linux-kernel - Re: [PATCH 07/23] io-controller: Common hierarchical fair queuing code in elevaotor layer

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Message-ID: <4A9F3319.8040509@ds.jp.nec.com>
Date:	Wed, 02 Sep 2009 23:08:09 -0400
From:	Munehiro Ikeda <m-ikeda@...jp.nec.com>
To:	Vivek Goyal <vgoyal@...hat.com>
CC:	linux-kernel@...r.kernel.org, jens.axboe@...cle.com,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	nauman@...gle.com, dpshah@...gle.com, lizf@...fujitsu.com,
	mikew@...gle.com, fchecconi@...il.com, paolo.valente@...more.it,
	ryov@...inux.co.jp, fernando@....ntt.co.jp, s-uchida@...jp.nec.com,
	taka@...inux.co.jp, guijianfeng@...fujitsu.com, jmoyer@...hat.com,
	dhaval@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com,
	righi.andrea@...il.com, agk@...hat.com, akpm@...ux-foundation.org,
	peterz@...radead.org, jmarchan@...hat.com,
	torvalds@...ux-foundation.org, mingo@...e.hu, riel@...hat.com
Subject: Re: [PATCH 07/23] io-controller: Common hierarchical fair queuing
 code in elevaotor layer

Hi,

Vivek Goyal wrote, on 08/28/2009 05:30 PM:
> +static struct io_group *io_find_alloc_group(struct request_queue *q,
> +			struct cgroup *cgroup, struct elv_fq_data *efqd,
> +			int create)
> +{
> +	struct io_cgroup *iocg = cgroup_to_io_cgroup(cgroup);
> +	struct io_group *iog = NULL;
> +	/* Note: Use efqd as key */
> +	void *key = efqd;
> +
> +	/*
> +	 * Take a refenrece to css object. Don't want to map a bio to
> +	 * a group if it has been marked for deletion
> +	 */
> +
> +	if (!css_tryget(&iocg->css))
> +		return iog;

cgroup_to_io_cgroup() returns NULL if only blkio subsystem
is mounted but io subsystem is not.  It can cause NULL pointer
access.

Signed-off-by: Munehiro "Muuhh" Ikeda <m-ikeda@...jp.nec.com>
---
 block/elevator-fq.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/block/elevator-fq.c b/block/elevator-fq.c
index b723c12..6714e73 100644
--- a/block/elevator-fq.c
+++ b/block/elevator-fq.c
@@ -1827,7 +1827,7 @@ static struct io_group *io_find_alloc_group(struct request_queue *q,
         * a group if it has been marked for deletion
         */
 
-       if (!css_tryget(&iocg->css))
+       if (!iocg || !css_tryget(&iocg->css))
                return iog;
 
        iog = io_cgroup_lookup_group(iocg, key);
-- 
1.6.2.5


-- 
IKEDA, Munehiro
  NEC Corporation of America
    m-ikeda@...jp.nec.com

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