linux-kernel - Re: [bug] ata subsystem related crash with latest -git

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Message-ID: <20071018135526.GK5063@kernel.dk>
Date:	Thu, 18 Oct 2007 15:55:28 +0200
From:	Jens Axboe <jens.axboe@...cle.com>
To:	Benny Halevy <bhalevy@...asas.com>
Cc:	David Miller <davem@...emloft.net>, torvalds@...ux-foundation.org,
	fujita.tomonori@....ntt.co.jp, mingo@...e.hu,
	linux-kernel@...r.kernel.org, jgarzik@...ox.com,
	alan@...rguk.ukuu.org.uk, tomof@....org
Subject: Re: [bug] ata subsystem related crash with latest -git

On Thu, Oct 18 2007, Benny Halevy wrote:
> On Oct. 18, 2007, 15:32 +0200, Jens Axboe <jens.axboe@...cle.com> wrote:
> >  static inline struct scatterlist *sg_next(struct scatterlist *sg)
> >  {
> > -	sg++;
> > -
> > -	if (unlikely(sg_is_chain(sg)))
> > +#ifdef CONFIG_DEBUG_SG
> > +	BUG_ON(sg->sg_magic != SG_MAGIC);
> > +#endif
> > +	if (sg_is_last(sg))
> > +		sg = NULL;
> > +	else if (sg_is_chain(sg))
> >  		sg = sg_chain_ptr(sg);
> > +	else
> > +		sg++;
> >  
> 
> Jens, again, please correct me if I'm wrong, but when sg points at the
> entry right before a chain entry this implementation of sg_next will
> return a pointer to the chain entry here, which I believe it must not.
> 
> >  	return sg;
> >  }
> > 
> 
> here's how I think sg_next should be implemented:
> 
>   */
>  static inline struct scatterlist *sg_next(struct scatterlist *sg)
>  {
> +#ifdef CONFIG_DEBUG_SG
> +	BUG_ON(sg->sg_magic != SG_MAGIC);
> +#endif
> +	if (sg_is_last(sg))
> +		return NULL;
> +
>  	sg++;
>  
>  	if (unlikely(sg_is_chain(sg)))
>  		sg = sg_chain_ptr(sg);
>  
>  	return sg;
>  }

Yep, thanks for catching that!

-- 
Jens Axboe

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