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FAILED: patch "[PATCH] mptcp: do not reschedule the RTX timer for fallback sockets" failed to apply to 6.6-stable tree

PATCH New [email protected] 2 participants 2 messages Sep 16 – Sep 17

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#0 lore raw

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x e2ab913f68c7d11e2561b8a8ad0b87ffefcad667
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2026091614-winking-gigahertz-a159@gregkh' --subject-prefix 'PATCH 6.6.y' 'HEAD^..'

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From e2ab913f68c7d11e2561b8a8ad0b87ffefcad667 Mon Sep 17 00:00:00 2001
From: Paolo Abeni <[email protected]>
Date: Tue, 8 Sep 2026 16:07:06 +0200
Subject: [PATCH] mptcp: do not reschedule the RTX timer for fallback sockets

On fallback socket the retrans timer is a quite convoluted no-op, but currently nothing prevents the MPTCP core to keep rescheduling it.

Additionally gate RTX timer reset to the msk not being fallen back to TCP yet. To avoid adding multiple tests in fast-path, use a new flags bit for such condition.

The RTX enable bit is clear at close time and set before the msk could start retransmitting, with a couple of caveats:

- passive sockets inherit the bit from the listener msk; set the bit on such socket to avoid flipping it in the fast-path, even if the listener will obviously never retransmit.

- while fastopening (MPTFO), mptcp_sendmsg_fastopen still ends-up calling mptcp_connect via tcp_sendmsg_fastopen -> __inet_stream_connect(ssk->sk_socket), and the first subflow's sk_socket points to the msk one.

Fixes b51f9b80c032 ("mptcp: introduce MPTCP retransmission timer")
Cc [email protected]
Signed-off-by Paolo Abeni <[email protected]>
Reviewed-by Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by Matthieu Baerts (NGI0) <[email protected]>
Link https://patch.msgid.link/20260908-net-mptcp-misc-fixes-7-3-rc1-v2-1-df1de70348b6@kernel.org open here
Signed-off-by Jakub Kicinski <[email protected]>
net/mptcp/protocol.c +10 -3
index e1f08f71cdb1..be59651e708e 100644
@@ -95,6 +95,7 @@ bool __mptcp_try_fallback(struct mptcp_sock *msk, int fb_mib)
 
 	msk->allow_subflows = false;
 	set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
+	clear_bit(MPTCP_RTX_ENABLED, &msk->flags);
 	__MPTCP_INC_STATS(net, fb_mib);
 	spin_unlock_bh(&msk->fallback_lock);
 	return true;

@@ -1084,13 +1085,14 @@ static bool mptcp_rtx_timer_pending(struct sock *sk)
 
 static void mptcp_reset_rtx_timer(struct sock *sk)
 {
+	struct mptcp_sock *msk = mptcp_sk(sk);
 	unsigned long tout;
 
-	/* prevent rescheduling on close */
-	if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
+	/* Prevent rescheduling on close and in case of fallback. */
+	if (!test_bit(MPTCP_RTX_ENABLED, &msk->flags))
 		return;
 
-	tout = mptcp_sk(sk)->timer_ival;
+	tout = msk->timer_ival;
 	sk_reset_timer(sk, &sk->mptcp_retransmit_timer, jiffies + tout);
 }
 

@@ -3323,6 +3325,9 @@ void mptcp_set_state(struct sock *sk, int state)
 		 * transition from TCP_SYN_RECV to TCP_CLOSE_WAIT.
 		 */
 		break;
+	case TCP_CLOSE:
+		clear_bit(MPTCP_RTX_ENABLED, &mptcp_sk(sk)->flags);
+		fallthrough;
 	default:
 		if (oldstate == TCP_ESTABLISHED || oldstate == TCP_CLOSE_WAIT)
 			MPTCP_DEC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);

@@ -4141,6 +4146,7 @@ static int mptcp_connect(struct sock *sk, struct sockaddr_unsized *uaddr,
 	if (IS_ERR(ssk))
 		return PTR_ERR(ssk);
 
+	set_bit(MPTCP_RTX_ENABLED, &msk->flags);
 	mptcp_set_state(sk, TCP_SYN_SENT);
 	subflow = mptcp_subflow_ctx(ssk);
 #ifdef CONFIG_TCP_MD5SIG

@@ -4288,6 +4294,7 @@ static int mptcp_listen(struct socket *sock, int backlog)
 		goto unlock;
 	}
 
+	set_bit(MPTCP_RTX_ENABLED, &msk->flags);
 	mptcp_set_state(sk, TCP_LISTEN);
 	sock_set_flag(sk, SOCK_RCU_FREE);
net/mptcp/protocol.h +1 -0
index 87ccb84e9927..2b4c27426477 100644
@@ -116,6 +116,7 @@
 #define MPTCP_WORK_RTX		1
 #define MPTCP_FALLBACK_DONE	2
 #define MPTCP_WORK_CLOSE_SUBFLOW 3
+#define MPTCP_RTX_ENABLED	4
 
 /* MPTCP socket release cb flags */
 #define MPTCP_PUSH_PENDING	1
maintainer
#1 lore raw

PATCH 1/1 mptcp: do not reschedule the RTX timer for fallback sockets

From: Paolo Abeni <[email protected]>

[ Upstream commit e2ab913f68c7d11e2561b8a8ad0b87ffefcad667 ]

On fallback socket the retrans timer is a quite convoluted no-op, but currently nothing prevents the MPTCP core to keep rescheduling it.

