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From: Tetsuo Handa <>
To: Guillaume Nault <>
Cc: Jakub Sitnicki <>,, "David S. Miller" <>,
	Eric Dumazet <>,
	Jakub Kicinski <>, Paolo Abeni <>,
	Tom Parkin <>,,,
Subject: Re: [PATCH net] l2tp: Don't sleep and disable BH under writer-side sk_callback_lock
Date: Tue, 22 Nov 2022 23:28:45 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <20221122141011.GA3303@pc-4.home>

On 2022/11/22 23:10, Guillaume Nault wrote:
> User space uses this socket to send and receive L2TP control packets
> (tunnel and session configuration, keep alive and tear down). Therefore
> it absolutely needs to continue using this socket after the
> registration phase.

Thank you for explanation.

>> If the userspace might continue using the socket, we would
>>   create a new socket, copy required attributes (the source and destination addresses?) from
>>   the socket fetched via sockfd_lookup(), and call replace_fd() like e.g. umh_pipe_setup() does
>> inside l2tp_tunnel_register(). i-node number of the socket would change, but I assume that
>> the process which called l2tp_tunnel_register() is not using that i-node number.
>> Since the socket is a datagram socket, I think we can copy required attributes. But since
>> I'm not familiar with networking code, I don't know what attributes need to be copied. Thus,
>> I leave implementing it to netdev people.
> That looks fragile to me. If the problem is that setup_udp_tunnel_sock()
> can sleep, we can just drop the udp_tunnel_encap_enable() call from
> setup_udp_tunnel_sock(), rename it __udp_tunnel_encap_enable() and make
> make udp_tunnel_encap_enable() a wrapper around it that'd also call
> udp_tunnel_encap_enable().

That's what I thought at .

But the problem is not that setup_udp_tunnel_sock() can sleep. The problem is that lockdep
gets confused due to changing lockdep class after the socket is already published. We need
to avoid calling lockdep_set_class_and_name() on a socket retrieved via sockfd_lookup().

  reply	other threads:[~2022-11-22 14:29 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-11-19 13:03 [PATCH net] l2tp: Don't sleep and disable BH under writer-side sk_callback_lock Jakub Sitnicki
2022-11-19 13:52 ` Tetsuo Handa
2022-11-19 14:27   ` Tetsuo Handa
2022-11-21  9:00     ` Jakub Sitnicki
2022-11-21 10:03       ` Tetsuo Handa
2022-11-21 21:55         ` Jakub Sitnicki
2022-11-22  9:48           ` Tetsuo Handa
2022-11-22 10:46             ` Jakub Sitnicki
2022-11-22 11:14               ` Tetsuo Handa
2022-11-22 14:10                 ` Guillaume Nault
2022-11-22 14:28                   ` Tetsuo Handa [this message]
2022-11-23 15:24                     ` Guillaume Nault
2022-11-24 10:07                       ` Tom Parkin
2022-11-24 10:27                         ` Guillaume Nault
2022-11-21  9:00   ` Jakub Sitnicki

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