From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754323AbbDHP3G (ORCPT ); Wed, 8 Apr 2015 11:29:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:39019 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753994AbbDHP26 (ORCPT ); Wed, 8 Apr 2015 11:28:58 -0400 Date: Wed, 8 Apr 2015 11:28:57 -0400 From: Jarod Wilson To: Ming Lei Cc: Linux Kernel Mailing List , Christoph Hellwig , Jens Axboe , Tejun Heo , Alexander Viro , Markus Pargmann , Stefan Weinhuber , Stefan Haberland , Sebastian Ott , Fabian Frederick , David Herrmann , Mike Galbraith , Andrew Morton , Peter Zijlstra , "nbd-general@lists.sourceforge.net" , linux-s390@vger.kernel.org Subject: Re: [PATCH 2/7] block: loop: don't hold lo_ctl_mutex in lo_open Message-ID: <20150408152857.GK14217@redhat.com> References: <1428218688-4092-1-git-send-email-ming.lei@canonical.com> <1428474226-27386-1-git-send-email-jarod@redhat.com> <1428474226-27386-3-git-send-email-jarod@redhat.com> <20150408134034.GH14217@redhat.com> <20150408140028.GI14217@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 08, 2015 at 10:20:22PM +0800, Ming Lei wrote: > On Wed, Apr 8, 2015 at 10:00 PM, Jarod Wilson wrote: > > On Wed, Apr 08, 2015 at 09:40:34AM -0400, Jarod Wilson wrote: > >> On Wed, Apr 08, 2015 at 02:50:59PM +0800, Ming Lei wrote: > >> > Hi Jarod, > >> > > >> > On Wed, Apr 8, 2015 at 2:23 PM, Jarod Wilson wrote: > >> > > From: Ming Lei > >> > > > >> > > The lo_ctl_mutex is held for running all ioctl handlers, and > >> > > in some ioctl handlers, ioctl_by_bdev(BLKRRPART) is called for > >> > > rereading partitions, which requires bd_mutex. > >> > > > >> > > So it is easy to cause failure because trylock(bd_mutex) may > >> > > fail inside blkdev_reread_part(), and follows the lock context: > >> > > > >> > > blkid or other application: > >> > > ->open() > >> > > ->mutex_lock(bd_mutex) > >> > > ->lo_open() > >> > > ->mutex_lock(lo_ctl_mutex) > >> > > > >> > > losetup(set fd ioctl): > >> > > ->mutex_lock(lo_ctl_mutex) > >> > > ->ioctl_by_bdev(BLKRRPART) > >> > > ->trylock(bd_mutex) > >> > > > >> > > This patch trys to eliminate the ABBA lock dependency by removing > >> > > lo_ctl_mutext in lo_open() with the following approach: > >> > > > >> > > 1) introduce lo_open_mutex to protect lo_refcnt and avoid acquiring > >> > > lo_ctl_mutex in lo_open(): > >> > > >> > It is a bit quick since I said the lo_open_mutex can be removed, > >> > and Christoph agreed that too. > >> > > >> > So looks we still need to post another version, :-) > >> > >> Ah. I missed that bit. Just trying to keep up momentum. > > > > Are you working on that atomic_t version then, or should I dive into it? > > It has been ready, and I will post them out once it passes my tests. Okay, I'll hold tight then. Sorry for the noise. :p -- Jarod Wilson jarod@redhat.com