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From: Jakub Sitnicki <>
To: Tetsuo Handa <>
Cc:, "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 11:46:58 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On Tue, Nov 22, 2022 at 06:48 PM +09, Tetsuo Handa wrote:
> On 2022/11/22 6:55, Jakub Sitnicki wrote:
>> First, let me say, that I get the impression that setup_udp_tunnel_sock
>> was not really meant to be used on pre-existing sockets created by
>> user-space. Even though l2tp and gtp seem to be doing that.
>> That is because, I don't see how it could be used properly. Given that
>> we need to check-and-set sk_user_data under sk_callback_lock, which
>> setup_udp_tunnel_sock doesn't grab itself. At the same time it might
>> sleep. There is no way to apply it without resorting to tricks, like we
>> did here.
>> So - yeah - there may be other problems. But if there are, they are not
>> related to the faulty commit b68777d54fac ("l2tp: Serialize access to
>> sk_user_data with sk_callback_lock"), which we're trying to fix. There
>> was no locking present in l2tp_tunnel_register before that point.
> is the one
> where changing lockdep class is concurrently done on pre-existing sockets.
> I think we need to always create a new socket inside l2tp_tunnel_register(),
> rather than trying to serialize setting of sk_user_data under sk_callback_lock.

While that would be easier to handle, I don't see how it can be done in
a backward-compatible way. User-space is allowed to pass a socket to
l2tp today [1].

>> However, that is also not related to the race to check-and-set
>> sk_user_data, which commit b68777d54fac is trying to fix.
> Therefore, I feel that reverting commit b68777d54fac "l2tp: Serialize access
> to sk_user_data with sk_callback_lock" might be the better choice.

I'm okay with that. Providing we can come up with have an alternative
fix to the race between l2tp and other sk_user_data users.


  reply	other threads:[~2022-11-22 10:53 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 [this message]
2022-11-22 11:14               ` Tetsuo Handa
2022-11-22 14:10                 ` Guillaume Nault
2022-11-22 14:28                   ` Tetsuo Handa
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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