[3.16.y-ckt stable] Patch "md/raid5: fix another livelock caused by non-aligned writes." 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 another livelock caused by non-aligned writes.

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-ckt7.

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 9aae570c5453e0d7fd7fafd07f9cabb5bec9386a Mon Sep 17 00:00:00 2001
From: NeilBrown <neilb at suse.de>
Date: Mon, 2 Feb 2015 10:44:29 +1100
Subject: md/raid5: fix another livelock caused by non-aligned writes.

commit b1b02fe97f75b12ab34b2303bfd4e3526d903a58 upstream.

If a non-page-aligned write is destined for a device which
is missing/faulty, we can deadlock.

As the target device is missing, a read-modify-write cycle
is not possible.
As the write is not for a full-page, a recontruct-write cycle
is not possible.

This should be handled by logic in fetch_block() which notices
there is a non-R5_OVERWRITE write to a missing device, and so
loads all blocks.

However since commit 67f455486d2ea2, that code requires
STRIPE_PREREAD_ACTIVE before it will active, and those circumstances
never set STRIPE_PREREAD_ACTIVE.

So: in handle_stripe_dirtying, if neither rmw or rcw was possible,
set STRIPE_DELAYED, which will cause STRIPE_PREREAD_ACTIVE be set
after a suitable delay.

Fixes: 67f455486d2ea20b2d94d6adf5b9b783d079e321
Reported-by: Mikulas Patocka <mpatocka at redhat.com>
Tested-by: Heinz Mauelshagen <heinzm at redhat.com>
Signed-off-by: NeilBrown <neilb at suse.de>
Signed-off-by: Luis Henriques <luis.henriques at canonical.com>
---
 drivers/md/raid5.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 222aa7521877..68a03d7f25ee 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -3204,6 +3204,11 @@ static void handle_stripe_dirtying(struct r5conf *conf,
 					  (unsigned long long)sh->sector,
 					  rcw, qread, test_bit(STRIPE_DELAYED, &sh->state));
 	}
+
+	if (rcw > disks && rmw > disks &&
+	    !test_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
+		set_bit(STRIPE_DELAYED, &sh->state);
+
 	/* now if nothing is locked, and if we have enough data,
 	 * we can start a write request
 	 */
--
2.1.4