Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754827Ab0D1PKH (ORCPT ); Wed, 28 Apr 2010 11:10:07 -0400 Received: from mx1.redhat.com ([209.132.183.28]:53601 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752259Ab0D1PKF (ORCPT ); Wed, 28 Apr 2010 11:10:05 -0400 Date: Wed, 28 Apr 2010 11:09:59 -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: <20100428150959.GA16033@redhat.com> References: <877hnrg30c.fsf@openvz.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <877hnrg30c.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: 2981 Lines: 89 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. 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. cfq-iosched: fix cfq crash with CFQ_GROUP_IOSCHED=n Dmitry reported an oops with CFQ when booted with BLK_CGROUP=y and CFQ_GROUP_IOSCHED=n. This patch fixes it. We maintain a root group even if group ioscheduling is not enabled. Hence don't store NULL in elevator_private3 in that case. Signed-off-by: Vivek Goyal --- block/cfq-iosched.c | 11 ++++------- 1 files changed, 4 insertions(+), 7 deletions(-) diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c index 286008c..5aa5364 100644 --- a/block/cfq-iosched.c +++ b/block/cfq-iosched.c @@ -1002,10 +1002,9 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create) return cfqg; } -static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg) +static inline void cfq_ref_get_cfqg(struct cfq_group *cfqg) { atomic_inc(&cfqg->ref); - return cfqg; } static void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) @@ -1092,10 +1091,7 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create) return &cfqd->root_group; } -static inline struct cfq_group *cfq_ref_get_cfqg(struct cfq_group *cfqg) -{ - return NULL; -} +static inline void cfq_ref_get_cfqg(struct cfq_group *cfqg) {} static inline void cfq_link_cfqq_cfqg(struct cfq_queue *cfqq, struct cfq_group *cfqg) { @@ -3574,7 +3570,8 @@ new_queue: rq->elevator_private = cic; rq->elevator_private2 = cfqq; - rq->elevator_private3 = cfq_ref_get_cfqg(cfqq->cfqg); + rq->elevator_private3 = cfqq->cfqg; + cfq_ref_get_cfqg(cfqq->cfqg); return 0; queue_fail: -- 1.6.2.5 -- 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/