At 2017-08-03 01:13:36, "Cong Wang" <xiyou.wangc...@gmail.com> wrote: >Hi, Gao > >On Tue, Aug 1, 2017 at 1:39 PM, Cong Wang <xiyou.wangc...@gmail.com> wrote: >> From my understanding, this RCU is supposed to protect the pppox_sock >> pointers in 'callid_sock' which could be NULL'ed in del_chan(). And the >> pppox_sock is freed when the last refcnt is gone, that is, when sock >> dctor is called. pptp_release() is ONLY called when the fd in user-space >> is gone, not necessarily the last refcnt.
Hi Cong, I am sorry to reply you so late, because I took a short trip recently, and didn't check my emails. I think the RCU should be supposed to avoid the race between del_chan and lookup_chan. The synchronize_rcu could make sure if there was one which calls lookup_chan in this period, it would be finished and the sock refcnt is increased if necessary. So I think it is ok to invoke sock_put directly without SOCK_RCU_FREE, because the lookup_chan caller has already hold the sock refcnt, Best Regards Feng > >Your commit is probably not the right fix. Can you try the following fix? > >diff --git a/drivers/net/ppp/pptp.c b/drivers/net/ppp/pptp.c >index 6dde9a0cfe76..e75bb95c107f 100644 >--- a/drivers/net/ppp/pptp.c >+++ b/drivers/net/ppp/pptp.c >@@ -519,7 +519,6 @@ static int pptp_release(struct socket *sock) > > po = pppox_sk(sk); > del_chan(po); >- synchronize_rcu(); > > pppox_unbind_sock(sk); > sk->sk_state = PPPOX_DEAD; >@@ -564,6 +563,7 @@ static int pptp_create(struct net *net, struct >socket *sock, int kern) > sk->sk_family = PF_PPPOX; > sk->sk_protocol = PX_PROTO_PPTP; > sk->sk_destruct = pptp_sock_destruct; >+ sock_set_flag(sk, SOCK_RCU_FREE); > > po = pppox_sk(sk); > opt = &po->proto.pptp;
