From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH 20/24] block: RCU free request_queue Date: Wed, 2 Jan 2013 15:43:55 -0500 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-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20130102184814.GD4306-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: containers-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Vivek Goyal Cc: axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org, ctalbott-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, rni-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org, containers-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: containers.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