Re: [Xen-devel] [PATCH 1/2] xen/blkback: Copy id field when doing BLKIF_DISCARD.

[Stefano Stabellini <stefano.stabellini@eu.citrix.com>]

On Fri, 25 May 2012, Konrad Rzeszutek Wilk wrote:
> We weren't copying the id field so when we sent the response
> back to the frontend (especially with a 64-bit host and 32-bit
> guest), we ended up using a random value. This lead to the
> frontend crashing as it would try to pass to __blk_end_request_all
> a NULL 'struct request' (b/c it would use the 'id' to find the
> proper 'struct request' in its shadow array) and end up crashing:
> 
> BUG: unable to handle kernel NULL pointer dereference at 000000e4
> IP: [<c0646d4c>] __blk_end_request_all+0xc/0x40
> .. snip..
> EIP is at __blk_end_request_all+0xc/0x40
> .. snip..
>  [<ed95db72>] blkif_interrupt+0x172/0x330 [xen_blkfront]
> 
> This fixes the bug by passing in the proper id for the response.
> 
> Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=824641
> CC: stable@kernel.org
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

Acked-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

>  drivers/block/xen-blkback/common.h |    2 ++
>  1 files changed, 2 insertions(+), 0 deletions(-)
> 
> diff --git a/drivers/block/xen-blkback/common.h b/drivers/block/xen-blkback/common.h
> index 773cf27..9ad3b5e 100644
> --- a/drivers/block/xen-blkback/common.h
> +++ b/drivers/block/xen-blkback/common.h
> @@ -257,6 +257,7 @@ static inline void blkif_get_x86_32_req(struct blkif_request *dst,
>  		break;
>  	case BLKIF_OP_DISCARD:
>  		dst->u.discard.flag = src->u.discard.flag;
> +		dst->u.discard.id = src->u.discard.id;
>  		dst->u.discard.sector_number = src->u.discard.sector_number;
>  		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
>  		break;
> @@ -287,6 +288,7 @@ static inline void blkif_get_x86_64_req(struct blkif_request *dst,
>  		break;
>  	case BLKIF_OP_DISCARD:
>  		dst->u.discard.flag = src->u.discard.flag;
> +		dst->u.discard.id = src->u.discard.id;
>  		dst->u.discard.sector_number = src->u.discard.sector_number;
>  		dst->u.discard.nr_sectors = src->u.discard.nr_sectors;
>  		break;
> -- 
> 1.7.7.6
> 
> 
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