dm thin: fix to consistently zero-fill reads to unprovisioned blocks

[ Upstream commit 5f027a3bf184d1d36e68745f7cd3718a8b879cc0 ]

It was always intended that a read to an unprovisioned block will return
zeroes regardless of whether the pool is in read-only or read-write
mode.  thin_bio_map() was inconsistent with its handling of such reads
when the pool is in read-only mode, it now properly zero-fills the bios
it returns in response to unprovisioned block reads.

Eliminate thin_bio_map()'s special read-only mode handling of -ENODATA
and just allow the IO to be deferred to the worker which will result in
pool->process_bio() handling the IO (which already properly zero-fills
reads to unprovisioned blocks).

Reported-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index ac6b0ff..0801e35 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -2003,17 +2003,6 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                return DM_MAPIO_REMAPPED;
 
        case -ENODATA:
-               if (get_pool_mode(tc->pool) == PM_READ_ONLY) {
-                       /*
-                        * This block isn't provisioned, and we have no way
-                        * of doing so.
-                        */
-                       handle_unserviceable_bio(tc->pool, bio);
-                       cell_defer_no_holder_no_free(tc, &cell1);
-                       return DM_MAPIO_SUBMITTED;
-               }
-               /* fall through */
-
        case -EWOULDBLOCK:
                /*
                 * In future, the failed dm_thin_find_block above could