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

commit f29a3147e251d7ae20d3194ff67f109d71e501b4 upstream.

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>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index c892e48655c2f052374b38adebacc895729e9496..e5bb12810cccd78f517332c63267479fd5e34cde 100644 (file)
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1043,7 +1043,8 @@ static void issue_copy(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;
                }