linux-kernel - Re: data-race in cgroup_get_tree / proc_cgroup

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Message-ID: <20220829072741.tsxfgjp75lywzlgn@wittgenstein>
Date:   Mon, 29 Aug 2022 09:27:41 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Tejun Heo <tj@...nel.org>
Cc:     Gabriel Ryan <gabe@...columbia.edu>,
        Abhishek Shah <abhishek.shah@...umbia.edu>,
        linux-kernel@...r.kernel.org, andrii@...nel.org, ast@...nel.org,
        bpf@...r.kernel.org, cgroups@...r.kernel.org, daniel@...earbox.net,
        hannes@...xchg.org, john.fastabend@...il.com, kafai@...com,
        kpsingh@...nel.org, lizefan.x@...edance.com,
        netdev@...r.kernel.org, songliubraving@...com, yhs@...com
Subject: Re: data-race in cgroup_get_tree / proc_cgroup_show

On Sun, Aug 28, 2022 at 08:22:02AM -1000, Tejun Heo wrote:
> On Mon, Aug 22, 2022 at 01:04:58PM -0400, Gabriel Ryan wrote:
> > Hi Christian,
> > 
> > We ran a quick test and confirm your suggestion would eliminate the
> > data race alert we observed. If the data race is benign (and it
> > appears to be), using WRITE_ONCE(cgrp_dfl_visible, true) instead of
> > cmpxchg in cgroup_get_tree() would probably also be ok.
> 
> I don't see how the data race can lead to anything but would the following
> work?

Yep. You can take my,
Reviewed-by: Christian Brauner (Microsoft) <brauner@...nel.org>
when you turn it into a patch.