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

[Benny Halevy <bhalevy@panasas.com>]

On Oct. 18, 2007, 14:15 +0200, Jens Axboe <jens.axboe@oracle.com> wrote:
<snip>
>  /**
>   * sg_next - return the next scatterlist entry in a list
> @@ -43,10 +51,15 @@ static inline void sg_init_one(struct scatterlist *sg, const void *buf,
>   */
>  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++;

Hmm, sg_next is not supposed to return a pointer to the chain entry
itself, but rather skip it.  I think that the fix needs only
check the "last" flag before incrementing 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;
>  }
> @@ -83,6 +96,9 @@ static inline struct scatterlist *sg_last(struct scatterlist *sgl,
>  		ret = sg;
>  
>  #endif
> +#ifdef CONFIG_DEBUG_SG
> +	BUG_ON(sgl[0].sg_magic != SG_MAGIC);

can it also do BUG_ON(!sg_is_last(sg))?

> +#endif
>  	return ret;
>  }
>