From mboxrd@z Thu Jan  1 00:00:00 1970
From: Quanyang Wang <quanyang.wang-CWA4WttNNZF54TAoqtyWWQ@public.gmane.org>
Subject: Re: [V2][PATCH] cgroup: fix memory leak caused by missing
 cgroup_bpf_offline
Date: Wed, 20 Oct 2021 13:16:01 +0800
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Cc: Ming Lei <ming.lei-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>, Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>, Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>, Alexei Starovoitov <ast-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Daniel Borkmann <daniel-FeC+5ew28dpmcu3hnIyYJQ@public.gmane.org>, Andrii Nakryiko <andrii-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Jens Axboe <axboe-tSWWG44O7X1aa/9Udqfwiw@public.gmane.org>, Roman Gushchin <guro-b10kYP2dOMg@public.gmane.org>, cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, bpf-u79uwXL29TY76Z2rM5mHXA@public.gmane.org

Hi Michal,

On 10/20/21 1:10 AM, Michal Koutn=C3=BD wrote:
> Hi.
>=20
> On Tue, Oct 19, 2021 at 06:41:14PM +0800, Quanyang Wang <quanyang.wang-CW=
A4WttNNZF54TAoqtyWWQ@public.gmane.org> wrote:
>> So I add 2 "Fixes tags" here to indicate that 2 commits introduce two
>> different issues.
>=20
> 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.)
Yes, I back to the earlier commit 4bfc0bb2c60e and no memory leak is=20
observed.
>=20
> 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?
No, the earlier commit 4bfc0bb2c60e introduces a imbalance and the later
commit 2b0d3d3e4fcf introduces a visible leak.

Thanks,
Quanyang
>=20
> I agree the commit 2b0d3d3e4fcf ("percpu_ref: reduce memory footprint of
> percpu_ref in fast path") alone did nothing wrong.
>=20
> [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
> hierarchies.]
>=20
> Regards,
> Michal
>=20