From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Serge E. Hallyn" <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>
Subject: Re: namespaces?: bug at mm/slub.c:2750
Date: Wed, 11 Feb 2009 11:24:16 -0600
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To: David Howells <dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Cc: Dhaval Giani <dhaval-23VcF4HTsmIX0ybBhKVfKdBPR1lH4CV8@public.gmane.org>, Vegard Nossum <vegard.nossum-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>, Eric Sesterhenn <snakebyte-Mmb7MZpHnFY@public.gmane.org>, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, containers-qjLDD68F18O7TbgM5vRIOg@public.gmane.org, Andrew Morton <akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>, Peter Zijlstra <a.p.zijlstra-/NLkJaSkS4VmR6Xm/wNWPw@public.gmane.org>
List-Id: containers.vger.kernel.org

Quoting David Howells (dhowells-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org):
> Serge E. Hallyn <serue-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org> wrote:
> 
> >  static void uid_hash_remove(struct user_struct *up)
> >  {
> > +	put_user_ns(up->user_ns);
> >  	hlist_del_init(&up->uidhash_node);
> >  }
> 
> Don't you need to do the hlist_del_init() first?  Otherwise, mightn't the
> put_user_ns() cause the namespace to be freed before hlist_del_init() removes
> the user_struct from it?

It's called under uidhash_lock spinlock so should be ok, but in
principle you're right so it's probably a good idea.

The main point is that without this patch, put_user_ns is done before
the hlist_del_init and *not* atomically under uidhash_lock.

thanks,
-serge