selftests/bpf: Test subprog jit when toggle bpf_jit_harden repeatedly

When bpf_jit_harden is toggled between 0 and 2, subprog jit may fail
due to inconsistent twice read values of bpf_jit_harden during jit. So
add a test to ensure the problem is fixed.
Signed-off-by: Hou Tao <houtao1@huawei.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220309123321.2400262-5-houtao1@huawei.com

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

 // SPDX-License-Identifier: GPL-2.0
 /* Copyright (c) 2020 Facebook */
 #include <test_progs.h>
-#include <time.h>
 #include "test_subprogs.skel.h"
 #include "test_subprogs_unused.skel.h"
 
-static int duration;
+struct toggler_ctx {
+	int fd;
+	bool stop;
+};
 
-void test_subprogs(void)
+static void *toggle_jit_harden(void *arg)
+{
+	struct toggler_ctx *ctx = arg;
+	char two = '2';
+	char zero = '0';
+
+	while (!ctx->stop) {
+		lseek(ctx->fd, SEEK_SET, 0);
+		write(ctx->fd, &two, sizeof(two));
+		lseek(ctx->fd, SEEK_SET, 0);
+		write(ctx->fd, &zero, sizeof(zero));
+	}
+
+	return NULL;
+}
+
+static void test_subprogs_with_jit_harden_toggling(void)
+{
+	struct toggler_ctx ctx;
+	pthread_t toggler;
+	int err;
+	unsigned int i, loop = 10;
+
+	ctx.fd = open("/proc/sys/net/core/bpf_jit_harden", O_RDWR);
+	if (!ASSERT_GE(ctx.fd, 0, "open bpf_jit_harden"))
+		return;
+
+	ctx.stop = false;
+	err = pthread_create(&toggler, NULL, toggle_jit_harden, &ctx);
+	if (!ASSERT_OK(err, "new toggler"))
+		goto out;
+
+	/* Make toggler thread to run */
+	usleep(1);
+
+	for (i = 0; i < loop; i++) {
+		struct test_subprogs *skel = test_subprogs__open_and_load();
+
+		if (!ASSERT_OK_PTR(skel, "skel open"))
+			break;
+		test_subprogs__destroy(skel);
+	}
+
+	ctx.stop = true;
+	pthread_join(toggler, NULL);
+out:
+	close(ctx.fd);
+}
+
+static void test_subprogs_alone(void)
 {
 	struct test_subprogs *skel;
 	struct test_subprogs_unused *skel2;
 	int err;
 
 	skel = test_subprogs__open_and_load();
-	if (CHECK(!skel, "skel_open", "failed to open skeleton\n"))
+	if (!ASSERT_OK_PTR(skel, "skel_open"))
 		return;
 
 	err = test_subprogs__attach(skel);
-	if (CHECK(err, "skel_attach", "failed to attach skeleton: %d\n", err))
+	if (!ASSERT_OK(err, "skel attach"))
 		goto cleanup;
 
 	usleep(1);
 
-	CHECK(skel->bss->res1 != 12, "res1", "got %d, exp %d\n", skel->bss->res1, 12);
-	CHECK(skel->bss->res2 != 17, "res2", "got %d, exp %d\n", skel->bss->res2, 17);
-	CHECK(skel->bss->res3 != 19, "res3", "got %d, exp %d\n", skel->bss->res3, 19);
-	CHECK(skel->bss->res4 != 36, "res4", "got %d, exp %d\n", skel->bss->res4, 36);
+	ASSERT_EQ(skel->bss->res1, 12, "res1");
+	ASSERT_EQ(skel->bss->res2, 17, "res2");
+	ASSERT_EQ(skel->bss->res3, 19, "res3");
+	ASSERT_EQ(skel->bss->res4, 36, "res4");
 
 	skel2 = test_subprogs_unused__open_and_load();
 	ASSERT_OK_PTR(skel2, "unused_progs_skel");
@@ -35,3 +86,11 @@ void test_subprogs(void)
 cleanup:
 	test_subprogs__destroy(skel);
 }
+
+void test_subprogs(void)
+{
+	if (test__start_subtest("subprogs_alone"))
+		test_subprogs_alone();
+	if (test__start_subtest("subprogs_and_jit_harden"))
+		test_subprogs_with_jit_harden_toggling();
+}