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