[3.16.y-ckt stable] Patch "md/raid5: Fix livelock when array is both resyncing and degraded." has been added to staging queue

[Luis Henriques]

This is a note to let you know that I have just added a patch titled

    md/raid5: Fix livelock when array is both resyncing and degraded.

to the linux-3.16.y-queue branch of the 3.16.y-ckt extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.16.y-queue

This patch is scheduled to be released in version 3.16.7-ckt8.

If you, or anyone else, feels it should not be added to this tree, please 
reply to this email.

For more information about the 3.16.y-ckt tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Luis

------

>From b5fdd9498e642d232785656059068ea52bfde9ca Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.de>
Date: Wed, 18 Feb 2015 11:35:14 +1100
Subject: md/raid5: Fix livelock when array is both resyncing and degraded.

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 at amiindia.co.in>
Bisected-by: Jes Sorensen <Jes.Sorensen at redhat.com>
Tested-by: Jes Sorensen <Jes.Sorensen at redhat.com>
Signed-off-by: NeilBrown <neilb at suse.de>
Fixes: a7854487cd7128a30a7f4f5259de9f67d5efb95f
Signed-off-by: Luis Henriques <luis.henriques at canonical.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
 		 */