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 /* In all implementations count != 0 means locked */ 70 static inline int rwsem_is_locked(struct rw_semaphore *sem) 71 { 72 return atomic_long_read(&sem->count) != 0; 73 } 74 75 #define RWSEM_UNLOCKED_VALUE 0L 76 #define __RWSEM_COUNT_INIT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) 77 78 /* Common initializer macros and functions */ 79 80 #ifdef CONFIG_DEBUG_RWSEMS 81 # define __RWSEM_DEBUG_INIT(lockname) .magic = &lockname, 82 #else 83 # define __RWSEM_DEBUG_INIT(lockname) 84 #endif 85 86 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 87 #define __RWSEM_OPT_INIT(lockname) .osq = OSQ_LOCK_UNLOCKED, 88 #else 89 #define __RWSEM_OPT_INIT(lockname) 90 #endif 91 92 #define __RWSEM_INITIALIZER(name) \ 93 { __RWSEM_COUNT_INIT(name), \ 94 .owner = ATOMIC_LONG_INIT(0), \ 95 __RWSEM_OPT_INIT(name) \ 96 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock),\ 97 .wait_list = LIST_HEAD_INIT((name).wait_list), \ 98 __RWSEM_DEBUG_INIT(name) \ 99 __RWSEM_DEP_MAP_INIT(name) } 100 101 #define DECLARE_RWSEM(name) \ 102 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 103 104 extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 105 struct lock_class_key *key); 106 107 #define init_rwsem(sem) \ 108 do { \ 109 static struct lock_class_key __key; \ 110 \ 111 __init_rwsem((sem), #sem, &__key); \ 112 } while (0) 113 114 /* 115 * This is the same regardless of which rwsem implementation that is being used. 116 * It is just a heuristic meant to be called by somebody already holding the 117 * rwsem to see if somebody from an incompatible type is wanting access to the 118 * lock. 119 */ 120 static inline int rwsem_is_contended(struct rw_semaphore *sem) 121 { 122 return !list_empty(&sem->wait_list); 123 } 124 125 #else /* !CONFIG_PREEMPT_RT */ 126 127 #include <linux/rwbase_rt.h> 128 129 struct rw_semaphore { 130 struct rwbase_rt rwbase; 131 #ifdef CONFIG_DEBUG_LOCK_ALLOC 132 struct lockdep_map dep_map; 133 #endif 134 }; 135 136 #define __RWSEM_INITIALIZER(name) \ 137 { \ 138 .rwbase = __RWBASE_INITIALIZER(name), \ 139 __RWSEM_DEP_MAP_INIT(name) \ 140 } 141 142 #define DECLARE_RWSEM(lockname) \ 143 struct rw_semaphore lockname = __RWSEM_INITIALIZER(lockname) 144 145 extern void __init_rwsem(struct rw_semaphore *rwsem, const char *name, 146 struct lock_class_key *key); 147 148 #define init_rwsem(sem) \ 149 do { \ 150 static struct lock_class_key __key; \ 151 \ 152 __init_rwsem((sem), #sem, &__key); \ 153 } while (0) 154 155 static __always_inline int rwsem_is_locked(struct rw_semaphore *sem) 156 { 157 return rw_base_is_locked(&sem->rwbase); 158 } 159 160 static __always_inline int rwsem_is_contended(struct rw_semaphore *sem) 161 { 162 return rw_base_is_contended(&sem->rwbase); 163 } 164 165 #endif /* CONFIG_PREEMPT_RT */ 166 167 /* 168 * The functions below are the same for all rwsem implementations including 169 * the RT specific variant. 170 */ 171 172 /* 173 * lock for reading 174 */ 175 extern void down_read(struct rw_semaphore *sem); 176 extern int __must_check down_read_interruptible(struct rw_semaphore *sem); 177 extern int __must_check down_read_killable(struct rw_semaphore *sem); 178 179 /* 180 * trylock for reading -- returns 1 if successful, 0 if contention 181 */ 182 extern int down_read_trylock(struct rw_semaphore *sem); 183 184 /* 185 * lock for writing 186 */ 187 extern void down_write(struct rw_semaphore *sem); 188 extern int __must_check down_write_killable(struct rw_semaphore *sem); 189 190 /* 191 * trylock for writing -- returns 1 if successful, 0 if contention 192 */ 193 extern int down_write_trylock(struct rw_semaphore *sem); 194 195 /* 196 * release a read lock 197 */ 198 extern void up_read(struct rw_semaphore *sem); 199 200 /* 201 * release a write lock 202 */ 203 extern void up_write(struct rw_semaphore *sem); 204 205 DEFINE_GUARD(rwsem_read, struct rw_semaphore *, down_read(_T), up_read(_T)) 206 DEFINE_GUARD_COND(rwsem_read, _try, down_read_trylock(_T)) 207 DEFINE_GUARD_COND(rwsem_read, _intr, down_read_interruptible(_T) == 0) 208 209 DEFINE_GUARD(rwsem_write, struct rw_semaphore *, down_write(_T), up_write(_T)) 210 DEFINE_GUARD_COND(rwsem_write, _try, down_write_trylock(_T)) 211 212 /* 213 * downgrade write lock to read lock 214 */ 215 extern void downgrade_write(struct rw_semaphore *sem); 216 217 #ifdef CONFIG_DEBUG_LOCK_ALLOC 218 /* 219 * nested locking. NOTE: rwsems are not allowed to recurse 220 * (which occurs if the same task tries to acquire the same 221 * lock instance multiple times), but multiple locks of the 222 * same lock class might be taken, if the order of the locks 223 * is always the same. This ordering rule can be expressed 224 * to lockdep via the _nested() APIs, but enumerating the 225 * subclasses that are used. (If the nesting relationship is 226 * static then another method for expressing nested locking is 227 * the explicit definition of lock class keys and the use of 228 * lockdep_set_class() at lock initialization time. 229 * See Documentation/locking/lockdep-design.rst for more details.) 230 */ 231 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 232 extern int __must_check down_read_killable_nested(struct rw_semaphore *sem, int subclass); 233 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 234 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); 235 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); 236 237 # define down_write_nest_lock(sem, nest_lock) \ 238 do { \ 239 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ 240 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ 241 } while (0) 242 243 /* 244 * Take/release a lock when not the owner will release it. 245 * 246 * [ This API should be avoided as much as possible - the 247 * proper abstraction for this case is completions. ] 248 */ 249 extern void down_read_non_owner(struct rw_semaphore *sem); 250 extern void up_read_non_owner(struct rw_semaphore *sem); 251 #else 252 # define down_read_nested(sem, subclass) down_read(sem) 253 # define down_read_killable_nested(sem, subclass) down_read_killable(sem) 254 # define down_write_nest_lock(sem, nest_lock) down_write(sem) 255 # define down_write_nested(sem, subclass) down_write(sem) 256 # define down_write_killable_nested(sem, subclass) down_write_killable(sem) 257 # define down_read_non_owner(sem) down_read(sem) 258 # define up_read_non_owner(sem) up_read(sem) 259 #endif 260 261 #endif /* _LINUX_RWSEM_H */ 262