netdev - Re: Re: Re:Re: Re: [PATCH net] ppp: Fix a scheduling-while-atomic bug in del

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Message-ID: <CAM_iQpU3hx-Y7OXTDWARFc08BE6qQ_cEjZb7ciVKrWPFh2j0JA@mail.gmail.com>
Date:   Wed, 9 Aug 2017 11:18:44 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Gao Feng <gfree.wind@....163.com>
Cc:     xeb@...l.ru, David Miller <davem@...emloft.net>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>
Subject: Re: Re: Re:Re: Re: [PATCH net] ppp: Fix a scheduling-while-atomic bug
 in del_chan

On Tue, Aug 8, 2017 at 10:13 PM, Gao Feng <gfree.wind@....163.com> wrote:
> Maybe I didn't show my explanation clearly.
> I think it won't happen as I mentioned in the last email.
> Because the pptp_release invokes the synchronize_rcu to make sure it, and actually there is no one which would invoke del_chan except pptp_release.
> It is guaranteed by that the pptp_release doesn't put the sock refcnt until complete all cleanup include marking sk_state as PPPOX_DEAD.
>
> In other words, even though the pptp_release is not the last user of this sock, the other one wouldn't invoke del_chan in pptp_sock_destruct.
> Because the condition "!(sk->sk_state & PPPOX_DEAD)" must be false.

Only if sock->sk is always non-NULL for pptp_release(), which
is what I am not sure. If you look at other ->release(), similar checks
are there too, so not just for pptp.

>
> As summary, the del_chan and pppox_unbind_sock in pptp_sock_destruct are unnecessary.
> And it even brings confusing.

Sorry, I can't draw any conclusion for this.