[MPTCP] Re: [PATCH v3 12/13] mptcp: keep track of advertised windows right edge

[Florian Westphal <fw at strlen.de>]

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Paolo Abeni <pabeni(a)redhat.com> wrote:
> From: Florian Westphal <fw(a)strlen.de>
> 
> Before sending 'x' new bytes also check that the new snd_una would
> be within the permitted receive window.
> 
> For every ACK that also contains a DSS ack, check whether its tcp-level
> receive window would advance the current mptcp window right edge and
> update it if so.
> 
> Co-developed-by: Paolo Abeni <pabeni(a)redhat.com>
> Signed-off-by: Paolo Abeni <pabeni(a)redhat.com>
> Signed-off-by: Florian Westphal <fw(a)strlen.de>
> ---
>  net/mptcp/options.c  | 24 ++++++++++++++++++----
>  static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
>  			      struct mptcp_data_frag *dfrag,
>  			      struct mptcp_sendmsg_info *info)
>  {
>  	u64 data_seq = dfrag->data_seq + info->sent;
>  	struct mptcp_sock *msk = mptcp_sk(sk);
> +	bool zero_window_probe = false;
>  	struct mptcp_ext *mpext = NULL;
>  	struct sk_buff *skb, *tail;
>  	bool can_collapse = false;
> @@ -950,6 +976,14 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
>  			avail_size = info->size_goal - skb->len;
>  	}
>  
> +	/* Zero window and all data acked? Probe. */
> +	avail_size = mptcp_check_allowed_size(msk, data_seq, avail_size);
> +	if (avail_size == 0 && atomic64_read(&msk->snd_una) == msk->snd_nxt) {

This needs to check "!skb" (or !mpext) as well, now that this is not connected to
previous conditional anymore.

> @@ -973,6 +1007,7 @@ static int mptcp_sendmsg_frag(struct sock *sk, struct sock *ssk,
>  	if (mpext && tail && mpext == skb_ext_find(tail, SKB_EXT_MPTCP)) {
>  		WARN_ON_ONCE(!can_collapse);
>  		mpext->data_len += ret;
> +		WARN_ON_ONCE(zero_window_probe);

I saw this trigger right now during a test run, should not happen
anymore after adding the check.