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Commit 3ee25485 authored by Mike Snitzer's avatar Mike Snitzer
Browse files

dm snapshot: fix oversights in optional discard support 



__find_snapshots_sharing_cow() should always be used with _origins_lock
held so fix snapshot_io_hints() accordingly.  Also, once a snapshot is
being merged discards must not be allowed -- otherwise incorrect or
duplicate work will be performed.

Fixes: 2e602385 ("dm snapshot: add optional discard support features")
Reported-by: default avatarNikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: default avatarMike Snitzer <snitzer@redhat.com>
parent 3b8cafdd

drivers/md/dm-snap.c

+10 −0
Original line number Diff line number Diff line
@@ -2072,6 +2072,12 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio) 
		return DM_MAPIO_REMAPPED;

	}



	if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {

		/* Once merging, discards no longer effect change */

		bio_endio(bio);

		return DM_MAPIO_SUBMITTED;

	}



	chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);



	down_write(&s->lock);
@@ -2331,6 +2337,8 @@ static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits) 
	if (snap->discard_zeroes_cow) {

		struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;



		down_read(&_origins_lock);



		(void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL);

		if (snap_src && snap_dest)

			snap = snap_src;
@@ -2338,6 +2346,8 @@ static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits) 
		/* All discards are split on chunk_size boundary */

		limits->discard_granularity = snap->store->chunk_size;

		limits->max_discard_sectors = snap->store->chunk_size;



		up_read(&_origins_lock);

	}

}