linux-kernel - [PATCH 3.16.y-ckt 14/58] md/raid5: fix another livelock caused by non-aligned writes.

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Message-Id: <1424353948-31863-15-git-send-email-luis.henriques@canonical.com>
Date:	Thu, 19 Feb 2015 13:51:44 +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 14/58] md/raid5: fix another livelock caused by non-aligned writes.

3.16.7-ckt7 -stable review patch.  If anyone has any objections, please let me know.

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

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

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@...hat.com>
Tested-by: Heinz Mauelshagen <heinzm@...hat.com>
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Luis Henriques <luis.henriques@...onical.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

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