[PATCH v2] sunrpc: fix waitqueue_active without memory barrier in sunrpc

[Kosuke Tatsukawa <tatsu@ab.jp.nec.com>]

There are several places in net/sunrpc/svcsock.c which calls
waitqueue_active() without calling a memory barrier.  Add a memory
barrier just as in wq_has_sleeper().

I found this issue when I was looking through the linux source code
for places calling waitqueue_active() before wake_up*(), but without
preceding memory barriers, after sending a patch to fix a similar
issue in drivers/tty/n_tty.c  (Details about the original issue can be
found here: https://lkml.org/lkml/2015/9/28/849).

Signed-off-by: Kosuke Tatsukawa <tatsu@ab.jp.nec.com>
---
v2:
  - Fixed compiler warnings caused by type mismatch
v1:
  - https://lkml.org/lkml/2015/10/8/993
---
 net/sunrpc/svcsock.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 0c81202..ec19444 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -414,6 +414,7 @@ static void svc_udp_data_ready(struct sock *sk)
 		set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
 		svc_xprt_enqueue(&svsk->sk_xprt);
 	}
+	smp_mb();
 	if (wq && waitqueue_active(wq))
 		wake_up_interruptible(wq);
 }
@@ -432,6 +433,7 @@ static void svc_write_space(struct sock *sk)
 		svc_xprt_enqueue(&svsk->sk_xprt);
 	}
 
+	smp_mb();
 	if (wq && waitqueue_active(wq)) {
 		dprintk("RPC svc_write_space: someone sleeping on %p\n",
 		       svsk);
@@ -787,6 +789,7 @@ static void svc_tcp_listen_data_ready(struct sock *sk)
 	}
 
 	wq = sk_sleep(sk);
+	smp_mb();
 	if (wq && waitqueue_active(wq))
 		wake_up_interruptible_all(wq);
 }
@@ -808,6 +811,7 @@ static void svc_tcp_state_change(struct sock *sk)
 		set_bit(XPT_CLOSE, &svsk->sk_xprt.xpt_flags);
 		svc_xprt_enqueue(&svsk->sk_xprt);
 	}
+	smp_mb();
 	if (wq && waitqueue_active(wq))
 		wake_up_interruptible_all(wq);
 }
@@ -823,6 +827,7 @@ static void svc_tcp_data_ready(struct sock *sk)
 		set_bit(XPT_DATA, &svsk->sk_xprt.xpt_flags);
 		svc_xprt_enqueue(&svsk->sk_xprt);
 	}
+	smp_mb();
 	if (wq && waitqueue_active(wq))
 		wake_up_interruptible(wq);
 }
@@ -1594,6 +1599,7 @@ static void svc_sock_detach(struct svc_xprt *xprt)
 	sk->sk_write_space = svsk->sk_owspace;
 
 	wq = sk_sleep(sk);
+	smp_mb();
 	if (wq && waitqueue_active(wq))
 		wake_up_interruptible(wq);
 }
-- 
1.7.1