From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755456AbaKLEGJ (ORCPT ); Tue, 11 Nov 2014 23:06:09 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:58704 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753872AbaKLBX6 (ORCPT ); Tue, 11 Nov 2014 20:23:58 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Bart Van Assche , Jens Axboe Subject: [PATCH 3.17 089/319] blk-mq: fix potential hang if rolling wakeup depth is too high Date: Wed, 12 Nov 2014 10:13:47 +0900 Message-Id: <20141112011007.296748779@linuxfoundation.org> X-Mailer: git-send-email 2.1.3 In-Reply-To: <20141112010952.553519040@linuxfoundation.org> References: <20141112010952.553519040@linuxfoundation.org> User-Agent: quilt/0.63-1 MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Jens Axboe commit abab13b5c4fd1fec4f9a61622548012d93dc2831 upstream. We currently divide the queue depth by 4 as our batch wakeup count, but we split the wakeups over BT_WAIT_QUEUES number of wait queues. This defaults to 8. If the product of the resulting batch wake count and BT_WAIT_QUEUES is higher than the device queue depth, we can get into a situation where a task goes to sleep waiting for a request, but never gets woken up. Reported-by: Bart Van Assche Fixes: 4bb659b156996 Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- block/blk-mq-tag.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -463,8 +463,8 @@ static void bt_update_count(struct blk_m } bt->wake_cnt = BT_WAIT_BATCH; - if (bt->wake_cnt > depth / 4) - bt->wake_cnt = max(1U, depth / 4); + if (bt->wake_cnt > depth / BT_WAIT_QUEUES) + bt->wake_cnt = max(1U, depth / BT_WAIT_QUEUES); bt->depth = depth; }