linux-kernel - [PATCH 3.17 21/73] dm cache: only use overwrite optimisation for promotion when in writeback mode

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Message-Id: <20150107021558.166859490@linuxfoundation.org>
Date:	Tue,  6 Jan 2015 18:15:42 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	stable@...r.kernel.org, Joe Thornber <ejt@...hat.com>,
	Mike Snitzer <snitzer@...hat.com>
Subject: [PATCH 3.17 21/73] dm cache: only use overwrite optimisation for promotion when in writeback mode

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

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

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

---
 drivers/md/dm-cache-target.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/dm-cache-target.c
+++ b/drivers/md/dm-cache-target.c
@@ -1070,7 +1070,8 @@ static void issue_copy(struct dm_cache_m
 
 		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;
 		}


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