 /* 227 * trylock for writing -- returns 1 if successful, 0 if contention 228 */ 229 extern int down_write_trylock(struct rw_semaphore *sem); 230 231 /* 232 * release a read lock 233 */ 234 extern void up_read(struct rw_semaphore *sem); 235 236 /* 237 * release a write lock 238 */ 239 extern void up_write(struct rw_semaphore *sem); 240 241 DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T)) 242 DEFINE_GUARD_COND(rwsem_read, _try, down_read_trylock(_T)) 243 DEFINE_GUARD_COND(rwsem_read, _intr, down_read_interruptible(_T) == 0) 244 245 DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T)) 246 DEFINE_GUARD_COND(rwsem_write, _try, down_write_trylock(_T)) 247 248 /* 249 * downgrade write lock to read lock 250 */ 251 extern void downgrade_write(struct rw_semaphore *sem); 252 253 #ifdef CONFIG_DEBUG_LOCK_ALLOC 254 /* 255 * nested locking. NOTE: rwsems are not allowed to recurse 256 * (which occurs if the same task tries to acquire the same 257 * lock instance multiple times), but multiple locks of the 258 * same lock class might be taken, if the order of the locks 259 * is always the same. This ordering rule can be expressed 260 * to lockdep via the _nested() APIs, but enumerating the 261 * subclasses that are used. (If the nesting relationship is 262 * static then another method for expressing nested locking is 263 * the explicit definition of lock class keys and the use of 264 * lockdep_set_class() at lock initialization time. 265 * See Documentation/locking/lockdep-design.rst for more details.) 266 */ 267 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 268 extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); 269 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 270 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); 271 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); 272 273 # define down_write_nest_lock(sem, nest_lock) \ 274 do { \ 275 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ 276 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ 277 } while (0) 278 279 /* 280 * Take/release a lock when not the owner will release it. 281 * 282 * [ This API should be avoided as much as possible - the 283 * proper abstraction for this case is completions. ] 284 */ 285 extern void down_read_non_owner(struct rw_semaphore *sem); 286 extern void up_read_non_owner(struct rw_semaphore *sem); 287 #else 288 # define down_read_nested(sem, subclass) down_read(sem) 289 # define down_read_killable_nested(sem, subclass) down_read_killable(sem) 290 # define down_write_nest_lock(sem, nest_lock) down_write(sem) 291 # define down_write_nested(sem, subclass) down_write(sem) 292 # define down_write_killable_nested(sem, subclass) down_write_killable(sem) 293 # define down_read_non_owner(sem) down_read(sem) 294 # define up_read_non_owner(sem) up_read(sem) 295 #endif 296 297 #endif /* _LINUX_RWSEM_H */ 298