Re: [PATCH 4.19 01/34] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug - Greg Kroah-Hartman

From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: Zhang Qiao <zhangqiao22@huawei.com>,
	linux-kernel@vger.kernel.org, stable@vger.kernel.org,
	Zhao Gongyi <zhaogongyi@huawei.com>,
	Waiman Long <longman@redhat.com>, Tejun Heo <tj@kernel.org>,
	Juri Lelli <juri.lelli@redhat.com>
Subject: Re: [PATCH 4.19 01/34] cgroup/cpuset: Fix a race between cpuset_attach() and cpu hotplug
Date: Wed, 16 Mar 2022 15:27:37 +0100	[thread overview]
Message-ID: <YjHz2bifJBuCs/UK@kroah.com> (raw)
In-Reply-To: <20220314111940.GC1035@blackbody.suse.cz>

On Mon, Mar 14, 2022 at 12:19:41PM +0100, Michal Koutný wrote:
> Hello.
> 
> In my opinion there are two approaches:
> a) drop this backport (given other races present),

I have no problem with that, want to send a revert patch?

> b) swap the locks compatible with v4.19 as this patch proposes.
> 
> On Mon, Mar 14, 2022 at 05:11:50PM +0800, Zhang Qiao <zhangqiao22@huawei.com> wrote:
> > +       /*
> > +        * It should hold cpus lock because a cpu offline event can
> > +        * cause set_cpus_allowed_ptr() failed.
> > +        */
> > +       cpus_read_lock();
> 
> Maybe just a nit, the old kernels before commit c5c63b9a6a2e ("cgroup:
> Replace deprecated CPU-hotplug functions.") v5.15-rc1~159^2~5
> would be more consistent with get_online_cpus() here (but they're
> equivalent functionally so the locking order is correct).

A fixed up patch would also be appreciated :)

thanks,

greg k-h