[ 3.5.y.z extended stable ] Patch "dm: fix deadlock with request based dm and queue request_fn" has been added to staging queue

[Herton Ronaldo Krzesinski]

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

    dm: fix deadlock with request based dm and queue request_fn

to the linux-3.5.y-queue branch of the 3.5.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-3.5.y-queue

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

For more information about the 3.5.y.z tree, see
https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable

Thanks.
-Herton

------

>From fdcb10668dc4539e4c38afbcb4714d542e3c5401 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe at kernel.dk>
Date: Tue, 6 Nov 2012 12:24:26 +0100
Subject: [PATCH] dm: fix deadlock with request based dm and queue request_fn
 recursion

commit a8c32a5c98943d370ea606a2e7dc04717eb92206 upstream.

Request based dm attempts to re-run the request queue off the
request completion path. If used with a driver that potentially does
end_io from its request_fn, we could deadlock trying to recurse
back into request dispatch. Fix this by punting the request queue
run to kblockd.

Tested to fix a quickly reproducible deadlock in such a scenario.

Acked-by: Alasdair G Kergon <agk at redhat.com>
Signed-off-by: Jens Axboe <axboe at kernel.dk>
Signed-off-by: Herton Ronaldo Krzesinski <herton.krzesinski at canonical.com>
---
 drivers/md/dm.c |    8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 9ff3019..32370ea 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -754,8 +754,14 @@ static void rq_completed(struct mapped_device *md, int rw, int run_queue)
 	if (!md_in_flight(md))
 		wake_up(&md->wait);

+	/*
+	 * Run this off this callpath, as drivers could invoke end_io while
+	 * inside their request_fn (and holding the queue lock). Calling
+	 * back into ->request_fn() could deadlock attempting to grab the
+	 * queue lock again.
+	 */
 	if (run_queue)
-		blk_run_queue(md->queue);
+		blk_run_queue_async(md->queue);

 	/*
 	 * dm_put() must be at the end of this function. See the comment above
--
1.7.9.5