From: gfree.wind@vip.163.com
Date: Mon, 31 Jul 2017 18:07:38 +0800

From: Gao Feng <redacted>

The PPTP set the pptp_sock_destruct as the sock's sk_destruct, it would
trigger this bug when __sk_free is invoked in atomic context, because of
the call path pptp_sock_destruct->del_chan->synchronize_rcu.

Now move the synchronize_rcu to pptp_release from del_chan. This is the
only one case which would free the sock and need the synchronize_rcu.

The following is the panic I met with kernel 3.3.8, but this issue should
exist in current kernel too according to the codes.

 ...

Signed-off-by: Gao Feng <redacted>

Applied, thanks.