[PATCH 3.13.y-ckt 059/139] dm cache: only use overwrite optimisation for promotion when in writeback mode

[Kamal Mostafa]

3.13.11-ckt15 -stable review patch.  If anyone has any objections, please let me know.

------------------

From: Joe Thornber <ejt at redhat.com>

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 at redhat.com>
Signed-off-by: Mike Snitzer <snitzer at redhat.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/dm-cache-target.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm-cache-target.c b/drivers/md/dm-cache-target.c
index 99474ef..b943ef1 100644
--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1049,7 +1049,8 @@ 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;
 		}
-- 
1.9.1