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/sched/debug.h>
  11 #include <linux/export.h>
  12 #include <linux/rwsem.h>
  13 #include <linux/atomic.h>
  14
  15 #include "rwsem.h"
  16
  17 /*
  18  * lock for reading
  19  */
  20 void __sched down_read(struct rw_semaphore *sem)
  21 {
  22         might_sleep();
  23         rwsem_acquire_read(&sem->dep_map, 0, 0, _RET_IP_);
  24
  25         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
  26         rwsem_set_reader_owned(sem);
  27 }
  28
  29 EXPORT_SYMBOL(down_read);
  30
  31 /*
  32  * trylock for reading -- returns 1 if successful, 0 if contention
  33  */
  34 int down_read_trylock(struct rw_semaphore *sem)
  35 {
  36         int ret = __down_read_trylock(sem);
  37
  38         if (ret == 1) {
  39                 rwsem_acquire_read(&sem->dep_map, 0, 1, _RET_IP_);
  40                 rwsem_set_reader_owned(sem);
  41         }
  42         return ret;
  43 }
  44
  45 EXPORT_SYMBOL(down_read_trylock);
  46
  47 /*
  48  * lock for writing
  49  */
  50 void __sched down_write(struct rw_semaphore *sem)
  51 {
  52         might_sleep();
  53         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  54
  55         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
  56         rwsem_set_owner(sem);
  57 }
  58
  59 EXPORT_SYMBOL(down_write);
  60
  61 /*
  62  * lock for writing
  63  */
  64 int __sched down_write_killable(struct rw_semaphore *sem)
  65 {
  66         might_sleep();
  67         rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_);
  68
  69         if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
  70                 rwsem_release(&sem->dep_map, 1, _RET_IP_);
  71                 return -EINTR;
  72         }
  73
  74         rwsem_set_owner(sem);
  75         return 0;
  76 }
  77
  78 EXPORT_SYMBOL(down_write_killable);
  79
  80 /*
  81  * trylock for writing -- returns 1 if successful, 0 if contention
  82  */
  83 int down_write_trylock(struct rw_semaphore *sem)
  84 {
  85         int ret = __down_write_trylock(sem);
  86
  87         if (ret == 1) {
  88                 rwsem_acquire(&sem->dep_map, 0, 1, _RET_IP_);
  89                 rwsem_set_owner(sem);
  90         }
  91
  92         return ret;
  93 }
  94
  95 EXPORT_SYMBOL(down_write_trylock);
  96
  97 /*
  98  * release a read lock
  99  */
 100 void up_read(struct rw_semaphore *sem)
 101 {
 102         rwsem_release(&sem->dep_map, 1, _RET_IP_);
 103
 104         __up_read(sem);
 105 }
 106
 107 EXPORT_SYMBOL(up_read);
 108
 109 /*
 110  * release a write lock
 111  */
 112 void up_write(struct rw_semaphore *sem)
 113 {
 114         rwsem_release(&sem->dep_map, 1, _RET_IP_);
 115
 116         rwsem_clear_owner(sem);
 117         __up_write(sem);
 118 }
 119
 120 EXPORT_SYMBOL(up_write);
 121
 122 /*
 123  * downgrade write lock to read lock
 124  */
 125 void downgrade_write(struct rw_semaphore *sem)
 126 {
 127         /*
 128          * lockdep: a downgraded write will live on as a write
 129          * dependency.
 130          */
 131         rwsem_set_reader_owned(sem);
 132         __downgrade_write(sem);
 133 }
 134
 135 EXPORT_SYMBOL(downgrade_write);
 136
 137 #ifdef CONFIG_DEBUG_LOCK_ALLOC
 138
 139 void down_read_nested(struct rw_semaphore *sem, int subclass)
 140 {
 141         might_sleep();
 142         rwsem_acquire_read(&sem->dep_map, subclass, 0, _RET_IP_);
 143
 144         LOCK_CONTENDED(sem, __down_read_trylock, __down_read);
 145         rwsem_set_reader_owned(sem);
 146 }
 147
 148 EXPORT_SYMBOL(down_read_nested);
 149
 150 void _down_write_nest_lock(struct rw_semaphore *sem, struct lockdep_map *nest)
 151 {
 152         might_sleep();
 153         rwsem_acquire_nest(&sem->dep_map, 0, 0, nest, _RET_IP_);
 154
 155         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 156         rwsem_set_owner(sem);
 157 }
 158
 159 EXPORT_SYMBOL(_down_write_nest_lock);
 160
 161 void down_read_non_owner(struct rw_semaphore *sem)
 162 {
 163         might_sleep();
 164
 165         __down_read(sem);
 166 }
 167
 168 EXPORT_SYMBOL(down_read_non_owner);
 169
 170 void down_write_nested(struct rw_semaphore *sem, int subclass)
 171 {
 172         might_sleep();
 173         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 174
 175         LOCK_CONTENDED(sem, __down_write_trylock, __down_write);
 176         rwsem_set_owner(sem);
 177 }
 178
 179 EXPORT_SYMBOL(down_write_nested);
 180
 181 int __sched down_write_killable_nested(struct rw_semaphore *sem, int subclass)
 182 {
 183         might_sleep();
 184         rwsem_acquire(&sem->dep_map, subclass, 0, _RET_IP_);
 185
 186         if (LOCK_CONTENDED_RETURN(sem, __down_write_trylock, __down_write_killable)) {
 187                 rwsem_release(&sem->dep_map, 1, _RET_IP_);
 188                 return -EINTR;
 189         }
 190
 191         rwsem_set_owner(sem);
 192         return 0;
 193 }
 194
 195 EXPORT_SYMBOL(down_write_killable_nested);
 196
 197 void up_read_non_owner(struct rw_semaphore *sem)
 198 {
 199         __up_read(sem);
 200 }
 201
 202 EXPORT_SYMBOL(up_read_non_owner);
 203
 204 #endif
 205
 206