netdev - Re: [V2][PATCH] cgroup: fix memory leak caused by missing cgroup_bpf

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Date:   Wed, 20 Oct 2021 13:22:06 +0800
From:   Quanyang Wang <quanyang.wang@...driver.com>
To:     Ming Lei <ming.lei@...hat.com>,
        Michal Koutný <mkoutny@...e.com>
Cc:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Jens Axboe <axboe@...nel.dk>, Roman Gushchin <guro@...com>,
        cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing
 cgroup_bpf_offline

Hi Ming,

On 10/20/21 10:17 AM, Ming Lei wrote:
> On Tue, Oct 19, 2021 at 07:10:26PM +0200, Michal Koutný wrote:
>> Hi.
>>
>> On Tue, Oct 19, 2021 at 06:41:14PM +0800, Quanyang Wang <quanyang.wang@...driver.com> wrote:
>>> So I add 2 "Fixes tags" here to indicate that 2 commits introduce two
>>> different issues.
>>
>> AFAIU, both the changes are needed to cause the leak, a single patch
>> alone won't cause the issue. Is that correct? (Perhaps not as I realize,
>> see below.)
>>
>> But on second thought, the problem is the missing percpu_ref_exit() in
>> the (root) cgroup release path and percpu counter would allocate the
>> percpu_count_ptr anyway, so 4bfc0bb2c60e is only making the leak more
>> visible. Is this correct?
>>
>> I agree the commit 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of
>> percpu_ref in fast path") alone did nothing wrong.
> 
> If only precpu_ref data is leaked, it is fine to add "Fixes: 2b0d3d3e4fcf",
> I thought cgroup_bpf_release() needs to release more for root cgroup, but
> looks not true.
For now, I can only observe that precpu_ref data is leaked when running 
ltp testsuite.
Thanks,
Quanyang
> 
> 
> Thanks,
> Ming
>