2016-05-18 08:26:19 +07:00
|
|
|
/*
|
|
|
|
* The owner field of the rw_semaphore structure will be set to
|
|
|
|
* RWSEM_READ_OWNED when a reader grabs the lock. A writer will clear
|
|
|
|
* the owner field when it unlocks. A reader, on the other hand, will
|
|
|
|
* not touch the owner field when it unlocks.
|
|
|
|
*
|
|
|
|
* In essence, the owner field now has the following 3 states:
|
|
|
|
* 1) 0
|
|
|
|
* - lock is free or the owner hasn't set the field yet
|
|
|
|
* 2) RWSEM_READER_OWNED
|
|
|
|
* - lock is currently or previously owned by readers (lock is free
|
|
|
|
* or not set by owner yet)
|
|
|
|
* 3) Other non-zero value
|
|
|
|
* - a writer owns the lock
|
|
|
|
*/
|
|
|
|
#define RWSEM_READER_OWNED ((struct task_struct *)1UL)
|
|
|
|
|
2015-01-30 16:14:25 +07:00
|
|
|
#ifdef CONFIG_RWSEM_SPIN_ON_OWNER
|
2016-05-18 08:26:20 +07:00
|
|
|
/*
|
|
|
|
* All writes to owner are protected by WRITE_ONCE() to make sure that
|
|
|
|
* store tearing can't happen as optimistic spinners may read and use
|
|
|
|
* the owner value concurrently without lock. Read from owner, however,
|
|
|
|
* may not need READ_ONCE() as long as the pointer value is only used
|
|
|
|
* for comparison and isn't being dereferenced.
|
|
|
|
*/
|
2015-01-30 16:14:25 +07:00
|
|
|
static inline void rwsem_set_owner(struct rw_semaphore *sem)
|
|
|
|
{
|
2016-05-18 08:26:20 +07:00
|
|
|
WRITE_ONCE(sem->owner, current);
|
2015-01-30 16:14:25 +07:00
|
|
|
}
|
|
|
|
|
|
|
|
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
|
|
|
|
{
|
2016-05-18 08:26:20 +07:00
|
|
|
WRITE_ONCE(sem->owner, NULL);
|
2015-01-30 16:14:25 +07:00
|
|
|
}
|
|
|
|
|
2016-05-18 08:26:19 +07:00
|
|
|
static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
/*
|
|
|
|
* We check the owner value first to make sure that we will only
|
|
|
|
* do a write to the rwsem cacheline when it is really necessary
|
|
|
|
* to minimize cacheline contention.
|
|
|
|
*/
|
|
|
|
if (sem->owner != RWSEM_READER_OWNED)
|
2016-05-18 08:26:20 +07:00
|
|
|
WRITE_ONCE(sem->owner, RWSEM_READER_OWNED);
|
2016-05-18 08:26:19 +07:00
|
|
|
}
|
|
|
|
|
|
|
|
static inline bool rwsem_owner_is_writer(struct task_struct *owner)
|
|
|
|
{
|
|
|
|
return owner && owner != RWSEM_READER_OWNED;
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline bool rwsem_owner_is_reader(struct task_struct *owner)
|
|
|
|
{
|
|
|
|
return owner == RWSEM_READER_OWNED;
|
|
|
|
}
|
2015-01-30 16:14:25 +07:00
|
|
|
#else
|
|
|
|
static inline void rwsem_set_owner(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
}
|
|
|
|
|
|
|
|
static inline void rwsem_clear_owner(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
}
|
2016-05-18 08:26:19 +07:00
|
|
|
|
|
|
|
static inline void rwsem_set_reader_owned(struct rw_semaphore *sem)
|
|
|
|
{
|
|
|
|
}
|
2015-01-30 16:14:25 +07:00
|
|
|
#endif
|