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

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