selftests/bpf: Fix failure path in send_signal test

When test_send_signal_kern__open_and_load() fails parent closes the
pipe which cases ASSERT_EQ(read(pipe_p2c...)) to fail, but child
continues and enters infinite loop, while parent is stuck in wait(NULL).

Fix the issue by killing the child before jumping to skel_open_load_failure.

The bug was discovered while compiling all of selftests with -O1 instead of -O2
which caused progs/test_send_signal_kern.c to fail to load.

Signed-off-by: Alexei Starovoitov <[email protected]>

Author: Alexei Starovoitov

tools/testing/selftests/bpf/prog_tests/send_signal.c

@@ -110,8 +110,10 @@ static void test_send_signal_common(struct perf_event_attr *attr,
 	close(pipe_p2c[0]); /* close read */
 
 	skel = test_send_signal_kern__open_and_load();
-	if (!ASSERT_OK_PTR(skel, "skel_open_and_load"))
+	if (!ASSERT_OK_PTR(skel, "skel_open_and_load")) {
+		kill(pid, SIGKILL);
 		goto skel_open_load_failure;
+	}
 
 	/* boost with a high priority so we got a higher chance
 	 * that if an interrupt happens, the underlying task