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From: "Michal Koutný" <mkoutny@suse.com>
To: Hao Sun <sunhao.th@gmail.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
Subject: Re: KCSAN: data-race in cgroup_rstat_flush_locked / cgroup_rstat_updated
Date: Mon, 20 Sep 2021 20:09:56 +0200	[thread overview]
Message-ID: <20210920180956.GA15043@blackbody.suse.cz> (raw)
In-Reply-To: <CACkBjsZnp8Kf26tR3anbcLQNiMJ9=bqYMJ66tKBvXO6tkV3qyw@mail.gmail.com>

On Sat, Sep 18, 2021 at 09:27:08AM +0800, Hao Sun <sunhao.th@gmail.com> wrote:
> Would it be better to add a `data_race` macro to the corresponding
> location so that the false report can be disabled?

Something like this

--- a/kernel/cgroup/rstat.c
+++ b/kernel/cgroup/rstat.c
@@ -35,7 +35,7 @@ void cgroup_rstat_updated(struct cgroup *cgrp, int cpu)
         * instead of NULL, we can tell whether @cgrp is on the list by
         * testing the next pointer for NULL.
         */
-       if (cgroup_rstat_cpu(cgrp, cpu)->updated_next)
+       if (data_race(cgroup_rstat_cpu(cgrp, cpu)->updated_next))
                return;

        raw_spin_lock_irqsave(cpu_lock, flags);
?

Makes sense to me. Will you send a patch (if this resolves your KCSAN
noise)?

(IIUC, this becase more visible after commit aa48e47e3906 ("memcg:
infrastructure to flush memcg stats") v5.15-rc1 but it was present since
d8ef4b38cb69 ("Revert "cgroup: Add memory barriers to plug
cgroup_rstat_updated() race window"") v5.7.)

> 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.

(Interesting, learning...)

Thanks,
Michal

      reply	other threads:[~2021-09-20 18:14 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-16 13:53 KCSAN: data-race in cgroup_rstat_flush_locked / cgroup_rstat_updated Hao Sun
2021-09-17 16:41 ` Michal Koutný
2021-09-18  1:27   ` Hao Sun
2021-09-20 18:09     ` Michal Koutný [this message]

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