From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161043Ab2COQvI (ORCPT ); Thu, 15 Mar 2012 12:51:08 -0400 Received: from mail-yx0-f174.google.com ([209.85.213.174]:56177 "EHLO mail-yx0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031785Ab2COQvD (ORCPT ); Thu, 15 Mar 2012 12:51:03 -0400 Date: Thu, 15 Mar 2012 09:50:57 -0700 From: Tejun Heo To: Vivek Goyal Cc: Fengguang Wu , Jens Axboe , LKML Subject: Re: [PATCH block/for-3.4/core] cfq: fix cfqg ref handling when BLK_CGROUP && !CFQ_GROUP_IOSCHED Message-ID: <20120315165057.GB32137@google.com> References: <20120315094945.GA3205@localhost> <20120315163546.GA32137@google.com> <20120315164621.GD3253@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120315164621.GD3253@redhat.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hello, On Thu, Mar 15, 2012 at 12:46:21PM -0400, Vivek Goyal wrote: > On Thu, Mar 15, 2012 at 09:35:46AM -0700, Tejun Heo wrote: > > [..] > > --- > > Yeap, forgot to test that config combination. Fengguang, can you > > please test this patch? Jens, once Fengguang confirms the fix, can > > you please apply this on top of for-3.4/core along with the pending > > stats updates? > > I was working on similar patch and you beat me to it. :-) One comment > below. :) > [..] > > @@ -3533,7 +3551,7 @@ static int cfq_init_queue(struct request > > > > spin_lock_irq(q->queue_lock); > > cfq_link_cfqq_cfqg(&cfqd->oom_cfqq, cfqd->root_group); > > - blkg_put(cfqg_to_blkg(cfqd->root_group)); > > + cfqg_put(cfqd->root_group); > > This seems to be a spurious cfqg_put()? Which reference we are putting > down here? The extra ref from cfq_link_cfqq_cfqg() for oom_cfqq; otherwise, we need an extra cfq_put() in cfq_exit_queue(). I thought I wrote comment about that somewhere. Hmmm.... apparently not. The thing is that oom_cfqq doesn't go through proper cfqq destruction and thus never puts the extra ref to root cfqg. Thanks. -- tejun