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 <20210917164123.GA13346@blackbody.suse.cz>
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From:   Hao Sun <sunhao.th@gmail.com>
Date:   Sat, 18 Sep 2021 09:27:08 +0800
Message-ID: <CACkBjsZnp8Kf26tR3anbcLQNiMJ9=bqYMJ66tKBvXO6tkV3qyw@mail.gmail.com>
Subject: Re: KCSAN: data-race in cgroup_rstat_flush_locked / cgroup_rstat_updated
To:     =?UTF-8?Q?Michal_Koutn=C3=BD?= <mkoutny@suse.com>
Cc:     Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        cgroups@vger.kernel.org, hannes@cmpxchg.org,
        lizefan.x@bytedance.com, tj@kernel.org
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Hi Michal,

Michal Koutn=C3=BD <mkoutny@suse.com> =E4=BA=8E2021=E5=B9=B49=E6=9C=8818=E6=
=97=A5=E5=91=A8=E5=85=AD =E4=B8=8A=E5=8D=8812:41=E5=86=99=E9=81=93=EF=BC=9A
>
> Hello Hao.
>
> On Thu, Sep 16, 2021 at 09:53:55PM +0800, Hao Sun <sunhao.th@gmail.com> w=
rote:
> > KCSAN reported the following data race during the kernel booting when
> > using Healer to fuzz the latest Linux kernel.
> > [...]
> >  cgroup_rstat_cpu_pop_updated kernel/cgroup/rstat.c:139 [inline]
> >  [...]
> >  cgroup_rstat_updated+0x53/0x1b0 kernel/cgroup/rstat.c:38
>
> FWIW, it's a "safe" race between updaters and flushers (possibly
> missing the latest update(s)). This is expected as explained in
> cgroup_rstat_updated() comment.
>

Would it be better to add a `data_race` macro to the corresponding
location so that the false report can be disabled?
See https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree=
/tools/memory-model/Documentation/access-marking.txt#n58
for more details.
Currently, fuzzer can not test the kernel with KCSAN enabled for a
long time, because cgroups setup is the basic step before executing
any test case.

Regards
Hao