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

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Date:	Thu, 10 Sep 2009 16:11:48 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Munehiro Ikeda <m-ikeda@...jp.nec.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

On Wed, Sep 02, 2009 at 11:08:09PM -0400, Munehiro Ikeda wrote:
> 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.
> 

Good catch Muuhh.  Thanks. Applied for next release.

Thanks
Vivek

> 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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