From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753036Ab0ESOp6 (ORCPT ); Wed, 19 May 2010 10:45:58 -0400 Received: from mx1.redhat.com ([209.132.183.28]:5739 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753079Ab0ESOp5 (ORCPT ); Wed, 19 May 2010 10:45:57 -0400 Date: Wed, 19 May 2010 10:45:42 -0400 From: Mike Snitzer To: Kiyoshi Ueda Cc: Nikanth Karthikesan , linux-kernel@vger.kernel.org, dm-devel@redhat.com, Vivek Goyal , Jens Axboe , "Jun'ichi Nomura" , Alasdair Kergon Subject: Re: [RFC PATCH 2/2] dm: only initialize full request_queue for request-based device Message-ID: <20100519144542.GD24618@redhat.com> References: <20100513035750.GA25523@redhat.com> <4BED049C.5040409@ct.jp.nec.com> <20100514140852.GA10373@redhat.com> <4BF10BF1.3040108@ct.jp.nec.com> <20100517172737.GA24591@redhat.com> <4BF25091.3000507@ct.jp.nec.com> <20100518134639.GA27582@redhat.com> <4BF37DD5.9050409@ct.jp.nec.com> <20100519143900.GC24618@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20100519143900.GC24618@redhat.com> User-Agent: Mutt/1.5.20 (2009-08-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 19 2010 at 10:39am -0400, Mike Snitzer wrote: > > On Wed, May 19, 2010 at 1:57 AM, Kiyoshi Ueda wrote: > > > Hi Mike, > > > > > > dm_table_setup_md_queue() may allocate memory with blocking mode. > > > Blocking allocation inside exclusive _hash_lock can cause deadlock; > > > e.g. when it has to wait for other dm devices to resume to free some > > > memory. > We discussed this and I understand the scope of the problem now. > > Just reiterating what you covered when you first pointed this issue out: > > It could be that a table load gets blocked (waiting on a memory > allocation). The table load can take as long as it needs. But we can't > have it block holding the exclusive _hash_lock while blocking. Having > _hash_lock prevents further DM ioctls. The table load's allocation may > be blocking waiting for writeback to a DM device that will be resumed by > another thread. > > Thanks again for pointing this out; I'll work to arrive at an > alternative locking scheme. Likely introduce a lock local to the > multiple_device (effectively the 'queue_lock' I had before). But s/multiple_device/mapped_device/ Mike