From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932285Ab2LCOxD (ORCPT ); Mon, 3 Dec 2012 09:53:03 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:43676 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755318Ab2LCOgI (ORCPT ); Mon, 3 Dec 2012 09:36:08 -0500 Message-Id: <20121203143158.704079874@decadent.org.uk> User-Agent: quilt/0.60-1 Date: Mon, 03 Dec 2012 14:33:05 +0000 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Jens Axboe , Alasdair G Kergon Subject: [ 79/89] dm: fix deadlock with request based dm and queue request_fn recursion In-Reply-To: <20121203143146.549859007@decadent.org.uk> X-SA-Exim-Connect-IP: 2001:470:1f08:1539:21c:bfff:fe03:f805 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jens Axboe 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 Signed-off-by: Jens Axboe Signed-off-by: Ben Hutchings --- 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 02db918..77e6eff 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -740,8 +740,14 @@ 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