On Fri, 2017-05-05 at 08:57 +0530, Anand H. Krishnan wrote:
> Hello,
>
> Is skb_gro_receive doing the right thing for cloned packets?
>
> When we are merging fragments, we do not seem to be taking a reference
> to the underlying page. To me, it looks like it should work fine for
> non-cloned
> packets. However, for cloned packets, when the gro-ed packet is eventually
> freed (because the original skb was not cloned and hence reference was 1),
> the merged skb's frags also get freed (put_page-ed) without taking into
> account
> the other references that were held for the fragments (dataref).
>
> We saw crashes because of this behavior. Our setup had a third party kernel
> forwarding module which uses GRO (napi_gro_receive). Doing iperf3 with small
> packets and doing tcpdump on the receiving tap interface results in the
> problem.
> With DEBUG_VM enabled, put page crashes. Without DEBUG_VM, bad page
> state results.
Yep, GRO must not be used with cloned skb.
This is why gro_cells_receive() has this check :
if (!gcells->cells || skb_cloned(skb) || netif_elide_gro(dev))
return netif_rx(skb);
(But not the main napi_gro_receive() that is supposed to be used by
driver before any tap)
