Commit 4a444b1f authored by Josef Bacik's avatar Josef Bacik Committed by Chris Mason

rwsem: add rwsem_is_contended

Btrfs needs a simple way to know if it needs to let go of it's read lock on a
rwsem.  Introduce rwsem_is_contended to check to see if there are any waiters on
this rwsem currently.  This is just a hueristic, it is meant to be light and not
100% accurate and called by somebody already holding on to the rwsem in either
read or write.  Thanks,
Signed-off-by: default avatarJosef Bacik <jbacik@fusionio.com>
Signed-off-by: default avatarChris Mason <clm@fb.com>
Acked-by: default avatarIngo Molnar <mingo@kernel.org>
parent 67de1176
...@@ -74,6 +74,17 @@ do { \ ...@@ -74,6 +74,17 @@ do { \
__init_rwsem((sem), #sem, &__key); \ __init_rwsem((sem), #sem, &__key); \
} while (0) } while (0)
/*
* This is the same regardless of which rwsem implementation that is being used.
* It is just a heuristic meant to be called by somebody alreadying holding the
* rwsem to see if somebody from an incompatible type is wanting access to the
* lock.
*/
static inline int rwsem_is_contended(struct rw_semaphore *sem)
{
return !list_empty(&sem->wait_list);
}
/* /*
* lock for reading * lock for reading
*/ */
......
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