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