Re: [PATCH v2 bpf-next 4/4] selftests/bpf: add auto-detach test

[Roman Gushchin <guro@fb.com>]

On Wed, May 22, 2019 at 10:47:24PM -0700, Yonghong Song wrote:
> 
> 
> On 5/22/19 4:20 PM, Roman Gushchin wrote:
> > Add a kselftest to cover bpf auto-detachment functionality.
> > The test creates a cgroup, associates some resources with it,
> > attaches a couple of bpf programs and deletes the cgroup.
> > 
> > Then it checks that bpf programs are going away in 5 seconds.
> > 
> > Expected output:
> >    $ ./test_cgroup_attach
> >    #override:PASS
> >    #multi:PASS
> >    #autodetach:PASS
> >    test_cgroup_attach:PASS
> > 
> > On a kernel without auto-detaching:
> >    $ ./test_cgroup_attach
> >    #override:PASS
> >    #multi:PASS
> >    #autodetach:FAIL
> >    test_cgroup_attach:FAIL
> 
> I ran this problem without both old and new kernels and
> both get all PASSes. My testing environment is a VM.
> Could you specify how to trigger the above failure?

Most likely you're running cgroup v1, so the memory controller
is not enabled on unified hierarchy. You need to pass
"cgroup_no_v1=all systemd.unified_cgroup_hierarchy=1"
as boot time options to run fully on cgroup v2.

But generally speaking, the lifecycle of a dying cgroup is
completely implementation-defined. No guarantees are provided.
So false positives are fine here, and shouldn't be considered as
something bad.

At the end all we want it to detach programs in a reasonable time
after rmdir.

Btw, thank you for the careful review of the patchset. I'll
address your comments, add acks and will send out v3.

Thanks!