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 <asm/system.h>
  14 #include <linux/atomic.h>
  15
  16 /*
  17  * lock for reading
  18  */
  19 void __sched down_read(struct rw_semaphore *sem)
  20 {
  21         might_sleep();
  22         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
  23
  24         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
  25 }
  26
  27 EXPORT_SYMBOL(down_read);
  28
  29 /*
  30  * trylock for reading -- returns 1 if successful, 0 if contention
  31  */
  32 int down_read_trylock(struct rw_semaphore *sem)
  33 {
  34         int ret = __down_read_trylock(sem);
  35
  36         if (ret == 1)
  37                 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  38         return ret;
  39 }
  40
  41 EXPORT_SYMBOL(down_read_trylock);
  42
  43 /*
  44  * lock for writing
  45  */
  46 void __sched down_write(struct rw_semaphore *sem)
  47 {
  48         might_sleep();
  49         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  50
  51         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
  52 }
  53
  54 EXPORT_SYMBOL(down_write);
  55
  56 /*
  57  * trylock for writing -- returns 1 if successful, 0 if contention
  58  */
  59 int down_write_trylock(struct rw_semaphore *sem)
  60 {
  61         int ret = __down_write_trylock(sem);
  62
  63         if (ret == 1)
  64                 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
  65         return ret;
  66 }
  67
  68 EXPORT_SYMBOL(down_write_trylock);
  69
  70 /*
  71  * release a read lock
  72  */
  73 void up_read(struct rw_semaphore *sem)
  74 {
  75         rwsem_release(&sem->dep_map, 1, _RET_IP_);
  76
  77         __up_read(sem);
  78 }
  79
  80 EXPORT_SYMBOL(up_read);
  81
  82 /*
  83  * release a write lock
  84  */
  85 void up_write(struct rw_semaphore *sem)
  86 {
  87         rwsem_release(&sem->dep_map, 1, _RET_IP_);
  88
  89         __up_write(sem);
  90 }
  91
  92 EXPORT_SYMBOL(up_write);
  93
  94 /*
  95  * downgrade write lock to read lock
  96  */
  97 void downgrade_write(struct rw_semaphore *sem)
  98 {
  99         /*
 100          * lockdep: a downgraded write will live on as a write
 101          * dependency.
 102          */
 103         __downgrade_write(sem);
 104 }
 105
 106 EXPORT_SYMBOL(downgrade_write);
 107
 108 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 109
 110 void down_read_nested(struct rw_semaphore *sem, int subclass)
 111 {
 112         might_sleep();
 113         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 114
 115         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 116 }
 117
 118 EXPORT_SYMBOL(down_read_nested);
 119
 120 void down_write_nested(struct rw_semaphore *sem, int subclass)
 121 {
 122         might_sleep();
 123         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 124
 125         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 126 }
 127
 128 EXPORT_SYMBOL(down_write_nested);
 129
 130 #endif
 131
 132