[PATCH mptcp-next v2 0/5] Fix socket options used by NVMe over MPTCP

[PATCH mptcp-next v2 0/5] Fix socket options used by NVMe over MPTCP

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

NVMe over MPTCP relies on SO_LINGER, SO_PRIORITY, SO_REUSEADDR, TCP_SYNCNT,
TCP_NODELAY, IP_TOS, and SO_BINDTODEVICE. This series contains fixes to
make all of them work correctly. Patch 4 is a cleanup needed by patch 5.

v2:
 - Drop "mptcp: don't reset dst when setting default 0 tos"
   and "selftests: mptcp: sockopt: cover LINGER, REUSEADDR,
   PRIORITY, NODELAY, SYNCNT": the 'if (val > 0)' guard
   blocked the legitimate "reset to 0" path, and the test
   only ran val_in=1, missing the SK_CAN_REUSE "any non-zero
   -> 1" normalization.
 - mptcp: bump setsockopt_seq for subflow-only socket options,
   so secondary subflows created via MP_JOIN re-sync
   sk_reuse / sk_reuseport / sk_bound_dev_if from msk.
 - mptcp: copy the subflow's TOS to the msk on accept
   (alongside the existing ssk->rcv_tos copy), so MP_JOIN'd
   subflows inherit the reflected outgoing TOS.
 - mptcp: propagate sk_reuseport to subflows via
   sync_socket_options, so secondary subflows inherit
   SO_REUSEPORT, not just SO_REUSEADDR.
 - mptcp: tighten TCP_SYNCNT bounds check
   ('val < 1 || val > MAX_TCP_SYNCNT'), so out-of-bounds
   values are rejected even when msk has no subflows yet
   (where __mptcp_setsockopt_set_val would otherwise return 0
   without invoking the set_val callback).

v1:
 - https://patchwork.kernel.org/project/mptcp/cover/cover.1784985085.git.tanggeliang@kylinos.cn/

Geliang Tang (5):
  mptcp: copy the subflow's tos to the msk on accept
  mptcp: inherit sk_reuse/sk_reuseport on subflow creation
  mptcp: bump setsockopt_seq for subflow-only socket options
  mptcp: handle TCP_MAXSEG getsockopt in common case
  mptcp: add TCP_SYNCNT setsockopt/getsockopt

 net/mptcp/protocol.c |  3 +++
 net/mptcp/sockopt.c  | 35 ++++++++++++++++++++++++++++++++---
 2 files changed, 35 insertions(+), 3 deletions(-)

-- 
2.53.0

[PATCH mptcp-next v2 1/5] mptcp: copy the subflow's tos to the msk on accept

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

mptcp_sk_clone_init() now copies both inet->tos and inet->rcv_tos
from the first subflow onto the accepted msk, mirroring plain TCP's
tcp_v4_syn_recv_sock() which sets both fields from ip_hdr(skb)->tos on
the accepted socket. Without this, MP_JOIN'd subflows would inherit
tos=0 from the msk and lose the peer's reflected value.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/protocol.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index 954e20bb27de..1152f1d0c24f 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -3699,6 +3699,9 @@ struct sock *mptcp_sk_clone_init(const struct sock *sk,
 #endif
 		mptcp_copy_ip_options(nsk, sk);
 
+	inet_sk(nsk)->rcv_tos = inet_sk(ssk)->rcv_tos;
+	inet_sk(nsk)->tos = inet_sk(ssk)->tos;
+
 	msk = mptcp_sk(nsk);
 	WRITE_ONCE(msk->local_key, subflow_req->local_key);
 	WRITE_ONCE(msk->token, subflow_req->token);
-- 
2.53.0

[PATCH mptcp-next v2 2/5] mptcp: inherit sk_reuse/sk_reuseport on subflow creation

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

Propagate sk_reuse and sk_reuseport from the MPTCP master socket to
newly-created subflows in sync_socket_options(), mirroring how sk_reuse
and sk_reuseport are already handled for the subflow.

Without this, a subflow started after the master toggled SO_REUSEADDR
or SO_REUSEPORT would not inherit the setting, leading to inconsistent
reuse semantics between msk and ssk.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/sockopt.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index fcf6feb2a9eb..dc1ef52c2200 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1601,6 +1601,9 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
 	inet_assign_bit(FREEBIND, ssk, inet_test_bit(FREEBIND, sk));
 	inet_assign_bit(BIND_ADDRESS_NO_PORT, ssk, inet_test_bit(BIND_ADDRESS_NO_PORT, sk));
 	WRITE_ONCE(inet_sk(ssk)->local_port_range, READ_ONCE(inet_sk(sk)->local_port_range));
+
+	ssk->sk_reuse = sk->sk_reuse;
+	ssk->sk_reuseport = sk->sk_reuseport;
 }
 
 void mptcp_sockopt_sync_locked(struct mptcp_sock *msk, struct sock *ssk)
-- 
2.53.0

[PATCH mptcp-next v2 3/5] mptcp: bump setsockopt_seq for subflow-only socket options

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

mptcp_setsockopt_sol_socket()'s SO_REUSEPORT/SO_REUSEADDR/SO_BINDTODEVICE
/SO_BINDTOIFINDEX case applies the option to the nmpc subflow and copies
the result back onto msk, then early-returns without calling
sockopt_seq_inc(msk).

