Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755380Ab0D1PpG (ORCPT ); Wed, 28 Apr 2010 11:45:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:7777 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755186Ab0D1PpE (ORCPT ); Wed, 28 Apr 2010 11:45:04 -0400 Date: Wed, 28 Apr 2010 11:44:57 -0400 From: Vivek Goyal To: Dmitry Monakhov Cc: linux-kernel@vger.kernel.org, jens.axboe@oracle.com Subject: Re: CFQ is broken for CONFIG_BLK_CGROUP=y, CFQ_GROUP_IOSCHED=n Message-ID: <20100428154457.GC16033@redhat.com> References: <877hnrg30c.fsf@openvz.org> <20100428150959.GA16033@redhat.com> <87ljc7egil.fsf@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <87ljc7egil.fsf@openvz.org> User-Agent: Mutt/1.5.19 (2009-01-05) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2071 Lines: 55 On Wed, Apr 28, 2010 at 07:36:02PM +0400, Dmitry Monakhov wrote: > Vivek Goyal writes: > > > On Wed, Apr 28, 2010 at 04:44:51PM +0400, Dmitry Monakhov wrote: > >> > >> I've had an oops on kernel boot due to NULL pointer deference > >> linux-2.6-block/for-next HEAD:7eaed1226ab411ee5dc8c34fc0d8034e4c98e3c6 > >> I've enabled CONFIG_BLK_CGROUP, but not CFQ_GROUP_IOSCHED > >> In this case cfq_ref_get_cfqg() defined as > >> static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg) > >> { > >> return NULL; > >> } > >> So following call trace is simply NOOP > >> cfq_set_request() > >> rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg); > >> > >> Which later result in OOPS on bio insertion > >> cfq_insert_request > >> -> blkiocg_update_io_add_stats(&(RQ_CFQG(rq))->blkg,...) > >> -> spin_lock_irqsave(&blkg->stats_lock, flags); > >> > >> Bad commit. > >> >From 7f1dc8a2d2f45fc557b27fd56115338b1d34fc24 Mon Sep 17 00:00:00 2001 > >> From: Vivek Goyal > >> Date: Wed, 21 Apr 2010 17:44:16 +0200 > >> Subject: [PATCH] blkio: Fix blkio crash during rq stat update > > > > Dmitry, this patch should fix the issue. Can you please give it a try. > Yes. the issue is gone. > > > > Jens, I know you don't like this form of cfq_ref_get_cfqg(), but this > > seems to be the simplest solution to fix it. > IMHO following fix is simpler, and cleaner. > diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c > index 286008c..0f3eb70 100644 > --- a/block/cfq-iosched.c > +++ b/block/cfq-iosched.c > @@ -1094,7 +1094,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create) > > static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg) > { > - return NULL; > + return cfqg; > } Thanks Dmitry. I like it. simpler. Vivek -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/