[3.13.y.z extended stable] Patch "md/raid6: avoid data corruption during recovery of double-degraded RAID6" has been added to staging queue

[Kamal Mostafa]

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

    md/raid6: avoid data corruption during recovery of double-degraded RAID6

to the linux-3.13.y-queue branch of the 3.13.y.z extended stable tree 
which can be found at:

 http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.13.y-queue

This patch is scheduled to be released in version 3.13.11.8.

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

For more information about the 3.13.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Kamal

------

>From 116360e007eda555024a5ced8db33ab3fd47e408 Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.de>
Date: Wed, 13 Aug 2014 09:57:07 +1000
Subject: md/raid6: avoid data corruption during recovery of double-degraded
 RAID6

commit 9c4bdf697c39805078392d5ddbbba5ae5680e0dd upstream.

During recovery of a double-degraded RAID6 it is possible for
some blocks not to be recovered properly, leading to corruption.

If a write happens to one block in a stripe that would be written to a
missing device, and at the same time that stripe is recovering data
to the other missing device, then that recovered data may not be written.

This patch skips, in the double-degraded case, an optimisation that is
only safe for single-degraded arrays.

Bug was introduced in 2.6.32 and fix is suitable for any kernel since
then.  In an older kernel with separate handle_stripe5() and
handle_stripe6() functions the patch must change handle_stripe6().

Fixes: 6c0069c0ae9659e3a91b68eaed06a5c6c37f45c8
Cc: Yuri Tikhonov <yur at emcraft.com>
Cc: Dan Williams <dan.j.williams at intel.com>
Reported-by: "Manibalan P" <pmanibalan at amiindia.co.in>
Tested-by: "Manibalan P" <pmanibalan at amiindia.co.in>
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1090423
Signed-off-by: NeilBrown <neilb at suse.de>
Acked-by: Dan Williams <dan.j.williams at intel.com>
Signed-off-by: Kamal Mostafa <kamal at canonical.com>
---
 drivers/md/raid5.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 48cdec8..fd900ef 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3779,6 +3779,8 @@ static void handle_stripe(struct stripe_head *sh)
 				set_bit(R5_Wantwrite, &dev->flags);
 				if (prexor)
 					continue;
+				if (s.failed > 1)
+					continue;
 				if (!test_bit(R5_Insync, &dev->flags) ||
 				    ((i == sh->pd_idx || i == sh->qd_idx)  &&
 				     s.failed == 0))
--
1.9.1