linux-kernel - [PATCH 3.16.y-ckt 130/183] md/raid5: Fix livelock when array is both resyncing and degraded.

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Message-Id: <1425635874-19087-131-git-send-email-luis.henriques@canonical.com>
Date:	Fri,  6 Mar 2015 09:57:01 +0000
From:	Luis Henriques <luis.henriques@...onical.com>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org,
	kernel-team@...ts.ubuntu.com
Cc:	NeilBrown <neilb@...e.de>,
	Luis Henriques <luis.henriques@...onical.com>
Subject: [PATCH 3.16.y-ckt 130/183] md/raid5: Fix livelock when array is both resyncing and degraded.

3.16.7-ckt8 -stable review patch.  If anyone has any objections, please let me know.

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

From: NeilBrown <neilb@...e.de>

commit 26ac107378c4742978216be1005b7291b799c7b2 upstream.

Commit a7854487cd7128a30a7f4f5259de9f67d5efb95f:
  md: When RAID5 is dirty, force reconstruct-write instead of read-modify-write.

Causes an RCW cycle to be forced even when the array is degraded.
A degraded array cannot support RCW as that requires reading all data
blocks, and one may be missing.

Forcing an RCW when it is not possible causes a live-lock and the code
spins, repeatedly deciding to do something that cannot succeed.

So change the condition to only force RCW on non-degraded arrays.

Reported-by: Manibalan P <pmanibalan@...india.co.in>
Bisected-by: Jes Sorensen <Jes.Sorensen@...hat.com>
Tested-by: Jes Sorensen <Jes.Sorensen@...hat.com>
Signed-off-by: NeilBrown <neilb@...e.de>
Fixes: a7854487cd7128a30a7f4f5259de9f67d5efb95f
Signed-off-by: Luis Henriques <luis.henriques@...onical.com>
---
 drivers/md/raid5.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 68a03d7f25ee..b1b9efb5359f 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3111,7 +3111,8 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 	 * generate correct data from the parity.
 	 */
 	if (conf->max_degraded == 2 ||
-	    (recovery_cp < MaxSector && sh->sector >= recovery_cp)) {
+	    (recovery_cp < MaxSector && sh->sector >= recovery_cp &&
+	     s->failed == 0)) {
 		/* Calculate the real rcw later - for now make it
 		 * look like rcw is cheaper
 		 */
--
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