Re: [PATCH] fix small highmem bio bounce bvec handling glitch

[Jens Axboe <axboe@suse.de>]

On Thu, Feb 26 2004, Christophe Saout wrote:
> Hi,
> 
> [Oops, forgot to Cc LKML]
> 
> while going through the bio highmem handling code I noticed a small
> glitch. __end_that_request_first might modify the bv_offset and bv_len
> if the segment was partially completed. The bio-read-bounce-back code
> should use the unmodified bv_offset when copying the segment data:
> 
> --- linux.orig/mm/highmem.c	2004-01-21 19:08:45.000000000 +0100
> +++ linux/mm/highmem.c	2004-02-26 15:47:14.574722576 +0100
> @@ -294,7 +294,12 @@
>  		if (tovec->bv_page == fromvec->bv_page)
>  			continue;
>  
> -		vfrom = page_address(fromvec->bv_page) + fromvec->bv_offset;
> +		/*
> +		 * fromvec->bv_offset and fromvec->bv_len might have been
> +		 * modified by the block layer, so use the original copy,
> +		 * bounce_copy_vec already uses tovec->bv_len
> +		 */
> +		vfrom = page_address(fromvec->bv_page) + tovec->bv_offset;
>  
>  		bounce_copy_vec(tovec, vfrom);

Irk yes, that's is pretty nasty, I really wish we could avoid screwing
with vec entries (it's pretty obscure for bio clones, too)... Fix is
correct, and good idea to add the comment!

-- 
Jens Axboe