linux-kernel - [ 03/82] md: protect against crash upon fsync on ro array

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Message-Id: <20130318042144.531436620@decadent.org.uk>
Date:	Mon, 18 Mar 2013 04:21:47 +0000
From:	Ben Hutchings <ben@...adent.org.uk>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	akpm@...ux-foundation.org,
	Sebastian Riemer <sebastian.riemer@...fitbricks.com>,
	Christoph Hellwig <hch@...radead.org>,
	NeilBrown <neilb@...e.de>,
	Paul Menzel <paulepanter@...rs.sourceforge.net>
Subject: [ 03/82] md: protect against crash upon fsync on ro array

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

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

From: Sebastian Riemer <sebastian.riemer@...fitbricks.com>

commit bbfa57c0f2243a7c31fd248d22e9861a2802cad5 upstream.

If an fsync occurs on a read-only array, we need to send a
completion for the IO and may not increment the active IO count.
Otherwise, we hit a bug trace and can't stop the MD array anymore.

By advice of Christoph Hellwig we return success upon a flush
request but we return -EROFS for other writes.
We detect flush requests by checking if the bio has zero sectors.

This patch is suitable to any -stable kernel to which it applies.

Cc: Christoph Hellwig <hch@...radead.org>
Cc: Ben Hutchings <ben@...adent.org.uk>
Cc: NeilBrown <neilb@...e.de>
Signed-off-by: Sebastian Riemer <sebastian.riemer@...fitbricks.com>
Reported-by: Ben Hutchings <ben@...adent.org.uk>
Acked-by: Paul Menzel <paulepanter@...rs.sourceforge.net>
Signed-off-by: NeilBrown <neilb@...e.de>
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/md/md.c |    4 ++++
 1 file changed, 4 insertions(+)

--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -345,6 +345,10 @@ static void md_make_request(struct reque
 		bio_io_error(bio);
 		return;
 	}
+	if (mddev->ro == 1 && unlikely(rw == WRITE)) {
+		bio_endio(bio, bio_sectors(bio) == 0 ? 0 : -EROFS);
+		return;
+	}
 	smp_rmb(); /* Ensure implications of  'active' are visible */
 	rcu_read_lock();
 	if (mddev->suspended) {


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