Commit 4a444b1f authored Aug 30, 2013 by Josef Bacik Committed by Chris Mason Jan 28, 2014

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: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <clm@fb.com>
Acked-by: Ingo Molnar <mingo@kernel.org>

parent 67de1176

include/linux/rwsem.h

+11 −0

Original line number	Diff line number	Diff line
		@@ -74,6 +74,17 @@ do { \
		__init_rwsem((sem), #sem, &__key); \
		} 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
		*/