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Date: Fri, 02 Aug 2002 10:37:22 -0700
From: Dave Hansen <haveblue@us.ibm.com>
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To: Oliver Neukum <Oliver.Neukum@lrz.uni-muenchen.de>
CC: Kasper Dupont <kasperd@daimi.au.dk>,
       Linux-Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] Race condition?
References: <3D4A8D45.49226E2B@daimi.au.dk> <200208021700.g72H0bm02654@fachschaft.cup.uni-muenchen.de>
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Oliver Neukum wrote:
> Am Freitag, 2. August 2002 15:46 schrieb Kasper Dupont:
> 
>>Is there a race condition in this piece of code from do_fork in
> 
> It would seem so. Perhaps the BKL was taken previously.
> 

Even if it was, I doubt the code ever knowingly relied upon it.  If I 
know that I'm protected under a lock, I rarely go to the trouble of 
atomic operations.

The root of the problem is that the reference count is being relied on 
for the wrong thing.  There is a race on p->user between the
dup_task_struct() and whenever the atomic_inc(&p->user->__count) 
occcurs.   The user reference count needs to be incremented in 
dup_task_struct(), before the copy occurs.
-- 
Dave Hansen
haveblue@us.ibm.com

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