SUNRPC: Fix a race in xs_tcp_state_change()

When scheduling the autoclose RPC call, we want to ensure that we don't
race against the test_bit() call in xprt_clear_locked().
Signed-off-by: NTrond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/xprt.h

@@ -246,6 +246,7 @@ struct rpc_rqst *	xprt_lookup_rqst(struct rpc_xprt *xprt, __be32 xid);
 void			xprt_complete_rqst(struct rpc_task *task, int copied);
 void			xprt_release_rqst_cong(struct rpc_task *task);
 void			xprt_disconnect(struct rpc_xprt *xprt);
+void			xprt_force_disconnect(struct rpc_xprt *xprt);
 
 /*
  * Reserved bit positions in xprt->state

net/sunrpc/xprt.c

@@ -570,6 +570,7 @@ static void xprt_autoclose(struct work_struct *work)
 
 	xprt_disconnect(xprt);
 	xprt->ops->close(xprt);
+	clear_bit(XPRT_CLOSE_WAIT, &xprt->state);
 	xprt_release_write(xprt, NULL);
 }
 
@@ -588,6 +589,25 @@ void xprt_disconnect(struct rpc_xprt *xprt)
 }
 EXPORT_SYMBOL_GPL(xprt_disconnect);
 
+/**
+ * xprt_force_disconnect - force a transport to disconnect
+ * @xprt: transport to disconnect
+ *
+ */
+void xprt_force_disconnect(struct rpc_xprt *xprt)
+{
+	/* Don't race with the test_bit() in xprt_clear_locked() */
+	spin_lock_bh(&xprt->transport_lock);
+	set_bit(XPRT_CLOSE_WAIT, &xprt->state);
+	/* Try to schedule an autoclose RPC call */
+	if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
+		queue_work(rpciod_workqueue, &xprt->task_cleanup);
+	else if (xprt->snd_task != NULL)
+		rpc_wake_up_task(xprt->snd_task);
+	spin_unlock_bh(&xprt->transport_lock);
+}
+EXPORT_SYMBOL_GPL(xprt_force_disconnect);
+
 static void
 xprt_init_autodisconnect(unsigned long data)
 {

net/sunrpc/xprtsock.c

@@ -1122,10 +1122,7 @@ static void xs_tcp_state_change(struct sock *sk)
 	case TCP_SYN_RECV:
 		break;
 	case TCP_CLOSE_WAIT:
-		/* Try to schedule an autoclose RPC calls */
-		set_bit(XPRT_CLOSE_WAIT, &xprt->state);
-		if (test_and_set_bit(XPRT_LOCKED, &xprt->state) == 0)
-			queue_work(rpciod_workqueue, &xprt->task_cleanup);
+		xprt_force_disconnect(xprt);
 	default:
 		xprt_disconnect(xprt);
 	}