Re: [PATCH net 01/14] mptcp: do not reschedule the RTX timer for fallback sockets

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [High] MPTCP_RTX_DISABLED is set on TCP_CLOSE but never cleared if a connection fails synchronously, permanently disabling retransmissions if the socket is retried.
--

--- Patch [1]: [PATCH net 01/14] mptcp: do not reschedule the RTX timer for fallback sockets ---
commit e15c87662e83ee7836d581b8ebc2d5e99a964d98
Author: Paolo Abeni <pabeni@redhat.com>

mptcp: do not reschedule the RTX timer for fallback sockets

This commit stops the MPTCP core from rescheduling the retransmission timer
for fallback sockets. It uses a new flag bit MPTCP_RTX_DISABLED to prevent
rescheduling during fallback and when transitioning to TCP_CLOSE.

> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index b474d03620a75..23dde0b7144bb 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
[ ... ]
> @@ -3324,6 +3326,9 @@ void mptcp_set_state(struct sock *sk, int state)
>  		 * transition from TCP_SYN_RECV to TCP_CLOSE_WAIT.
>  		 */
>  		break;
> +	case TCP_CLOSE:
> +		set_bit(MPTCP_RTX_DISABLED, &mptcp_sk(sk)->flags);
> +		fallthrough;

[Severity: High]
Does this permanently disable retransmissions if a socket is reused after a
failed connect?

If an application calls connect() and it fails synchronously (for example,
connection refused), mptcp_connect() handles the error by calling
mptcp_set_state(sk, TCP_CLOSE). This sets the MPTCP_RTX_DISABLED flag.

If the application then retries connect() on the same socket, mptcp_connect()
transitions the socket to TCP_SYN_SENT but never clears the sticky
MPTCP_RTX_DISABLED flag.

Because the flag remains set, mptcp_reset_rtx_timer() will permanently abort
arming the retransmission timer for this socket, which could cause the
reused connection to hang indefinitely upon packet loss.

>  	default:
>  		if (oldstate == TCP_ESTABLISHED || oldstate == TCP_CLOSE_WAIT)
>  			MPTCP_DEC_STATS(sock_net(sk), MPTCP_MIB_CURRESTAB);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260824-net-mptcp-misc-fixes-7-3-rc1-v1-0-a92309d121ca@kernel.org?part=1