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/kernel.h> 15 #include <linux/list.h> 16 #include <linux/spinlock.h> 17 #include <linux/atomic.h> 18 #include <linux/err.h> 19 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 20 #include <linux/osq_lock.h> 21 #endif 22 23 struct rw_semaphore; 24 25 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK 26 #include <linux/rwsem-spinlock.h> /* use a generic implementation */ 27 #define __RWSEM_INIT_COUNT(name) .count = RWSEM_UNLOCKED_VALUE 28 #else 29 /* All arch specific implementations share the same struct */ 30 struct rw_semaphore { 31 atomic_long_t count; 32 struct list_head wait_list; 33 raw_spinlock_t wait_lock; 34 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 35 struct optimistic_spin_queue osq; /* spinner MCS lock */ 36 /* 37 * Write owner. Used as a speculative check to see 38 * if the owner is running on the cpu. 39 */ 40 struct task_struct *owner; 41 #endif 42 #ifdef CONFIG_DEBUG_LOCK_ALLOC 43 struct lockdep_map dep_map; 44 #endif 45 }; 46 47 /* 48 * Setting bit 0 of the owner field with other non-zero bits will indicate 49 * that the rwsem is writer-owned with an unknown owner. 50 */ 51 #define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-1L) 52 53 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem); 54 extern struct rw_semaphore *rwsem_down_read_failed_killable(struct rw_semaphore *sem); 55 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem); 56 extern struct rw_semaphore *rwsem_down_write_failed_killable(struct rw_semaphore *sem); 57 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *); 58 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem); 59 60 /* Include the arch specific part */ 61 #include <asm/rwsem.h> 62 63 /* In all implementations count != 0 means locked */ 64 static inline int rwsem_is_locked(struct rw_semaphore *sem) 65 { 66 return atomic_long_read(&sem->count) != 0; 67 } 68 69 #define __RWSEM_INIT_COUNT(name) .count = ATOMIC_LONG_INIT(RWSEM_UNLOCKED_VALUE) 70 #endif 71 72 /* Common initializer macros and functions */ 73 74 #ifdef CONFIG_DEBUG_LOCK_ALLOC 75 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname } 76 #else 77 # define __RWSEM_DEP_MAP_INIT(lockname) 78 #endif 79 80 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER 81 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL 82 #else 83 #define __RWSEM_OPT_INIT(lockname) 84 #endif 85 86 #define __RWSEM_INITIALIZER(name) \ 87 { __RWSEM_INIT_COUNT(name), \ 88 .wait_list = LIST_HEAD_INIT((name).wait_list), \ 89 .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \ 90 __RWSEM_OPT_INIT(name) \ 91 __RWSEM_DEP_MAP_INIT(name) } 92 93 #define DECLARE_RWSEM(name) \ 94 struct rw_semaphore name = __RWSEM_INITIALIZER(name) 95 96 extern void __init_rwsem(struct rw_semaphore *sem, const char *name, 97 struct lock_class_key *key); 98 99 #define init_rwsem(sem) \ 100 do { \ 101 static struct lock_class_key __key; \ 102 \ 103 __init_rwsem((sem), #sem, &__key); \ 104 } while (0) 105 106 /* 107 * This is the same regardless of which rwsem implementation that is being used. 108 * It is just a heuristic meant to be called by somebody alreadying holding the 109 * rwsem to see if somebody from an incompatible type is wanting access to the 110 * lock. 111 */ 112 static inline int rwsem_is_contended(struct rw_semaphore *sem) 113 { 114 return !list_empty(&sem->wait_list); 115 } 116 117 /* 118 * lock for reading 119 */ 120 extern void down_read(struct rw_semaphore *sem); 121 extern int __must_check down_read_killable(struct rw_semaphore *sem); 122 123 /* 124 * trylock for reading -- returns 1 if successful, 0 if contention 125 */ 126 extern int down_read_trylock(struct rw_semaphore *sem); 127 128 /* 129 * lock for writing 130 */ 131 extern void down_write(struct rw_semaphore *sem); 132 extern int __must_check down_write_killable(struct rw_semaphore *sem); 133 134 /* 135 * trylock for writing -- returns 1 if successful, 0 if contention 136 */ 137 extern int down_write_trylock(struct rw_semaphore *sem); 138 139 /* 140 * release a read lock 141 */ 142 extern void up_read(struct rw_semaphore *sem); 143 144 /* 145 * release a write lock 146 */ 147 extern void up_write(struct rw_semaphore *sem); 148 149 /* 150 * downgrade write lock to read lock 151 */ 152 extern void downgrade_write(struct rw_semaphore *sem); 153 154 #ifdef CONFIG_DEBUG_LOCK_ALLOC 155 /* 156 * nested locking. NOTE: rwsems are not allowed to recurse 157 * (which occurs if the same task tries to acquire the same 158 * lock instance multiple times), but multiple locks of the 159 * same lock class might be taken, if the order of the locks 160 * is always the same. This ordering rule can be expressed 161 * to lockdep via the _nested() APIs, but enumerating the 162 * subclasses that are used. (If the nesting relationship is 163 * static then another method for expressing nested locking is 164 * the explicit definition of lock class keys and the use of 165 * lockdep_set_class() at lock initialization time. 166 * See Documentation/locking/lockdep-design.txt for more details.) 167 */ 168 extern void down_read_nested(struct rw_semaphore *sem, int subclass); 169 extern void down_write_nested(struct rw_semaphore *sem, int subclass); 170 extern int down_write_killable_nested(struct rw_semaphore *sem, int subclass); 171 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock); 172 173 # define down_write_nest_lock(sem, nest_lock) \ 174 do { \ 175 typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \ 176 _down_write_nest_lock(sem, &(nest_lock)->dep_map); \ 177 } while (0); 178 179 /* 180 * Take/release a lock when not the owner will release it. 181 * 182 * [ This API should be avoided as much as possible - the 183 * proper abstraction for this case is completions. ] 184 */ 185 extern void down_read_non_owner(struct rw_semaphore *sem); 186 extern void up_read_non_owner(struct rw_semaphore *sem); 187 #else 188 # define down_read_nested(sem, subclass) down_read(sem) 189 # define down_write_nest_lock(sem, nest_lock) down_write(sem) 190 # define down_write_nested(sem, subclass) down_write(sem) 191 # define down_write_killable_nested(sem, subclass) down_write_killable(sem) 192 # define down_read_non_owner(sem) down_read(sem) 193 # define up_read_non_owner(sem) up_read(sem) 194 #endif 195 196 #endif /* _LINUX_RWSEM_H */ 197