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From: Tetsuo Handa <>
To: Jakub Sitnicki <>
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: Mon, 21 Nov 2022 19:03:24 +0900	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

On 2022/11/21 18:00, Jakub Sitnicki wrote:
>> Is it safe to temporarily set a dummy pointer like below?
>> If it is not safe, what makes assignments done by
>> setup_udp_tunnel_sock() safe?
> Yes, I think so. Great idea. I've used it in v2.

So, you are sure that e.g.

	udp_sk(sk)->gro_receive = cfg->gro_receive;

in setup_udp_tunnel_sock() (where the caller is passing cfg->gro_receive == NULL)
never races with e.g. below check (because the socket might be sending/receiving
in progress since the socket is retrieved via user-specified file descriptor) ?

Then, v2 patch would be OK for fixing this regression. (But I think we still should
avoid retrieving a socket from user-specified file descriptor in order to avoid
lockdep race window.)

struct sk_buff *udp_gro_receive(struct list_head *head, struct sk_buff *skb,
                                struct udphdr *uh, struct sock *sk)
        if (!sk || !udp_sk(sk)->gro_receive) {
                /* no GRO, be sure flush the current packet */
                goto out;
        pp = call_gro_receive_sk(udp_sk(sk)->gro_receive, sk, head, skb);
        skb_gro_flush_final(skb, pp, flush);
        return pp;

> We can check & assign sk_user_data under sk_callback_lock, and then just
> let setup_udp_tunnel_sock overwrite it with the same value, without
> holding the lock.

Given that sk_user_data is RCU-protected on reader-side, don't we need to
wait for RCU grace period after resetting to NULL?

> I still think that it's best to keep the critical section as short as
> possible, though.

  reply	other threads:[~2022-11-21 10:03 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 [this message]
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
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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