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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: 2e6023850e ("dm snapshot: add optional discard support features")
Reported-by: Nikos Tsironis <ntsironis@arrikto.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
This commit is contained in:
Mike Snitzer 2019-07-17 11:12:30 -04:00
parent 3b8cafdd54
commit 3ee25485ba
1 changed files with 10 additions and 0 deletions
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10
drivers/md/dm-snap.c
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@ -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);
}
}