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Occasionally, with './test_progs -j' on my vm, I will hit the
following failure:
test_cgrp_local_storage:PASS:join_cgroup /cgrp_local_storage 0 nsec
test_cgroup_iter_sleepable:PASS:skel_open 0 nsec
test_cgroup_iter_sleepable:PASS:skel_load 0 nsec
test_cgroup_iter_sleepable:PASS:attach_iter 0 nsec
test_cgroup_iter_sleepable:PASS:iter_create 0 nsec
test_cgroup_iter_sleepable:FAIL:cgroup_id unexpected cgroup_id: actual 1 != expected 2812
#48/5 cgrp_local_storage/cgroup_iter_sleepable:FAIL
#48 cgrp_local_storage:FAIL
Finally, I decided to do some investigation since the test is introduced
by myself. It turns out the reason is due to cgroup_fd with value 0.
In cgroup_iter, a cgroup_fd of value 0 means the root cgroup.
/* from cgroup_iter.c */
if (fd)
cgrp = cgroup_v1v2_get_from_fd(fd);
else if (id)
cgrp = cgroup_get_from_id(id);
else /* walk the entire hierarchy by default. */
cgrp = cgroup_get_from_path("/");
That is why we got cgroup_id 1 instead of expected 2812.
Why we got a cgroup_fd 0? Nobody should really touch 'stdin' (fd 0) in
test_progs. I traced 'close' syscall with stack trace and found the root
cause, which is a bug in bpf_obj_pinning.c. Basically, the code closed
fd 0 although it should not. Fixing the bug in bpf_obj_pinning.c also
resolved the above cgroup_iter_sleepable subtest failure.
Fixes: 3b22f98e5a05 ("selftests/bpf: Add path_fd-based BPF_OBJ_PIN and BPF_OBJ_GET tests")
Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20230827150551.1743497-1-yonghong.song@linux.dev
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