linux-kernel - Re: [PATCH] blkio: Fix a crash during rq stats update

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Date:	Wed, 21 Apr 2010 11:11:15 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Divyesh Shah <dpshah@...gle.com>,
	Nauman Rafique <nauman@...gle.com>,
	Gui Jianfeng <guijianfeng@...fujitsu.com>
Subject: Re: [PATCH] blkio: Fix a crash during rq stats update

On Wed, Apr 21, 2010 at 04:55:14PM +0200, Jens Axboe wrote:
> On Wed, Apr 21 2010, Vivek Goyal wrote:
> > @@ -1001,6 +1002,10 @@ static struct cfq_group *cfq_get_cfqg(struct cfq_data *cfqd, int create)
> >  	return cfqg;
> >  }
> >  
> > +static inline void cfq_get_cfqg_ref(struct cfq_group *cfqg) {
> > +	atomic_inc(&cfqg->ref);
> > +}
> 
> Would be nicer as
> 
> static inline void cfq_ref_get_cfqg(struct cfq_group *cfqg)
> {

Chagne of name, will do.

> 	atomic_inc(&cfqg->ref);
>         return cfqg;
> }

So you want to return cfqg pointer here instead of return type being void?

> 
> ...
> 
> static inline void cfq_ref_get_cfqg(struct cfq_group *cfqg)
> {
>         return NULL;
> }

Will fix it.

Ok, so in case of CFQ_GROUP_IOSCHED, return a poitner to cfqg upon getting
the reference, otherwise NULL. Will fix it.

Thanks
Vivek
> 
> ...
> 
> > @@ -3560,6 +3570,9 @@ new_queue:
> >  
> >  	rq->elevator_private = cic;
> >  	rq->elevator_private2 = cfqq;
> > +	rq->elevator_private3 = cfqq->cfqg;
> > +	/* rq reference on cfqg */
> > +	cfq_get_cfqg_ref(RQ_CFQG(rq));
> >  	return 0;
> 
> rq->elevator_private3 = cfq_ref_get_cfqg(...);
> 
> -- 
> Jens Axboe
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