netdev - Re: [PATCH net,v3] tcp: fix forever orphan socket caused by tcp

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Message-ID: <CANn89iJqQXauMy9mWf7Y5LFNPwtxpfsgpJJtU83OFrzpomYZZQ@mail.gmail.com>
Date: Mon, 26 Aug 2024 14:11:42 +0200
From: Eric Dumazet <edumazet@...gle.com>
To: Xueming Feng <kuro@...oa.me>
Cc: "David S . Miller" <davem@...emloft.net>, netdev@...r.kernel.org, 
	Lorenzo Colitti <lorenzo@...gle.com>, Jason Xing <kerneljasonxing@...il.com>, 
	Paolo Abeni <pabeni@...hat.com>, Jakub Kicinski <kuba@...nel.org>, 
	Neal Cardwell <ncardwell@...gle.com>, Yuchung Cheng <ycheng@...gle.com>, 
	Soheil Hassas Yeganeh <soheil@...gle.com>, David Ahern <dsahern@...nel.org>, linux-kernel@...r.kernel.org, 
	bpf@...r.kernel.org
Subject: Re: [PATCH net,v3] tcp: fix forever orphan socket caused by tcp_abort

On Mon, Aug 26, 2024 at 12:23 PM Xueming Feng <kuro@...oa.me> wrote:
>
> 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@...oa.me>
> Tested-by: Lorenzo Colitti <lorenzo@...gle.com>
> Reviewed-by: Jason Xing <kerneljasonxing@...il.com>

Reviewed-by: Eric Dumazet <edumazet@...gle.com>