dm thin: grab a virtual cell before looking up the mapping

commit c822ed967cba38505713d59ed40a114386ef6c01 upstream.

Avoids normal IO racing with discard.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/md/dm-thin.c b/drivers/md/dm-thin.c
index 359af3a..37f2648 100644 (file)
--- a/drivers/md/dm-thin.c
+++ b/drivers/md/dm-thin.c
@@ -1704,6 +1704,14 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                return DM_MAPIO_SUBMITTED;
        }
 
+       /*
+        * We must hold the virtual cell before doing the lookup, otherwise
+        * there's a race with discard.
+        */
+       build_virtual_key(tc->td, block, &key);
+       if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))
+               return DM_MAPIO_SUBMITTED;
+
        r = dm_thin_find_block(td, block, 0, &result);
 
        /*
@@ -1727,13 +1735,10 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                         * shared flag will be set in their case.
                         */
                        thin_defer_bio(tc, bio);
+                       cell_defer_no_holder_no_free(tc, &cell1);
                        return DM_MAPIO_SUBMITTED;
                }
 
-               build_virtual_key(tc->td, block, &key);
-               if (dm_bio_detain(tc->pool->prison, &key, bio, &cell1, &cell_result))
-                       return DM_MAPIO_SUBMITTED;
-
                build_data_key(tc->td, result.block, &key);
                if (dm_bio_detain(tc->pool->prison, &key, bio, &cell2, &cell_result)) {
                        cell_defer_no_holder_no_free(tc, &cell1);
@@ -1754,6 +1759,7 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                         * of doing so.
                         */
                        handle_unserviceable_bio(tc->pool, bio);
+                       cell_defer_no_holder_no_free(tc, &cell1);
                        return DM_MAPIO_SUBMITTED;
                }
                /* fall through */
@@ -1764,6 +1770,7 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                 * provide the hint to load the metadata into cache.
                 */
                thin_defer_bio(tc, bio);
+               cell_defer_no_holder_no_free(tc, &cell1);
                return DM_MAPIO_SUBMITTED;
 
        default:
@@ -1773,6 +1780,7 @@ static int thin_bio_map(struct dm_target *ti, struct bio *bio)
                 * pool is switched to fail-io mode.
                 */
                bio_io_error(bio);
+               cell_defer_no_holder_no_free(tc, &cell1);
                return DM_MAPIO_SUBMITTED;
        }
 }