At 2017-08-10 02:08:30, "Cong Wang" <> wrote:
>On Wed, Aug 9, 2017 at 8:57 AM,  <> wrote:
>> From: Gao Feng <>
>> In the commit ddab82821fa6 ("ppp: Fix a scheduling-while-atomic bug in
>> del_chan"), I moved the synchronize_rcu() from del_chan() to pptp_release
>> after del_chan() to avoid one scheduling-while-atomic bug.
>> Actually the del_chan() and pppox_unbind_sock are unneccessary in the
>> pptp_sock_destruct. Because the pptp sock refcnt wouldn't reach zero until
>> sk_state is set as PPPOX_DEAD in pptp_release. By that time, the del_chan()
>> and pppox_unbind_sock() have been invoked already and the condition check
>> "!(sk->sk_state & PPPOX_DEAD)" of this sock must be false in 
>> pptp_sock_destruct.
>I am not sure. The check for sock->sk in the beginning of pptp_release()
>indicates there could be a case we could skip del_chan() in pptp_release(),
>although I can't figure out how.
>Also there is a suspicious sock_put() in pptp_release().

Hi Cong, 

Thank you.  I also failed to find the case which causes the sock->sk is null in 

There is a suspicious case in __sock_create following.
        err = pf->create(net, sock, protocol, kern);
        if (err < 0)
                goto out_module_put;
        sock->ops = NULL;
        return err;
In the beginning, I thought when create is failed and the sock->sk is null, 
then the sock_release is invoked.
It could cause the sk is null in the release().
But I find  it has already reset the sock->ops as NULL before sock_release 
later, so the release() wouldn't be invoked actually.

Best Regards

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