kernel/rwsem.c

   1 /* kernel/rwsem.c: R/W semaphores, public implementation
   2  *
   3  * Written by David Howells (dhowells@redhat.com).
   4  * Derived from asm-i386/semaphore.h
   5  */
   6
   7 #include <linux/types.h>
   8 #include <linux/kernel.h>
   9 #include <linux/sched.h>
  10 #include <linux/export.h>
  11 #include <linux/rwsem.h>
  12
  13 #include <linux/atomic.h>
  14
  15 /*
  16  * lock for reading
  17  */
  18 void __sched down_read(struct rw_semaphore *sem)
  19 {
  20         might_sleep();
  21         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
  22
  23         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
  24 }
  25
  26 EXPORT_SYMBOL(down_read);
  27
  28 /*
  29  * trylock for reading -- returns 1 if successful, 0 if contention
  30  */
  31 int down_read_trylock(struct rw_semaphore *sem)
  32 {
  33         int ret = __down_read_trylock(sem);
  34
  35         if (ret == 1)
  36                 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  37         return ret;
  38 }
  39
  40 EXPORT_SYMBOL(down_read_trylock);
  41
  42 /*
  43  * lock for writing
  44  */
  45 void __sched down_write(struct rw_semaphore *sem)
  46 {
  47         might_sleep();
  48         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  49
  50         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
  51 }
  52
  53 EXPORT_SYMBOL(down_write);
  54
  55 /*
  56  * trylock for writing -- returns 1 if successful, 0 if contention
  57  */
  58 int down_write_trylock(struct rw_semaphore *sem)
  59 {
  60         int ret = __down_write_trylock(sem);
  61
  62         if (ret == 1)
  63                 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
  64         return ret;
  65 }
  66
  67 EXPORT_SYMBOL(down_write_trylock);
  68
  69 /*
  70  * release a read lock
  71  */
  72 void up_read(struct rw_semaphore *sem)
  73 {
  74         rwsem_release(&sem->dep_map, 1, _RET_IP_);
  75
  76         __up_read(sem);
  77 }
  78
  79 EXPORT_SYMBOL(up_read);
  80
  81 /*
  82  * release a write lock
  83  */
  84 void up_write(struct rw_semaphore *sem)
  85 {
  86         rwsem_release(&sem->dep_map, 1, _RET_IP_);
  87
  88         __up_write(sem);
  89 }
  90
  91 EXPORT_SYMBOL(up_write);
  92
  93 /*
  94  * downgrade write lock to read lock
  95  */
  96 void downgrade_write(struct rw_semaphore *sem)
  97 {
  98         /*
  99          * lockdep: a downgraded write will live on as a write
 100          * dependency.
 101          */
 102         __downgrade_write(sem);
 103 }
 104
 105 EXPORT_SYMBOL(downgrade_write);
 106
 107 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 108
 109 void down_read_nested(struct rw_semaphore *sem, int subclass)
 110 {
 111         might_sleep();
 112         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 113
 114         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 115 }
 116
 117 EXPORT_SYMBOL(down_read_nested);
 118
 119 void down_write_nested(struct rw_semaphore *sem, int subclass)
 120 {
 121         might_sleep();
 122         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 123
 124         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 125 }
 126
 127 EXPORT_SYMBOL(down_write_nested);
 128
 129 #endif
 130
 131