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From: ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman)
Subject: Re: [CFT][PATCH 6/7] userns: Add a knob to disable setgroups on a per
	user namespace basis
Date: Tue, 09 Dec 2014 13:31:39 -0600
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ebiederm-aS9lmoZGLiVWk0Htik3J/w@public.gmane.org (Eric W. Biederman) writes:

> Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org> writes:
>
>>
>> This text was actually my suggested comment text.
>
> Now I see.
>
>> If you put smp_rmb() in this function with a comment like that, then I
>> think it will all make sense and be obviously correct (even with most
>> of the other barriers removed).
>
> Right.
>
> Given that we have to be careful when using these things anyway what
> I was hoping to achieve with the barriers appears impossible, and
> confusing so I will see about just adding barriers where we need them
> for real.  Sigh.

Doh.  The code has been entirely too clever.

There are no need for atomics or other cleverness, I just need to
generalize id_map_mutex.  I knew that had to be a trivially correct
way of handling this mess.

Eric