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

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Date:   Thu, 23 May 2019 17:58:40 +0000
From:   Roman Gushchin <guro@...com>
To:     Yonghong Song <yhs@...com>
CC:     Alexei Starovoitov <ast@...nel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Tejun Heo <tj@...nel.org>, Kernel Team <Kernel-team@...com>,
        "cgroups@...r.kernel.org" <cgroups@...r.kernel.org>,
        Stanislav Fomichev <sdf@...ichev.me>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 bpf-next 4/4] selftests/bpf: add auto-detach test

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!