include/linux/rwsem.h

   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 */