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 #include <linux/atomic.h>
  13
  14 #include "rwsem.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         rwsem_set_reader_owned(sem);
  26 }
  27
  28 EXPORT_SYMBOL(down_read);
  29
  30 /*
  31  * trylock for reading -- returns 1 if successful, 0 if contention
  32  */
  33 int down_read_trylock(struct rw_semaphore *sem)
  34 {
  35         int ret = __down_read_trylock(sem);
  36
  37         if (ret == 1) {
  38                 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  39                 rwsem_set_reader_owned(sem);
  40         }
  41         return ret;
  42 }
  43
  44 EXPORT_SYMBOL(down_read_trylock);
  45
  46 /*
  47  * lock for writing
  48  */
  49 void __sched down_write(struct rw_semaphore *sem)
  50 {
  51         might_sleep();
  52         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  53
  54         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
  55         rwsem_set_owner(sem);
  56 }
  57
  58 EXPORT_SYMBOL(down_write);
  59
  60 /*
  61  * lock for writing
  62  */
  63 int __sched down_write_killable(struct rw_semaphore *sem)
  64 {
  65         might_sleep();
  66         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  67
  68         if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
  69                 rwsem_release(&sem->dep_map, 1, _RET_IP_);
  70                 return -EINTR;
  71         }
  72
  73         rwsem_set_owner(sem);
  74         return 0;
  75 }
  76
  77 EXPORT_SYMBOL(down_write_killable);
  78
  79 /*
  80  * trylock for writing -- returns 1 if successful, 0 if contention
  81  */
  82 int down_write_trylock(struct rw_semaphore *sem)
  83 {
  84         int ret = __down_write_trylock(sem);
  85
  86         if (ret == 1) {
  87                 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
  88                 rwsem_set_owner(sem);
  89         }
  90
  91         return ret;
  92 }
  93
  94 EXPORT_SYMBOL(down_write_trylock);
  95
  96 /*
  97  * release a read lock
  98  */
  99 void up_read(struct rw_semaphore *sem)
 100 {
 101         rwsem_release(&sem->dep_map, 1, _RET_IP_);
 102
 103         __up_read(sem);
 104 }
 105
 106 EXPORT_SYMBOL(up_read);
 107
 108 /*
 109  * release a write lock
 110  */
 111 void up_write(struct rw_semaphore *sem)
 112 {
 113         rwsem_release(&sem->dep_map, 1, _RET_IP_);
 114
 115         rwsem_clear_owner(sem);
 116         __up_write(sem);
 117 }
 118
 119 EXPORT_SYMBOL(up_write);
 120
 121 /*
 122  * downgrade write lock to read lock
 123  */
 124 void downgrade_write(struct rw_semaphore *sem)
 125 {
 126         /*
 127          * lockdep: a downgraded write will live on as a write
 128          * dependency.
 129          */
 130         rwsem_set_reader_owned(sem);
 131         __downgrade_write(sem);
 132 }
 133
 134 EXPORT_SYMBOL(downgrade_write);
 135
 136 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 137
 138 void down_read_nested(struct rw_semaphore *sem, int subclass)
 139 {
 140         might_sleep();
 141         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 142
 143         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 144         rwsem_set_reader_owned(sem);
 145 }
 146
 147 EXPORT_SYMBOL(down_read_nested);
 148
 149 void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
 150 {
 151         might_sleep();
 152         rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
 153
 154         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 155         rwsem_set_owner(sem);
 156 }
 157
 158 EXPORT_SYMBOL(_down_write_nest_lock);
 159
 160 void down_read_non_owner(struct rw_semaphore *sem)
 161 {
 162         might_sleep();
 163
 164         __down_read(sem);
 165 }
 166
 167 EXPORT_SYMBOL(down_read_non_owner);
 168
 169 void down_write_nested(struct rw_semaphore *sem, int subclass)
 170 {
 171         might_sleep();
 172         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 173
 174         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 175         rwsem_set_owner(sem);
 176 }
 177
 178 EXPORT_SYMBOL(down_write_nested);
 179
 180 int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
 181 {
 182         might_sleep();
 183         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 184
 185         if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
 186                 rwsem_release(&sem->dep_map, 1, _RET_IP_);
 187                 return -EINTR;
 188         }
 189
 190         rwsem_set_owner(sem);
 191         return 0;
 192 }
 193
 194 EXPORT_SYMBOL(down_write_killable_nested);
 195
 196 void up_read_non_owner(struct rw_semaphore *sem)
 197 {
 198         __up_read(sem);
 199 }
 200
 201 EXPORT_SYMBOL(up_read_non_owner);
 202
 203 #endif
 204
 205