Additionally gate RTX timer reset to the msk not being fallen back to TCP yet. To avoid adding multiple tests in fast-path, use a new flags bit for such condition.

The RTX enable bit is clear at close time and set before the msk could start retransmitting, with a couple of caveats:

- passive sockets inherit the bit from the listener msk; set the bit on such socket to avoid flipping it in the fast-path, even if the listener will obviously never retransmit.

- while fastopening (MPTFO), mptcp_sendmsg_fastopen still ends-up calling mptcp_connect via tcp_sendmsg_fastopen -> __inet_stream_connect(ssk->sk_socket), and the first subflow's sk_socket points to the msk one.

Fixes b51f9b80c032 ("mptcp: introduce MPTCP retransmission timer")
Cc [email protected]
Signed-off-by Paolo Abeni <[email protected]>
Reviewed-by Matthieu Baerts (NGI0) <[email protected]>
Signed-off-by Matthieu Baerts (NGI0) <[email protected]>
Link https://patch.msgid.link/20260908-net-mptcp-misc-fixes-7-3-rc1-v2-1-df1de70348b6@kernel.org open here
Signed-off-by Jakub Kicinski <[email protected]>
[ changed MPTCP_RTX_ENABLED from bit 4 to unused bit 6 to avoid conflicting with MPTCP_FALLBACK_DONE. ]
Signed-off-by Sasha Levin <[email protected]>
---
 net/mptcp/protocol.c | 12 +++++++++---
 net/mptcp/protocol.h |  2 ++
 2 files changed, 11 insertions(+), 3 deletions(-)
net/mptcp/protocol.c +9 -3
index 127438ef120e6..8de25a4571201 100644
@@ -977,13 +977,14 @@ static bool mptcp_rtx_timer_pending(struct sock *sk)
 static void mptcp_reset_rtx_timer(struct sock *sk)
 {
 	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct mptcp_sock *msk = mptcp_sk(sk);
 	unsigned long tout;
 
-	/* prevent rescheduling on close */
-	if (unlikely(inet_sk_state_load(sk) == TCP_CLOSE))
+	/* Prevent rescheduling on close and in case of fallback. */
+	if (!test_bit(MPTCP_RTX_ENABLED, &msk->flags))
 		return;
 
-	tout = mptcp_sk(sk)->timer_ival;
+	tout = msk->timer_ival;
 	sk_reset_timer(sk, &icsk->icsk_retransmit_timer, jiffies + tout);
 }
 

@@ -3064,6 +3065,9 @@ void mptcp_set_state(struct sock *sk, int state)
 		 * transition from TCP_SYN_RECV to TCP_CLOSE_WAIT.
 		 */
 		break;
+	case TCP_CLOSE:
+		clear_bit(MPTCP_RTX_ENABLED, &mptcp_sk(sk)->flags);
+		fallthrough;
 	default:
 		if (oldstate == TCP_ESTABLISHED || oldstate == TCP_CLOSE_WAIT)
 			MPTCP_DEC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);

@@ -3897,6 +3901,7 @@ static int mptcp_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
 	if (IS_ERR(ssk))
 		return PTR_ERR(ssk);
 
+	set_bit(MPTCP_RTX_ENABLED, &msk->flags);
 	mptcp_set_state(sk, TCP_SYN_SENT);
 	subflow = mptcp_subflow_ctx(ssk);
 #ifdef CONFIG_TCP_MD5SIG

@@ -4040,6 +4045,7 @@ static int mptcp_listen(struct socket *sock, int backlog)
 		goto unlock;
 	}
 
+	set_bit(MPTCP_RTX_ENABLED, &msk->flags);
 	mptcp_set_state(sk, TCP_LISTEN);
 	sock_set_flag(sk, SOCK_RCU_FREE);
net/mptcp/protocol.h +2 -0
index af00d64e61f4b..511f2adf19fd8 100644
@@ -116,6 +116,7 @@
 #define MPTCP_WORK_RTX		2
 #define MPTCP_FALLBACK_DONE	4
 #define MPTCP_WORK_CLOSE_SUBFLOW 5
+#define MPTCP_RTX_ENABLED	6
 
 /* MPTCP socket release cb flags */
 #define MPTCP_PUSH_PENDING	1

@@ -1133,6 +1134,7 @@ static inline bool __mptcp_try_fallback(struct mptcp_sock *msk)
 
 	msk->allow_subflows = false;
 	set_bit(MPTCP_FALLBACK_DONE, &msk->flags);
+	clear_bit(MPTCP_RTX_ENABLED, &msk->flags);
 	spin_unlock_bh(&msk->fallback_lock);
 	return true;
 }
Signature · 1 line
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