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From: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
To: "Michal Koutný" <mkoutny-IBi9RG/b67k@public.gmane.org>
Cc: Jing-Ting Wu
	<jing-ting.wu-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>,
	Johannes Weiner <hannes-druUgvl0LCNAfugRpC6u6w@public.gmane.org>,
	Zefan Li <lizefan.x-EC8Uxl6Npydl57MIdRCFDg@public.gmane.org>,
	Matthias Brugger
	<matthias.bgg-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
	cgroups-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	linux-mediatek-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org,
	Shakeel Butt <shakeelb-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>,
	wsd_upstream-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org,
	lixiong.liu-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org,
	wenju.xu-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org,
	jonathan.jmchen-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org
Subject: Re: [Bug] race condition at rebind_subsystems()
Date: Fri, 15 Jul 2022 06:47:59 -1000	[thread overview]
Message-ID: <YtGaP+e35DZYSQf0@slm.duckdns.org> (raw)
In-Reply-To: <20220715115938.GA8646-9OudH3eul5jcvrawFnH+a6VXKuFTiq87@public.gmane.org>

(resending, I messed up the message header, sorry)

Hello,

On Fri, Jul 15, 2022 at 01:59:38PM +0200, Michal Koutný wrote:
> The css->rstat_css_node should not be modified if there are possible RCU
> readers elsewhere.
> One way to fix this would be to insert synchronize_rcu() after
> list_del_rcu() and before list_add_rcu().
> (A further alternative (I've heard about) would be to utilize 'nulls'
> RCU lists [1] to make the move between lists detectable.)
> 
> But as I'm looking at it from distance, it may be simpler and sufficient
> to just take cgroup_rstat_lock around the list migration (the nesting
> under cgroup_mutex that's held with rebind_subsystems() is fine).

synchronize_rcu() prolly is the better fit here given how that list_node's
usage, but yeah, great find.

Thanks.

-- 
tejun

  parent reply	other threads:[~2022-07-15 16:47 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-06-30 10:52 [Bug] race condition at rebind_subsystems() Jing-Ting Wu
2022-07-15 11:59 ` Michal Koutný
     [not found]   ` <20220715115938.GA8646-9OudH3eul5jcvrawFnH+a6VXKuFTiq87@public.gmane.org>
2022-07-15 16:47     ` Tejun Heo [this message]
     [not found]       ` <YtGaP+e35DZYSQf0-NiLfg/pYEd1N0TnZuCh8vA@public.gmane.org>
2022-07-18  7:44         ` Jing-Ting Wu
2022-07-19 13:35           ` Michal Koutný
     [not found]             ` <20220719133512.GD897-9OudH3eul5jcvrawFnH+a6VXKuFTiq87@public.gmane.org>
2022-07-21  6:46               ` Jing-Ting Wu
     [not found]                 ` <98d738ec5d7d32441f6e62278fff32201fd948de.camel-NuS5LvNUpcJWk0Htik3J/w@public.gmane.org>
2022-08-07  6:58                   ` Jing-Ting Wu

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