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Date:   Tue, 14 Jan 2020 17:04:33 +0100
From:   Jakub Sitnicki <>
To:     Martin Lau <>
Cc:     "bpf\" <>,
        "netdev\" <>,
        "kernel-team\" <>,
        Eric Dumazet <>,
        "John Fastabend" <>,
        Lorenz Bauer <>
Subject: Re: [PATCH bpf-next v2 03/11] net, sk_msg: Clear sk_user_data pointer on clone if tagged

On Mon, Jan 13, 2020 at 09:15 PM CET, Martin Lau wrote:
> On Fri, Jan 10, 2020 at 11:50:19AM +0100, Jakub Sitnicki wrote:
>> sk_user_data can hold a pointer to an object that is not intended to be
>> shared between the parent socket and the child that gets a pointer copy on
>> clone. This is the case when sk_user_data points at reference-counted
>> object, like struct sk_psock.
>> One way to resolve it is to tag the pointer with a no-copy flag by
>> repurposing its lowest bit. Based on the bit-flag value we clear the child
>> sk_user_data pointer after cloning the parent socket.
> LGTM.  One nit, WARN_ON_ONCE should be enough for all the cases if they
> would ever happen.  Having continuous splat on the same thing is not
> necessary useful while it could be quite distributing for people
> capture/log them.

Will switch to WARN_ON_ONCE in v3. Thanks for the review!

> Acked-by: Martin KaFai Lau <>

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