Re: [PATCH mptcp-next 1/2] Squash to "mptcp: explicitly drop over memory limits"

[Matthieu Baerts <matttbe@kernel.org>]

Hello,

On 31/07/2026 11:23, Matthieu Baerts (NGI0) wrote:
> Address comments from Clashiko [1]:
> 
> - mib: typo: "constrains" -> "constraints".
> 
> - mptcp_over_limit: precise it is not only 0-win, but retrans, dup or
>   old acks.
> 
> - mptcp_over_limit: bump LINUX_MIB_TCPRCVQDROP, as previously discussed
>   in [2].
> 
> Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260724-net-next-mptcp-oooq-pruning-v1-0-5dd4dec63a54%40kernel.org?part=3 [1]
> Link: https://lore.kernel.org/b5244dd4-205d-4abd-8ea5-fd879a97038f@redhat.com
> Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
> ---
>  net/mptcp/mib.h     | 2 +-
>  net/mptcp/options.c | 6 +++++-
>  2 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
> index 18f35f7e0a2d..25f360724c57 100644
> --- a/net/mptcp/mib.h
> +++ b/net/mptcp/mib.h
> @@ -89,7 +89,7 @@ enum linux_mptcp_mib_field {
>  	MPTCP_MIB_FALLBACKFAILED,	/* Can't fallback due to msk status */
>  	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
>  	MPTCP_MIB_BACKLOGDROP,		/* Backlog over memory limit */
> -	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constrains */
> +	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constraints */
>  	MPTCP_MIB_OFO_PRUNED,		/* MPTCP-level OoO queue pruned */
>  	__MPTCP_MIB_MAX
>  };
> diff --git a/net/mptcp/options.c b/net/mptcp/options.c
> index d6b009319839..23503984a084 100644
> --- a/net/mptcp/options.c
> +++ b/net/mptcp/options.c
> @@ -1193,7 +1193,7 @@ static bool mptcp_over_limit(struct sock *sk, struct sock *ssk,
>  	if (likely(mem <= READ_ONCE(sk->sk_rcvbuf)))
>  		return false;
>  
> -	/* Avoid silently dropping pure acks, fin or zero win probes. */
> +	/* Avoid silently dropping pure acks, fin or already-acked segments. */
>  	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq ||
>  	    TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN ||
>  	    !after(TCP_SKB_CB(skb)->end_seq, tcp_sk(ssk)->rcv_nxt))
> @@ -1202,6 +1202,10 @@ static bool mptcp_over_limit(struct sock *sk, struct sock *ssk,
>  	/* Dropped due to memory constraints, schedule an ack. */
>  	inet_csk(ssk)->icsk_ack.pending |= ICSK_ACK_NOMEM | ICSK_ACK_NOW;
>  	inet_csk_schedule_ack(ssk);
> +
> +	/* In fallback mode: skb is dropped before the TCP recv queue. */
> +	MPTCP_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);

Arf, it should be NET_INC_STATS(), not the MPTCP version: I changed to
LINUX_MIB_TCPRCVQDROP just before sending the patches, without checking
in between...

Sorry for the noise, v2 is coming.

> +
>  	return true;
>  }
>  
> 

Cheers,
Matt
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