That leaves msk->setsockopt_seq unchanged, so any subflow created later
(e.g. via MP_JOIN) inherits the master socket's seq at creation time, and
mptcp_sockopt_sync_locked() sees 'seq matches' and skips
sync_socket_options() entirely. As a result, the new subflow's sk_reuse
/sk_reuseport/sk_bound_dev_if stay at the listener's default of 0 even
though the nmpc subflow (and msk) have the right value.

Bump the seq on this path so secondary subflows trigger the sync on join.
The actual field propagation lives in sync_socket_options(); this commit
only flips the trigger.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/sockopt.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index dc1ef52c2200..37e65923f544 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -326,6 +326,8 @@ static int mptcp_setsockopt_sol_socket(struct mptcp_sock *msk, int optname,
 				sk->sk_bound_dev_if = ssk->sk_bound_dev_if;
 			else if (optname == SO_BINDTOIFINDEX)
 				sk->sk_bound_dev_if = ssk->sk_bound_dev_if;
+
+			sockopt_seq_inc(msk);
 		}
 		release_sock(sk);
 		return ret;
-- 
2.53.0

[PATCH mptcp-next v2 4/5] mptcp: handle TCP_MAXSEG getsockopt in common case

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

The TCP_MAXSEG getsockopt() case was a tail-clause returning
mptcp_getsockopt_first_sf_only() while every other "first subflow
only" option (TCP_FASTOPEN_*) was already grouped in the common
case. Move it next to its peers so the dispatch reads uniformly.

No behavioural change; the lookup still returns the cached MSS
on the first subflow.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/sockopt.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 37e65923f544..34f6cd9c7967 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -1425,6 +1425,7 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 	case TCP_FASTOPEN_CONNECT:
 	case TCP_FASTOPEN_KEY:
 	case TCP_FASTOPEN_NO_COOKIE:
+	case TCP_MAXSEG:
 		return mptcp_getsockopt_first_sf_only(msk, SOL_TCP, optname,
 						      optval, optlen);
 	case TCP_INQ:
@@ -1449,9 +1450,6 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 		return mptcp_put_int_option(msk, optval, optlen, msk->notsent_lowat);
 	case TCP_IS_MPTCP:
 		return mptcp_put_int_option(msk, optval, optlen, 1);
-	case TCP_MAXSEG:
-		return mptcp_getsockopt_first_sf_only(msk, SOL_TCP, optname,
-						      optval, optlen);
 	}
 	return -EOPNOTSUPP;
 }
-- 
2.53.0

[PATCH mptcp-next v2 5/5] mptcp: add TCP_SYNCNT setsockopt/getsockopt

[Geliang Tang]

From: Geliang Tang <tanggeliang@kylinos.cn>

Surface TCP_SYNCNT to userspace on the MPTCP master socket.

setsockopt(TCP_SYNCNT) validates the value via __mptcp_setsockopt_set_val()
and stores it in inet_csk(sk)->icsk_syn_retries on the msk. getsockopt()
reads the same field back.

A newly created subflow picks up the master socket's syn_retries through
sync_socket_options(), so the setting takes effect for outgoing SYNs
without further plumbing.

Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
---
 net/mptcp/sockopt.c | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 34f6cd9c7967..6e4c5b5314af 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -898,6 +898,23 @@ static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 		ret = mptcp_setsockopt_all_sf(msk, SOL_TCP, optname, optval,
 					      optlen);
 		break;
+	case TCP_SYNCNT: {
+		int syncnt;
+
+		if (val < 1 || val > MAX_TCP_SYNCNT) {
+			ret = -EINVAL;
+			break;
+		}
+
+		syncnt = val;
+		ret = __mptcp_setsockopt_set_val(msk, MAX_TCP_SYNCNT,
+						 &tcp_sock_set_syncnt,
+						 &syncnt,
+						 val);
+		if (ret == 0)
+			inet_csk(sk)->icsk_syn_retries = syncnt;
+		break;
+	}
 	default:
 		ret = -ENOPROTOOPT;
 	}
@@ -1450,6 +1467,10 @@ static int mptcp_getsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 		return mptcp_put_int_option(msk, optval, optlen, msk->notsent_lowat);
 	case TCP_IS_MPTCP:
 		return mptcp_put_int_option(msk, optval, optlen, 1);
+	case TCP_SYNCNT:
+		return mptcp_put_int_option(msk, optval, optlen,
+					    inet_csk(sk)->icsk_syn_retries ? :
+					    READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_syn_retries));
 	}
 	return -EOPNOTSUPP;
 }
@@ -1604,6 +1625,11 @@ static void sync_socket_options(struct mptcp_sock *msk, struct sock *ssk)
 
 	ssk->sk_reuse = sk->sk_reuse;
 	ssk->sk_reuseport = sk->sk_reuseport;
+	if (inet_csk(sk)->icsk_syn_retries > 0) {
+		if (tcp_sock_set_syncnt(ssk, inet_csk(sk)->icsk_syn_retries))
+			pr_warn("Failed to sync TCP_SYNCNT=%u to subflow\n",
+				inet_csk(sk)->icsk_syn_retries);
+	}
 }
 
 void mptcp_sockopt_sync_locked(struct mptcp_sock *msk, struct sock *ssk)
-- 
2.53.0

Re: [PATCH mptcp-next v2 0/5] Fix socket options used by NVMe over MPTCP

[MPTCP CI]

Hi Geliang,

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/30195236916

Initiator: Patchew Applier
Commits: https://github.com/multipath-tcp/mptcp_net-next/commits/006edc38647a
Patchwork: https://patchwork.kernel.org/project/mptcp/list/?series=1134602


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)