linux-kernel - Re: [PATCH 22/25] io-controller: Per io group bdi congestion interface

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Date:	Fri, 17 Jul 2009 09:52:46 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Munehiro Ikeda <m-ikeda@...jp.nec.com>
Cc:	linux-kernel@...r.kernel.org,
	containers@...ts.linux-foundation.org, dm-devel@...hat.com,
	jens.axboe@...cle.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, jbaron@...hat.com, agk@...hat.com,
	snitzer@...hat.com, akpm@...ux-foundation.org, peterz@...radead.org
Subject: Re: [PATCH 22/25] io-controller: Per io group bdi congestion
	interface

On Thu, Jul 16, 2009 at 08:16:10PM -0400, Munehiro Ikeda wrote:
> Hi,
> 
> Vivek Goyal wrote, on 07/02/2009 04:01 PM:
> > diff --git a/block/blk-core.c b/block/blk-core.c
> > index 2035c20..79fe6a9 100644
> > --- a/block/blk-core.c
> > +++ b/block/blk-core.c
> > @@ -90,6 +90,27 @@ void blk_queue_congestion_threshold(struct request_queue *q)
> >   	q->nr_congestion_off = nr;
> >   }
> > 
> > +#ifdef CONFIG_GROUP_IOSCHED
> > +int blk_queue_io_group_congested(struct backing_dev_info *bdi, int bdi_bits,
> > +					struct page *page)
> > +{
> > +	int ret = 0;
> > +	struct request_queue *q = bdi->unplug_io_data;
> > +
> > +	if (!q&&  !q->elevator)
> > +		return bdi_congested(bdi, bdi_bits);
> 
> It causes NULL pointer dereference for brd etc.
> 
> Signed-off-by: Munehiro "Muuhh" Ikeda <m-ikeda@...jp.nec.com>
> ---
>  block/blk-core.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/block/blk-core.c b/block/blk-core.c
> index 79fe6a9..39fab66 100644
> --- a/block/blk-core.c
> +++ b/block/blk-core.c
> @@ -97,7 +97,7 @@ int blk_queue_io_group_congested(struct backing_dev_info *bdi, int bdi_bits,
>  	int ret = 0;
>  	struct request_queue *q = bdi->unplug_io_data;
>  
> -	if (!q && !q->elevator)
> +	if (!q || !q->elevator)
>  		return bdi_congested(bdi, bdi_bits);
>  

Hi,

Thanks for the patch. I also noticed this recently and fixed it for next
to be posted version.

Thanks
Vivek

>  	/* Do we need to hold queue lock? */
> -- 
> 1.6.2.5
> 
> 
> -- 
> IKEDA, Munehiro
>   NEC Corporation of America
>     m-ikeda@...jp.nec.com
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