[PATCH bpf-next v5 4/4] selftests/bpf: Wait for the struct_ops map to be freed in assoc_in_timer

[Qiliang Yuan]

st_ops_assoc_in_timer_no_uref runs .test_1, which starts a timer to
call it again 500ms later, drops every reference to the struct_ops map,
and expects the timer callback to find no struct_ops associated with
its program anymore.

The association goes away only when the last reference to the map is
dropped. syscall_prog holds one through its own association and drops
it only when it is freed, in a work item after an RCU tasks trace grace
period. With other tests running in parallel, that can take longer than
500ms, and the callback still reaches the struct_ops and gets MAP_MAGIC
instead of -1.

Have the timer callback restart the timer until the map is gone, as it
does for st_ops_assoc_in_timer_free. Calling the struct_ops through the
association until then is safe, as the map is freed only after a grace
period that follows clearing the association.

st_ops_assoc_in_timer_no_uref run 100 times with test_progs -j32 running
in the background, on a KASAN kernel with the fix, x86_64 VM with 32
vCPUs, before and after this patch:

              before                       after
  outcome     2 of 100 failed (MAP_MAGIC)  0 of 100 failed (MAP_MAGIC)

Fixes: 0e841d19263a ("selftests/bpf: Test getting associated struct_ops in timer callback")
Signed-off-by: Qiliang Yuan <odys.yuan@xxxxxxxxx>
---
 tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
index 6c85d368bf167..9b646d134a45e 100644
--- a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
@@ -188,7 +188,7 @@ static void run_st_ops_assoc_in_timer_no_uref(int timer_ns, int wait_map_free,
 
 static void test_st_ops_assoc_in_timer_no_uref(void)
 {
-	run_st_ops_assoc_in_timer_no_uref(500000000, 0, 0);
+	run_st_ops_assoc_in_timer_no_uref(500000000, 1, 0);
 }
 
 /*

-- 
2.43.0