selftests/bpf: Fix map_kptr test failure

On my arm64 machine, I get the following failure:
  ...
  tester_init:PASS:tester_log_buf 0 nsec
  process_subtest:PASS:obj_open_mem 0 nsec
  process_subtest:PASS:specs_alloc 0 nsec
  serial_test_map_kptr:PASS:rcu_tasks_trace_gp__open_and_load 0 nsec
  ...
  test_map_kptr_success:PASS:map_kptr__open_and_load 0 nsec
  test_map_kptr_success:PASS:test_map_kptr_ref1 refcount 0 nsec
  test_map_kptr_success:FAIL:test_map_kptr_ref1 retval unexpected error: 2 (errno 2)
  test_map_kptr_success:PASS:test_map_kptr_ref2 refcount 0 nsec
  test_map_kptr_success:FAIL:test_map_kptr_ref2 retval unexpected error: 1 (errno 2)
  ...
  #201/21  map_kptr/success-map:FAIL

In serial_test_map_kptr(), before test_map_kptr_success(), one
kern_sync_rcu() is used to have some delay for freeing the map.
But in my environment, one kern_sync_rcu() seems not enough and
caused the test failure.

In bpf_map_free_in_work() in syscall.c, the queue time for
  queue_work(system_dfl_wq, &map->work)
may be longer than expected. This may cause the test failure
since test_map_kptr_success() expects all previous maps having been freed.

Since it is not clear how long queue_work() time takes, a bpf prog
is added to count the reference after bpf_kfunc_call_test_acquire().
If the number of references is 2 (for initial ref and the one just
acquired), all previous maps should have been released. This will
resolve the above 'retval unexpected error' issue.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/bpf/20260116052245.3692405-1-yonghong.song@linux.dev

diff --git a/tools/testing/selftests/bpf/prog_tests/map_kptr.c b/tools/testing/selftests/bpf/prog_tests/map_kptr.c
index 8743df5995673be0ed6f6740b8b96940250dec72..f372162c0280c512aa3dc7db37b62e905f5e28f6 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/map_kptr.c
+++ b/tools/testing/selftests/bpf/prog_tests/map_kptr.c
@@ -131,6 +131,25 @@ static int kern_sync_rcu_tasks_trace(struct rcu_tasks_trace_gp *rcu)
        return 0;
 }
 
+static void wait_for_map_release(void)
+{
+       LIBBPF_OPTS(bpf_test_run_opts, lopts);
+       struct map_kptr *skel;
+       int ret;
+
+       skel = map_kptr__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "map_kptr__open_and_load"))
+               return;
+
+       do {
+               ret = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.count_ref), &lopts);
+               ASSERT_OK(ret, "count_ref ret");
+               ASSERT_OK(lopts.retval, "count_ref retval");
+       } while (skel->bss->num_of_refs != 2);
+
+       map_kptr__destroy(skel);
+}
+
 void serial_test_map_kptr(void)
 {
        struct rcu_tasks_trace_gp *skel;
@@ -148,11 +167,15 @@ void serial_test_map_kptr(void)
 
                ASSERT_OK(kern_sync_rcu_tasks_trace(skel), "sync rcu_tasks_trace");
                ASSERT_OK(kern_sync_rcu(), "sync rcu");
+               wait_for_map_release();
+
                /* Observe refcount dropping to 1 on bpf_map_free_deferred */
                test_map_kptr_success(false);
 
                ASSERT_OK(kern_sync_rcu_tasks_trace(skel), "sync rcu_tasks_trace");
                ASSERT_OK(kern_sync_rcu(), "sync rcu");
+               wait_for_map_release();
+
                /* Observe refcount dropping to 1 on synchronous delete elem */
                test_map_kptr_success(true);
        }

diff --git a/tools/testing/selftests/bpf/progs/map_kptr.c b/tools/testing/selftests/bpf/progs/map_kptr.c
index edaba481db9d83fb47b255c90369f8dde5448449..e708ffbe1f610029c06cba3114fa94f4d639834f 100644 (file)
--- a/tools/testing/selftests/bpf/progs/map_kptr.c
+++ b/tools/testing/selftests/bpf/progs/map_kptr.c
@@ -487,6 +487,24 @@ int test_map_kptr_ref3(struct __sk_buff *ctx)
        return 0;
 }
 
+int num_of_refs;
+
+SEC("syscall")
+int count_ref(void *ctx)
+{
+       struct prog_test_ref_kfunc *p;
+       unsigned long arg = 0;
+
+       p = bpf_kfunc_call_test_acquire(&arg);
+       if (!p)
+               return 1;
+
+       num_of_refs = p->cnt.refs.counter;
+
+       bpf_kfunc_call_test_release(p);
+       return 0;
+}
+
 SEC("syscall")
 int test_ls_map_kptr_ref1(void *ctx)
 {