btrfs: Remove redundant memory barriers around dio_private error status (de224b7c) · Commits · 戴 / test

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:

Nikolay Borisov <nborisov@suse.com> Reviewed-by:

David Sterba <dsterba@suse.com> Signed-off-by:

David Sterba <dsterba@suse.com>

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 @@ submit:
		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);

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