netdev - Re: [PATCH net-next v19 00/26] Introducing OpenVPN Data Channel Offload

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Message-ID: <Z60wIRjw5Id1VTal@hog>
Date: Thu, 13 Feb 2025 00:34:57 +0100
From: Sabrina Dubroca <sd@...asysnail.net>
To: Antonio Quartulli <antonio@...nvpn.net>
Cc: netdev@...r.kernel.org, Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Donald Hunter <donald.hunter@...il.com>,
	Shuah Khan <shuah@...nel.org>, ryazanov.s.a@...il.com,
	Andrew Lunn <andrew+netdev@...n.ch>,
	Simon Horman <horms@...nel.org>, linux-kernel@...r.kernel.org,
	linux-kselftest@...r.kernel.org, Xiao Liang <shaw.leon@...il.com>,
	steffen.klassert@...unet.com, antony.antony@...unet.com,
	willemdebruijn.kernel@...il.com, David Ahern <dsahern@...nel.org>,
	Andrew Lunn <andrew@...n.ch>,
	Shuah Khan <skhan@...uxfoundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH net-next v19 00/26] Introducing OpenVPN Data Channel
 Offload

Hello,

2025-02-11, 01:39:53 +0100, Antonio Quartulli wrote:
> All minor and major reported problems have been finally addressed.
> Big thanks to Sabrina, who took the time to guide me through
> converting the peer socket to an RCU pointer.

Something is off (not sure if it's new to this version): if I use
test-tcp.sh to setup a set of interfaces and peers (I stop the test
just after setup to keep the environment alive), then remove all netns
with "ip -all netns delete", I expect all devices to go away, but they
don't. With debug messages enabled I'm seeing some activity from the
module ("tun0: sending keepalive to peer 3" and so on), and
ovpn_net_uninit/ovpn_priv_free never got called.

[...]
> So there is NO risk of deadlock (and indeed nothing hangs), but I
> couldn't find a way to make the warning go away.

I've spotted another splat on strparser cleanup that looked like an
actual deadlock, but it's not very reproducible. Still looking into
it, but I'm not convinced it's ok to call strp_done (as is done from
ovpn_tcp_socket_detach) while under lock_sock, because AFAIU
cancel_work_sync(&strp->work) may be waiting for a work that needs to
lock the socket (cb.lock in do_strp_work). I guess tcp_tx_work would
have the same problem.

-- 
Sabrina