dm cache: only use overwrite optimisation for promotion when in writeback mode

Overwrite causes the cache block and origin blocks to diverge, which
is only allowed in writeback mode.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Cc: stable@vger.kernel.org

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index fd7f613872833afba7eb56033580333b2236af00..ef842feda1015b51e2fd66e53ec4d7cfb42dde3e 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1142,7 +1142,8 @@ static void issue_copy_or_discard(struct dm_cache_migration *mg)
 
                avoid = is_discarded_oblock(cache, mg->new_oblock);
 
-               if (!avoid && bio_writes_complete_block(cache, bio)) {
+               if (writeback_mode(&cache->features) &&
+                   !avoid && bio_writes_complete_block(cache, bio)) {
                        issue_overwrite(mg, bio);
                        return;
                }