linux-kernel - Re: [PATCH net-next v15 11/22] ovpn: implement TCP transport

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Message-ID: <Z2A3DW2GeMVzBa4R@hog>
Date: Mon, 16 Dec 2024 15:19:57 +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>,
	dsahern@...nel.org
Subject: Re: [PATCH net-next v15 11/22] ovpn: implement TCP transport

2024-12-16, 15:09:17 +0100, Antonio Quartulli wrote:
> On 16/12/2024 14:59, Sabrina Dubroca wrote:
> > 2024-12-11, 22:15:15 +0100, Antonio Quartulli wrote:
> > > +static void ovpn_tcp_close(struct sock *sk, long timeout)
> > > +{
> > > +	struct ovpn_socket *sock;
> > > +
> > > +	rcu_read_lock();
> > 
> > [can't sleep until unlock]
> > 
> > > +	sock = rcu_dereference_sk_user_data(sk);
> > > +
> > > +	strp_stop(&sock->peer->tcp.strp);
> > > +
> > > +	tcp_close(sk, timeout);
> > 
> > 
> >      void tcp_close(struct sock *sk, long timeout)
> >      {
> >      	lock_sock(sk);
> > 
> > but this can sleep.
> 
> Ouch.. I wonder why I have never seen the might_sleep() trigger this, but
> probably that's due to the fact that we hardly hit this cb in the classic
> use case.

Probably. You'd only see it when you close the TCP socket before
detaching (otherwise the close CB is restored to tcp_close), which I
guess ovpn never does.

> 
> > 
> > Is there anything that prevents delaying tcp_close until after
> > ovpn_peer_del and rcu_read_unlock?
> 
> not really.
> 
> > 
> > > +	ovpn_peer_del(sock->peer, OVPN_DEL_PEER_REASON_TRANSPORT_ERROR);
> > > +	rcu_read_unlock();
> 
> I will move the tcp_close() here.

Thanks.

-- 
Sabrina