Re: [PATCH net v1 1/2] net: gro: add flush check in udp_gro_receive_segment

[Willem de Bruijn <willemdebruijn.kernel@gmail.com>]

Richard Gobert wrote:
> GRO-GSO path is supposed to be transparent and as such L3 flush checks are
> relevant to all flows which call skb_gro_receive. This patch uses the same
> logic and code from tcp_gro_receive but in the relevant flow path in
> udp_gro_receive_segment.
> 
> Fixes: 36707061d6ba ("udp: allow forwarding of plain (non-fraglisted) UDP GRO packets")
> Signed-off-by: Richard Gobert <richardbgobert@gmail.com>

Reviewed-by: Willem de Bruijn <willemb@google.com>

> ---
>  net/ipv4/udp_offload.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/net/ipv4/udp_offload.c b/net/ipv4/udp_offload.c
> index 3498dd1d0694..1f4e08f43c4b 100644
> --- a/net/ipv4/udp_offload.c
> +++ b/net/ipv4/udp_offload.c
> @@ -471,6 +471,7 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
>  	struct sk_buff *p;
>  	unsigned int ulen;
>  	int ret = 0;
> +	int flush;
>  
>  	/* requires non zero csum, for symmetry with GSO */
>  	if (!uh->check) {
> @@ -528,7 +529,17 @@ static struct sk_buff *udp_gro_receive_segment(struct list_head *head,
>  				skb_gro_postpull_rcsum(skb, uh,
>  						       sizeof(struct udphdr));
>  
> -				ret = skb_gro_receive(p, skb);
> +				flush = NAPI_GRO_CB(p)->flush;
> +
> +				if (NAPI_GRO_CB(p)->flush_id != 1 ||
> +				    NAPI_GRO_CB(p)->count != 1 ||
> +				    !NAPI_GRO_CB(p)->is_atomic)
> +					flush |= NAPI_GRO_CB(p)->flush_id;
> +				else
> +					NAPI_GRO_CB(p)->is_atomic = false;
> +
> +				if (flush || skb_gro_receive(p, skb))
> +					ret = 1;

UDP_L4 does not have the SKB_GSO_TCP_FIXEDID that uses is_atomic as
input.

And I still don't fully internalize the flush_id logic after staring
at it for more than one coffee.

But even ignoring those, the flush signal of NAPI_GRO_CB(p)->flush
set the network layer must be followed, so ACK. Thanks for the fix.