[PATCH AUTOSEL 6.6 03/21] selftests/bpf: Fix flaky test btf_map_in_map/lookup_update

Sasha Levin
2024-05-27T14:16:09Z

From: Yonghong Song <yonghong.song@linux.dev>

[ Upstream commit 14bb1e8c8d4ad5d9d2febb7d19c70a3cf536e1e5 ]

Recently, I frequently hit the following test failure:

[root@arch-fb-vm1 bpf]# ./test_progs -n 33/1
test_lookup_update:PASS:skel_open 0 nsec
[...]
test_lookup_update:PASS:sync_rcu 0 nsec
test_lookup_update:FAIL:map1_leak inner_map1 leaked!
#33/1 btf_map_in_map/lookup_update:FAIL
#33 btf_map_in_map:FAIL

In the test, after map is closed and then after two rcu grace periods,
it is assumed that map_id is not available to user space.

But the above assumption cannot be guaranteed. After zero or one
or two rcu grace periods in different siturations, the actual
freeing-map-work is put into a workqueue. Later on, when the work
is dequeued, the map will be actually freed.
See bpf_map_put() in kernel/bpf/syscall.c.

By using workqueue, there is no ganrantee that map will be actually
freed after a couple of rcu grace periods. This patch removed
such map leak detection and then the test can pass consistently.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20240322061353.632136-1-yonghong.song@linux.dev
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
.../selftests/bpf/prog_tests/btf_map_in_map.c | 26 +------------------
1 file changed, 1 insertion(+), 25 deletions(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c b/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
index a8b53b8736f01..f66ceccd7029c 100644
--- a/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
+++ b/tools/testing/selftests/bpf/prog_tests/btf_map_in_map.c
@@ -25,7 +25,7 @@ static void test_lookup_update(void)
int map1_fd, map2_fd, map3_fd, map4_fd, map5_fd, map1_id, map2_id;
int outer_arr_fd, outer_hash_fd, outer_arr_dyn_fd;
struct test_btf_map_in_map *skel;
- int err, key = 0, val, i, fd;
+ int err, key = 0, val, i;

skel = test_btf_map_in_map__open_and_load();
if (CHECK(!skel, "skel_open", "failed to open&load skeleton\n"))
@@ -102,30 +102,6 @@ static void test_lookup_update(void)
CHECK(map1_id == 0, "map1_id", "failed to get ID 1\n");
CHECK(map2_id == 0, "map2_id", "failed to get ID 2\n");

- test_btf_map_in_map__destroy(skel);
- skel = NULL;
-
- /* we need to either wait for or force synchronize_rcu(), before
- * checking for "still exists" condition, otherwise map could still be
- * resolvable by ID, causing false positives.
- *
- * Older kernels (5.8 and earlier) freed map only after two
- * synchronize_rcu()s, so trigger two, to be entirely sure.
- */
- CHECK(kern_sync_rcu(), "sync_rcu", "failed\n");
- CHECK(kern_sync_rcu(), "sync_rcu", "failed\n");
-
- fd = bpf_map_get_fd_by_id(map1_id);
- if (CHECK(fd >= 0, "map1_leak", "inner_map1 leaked!\n")) {
- close(fd);
- goto cleanup;
- }
- fd = bpf_map_get_fd_by_id(map2_id);
- if (CHECK(fd >= 0, "map2_leak", "inner_map2 leaked!\n")) {
- close(fd);
- goto cleanup;
- }
-
cleanup:
test_btf_map_in_map__destroy(skel);
}
--
2.43.0