Commit 4660c49f authored Oct 20, 2017 by Nikolay Borisov Committed by David Sterba Jan 22, 2018

btrfs: Remove redundant memory barrier in dev stats



As per atomic_t.txt documentation :
 - RMW operations that have a return value are fully ordered;

atomic_xchg is one such operation so it already includes everything it
needs w.r.t memory ordering and add a comment to be more explicit about
that.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

parent 9deae968

fs/btrfs/volumes.h

+7 −1

Original line number	Diff line number	Diff line
		@@ -519,7 +519,13 @@ static inline int btrfs_dev_stat_read_and_reset(struct btrfs_device *dev,
		int ret;

		ret = atomic_xchg(dev->dev_stat_values + index, 0);
		smp_mb__before_atomic();
		/*
		* atomic_xchg implies a full memory barriers as per atomic_t.txt:
		* - RMW operations that have a return value are fully ordered;
		*
		* This implicit memory barriers is paired with the smp_rmb in
		* btrfs_run_dev_stats
		*/
		atomic_inc(&dev->dev_stats_ccnt);
		return ret;
		}