Re: [Xen-devel] [PATCH v2 3/4] xen-blkback: check the number of iovecs before allocating a bios

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Sat, Jun 22, 2013 at 09:59:17AM +0200, Roger Pau Monne wrote:
> With the introduction of indirect segments we can receive requests
> with a number of segments bigger than the maximum number of allowed
> iovecs in a bios, so make sure that blkback doesn't try to allocate a
> bios with more iovecs than BIO_MAX_PAGES

Shouldn't we just gate the feature-indirect-descriptor value to
take this into account?

What happens if the nseg is > BIO_MAX_PAGES? Do we "lose" the request
for the remaining segments?

> 
> Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> ---
>  drivers/block/xen-blkback/blkback.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/blkback.c 
> b/drivers/block/xen-blkback/blkback.c
> index d622d86..b3897f5d 100644
> --- a/drivers/block/xen-blkback/blkback.c
> +++ b/drivers/block/xen-blkback/blkback.c
> @@ -1236,7 +1236,8 @@ static int dispatch_rw_block_io(struct xen_blkif *blkif,
>                                    seg[i].nsec << 9,
>                                    seg[i].offset) == 0)) {
>  
> -                     bio = bio_alloc(GFP_KERNEL, nseg-i);
> +                     int nr_iovecs = min_t(int, (nseg-i), BIO_MAX_PAGES);
> +                     bio = bio_alloc(GFP_KERNEL, nr_iovecs);
>                       if (unlikely(bio == NULL))
>                               goto fail_put_bio;
>  
> -- 
> 1.7.7.5 (Apple Git-26)
> 

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