From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752757Ab3ABUoA (ORCPT ); Wed, 2 Jan 2013 15:44:00 -0500 Received: from mail-qa0-f51.google.com ([209.85.216.51]:47070 "EHLO mail-qa0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752696Ab3ABUn6 (ORCPT ); Wed, 2 Jan 2013 15:43:58 -0500 Date: Wed, 2 Jan 2013 15:43:55 -0500 From: Tejun Heo To: Vivek Goyal Cc: lizefan@huawei.com, axboe@kernel.dk, containers@lists.linux-foundation.org, cgroups@vger.kernel.org, linux-kernel@vger.kernel.org, ctalbott@google.com, rni@google.com Subject: Re: [PATCH 20/24] block: RCU free request_queue Message-ID: <20130102204355.GF11220@mtj.dyndns.org> References: <1356726946-26037-1-git-send-email-tj@kernel.org> <1356726946-26037-21-git-send-email-tj@kernel.org> <20130102184814.GD4306@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20130102184814.GD4306@redhat.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, Jan 02, 2013 at 01:48:15PM -0500, Vivek Goyal wrote: > On Fri, Dec 28, 2012 at 12:35:42PM -0800, Tejun Heo wrote: > > RCU free request_queue so that blkcg_gq->q can be dereferenced under > > RCU lock. This will be used to implement hierarchical stats. > > Can we just take a blkg reference on ->q in blkg_alloc() and drop that > reference in blkg_free(), instead of RCU freeing up queue. I don't think we can invoke blk_release_queue() from RCU free contxt, so we can't put request_queue from blkg_rcu_free(). Maybe we can go through a work item but that's uglier. Thanks. -- tejun