SUNRPC: timeout and cancel TLS handshake with -ETIMEDOUT

We've noticed a situation where an unstable TCP connection can cause the
TLS handshake to timeout waiting for userspace to complete it.  When this
happens, we don't want to return from xs_tls_handshake_sync() with zero, as
this will cause the upper xprt to be set CONNECTED, and subsequent attempts
to transmit will be returned with -EPIPE.  The sunrpc machine does not
recover from this situation and will spin attempting to transmit.

The return value of tls_handshake_cancel() can be used to detect a race
with completion:

 * tls_handshake_cancel - cancel a pending handshake
 * Return values:
 *   %true - Uncompleted handshake request was canceled
 *   %false - Handshake request already completed or not found

If true, we do not want the upper xprt to be connected, so return
-ETIMEDOUT.  If false, its possible the handshake request was lost and
that may be the reason for our timeout.  Again we do not want the upper
xprt to be connected, so return -ETIMEDOUT.

Ensure that we alway return an error from xs_tls_handshake_sync() if we
call tls_handshake_cancel().

Signed-off-by: Benjamin Coddington <bcodding@redhat.com>
Reviewed-by: Chuck Lever <chuck.lever@oracle.com>
Fixes: 75eb6af ("SUNRPC: Add a TCP-with-TLS RPC transport class")
Signed-off-by: Trond Myklebust <trond.myklebust@hammerspace.com>

net/sunrpc/xprtsock.c

@@ -2616,11 +2616,10 @@ static int xs_tls_handshake_sync(struct rpc_xprt *lower_xprt, struct xprtsec_par
 	rc = wait_for_completion_interruptible_timeout(&lower_transport->handshake_done,
 						       XS_TLS_HANDSHAKE_TO);
 	if (rc <= 0) {
-		if (!tls_handshake_cancel(sk)) {
-			if (rc == 0)
-				rc = -ETIMEDOUT;
-			goto out_put_xprt;
-		}
+		tls_handshake_cancel(sk);
+		if (rc == 0)
+			rc = -ETIMEDOUT;
+		goto out_put_xprt;
 	}
 
 	rc = lower_transport->xprt_err;