From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752621Ab1JZUiw (ORCPT ); Wed, 26 Oct 2011 16:38:52 -0400 Received: from mx1.redhat.com ([209.132.183.28]:11171 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750910Ab1JZUiv (ORCPT ); Wed, 26 Oct 2011 16:38:51 -0400 Date: Wed, 26 Oct 2011 16:38:46 -0400 From: Vivek Goyal To: Tejun Heo Cc: axboe@kernel.dk, ctalbott@google.com, rni@google.com, linux-kernel@vger.kernel.org Subject: Re: [PATCH 10/13] block, cfq: unlink cfq_io_context's immediately Message-ID: <20111026203846.GG355@redhat.com> References: <1319593719-19132-1-git-send-email-tj@kernel.org> <1319593719-19132-11-git-send-email-tj@kernel.org> <20111026194857.GF355@redhat.com> <20111026195506.GD24261@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20111026195506.GD24261@google.com> 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, Oct 26, 2011 at 12:55:06PM -0700, Tejun Heo wrote: > Hello, > > On Wed, Oct 26, 2011 at 03:48:57PM -0400, Vivek Goyal wrote: > > > + ioc_release_depth_inc(cic->q); > > > + cic->exit(cic); > > > + cic->release(cic); > > > + ioc_release_depth_dec(cic->q); > > > > cic->release(cic) can free the cic? Are we accessing cic after freeing it > > up in ioc_release_depth_dec(cic->q); > > As cic is RCU freed and we're running w/ irq disabled, this shouldn't > blow up, but yeah, I'll update it to use local variable instead. Tejun, So the only reason that cic needs to be rcu protected because in cfq_cic_lookup() we can access ioc->ioc_data which can point to a cic which is not ours and we are not holding queue lock for that and we can't access cic->q ? Rest of the places we are either holding ioc_lock or accessing our own cic under associated queue lock so it should be safe? I am wondering if there should be a small text file explaining all the locking in this area. Good to see that you are cleaning it all up. Thanks Vivek