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