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

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Message-ID: <5a44b791-899b-5638-4c75-235a31a0cb4d@fb.com>
Date:   Thu, 23 May 2019 23:06:02 +0000
From:   Yonghong Song <yhs@...com>
To:     Roman Gushchin <guro@...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 5/23/19 10:58 AM, Roman Gushchin wrote:
> 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.

I tested on a cgroup v2 machine and it indeed failed without
the core patch. Thanks!

> 
> 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!
>