Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Commit de224b7c authored by Nikolay Borisov's avatar Nikolay Borisov Committed by David Sterba
Browse files

btrfs: Remove redundant memory barriers around dio_private error status 



Using any kind of memory barriers around atomic operations which have
a return value is redundant, since those operations themselves are
fully ordered. atomic_t.txt states:

    - RMW operations that have a return value are fully ordered;

    Fully ordered primitives are ordered against everything prior and
    everything subsequent. Therefore a fully ordered primitive is like
    having an smp_mb() before and an smp_mb() after the primitive.

Given this let's replace the extra memory barriers with comments.

Signed-off-by: default avatarNikolay Borisov <nborisov@suse.com>
Reviewed-by: default avatarDavid Sterba <dsterba@suse.com>
Signed-off-by: default avatarDavid Sterba <dsterba@suse.com>
parent 16db5758

fs/btrfs/inode.c

+9 −8
Original line number Diff line number Diff line
@@ -8322,13 +8322,13 @@ static void btrfs_end_dio_bio(struct bio *bio) 
		err = dip->subio_endio(dip->inode, btrfs_io_bio(bio), err);



	if (err) {

		dip->errors = 1;



		/*

		 * before atomic variable goto zero, we must make sure

		 * dip->errors is perceived to be set.

		 * We want to perceive the errors flag being set before

		 * decrementing the reference count. We don't need a barrier

		 * since atomic operations with a return value are fully

		 * ordered as per atomic_t.txt

		 */

		smp_mb__before_atomic();

		dip->errors = 1;

	}



	/* if there are more bios still pending for this dio, just exit */
@@ -8516,10 +8516,11 @@ static int btrfs_submit_direct_hook(struct btrfs_dio_private *dip) 
out_err:

	dip->errors = 1;

	/*

	 * before atomic variable goto zero, we must

	 * make sure dip->errors is perceived to be set.

	 * Before atomic variable goto zero, we must  make sure dip->errors is

	 * perceived to be set. This ordering is ensured by the fact that an

	 * atomic operations with a return value are fully ordered as per

	 * atomic_t.txt

	 */

	smp_mb__before_atomic();

	if (atomic_dec_and_test(&dip->pending_bios))

		bio_io_error(dip->orig_bio);