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Date:   Tue, 19 Oct 2021 19:10:26 +0200
From:   Michal Koutný <>
To:     Quanyang Wang <>
Cc:     Ming Lei <>, 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


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.

[On a related (but independent) note, there seems to be an optimization
opportunity in not dealing with cgroup_bpf at all on the non-default


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