varnishd: always shutdown both ends to a backend

Signed-off-by: Asad Sajjad Ahmed <asadsa@varnish-software.com>

bin/varnishd/cache/cache_conn_pool.c

@@ -231,7 +231,7 @@ VCP_Rel(struct conn_pool **cpp)
 		cp->n_conn--;
 		assert(pfd->state == PFD_STATE_AVAIL);
 		pfd->state = PFD_STATE_CLEANUP;
-		(void)shutdown(pfd->fd, SHUT_WR);
+		(void)shutdown(pfd->fd, SHUT_RDWR);
 		cp->n_kill++;
 	}
 	while (cp->n_kill) {

bin/varnishtest/tests/b00083.vtc

@@ -0,0 +1,47 @@
+varnishtest "VCP FIN-WAIT2"
+
+server s1 {
+	rxreq
+	txresp
+
+	# Leave the TCP connection open in the FIN-WAIT2 state
+	delay 1000
+} -start
+
+server s2 {
+	rxreq
+	txresp
+} -start
+
+varnish v1 -vcl {
+	backend s1 {
+	    .host = "${s1_sock}";
+	}
+} -start
+
+# The waiter depend on the backend_idle_timeout for when to give up and
+# close the connection, so bump it up a bit.
+varnish v1 -cliok "param.set backend_idle_timeout 120"
+
+# The shutdown is done on the CLI thread, and it blocks until the waiter has
+# killed the connection. So bump cli_timeout up as well
+varnish v1 -cliok "param.set cli_timeout 120"
+
+client c1 {
+	txreq -url "/"
+	rxresp
+} -run
+
+varnish v1 -vcl {
+	backend s2 {
+	    .host = "${s2_sock}";
+	}
+}
+
+varnish v1 -cliok "vcl.use vcl2"
+varnish v1 -cliok "vcl.discard vcl1"
+
+varnish v1 -expect n_backend == 1
+varnish v1 -expect backend_conn == 1
+varnish v1 -expect backend_reuse == 0
+varnish v1 -expect backend_recycle == 1