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Date: Wed, 29 Mar 2017 19:31:30 -0700 From: Eric Dumazet <eric.dumazet@...il.com> To: Seiichi Ikarashi <s.ikarashi@...fujitsu.com> Cc: netdev@...r.kernel.org Subject: Re: [PATCH] tcp: possible race between tcp_done() and tcp_poll() On Thu, 2017-03-30 at 09:35 +0900, Seiichi Ikarashi wrote: > Similar to a4d258036ed9 ("tcp: Fix race in tcp_poll"). > > Between receiving a packet and tcp_poll(), sk->sk_err is protected by memory barriers but > sk->sk_shutdown and sk->sk_state are not. ... > So possibly, POLLIN|POLLRDNORM|POLLRDHUP might > not be set even when receiving a RST packet. > > Signed-off-by: Seiichi Ikarashi <s.ikarashi@...fujitsu.com> > > --- > net/ipv4/tcp.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c > index cf45555..c8bc86e 100644 > --- a/net/ipv4/tcp.c > +++ b/net/ipv4/tcp.c > @@ -456,6 +456,8 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait) > > sock_poll_wait(file, sk_sleep(sk), wait); > > + /* This barrier is coupled with smp_wmb() in tcp_reset() */ > + smp_rmb(); > state = sk_state_load(sk); Are you telling us that sk_state_load() has no barrier ? This would imply that smp_load_acquire() should be replaced ? > if (state == TCP_LISTEN) > return inet_csk_listen_poll(sk); > @@ -540,8 +542,6 @@ unsigned int tcp_poll(struct file *file, struct socket *sock, poll_table *wait) > */ > mask |= POLLOUT | POLLWRNORM; > } > - /* This barrier is coupled with smp_wmb() in tcp_reset() */ > - smp_rmb(); > if (sk->sk_err || !skb_queue_empty(&sk->sk_error_queue)) > mask |= POLLERR; > > @@ -3291,6 +3291,9 @@ void tcp_done(struct sock *sk) > > sk->sk_shutdown = SHUTDOWN_MASK; > > + /* This barrier is coupled with smp_rmb() in tcp_poll() */ > + smp_wmb(); > + > if (!sock_flag(sk, SOCK_DEAD)) > sk->sk_state_change(sk); > else Might I ask on which arch you got a problem ? Thanks !
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