kernel/locking/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 #ifdef CONFIG_RWSEM_SPIN_ON_OWNER
  16 static inline void rwsem_set_owner(struct rw_semaphore *sem)
  17 {
  18         sem->owner = current;
  19 }
  20
  21 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
  22 {
  23         sem->owner = NULL;
  24 }
  25
  26 #else
  27 static inline void rwsem_set_owner(struct rw_semaphore *sem)
  28 {
  29 }
  30
  31 static inline void rwsem_clear_owner(struct rw_semaphore *sem)
  32 {
  33 }
  34 #endif
  35
  36 /*
  37  * lock for reading
  38  */
  39 void __sched down_read(struct rw_semaphore *sem)
  40 {
  41         might_sleep();
  42         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
  43
  44         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
  45 }
  46
  47 EXPORT_SYMBOL(down_read);
  48
  49 /*
  50  * trylock for reading -- returns 1 if successful, 0 if contention
  51  */
  52 int down_read_trylock(struct rw_semaphore *sem)
  53 {
  54         int ret = __down_read_trylock(sem);
  55
  56         if (ret == 1)
  57                 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  58         return ret;
  59 }
  60
  61 EXPORT_SYMBOL(down_read_trylock);
  62
  63 /*
  64  * lock for writing
  65  */
  66 void __sched down_write(struct rw_semaphore *sem)
  67 {
  68         might_sleep();
  69         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  70
  71         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
  72         rwsem_set_owner(sem);
  73 }
  74
  75 EXPORT_SYMBOL(down_write);
  76
  77 /*
  78  * trylock for writing -- returns 1 if successful, 0 if contention
  79  */
  80 int down_write_trylock(struct rw_semaphore *sem)
  81 {
  82         int ret = __down_write_trylock(sem);
  83
  84         if (ret == 1) {
  85                 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
  86                 rwsem_set_owner(sem);
  87         }
  88
  89         return ret;
  90 }
  91
  92 EXPORT_SYMBOL(down_write_trylock);
  93
  94 /*
  95  * release a read lock
  96  */
  97 void up_read(struct rw_semaphore *sem)
  98 {
  99         rwsem_release(&sem->dep_map, 1, _RET_IP_);
 100
 101         __up_read(sem);
 102 }
 103
 104 EXPORT_SYMBOL(up_read);
 105
 106 /*
 107  * release a write lock
 108  */
 109 void up_write(struct rw_semaphore *sem)
 110 {
 111         rwsem_release(&sem->dep_map, 1, _RET_IP_);
 112
 113         rwsem_clear_owner(sem);
 114         __up_write(sem);
 115 }
 116
 117 EXPORT_SYMBOL(up_write);
 118
 119 /*
 120  * downgrade write lock to read lock
 121  */
 122 void downgrade_write(struct rw_semaphore *sem)
 123 {
 124         /*
 125          * lockdep: a downgraded write will live on as a write
 126          * dependency.
 127          */
 128         rwsem_clear_owner(sem);
 129         __downgrade_write(sem);
 130 }
 131
 132 EXPORT_SYMBOL(downgrade_write);
 133
 134 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 135
 136 void down_read_nested(struct rw_semaphore *sem, int subclass)
 137 {
 138         might_sleep();
 139         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 140
 141         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 142 }
 143
 144 EXPORT_SYMBOL(down_read_nested);
 145
 146 void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
 147 {
 148         might_sleep();
 149         rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
 150
 151         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 152         rwsem_set_owner(sem);
 153 }
 154
 155 EXPORT_SYMBOL(_down_write_nest_lock);
 156
 157 void down_read_non_owner(struct rw_semaphore *sem)
 158 {
 159         might_sleep();
 160
 161         __down_read(sem);
 162 }
 163
 164 EXPORT_SYMBOL(down_read_non_owner);
 165
 166 void down_write_nested(struct rw_semaphore *sem, int subclass)
 167 {
 168         might_sleep();
 169         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 170
 171         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 172         rwsem_set_owner(sem);
 173 }
 174
 175 EXPORT_SYMBOL(down_write_nested);
 176
 177 void up_read_non_owner(struct rw_semaphore *sem)
 178 {
 179         __up_read(sem);
 180 }
 181
 182 EXPORT_SYMBOL(up_read_non_owner);
 183
 184 #endif
 185
 186