At 2017-08-10 02:08:30, "Cong Wang" <xiyou.wangc...@gmail.com> wrote: >On Wed, Aug 9, 2017 at 8:57 AM, <gfree.w...@vip.163.com> wrote: >> From: Gao Feng <gfree.w...@vip.163.com> >> >> 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 release(). There is a suspicious case in __sock_create following. err = pf->create(net, sock, protocol, kern); if (err < 0) goto out_module_put; ....... out_module_put: sock->ops = NULL; module_put(pf->owner); out_sock_release: sock_release(sock); 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 Feng