Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751914AbdHGTiX (ORCPT ); Mon, 7 Aug 2017 15:38:23 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55814 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751505AbdHGTiV (ORCPT ); Mon, 7 Aug 2017 15:38:21 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 61885883D4 Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx02.extmail.prod.ext.phx2.redhat.com; spf=fail smtp.mailfrom=djeffery@redhat.com Date: Mon, 7 Aug 2017 15:38:18 -0400 From: David Jeffery To: linux-block@vger.kernel.org Cc: linux-kernel@vger.kernel.org, axboe@kernel.dk Subject: [PATCH] block: Fix warning when I/O elevator is changed as request_queue is being removed Message-ID: <20170807193818.GA22737@rage> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline User-Agent: Mutt/1.8.3 (2017-05-23) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Mon, 07 Aug 2017 19:38:21 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1934 Lines: 54 There is a race between changing I/O elevator and request_queue removal which can trigger the warning in kobject_add_internal. A program can use sysfs to request a change of elevator at the same time another task is unregistering the request_queue the elevator would be attached to. The elevator's kobject will then attempt to be connected to the request_queue in the object tree when the request_queue has just been removed from sysfs. This triggers the warning in kobject_add_internal as the request_queue no longer has a sysfs directory: kobject_add_internal failed for iosched (error: -2 parent: queue) ------------[ cut here ]------------ WARNING: CPU: 3 PID: 14075 at lib/kobject.c:244 kobject_add_internal+0x103/0x2d0 To fix this warning, we can check the QUEUE_FLAG_REGISTERED flag when changing the elevator and use the request_queue's sysfs_lock to serialize between clearing the flag and the elevator testing the flag. Signed-off-by: David Jeffery --- block/blk-sysfs.c | 2 ++ block/elevator.c | 4 ++++ 2 files changed, 6 insertions(+) diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c index 27aceab..b8362c0 100644 --- a/block/blk-sysfs.c +++ b/block/blk-sysfs.c @@ -931,7 +931,9 @@ void blk_unregister_queue(struct gendisk *disk) if (WARN_ON(!q)) return; + mutex_lock(&q->sysfs_lock); queue_flag_clear_unlocked(QUEUE_FLAG_REGISTERED, q); + mutex_unlock(&q->sysfs_lock); wbt_exit(q); diff --git a/block/elevator.c b/block/elevator.c index 4bb2f0c..51da592 100644 --- a/block/elevator.c +++ b/block/elevator.c @@ -1055,6 +1055,10 @@ static int __elevator_change(struct request_queue *q, const char *name) char elevator_name[ELV_NAME_MAX]; struct elevator_type *e; + /* Make sure queue is not in the middle of being removed */ + if (!test_bit(QUEUE_FLAG_REGISTERED, &q->queue_flags)) + return -ENOENT; + /* * Special case for mq, turn off scheduling */