include/linux/rwsem.h

   1 /* rwsem.h: R/W semaphores, public interface
   2  *
   3  * Written by David Howells (dhowells@redhat.com).
   4  * Derived from asm-i386/semaphore.h
   5  */
   6
   7 #ifndef _LINUX_RWSEM_H
   8 #define _LINUX_RWSEM_H
   9
  10 #include <linux/linkage.h>
  11
  12 #include <linux/types.h>
  13 #include <linux/kernel.h>
  14 #include <linux/list.h>
  15 #include <linux/spinlock.h>
  16 #include <linux/atomic.h>
  17 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  18 #include <linux/osq_lock.h>
  19 #endif
  20
  21 struct rw_semaphore;
  22
  23 #ifdef CONFIG_RWSEM_GENERIC_SPINLOCK
  24 #include <linux/rwsem-spinlock.h> /* use a generic implementation */
  25 #else
  26 /* All arch specific implementations share the same struct */
  27 struct rw_semaphore {
  28         long count;
  29         struct list_head wait_list;
  30         raw_spinlock_t wait_lock;
  31 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  32         struct optimistic_spin_queue osq; /* spinner MCS lock */
  33         /*
  34          * Write owner. Used as a speculative check to see
  35          * if the owner is running on the cpu.
  36          */
  37         struct task_struct *owner;
  38 #endif
  39 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  40         struct lockdep_map      dep_map;
  41 #endif
  42 };
  43
  44 extern struct rw_semaphore *rwsem_down_read_failed(struct rw_semaphore *sem);
  45 extern struct rw_semaphore *rwsem_down_write_failed(struct rw_semaphore *sem);
  46 extern struct rw_semaphore *rwsem_wake(struct rw_semaphore *);
  47 extern struct rw_semaphore *rwsem_downgrade_wake(struct rw_semaphore *sem);
  48
  49 /* Include the arch specific part */
  50 #include <asm/rwsem.h>
  51
  52 /* In all implementations count != 0 means locked */
  53 static inline int rwsem_is_locked(struct rw_semaphore *sem)
  54 {
  55         return sem->count != 0;
  56 }
  57
  58 #endif
  59
  60 /* Common initializer macros and functions */
  61
  62 #ifdef CONFIG_DEBUG_LOCK_ALLOC
  63 # define __RWSEM_DEP_MAP_INIT(lockname) , .dep_map = { .name = #lockname }
  64 #else
  65 # define __RWSEM_DEP_MAP_INIT(lockname)
  66 #endif
  67
  68 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  69 #define __RWSEM_OPT_INIT(lockname) , .osq = OSQ_LOCK_UNLOCKED, .owner = NULL
  70 #else
  71 #define __RWSEM_OPT_INIT(lockname)
  72 #endif
  73
  74 #define __RWSEM_INITIALIZER(name)                               \
  75         { .count = RWSEM_UNLOCKED_VALUE,                        \
  76           .wait_list = LIST_HEAD_INIT((name).wait_list),        \
  77           .wait_lock = __RAW_SPIN_LOCK_UNLOCKED(name.wait_lock) \
  78           __RWSEM_OPT_INIT(name)                                \
  79           __RWSEM_DEP_MAP_INIT(name) }
  80
  81 #define DECLARE_RWSEM(name) \
  82         struct rw_semaphore name = __RWSEM_INITIALIZER(name)
  83
  84 extern void __init_rwsem(struct rw_semaphore *sem, const char *name,
  85                          struct lock_class_key *key);
  86
  87 #define init_rwsem(sem)                                         \
  88 do {                                                            \
  89         static struct lock_class_key __key;                     \
  90                                                                 \
  91         __init_rwsem((sem), #sem, &__key);                      \
  92 } while (0)
  93
  94 /*
  95  * This is the same regardless of which rwsem implementation that is being used.
  96  * It is just a heuristic meant to be called by somebody alreadying holding the
  97  * rwsem to see if somebody from an incompatible type is wanting access to the
  98  * lock.
  99  */
 100 static inline int rwsem_is_contended(struct rw_semaphore *sem)
 101 {
 102         return !list_empty(&sem->wait_list);
 103 }
 104
 105 /*
 106  * lock for reading
 107  */
 108 extern void down_read(struct rw_semaphore *sem);
 109
 110 /*
 111  * trylock for reading -- returns 1 if successful, 0 if contention
 112  */
 113 extern int down_read_trylock(struct rw_semaphore *sem);
 114
 115 /*
 116  * lock for writing
 117  */
 118 extern void down_write(struct rw_semaphore *sem);
 119
 120 /*
 121  * trylock for writing -- returns 1 if successful, 0 if contention
 122  */
 123 extern int down_write_trylock(struct rw_semaphore *sem);
 124
 125 /*
 126  * release a read lock
 127  */
 128 extern void up_read(struct rw_semaphore *sem);
 129
 130 /*
 131  * release a write lock
 132  */
 133 extern void up_write(struct rw_semaphore *sem);
 134
 135 /*
 136  * downgrade write lock to read lock
 137  */
 138 extern void downgrade_write(struct rw_semaphore *sem);
 139
 140 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 141 /*
 142  * nested locking. NOTE: rwsems are not allowed to recurse
 143  * (which occurs if the same task tries to acquire the same
 144  * lock instance multiple times), but multiple locks of the
 145  * same lock class might be taken, if the order of the locks
 146  * is always the same. This ordering rule can be expressed
 147  * to lockdep via the _nested() APIs, but enumerating the
 148  * subclasses that are used. (If the nesting relationship is
 149  * static then another method for expressing nested locking is
 150  * the explicit definition of lock class keys and the use of
 151  * lockdep_set_class() at lock initialization time.
 152  * See Documentation/locking/lockdep-design.txt for more details.)
 153  */
 154 extern void down_read_nested(struct rw_semaphore *sem, int subclass);
 155 extern void down_write_nested(struct rw_semaphore *sem, int subclass);
 156 extern void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest_lock);
 157
 158 # define down_write_nest_lock(sem, nest_lock)                   \
 159 do {                                                            \
 160         typecheck(struct lockdep_map *, &(nest_lock)->dep_map); \
 161         _down_write_nest_lock(sem, &(nest_lock)->dep_map);      \
 162 } while (0);
 163
 164 /*
 165  * Take/release a lock when not the owner will release it.
 166  *
 167  * [ This API should be avoided as much as possible - the
 168  *   proper abstraction for this case is completions. ]
 169  */
 170 extern void down_read_non_owner(struct rw_semaphore *sem);
 171 extern void up_read_non_owner(struct rw_semaphore *sem);
 172 #else
 173 # define down_read_nested(sem, subclass)                down_read(sem)
 174 # define down_write_nest_lock(sem, nest_lock)   down_write(sem)
 175 # define down_write_nested(sem, subclass)       down_write(sem)
 176 # define down_read_non_owner(sem)               down_read(sem)
 177 # define up_read_non_owner(sem)                 up_read(sem)
 178 #endif
 179
 180 #endif /* _LINUX_RWSEM_H */