[PATCH bpf-next 2/2] selftests/bpf: Verify no warning when close fexit link

[Leon Hwang <leon.hwang@linux.dev>]

Add a test to verify that there's no WARNING when detaching fexit link by
following the repro steps of previous commit.

Without the fix, the WARNING could be triggered by this test.

Signed-off-by: Leon Hwang <leon.hwang@linux.dev>
---
 .../selftests/bpf/prog_tests/tailcalls.c      | 51 +++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/tailcalls.c b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
index c66037162da5..86d87d5817cf 100644
--- a/tools/testing/selftests/bpf/prog_tests/tailcalls.c
+++ b/tools/testing/selftests/bpf/prog_tests/tailcalls.c
@@ -13,6 +13,8 @@
 #include "tailcall_cgrp_storage.skel.h"
 #include "tailcall_sleepable.skel.h"
 #include "tailcall_callback.skel.h"
+#include "tailcall_bpf2bpf2.skel.h"
+#include "tailcall_bpf2bpf_fexit.skel.h"
 
 /* test_tailcall_1 checks basic functionality by patching multiple locations
  * in a single program for a single tail call slot with nop->jmp, jmp->nop
@@ -1907,6 +1909,53 @@ static void test_tailcall_callback(void)
 	RUN_TESTS(tailcall_callback);
 }
 
+static void test_tailcall_bpf2bpf_fexit_links(void)
+{
+	struct tailcall_bpf2bpf_fexit *skel1 = NULL, *skel2 = NULL;
+	struct tailcall_bpf2bpf2 *skel_tc;
+	struct bpf_link *link;
+	int err, prog_fd;
+
+	skel_tc = tailcall_bpf2bpf2__open_and_load();
+	if (!ASSERT_OK_PTR(skel_tc, "tailcall_bpf2bpf2__open_and_load"))
+		return;
+
+	skel1 = tailcall_bpf2bpf_fexit__open();
+	if (!ASSERT_OK_PTR(skel1, "tailcall_bpf2bpf_fexit__open"))
+		goto out;
+
+	prog_fd = bpf_program__fd(skel_tc->progs.classifier_0);
+	err = bpf_program__set_attach_target(skel1->progs.fexit, prog_fd, "subprog_tail");
+	if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
+		goto out;
+
+	err = tailcall_bpf2bpf_fexit__load(skel1);
+	if (!ASSERT_OK(err, "tailcall_bpf2bpf_fexit__load"))
+		goto out;
+
+	link = bpf_program__attach_trace(skel1->progs.fexit);
+	if (!ASSERT_OK_PTR(link, "bpf_program__attach_trace"))
+		goto out;
+	skel1->links.fexit = link;
+
+	skel2 = tailcall_bpf2bpf_fexit__open();
+	if (!ASSERT_OK_PTR(skel2, "tailcall_bpf2bpf_fexit__open"))
+		goto out;
+
+	err = bpf_program__set_attach_target(skel2->progs.fexit, prog_fd, "subprog_tail");
+	if (!ASSERT_OK(err, "bpf_program__set_attach_target"))
+		goto out;
+
+	err = tailcall_bpf2bpf_fexit__load(skel2);
+	if (!ASSERT_OK(err, "tailcall_bpf2bpf_fexit__load"))
+		goto out;
+
+out:
+	tailcall_bpf2bpf_fexit__destroy(skel1);
+	tailcall_bpf2bpf_fexit__destroy(skel2);
+	tailcall_bpf2bpf2__destroy(skel_tc);
+}
+
 void test_tailcalls(void)
 {
 	if (test__start_subtest("tailcall_1"))
@@ -1974,4 +2023,6 @@ void test_tailcalls(void)
 	if (test__start_subtest("tailcall_cgrp_storage_no_storage_bridge"))
 		test_tailcall_cgrp_storage_no_storage_bridge();
 	test_tailcall_callback();
+	if (test__start_subtest("tailcall_bpf2bpf_fexit_links"))
+		test_tailcall_bpf2bpf_fexit_links();
 }
-- 
2.55.0