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

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

[Matthieu Baerts (NGI0)]

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) <matttbe@kernel.org>
---
Changes in v2:
- patch 1: s/MPTCP_INC_STATS/NET_INC_STATS/
- Link to v1: https://patch.msgid.link/20260731-mptcp-squash-ooo-pruning-v1-0-a5f5115e1e24@kernel.org

---
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) <matttbe@kernel.org>

[PATCH mptcp-next v2 1/2] Squash to "mptcp: explicitly drop over memory limits"

[Matthieu Baerts (NGI0)]

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..7c0bce3780c5 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. */
+	NET_INC_STATS(sock_net(sk), LINUX_MIB_TCPRCVQDROP);
+
 	return true;
 }
 

-- 
2.53.0

[PATCH mptcp-next v2 2/2] Squash to "mptcp: implemented OoO queue pruning"

[Matthieu Baerts (NGI0)]

Uniform the new counter with the other OFO ones.

Link: https://netdev-ai.bots.linux.dev/sashiko/#/patchset/20260724-net-next-mptcp-oooq-pruning-v1-0-5dd4dec63a54%40kernel.org?part=5
Signed-off-by: Matthieu Baerts (NGI0) <matttbe@kernel.org>
---
 net/mptcp/mib.c      | 2 +-
 net/mptcp/mib.h      | 2 +-
 net/mptcp/protocol.c | 2 +-
 3 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/net/mptcp/mib.c b/net/mptcp/mib.c
index d9bd4f4afcc0..2569385bab7c 100644
--- a/net/mptcp/mib.c
+++ b/net/mptcp/mib.c
@@ -87,7 +87,7 @@ static const struct snmp_mib mptcp_snmp_list[] = {
 	SNMP_MIB_ITEM("WinProbe", MPTCP_MIB_WINPROBE),
 	SNMP_MIB_ITEM("BacklogDrop", MPTCP_MIB_BACKLOGDROP),
 	SNMP_MIB_ITEM("RcvPruned", MPTCP_MIB_RCVPRUNED),
-	SNMP_MIB_ITEM("OfoPruned", MPTCP_MIB_OFO_PRUNED),
+	SNMP_MIB_ITEM("OFOPruned", MPTCP_MIB_OFOPRUNED),
 };
 
 /* mptcp_mib_alloc - allocate percpu mib counters
diff --git a/net/mptcp/mib.h b/net/mptcp/mib.h
index 25f360724c57..3a3425e258a7 100644
--- a/net/mptcp/mib.h
+++ b/net/mptcp/mib.h
@@ -90,7 +90,7 @@ enum linux_mptcp_mib_field {
 	MPTCP_MIB_WINPROBE,		/* MPTCP-level zero window probe */
 	MPTCP_MIB_BACKLOGDROP,		/* Backlog over memory limit */
 	MPTCP_MIB_RCVPRUNED,		/* Dropped due to memory constraints */
-	MPTCP_MIB_OFO_PRUNED,		/* MPTCP-level OoO queue pruned */
+	MPTCP_MIB_OFOPRUNED,		/* MPTCP-level OoO queue pruned */
 	__MPTCP_MIB_MAX
 };
 
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 90dc894cb976..f387f24904da 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -416,7 +416,7 @@ static bool mptcp_prune_ofo_queue(struct sock *sk, u64 seq)
 	} while (node);
 
 	if (pruned)
-		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFO_PRUNED);
+		MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_OFOPRUNED);
 
 out:
 	mem = (unsigned int)sk_rmem_alloc_get(sk);

-- 
2.53.0

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

[MPTCP CI]

Hi Matthieu,

Thank you for your modifications, that's great!

Our CI did some validations and here is its report:

- KVM Validation: normal (except selftest_mptcp_join): Success! ✅
- KVM Validation: normal (only selftest_mptcp_join): Success! ✅
- KVM Validation: debug (except selftest_mptcp_join): Success! ✅
- KVM Validation: debug (only selftest_mptcp_join): Success! ✅
- KVM Validation: btf-normal (only bpftest_all): Success! ✅
- KVM Validation: btf-debug (only bpftest_all): Success! ✅
- Task: https://github.com/multipath-tcp/mptcp_net-next/actions/runs/30624237503

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/94cf0d3c0576
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1138063


If there are some issues, you can reproduce them using the same environment as
the one used by the CI thanks to a docker image, e.g.:

    $ cd [kernel source code]
    $ docker run -v "${PWD}:${PWD}:rw" -w "${PWD}" --privileged --rm -it \
        --pull always mptcp/mptcp-upstream-virtme-docker:latest \
        auto-normal

For more details:

    https://github.com/multipath-tcp/mptcp-upstream-virtme-docker


Please note that despite all the efforts that have been already done to have a
stable tests suite when executed on a public CI like here, it is possible some
reported issues are not due to your modifications. Still, do not hesitate to
help us improve that ;-)

Cheers,
MPTCP GH Action bot
Bot operated by Matthieu Baerts (NGI0 Core)

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

[Geliang Tang]

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) <matttbe@kernel.org>

v2 looks good to me!

    Reviewed-by: Geliang Tang <geliang@kernel.org>

Thanks,
-Geliang

> ---
> Changes in v2:
> - patch 1: s/MPTCP_INC_STATS/NET_INC_STATS/
> - Link to v1:
> https://patch.msgid.link/20260731-mptcp-squash-ooo-pruning-v1-0-a5f5115e1e24@kernel.org
> 
> ---
> 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) <matttbe@kernel.org>
> 

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

[Matthieu Baerts]

Hi Geliang,

On 31/07/2026 14:22, Geliang Tang wrote:
> 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.

(...)

> v2 looks good to me!
> 
>     Reviewed-by: Geliang Tang <geliang@kernel.org>

Thanks!

Now in our tree:

- 49287a4134e2: "squashed" (with conflicts) in "mptcp: explicitly drop
over memory limits"
- 286cb9242882: mptcp: more precise comment for TCPRCVQDROP
- 555d2505efd7: conflict in t/mptcp-implemented-OoO-queue-pruning
- 56f9f21024c6: "squashed" patch 2/2 in "mptcp: implemented OoO queue
pruning"
- Results: 3a875e9130e6..e5730411f842 (export)

Tests are now in progress:

- export:
https://github.com/multipath-tcp/mptcp_net-next/commit/43b421437483dba551b2a21907703aea295b02c0/checks

Cheers,
Matt
-- 
Sponsored by the NGI0 Core fund.