On Thu, Jul 17, 2014 at 08:09:49PM +0100, Zoltan Kiss wrote:
> The error handling for skb's with frag_list was completely wrong, it caused
> double unmap attempts to happen if the error was on the first skb. Move it to
> the right place in the loop.
>
> Signed-off-by: Zoltan Kiss <[email protected]>
> Reported-by: Armin Zentai <[email protected]>
> Cc: [email protected]
> Cc: [email protected]
> Cc: [email protected]
> ---
> diff --git a/drivers/net/xen-netback/netback.c
> b/drivers/net/xen-netback/netback.c
> index 1844a47..604ff71 100644
> --- a/drivers/net/xen-netback/netback.c
> +++ b/drivers/net/xen-netback/netback.c
> @@ -1030,10 +1030,16 @@ static int xenvif_tx_check_gop(struct xenvif_queue
> *queue,
> {
> struct gnttab_map_grant_ref *gop_map = *gopp_map;
> u16 pending_idx = XENVIF_TX_CB(skb)->pending_idx;
> + /* This points to the shinfo of the actually checked skb, which could be
> + * either the first or the one on the frag_list
> + */
I think "checked skb" should be "skb being checked". Feel free to
disagree as I'm not native English speaker. :-/
> struct skb_shared_info *shinfo = skb_shinfo(skb);
> + /* If this is non-NULL, we are currently checking the frag_list skb, and
> + * this points to the shinfo of the first one
> + */
> + struct skb_shared_info *first_shinfo = NULL;
> int nr_frags = shinfo->nr_frags;
> int i, err;
> - struct sk_buff *first_skb = NULL;
>
> /* Check status of header. */
> err = (*gopp_copy)->status;
> @@ -1086,31 +1092,28 @@ check_frags:
> xenvif_idx_unmap(queue, pending_idx);
> }
>
> + /* And if we found the error while checking the frag_list, unmap
> + * the first skb's frags
> + */
> + if (first_shinfo) {
> + for (j = 0; j < first_shinfo->nr_frags; j++) {
> + pending_idx =
> frag_get_pending_idx(&first_shinfo->frags[j]);
> + xenvif_idx_unmap(queue, pending_idx);
> + }
> + }
> +
> /* Remember the error: invalidate all subsequent fragments. */
> err = newerr;
> }
>
> - if (skb_has_frag_list(skb)) {
> - first_skb = skb;
> - skb = shinfo->frag_list;
> - shinfo = skb_shinfo(skb);
> + if (skb_has_frag_list(skb) && !first_shinfo) {
Will it ever come to the point that we have another skb in this skb's
frag list? Is there any reason prevents you from looping over the
(possible) subsequent skbs? I guess if the error is deep in the list
it's a bit hard to bookkeep...
> + first_shinfo = skb_shinfo(skb);
> + shinfo = skb_shinfo(skb_shinfo(skb)->frag_list);
In that case I would suggest you add
BUG_ON(skb_has_frag_list(skb_shinfo(skb)->frag_list)). I think having
more nested frag_list should be a bug in current design.
Wei.
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