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>
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@ -2072,6 +2072,12 @@ static int snapshot_merge_map(struct dm_target *ti, struct bio *bio)
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return DM_MAPIO_REMAPPED;
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}
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if (unlikely(bio_op(bio) == REQ_OP_DISCARD)) {
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/* Once merging, discards no longer effect change */
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bio_endio(bio);
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return DM_MAPIO_SUBMITTED;
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}
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chunk = sector_to_chunk(s->store, bio->bi_iter.bi_sector);
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down_write(&s->lock);
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@ -2331,6 +2337,8 @@ static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
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if (snap->discard_zeroes_cow) {
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struct dm_snapshot *snap_src = NULL, *snap_dest = NULL;
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down_read(&_origins_lock);
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(void) __find_snapshots_sharing_cow(snap, &snap_src, &snap_dest, NULL);
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if (snap_src && snap_dest)
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snap = snap_src;
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@ -2338,6 +2346,8 @@ static void snapshot_io_hints(struct dm_target *ti, struct queue_limits *limits)
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/* All discards are split on chunk_size boundary */
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limits->discard_granularity = snap->store->chunk_size;
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limits->max_discard_sectors = snap->store->chunk_size;
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up_read(&_origins_lock);
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}
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}
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