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

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Date:	Thu, 18 Oct 2007 05:32:11 -0400
From:	Jeff Garzik <jeff@...zik.org>
To:	Jens Axboe <jens.axboe@...cle.com>
CC:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [bug] ata subsystem related crash with latest -git

Jens Axboe wrote:
> The sata_mv construct looks a bit odd. Does this work? That last

The sata_mv construct worked just fine before sg chaining :)


> end_mv_sg test should always be true, just being paranoid...
> 
> diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
> index 4df8311..5397eea 100644
> --- a/drivers/ata/sata_mv.c
> +++ b/drivers/ata/sata_mv.c
> @@ -1138,8 +1138,9 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
>  {
>  	struct mv_port_priv *pp = qc->ap->private_data;
>  	struct scatterlist *sg;
> -	struct mv_sg *mv_sg;
> +	struct mv_sg *mv_sg, *end_mv_sg;
>  
> +	end_mv_sg = NULL;
>  	mv_sg = pp->sg_tbl;
>  	ata_for_each_sg(sg, qc) {
>  		dma_addr_t addr = sg_dma_address(sg);
> @@ -1158,14 +1159,12 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
>  
>  			sg_len -= len;
>  			addr += len;
> -
> -			if (!sg_len && ata_sg_is_last(sg, qc))
> -				mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
> -
> +			end_mv_sg = mv_sg;
>  			mv_sg++;
>  		}
> -
>  	}
> +	if (end_mv_sg)
> +		end_mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
>  }
>  

I'm testing a similar patch based on ata_fill_sg()'s method, which 
basically does something similar to what you've done here (see 
attached).  I had noticed that ata_fill_sg() did not call ata_sg_is_last().

If this fixes the problem, I think the best solution would be to delete 
ata_sg_is_last().  In the few users that exist, we should be able to 
eliminate the test programmatically as you and ata_fill_sg() have done 
-- thereby eliminating a branch per loop in a hotpath.

Off to test the attached...  if that doesn't work I'll try your version, 
though there shouldn't be much difference.

	Jeff



View attachment "patch.sata_mv-fill-sg" of type "text/plain" (2998 bytes)