Re: [PATCH mptcp-next v2 0/2] Squash to "mptcp: out-of-order queue pruning"

Hi Matt,

On Fri, 2026-07-31 at 12:18 +0200, Matthieu Baerts (NGI0) wrote:
> Addressing comments reported by Clashiko [1], but not detected before
> with the AI review tools using a different model version.
> 
> Note: the last comment from the 3rd patch has not been addressed, as
> it
> is not clear to me whether this comment is valid:
> 
> ---------------------------------- 8< -------------------------------
> ---
> 
> > diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> > index 72b1fa3ca71c..5f7d8340a3d9 100644
> > --- a/net/mptcp/protocol.c
> > +++ b/net/mptcp/protocol.c
> 
> [ ... ]
> 
> > @@ -682,6 +693,16 @@ static void __mptcp_add_backlog(struct sock
> > *sk,
> >  		return;
> >  	}
> > 
> > +	/* Similar additional allowance as plain TCP. */
> > +	limit = READ_ONCE(sk->sk_rcvbuf);
> > +	limit += (limit >> 1) + 64 * 1024;
> > +	limit = min_t(u64, limit, UINT_MAX);
> > +	if (msk->backlog_len > limit &&
> > !__mptcp_check_fallback(msk)) {
> > +		__MPTCP_INC_STATS(sock_net(sk),
> > MPTCP_MIB_BACKLOGDROP);
> > +		kfree_skb_reason(skb,
> > SKB_DROP_REASON_SOCKET_BACKLOG);
> > +		return;
> > +	}
> > +
> 
> [Low]
> The check compares the current backlog_len against limit before the
> incoming skb's truesize is added (the truesize is folded in at the
> account: label further down). Was that intentional?
> TCP's sk_add_backlog() analog compares queue_size + skb->truesize
> against the limit, so a single skb can push msk->backlog_len past
> limit here and the drop only fires on the next admission. The
> overshoot
> is bounded by one skb's truesize and the commit message already notes
> "This is not a complete fix for the stall issue, as the drop strategy
> needs refinements that will come in the next patches.", so perhaps
> this
> is one of the follow-up items?
> 
> ---------------------------------- 8< -------------------------------
> ---
> 
> Link:
> https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260724-net-next-mptcp-oooq-pruning-v1-0-5dd4dec63a54%40kernel.org
> Signed-off-by: Matthieu Baerts (NGI0) <[email protected]>

v2 looks good to me!

    Reviewed-by: Geliang Tang <[email protected]>

Thanks,
-Geliang

> ---
> Changes in v2:
> - patch 1: s/MPTCP_INC_STATS/NET_INC_STATS/
> - Link to v1:
> https://patch.msgid.link/[email protected]
> 
> ---
> Matthieu Baerts (NGI0) (2):
>       Squash to "mptcp: explicitly drop over memory limits"
>       Squash to "mptcp: implemented OoO queue pruning"
> 
>  net/mptcp/mib.c      | 2 +-
>  net/mptcp/mib.h      | 4 ++--
>  net/mptcp/options.c  | 6 +++++-
>  net/mptcp/protocol.c | 2 +-
>  4 files changed, 9 insertions(+), 5 deletions(-)
> ---
> base-commit: 23c7cb4262d954b810468b0e661d48af82b418d5
> change-id: 20260730-mptcp-squash-ooo-pruning-53d668d4c2aa
> 
> Best regards,
> --  
> Matthieu Baerts (NGI0) <[email protected]>
>