ACK/Cmnt: [SRU][J:linux-bluefield][PATCH v1 1/1] tcp: fix forever orphan socket caused by tcp_abort

[John Cabaj]

On 7/6/25 7:47 AM, Stav Aviram wrote:
> From: Xueming Feng <kuro at kuroa.me>
> 
> BugLink: https://bugs.launchpad.net/bugs/2114965

This bug is currently targeting the Ubuntu package more broadly. I 
imagine there's a bluefield kernel that this should be targeting, with 
Jammy set as the targeted series.

> 
> We have some problem closing zero-window fin-wait-1 tcp sockets in our
> environment. This patch come from the investigation.
> 
> Previously tcp_abort only sends out reset and calls tcp_done when the
> socket is not SOCK_DEAD, aka orphan. For orphan socket, it will only
> purging the write queue, but not close the socket and left it to the
> timer.
> 
> While purging the write queue, tp->packets_out and sk->sk_write_queue
> is cleared along the way. However tcp_retransmit_timer have early
> return based on !tp->packets_out and tcp_probe_timer have early
> return based on !sk->sk_write_queue.
> 
> This caused ICSK_TIME_RETRANS and ICSK_TIME_PROBE0 not being resched
> and socket not being killed by the timers, converting a zero-windowed
> orphan into a forever orphan.
> 
> This patch removes the SOCK_DEAD check in tcp_abort, making it send
> reset to peer and close the socket accordingly. Preventing the
> timer-less orphan from happening.
> 
> According to Lorenzo's email in the v1 thread, the check was there to
> prevent force-closing the same socket twice. That situation is handled
> by testing for TCP_CLOSE inside lock, and returning -ENOENT if it is
> already closed.
> 
> The -ENOENT code comes from the associate patch Lorenzo made for
> iproute2-ss; link attached below, which also conform to RFC 9293.
> 
> At the end of the patch, tcp_write_queue_purge(sk) is removed because it
> was already called in tcp_done_with_error().
> 
> p.s. This is the same patch with v2. Resent due to mis-labeled "changes
> requested" on patchwork.kernel.org.
> 
> Link: https://patchwork.ozlabs.org/project/netdev/patch/1450773094-7978-3-git-send-email-lorenzo@google.com/
> Fixes: c1e64e298b8c ("net: diag: Support destroying TCP sockets.")
> Signed-off-by: Xueming Feng <kuro at kuroa.me>
> Tested-by: Lorenzo Colitti <lorenzo at google.com>
> Reviewed-by: Jason Xing <kerneljasonxing at gmail.com>
> Reviewed-by: Eric Dumazet <edumazet at google.com>
> Link: https://patch.msgid.link/20240826102327.1461482-1-kuro@kuroa.me
> Signed-off-by: Jakub Kicinski <kuba at kernel.org>
> (backported from commit bac76cf89816bff06c4ec2f3df97dc34e150a1c4)
> Signed-off-by: Stav Aviram <saviram at nvidia.com>

The comments surrounding the backport context should follow the SHA, and 
the sign off tag following the rest. Please re-order once the patch is 
applied.

> [The conflict arose due to differences in error handling and logging
> around tcp_send_active_reset(). The if (!sock_flag(sk, SOCK_DEAD)) check
> was removed as in the upstream, while preserving the surrounding logic
> from HEAD. In addition, !has_current_bpf_ctx() was replaced with
> !current->bpf_ctx for compatibility, as the helper is unavailable in
> this kernel version.]
> ---
>   net/ipv4/tcp.c | 16 ++++++++++------
>   1 file changed, 10 insertions(+), 6 deletions(-)
> 
> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index c1e624ca6a25..200dedcb24ac 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -4504,6 +4504,13 @@ int tcp_abort(struct sock *sk, int err)
>   	/* Don't race with userspace socket closes such as tcp_close. */
>   	lock_sock(sk);
>   
> +	/* Avoid closing the same socket twice. */
> +	if (sk->sk_state == TCP_CLOSE) {
> +		if (!current->bpf_ctx)
> +			release_sock(sk);
> +		return -ENOENT;
> +	}
> +
>   	if (sk->sk_state == TCP_LISTEN) {
>   		tcp_set_state(sk, TCP_CLOSE);
>   		inet_csk_listen_stop(sk);
> @@ -4513,15 +4520,12 @@ int tcp_abort(struct sock *sk, int err)
>   	local_bh_disable();
>   	bh_lock_sock(sk);
>   
> -	if (!sock_flag(sk, SOCK_DEAD)) {
> -		if (tcp_need_reset(sk->sk_state))
> -			tcp_send_active_reset(sk, GFP_ATOMIC);
> -		tcp_done_with_error(sk, err);
> -	}
> +	if (tcp_need_reset(sk->sk_state))
> +		tcp_send_active_reset(sk, GFP_ATOMIC);
> +	tcp_done_with_error(sk, err);
>   
>   	bh_unlock_sock(sk);
>   	local_bh_enable();
> -	tcp_write_queue_purge(sk);
>   	release_sock(sk);
>   	return 0;
>   }

Acked-by: John Cabaj <john.cabaj at canonical.com>