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Date: Thu, 16 Mar 2017 13:41:14 -0400
From: Tejun Heo <tj@kernel.org>
To: Oleg Nesterov <oleg@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
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        Li Zefan <lizefan@huawei.com>, Johannes Weiner <hannes@cmpxchg.org>,
        cgroups@vger.kernel.org
Subject: Re: [PATCH 2/2] kthread, cgroup: close race window where new
 kthreads can be migrated to non-root cgroups
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Hello,

On Thu, Mar 16, 2017 at 05:31:59PM +0100, Oleg Nesterov wrote:
> Or we can add another "unsigned no_cgroups:1" bit into task_struct,
> not sure.

To synchronize around initialization, a PF flag would be easier as we
can use wait_on_bit().

> Anyway, I do not understand the PF_NO_SETAFFINITY check in
> __cgroup_procs_write(). task_can_attach() checks it too, so cgroups
> can't change the affinity. Imo something explicit like no_cgroups
> makes more sense.

task_can_attach() predates the __cgroup_procs_write() and currently
doesn't do anything.  We can split the flag or rename it so that it's
more generic.  The reasons for disallowing cgroup migration have a lot
of crosssection with affinity, so it's not a complete misnomer.
Either way is fine by me.

Thanks.

-- 
tejun