Date: Mon, 28 Nov 2005 13:07:11 +0100
From: Andi Kleen <ak@suse.de>
To: Keith Owens <kaos@sgi.com>
Cc: Andi Kleen <ak@suse.de>, Andrew Morton <akpm@osdl.org>, paulmck@us.ibm.com,
       greg@kroah.com, sekharan@us.ibm.com, linux-kernel@vger.kernel.org,
       lse-tech@lists.sourceforge.net, Douglas_Warzecha@dell.com,
       Abhay_Salunke@dell.com, achim_leubner@adaptec.com,
       dmp@davidmpye.dyndns.org
Subject: Re: [Lse-tech] Re: [PATCH 0/7]: Fix for unsafe notifier chain
Message-ID: <20051128120711.GP20775@brahms.suse.de>
References: <20051128045922.GK20775@brahms.suse.de> <4544.1133166696@ocs3.ocs.com.au>
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On Mon, Nov 28, 2005 at 07:31:36PM +1100, Keith Owens wrote:
> On Mon, 28 Nov 2005 05:59:22 +0100, 
> Andi Kleen <ak@suse.de> wrote:
> >On Sun, Nov 27, 2005 at 08:57:45PM -0800, Andrew Morton wrote:
> >> "Paul E. McKenney" <paulmck@us.ibm.com> wrote:
> >> >
> >> > Any options I missed?
> >> 
> >> Stop using the notifier chains from NMI context - it's too hard.  Use a
> >> fixed-size array in the NMI code instead.
> >
> >Or just don't unregister. That is what I did for the debug notifiers.
> 
> Unregister is not the only problem.  Chain traversal races with
> register as well.

Either it follows the old next or the new next. Both are valid.
The only problem is that there isn't a write barrier between

 n->next = *list;
 *list=n;

in notifier_chain_register, which might hit on non i386 architectures. 

-Andi
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