selftest/bpf: Switch recursion test to use htab_map_delete_elem

Currently the recursion test is hooking __htab_map_lookup_elem
function, which is invoked both from bpf_prog and bpf syscall.

But in our kernel build, the __htab_map_lookup_elem gets inlined
within the htab_map_lookup_elem, so it's not trigered and the
test fails.

Fixing this by using htab_map_delete_elem, which is not inlined
for bpf_prog calls (like htab_map_lookup_elem is) and is used
directly as pointer for map_delete_elem, so it won't disappear
by inlining.

Signed-off-by: Jiri Olsa <[e-mail]>
Signed-off-by: Andrii Nakryiko <[e-mail]>
Acked-by: Song Liu <[e-mail]>
Link: https://lore.kernel.org/bpf/YVnfFTL/3T6jOwHI@krava

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

···
 		goto out;
 
 	ASSERT_EQ(skel->bss->pass1, 0, "pass1 == 0");
-	bpf_map_lookup_elem(bpf_map__fd(skel->maps.hash1), &key, 0);
+	bpf_map_delete_elem(bpf_map__fd(skel->maps.hash1), &key);
 	ASSERT_EQ(skel->bss->pass1, 1, "pass1 == 1");
-	bpf_map_lookup_elem(bpf_map__fd(skel->maps.hash1), &key, 0);
+	bpf_map_delete_elem(bpf_map__fd(skel->maps.hash1), &key);
 	ASSERT_EQ(skel->bss->pass1, 2, "pass1 == 2");
 
 	ASSERT_EQ(skel->bss->pass2, 0, "pass2 == 0");
-	bpf_map_lookup_elem(bpf_map__fd(skel->maps.hash2), &key, 0);
+	bpf_map_delete_elem(bpf_map__fd(skel->maps.hash2), &key);
 	ASSERT_EQ(skel->bss->pass2, 1, "pass2 == 1");
-	bpf_map_lookup_elem(bpf_map__fd(skel->maps.hash2), &key, 0);
+	bpf_map_delete_elem(bpf_map__fd(skel->maps.hash2), &key);
 	ASSERT_EQ(skel->bss->pass2, 2, "pass2 == 2");
 
-	err = bpf_obj_get_info_by_fd(bpf_program__fd(skel->progs.on_lookup),
+	err = bpf_obj_get_info_by_fd(bpf_program__fd(skel->progs.on_delete),
 				     &prog_info, &prog_info_len);
 	if (!ASSERT_OK(err, "get_prog_info"))
 		goto out;

tools/testing/selftests/bpf/progs/recursion.c

···
 int pass1 = 0;
 int pass2 = 0;
 
-SEC("fentry/__htab_map_lookup_elem")
-int BPF_PROG(on_lookup, struct bpf_map *map)
+SEC("fentry/htab_map_delete_elem")
+int BPF_PROG(on_delete, struct bpf_map *map)
 {
 	int key = 0;
 
···
 	}
 	if (map == (void *)&hash2) {
 		pass2++;
-		/* htab_map_gen_lookup() will inline below call
-		 * into direct call to __htab_map_lookup_elem()
-		 */
-		bpf_map_lookup_elem(&hash2, &key);
+		bpf_map_delete_elem(&hash2, &key);
 		return 0;
 	}