linux-kernel - [PATCH 3.19 156/175] md/raid5: Fix livelock when array is both resyncing and degraded.

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Message-Id: <20150304061051.697641882@linuxfoundation.org>
Date:	Tue,  3 Mar 2015 22:15:34 -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, Manibalan P <pmanibalan@...india.co.in>,
	Jes Sorensen <Jes.Sorensen@...hat.com>,
	NeilBrown <neilb@...e.de>
Subject: [PATCH 3.19 156/175] md/raid5: Fix livelock when array is both resyncing and degraded.

3.19-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: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/md/raid5.c |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3102,7 +3102,8 @@ static void handle_stripe_dirtying(struc
 	 * 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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