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Date:   Wed, 20 Oct 2021 13:22:06 +0800
From:   Quanyang Wang <>
To:     Ming Lei <>,
        Michal Koutný <>
Cc:     Tejun Heo <>, Zefan Li <>,
        Johannes Weiner <>,
        Alexei Starovoitov <>,
        Daniel Borkmann <>,
        Andrii Nakryiko <>,
        Jens Axboe <>, Roman Gushchin <>,,,,
Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing

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 <> 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,
> Ming

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