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

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Message-ID: <cd4d0dba-6818-12df-1d90-3ef5121e342f@windriver.com>
Date:   Fri, 22 Oct 2021 19:03:42 +0800
From:   Quanyang Wang <quanyang.wang@...driver.com>
To:     Michal Koutný <mkoutny@...e.com>
Cc:     Ming Lei <ming.lei@...hat.com>, 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 Michal,

On 10/21/21 1:28 AM, Michal Koutný wrote:
> On Wed, Oct 20, 2021 at 01:22:06PM +0800, Quanyang Wang <quanyang.wang@...driver.com> wrote:
>>> 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.
> 
> I assume you refer to ref->data. I considered the ref->percpu_count_ptr
> allocated with __alloc_percpu_gfp(). Could it be that kmemleak won't
> detect leaked percpu allocations?
Yes, kmemleak can't detect percpu allocations. I find some message about 
this:

commit f528f0b8e53d
Author: Catalin Marinas <catalin.marinas@....com>
Date:   Mon Sep 26 17:12:53 2011 +0100

kmemleak: Handle percpu memory allocation

This patch adds kmemleak callbacks from the percpu allocator, reducing a
number of false positives caused by kmemleak not scanning such memory
blocks. The percpu chunks are never reported as leaks because of current
kmemleak limitations with the __percpu pointer not pointing directly to
the actual chunks.

Thanks,
Quanyang
> 
> (The patch you sent resolves this as well, I'm just curious.)
> 
> Michal
>