linux-kernel - Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)

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Message-ID: <20090220172526.GM6960@linux.vnet.ibm.com>
Date:	Fri, 20 Feb 2009 09:25:26 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Vegard Nossum <vegard.nossum@...il.com>, stable@...nel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Nick Piggin <npiggin@...e.de>,
	Pekka Enberg <penberg@...helsinki.fi>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error)

On Fri, Feb 20, 2009 at 06:14:27PM +0100, Ingo Molnar wrote:
> 
> * Paul E. McKenney <paulmck@...ux.vnet.ibm.com> wrote:
> 
> > > > So, what flavor of RCU were you using?
> > > 
> > > well, even in preemptible RCU the grace period should be 
> > > extended as long as we are non-preempt (which we are here), 
> > > correct?
> > 
> > Given Classic RCU, you are quite correct.  With preemptable 
> > RCU, if there are no readers, and if irqs are enabled, the 
> > grace period could end within the spinlock's critical section.  
> > Of course, the spinlock would need to be held for an 
> > improbably long time -- many milliseconds.
> 
> ah. But we _can_ get unlucky there and get into 
> multiple-milliseconds of blockage: for example if some heavy 
> interrupt source or softirq processes stuff for many 
> milliseconds.
> 
> So it's a real fix needed both for mainline and for 2.6.28. 
> And kudos to kmemcheck ;-)

Kudos from me as well!!!  Sure beats the heck out of tracking down memory
corruption by hand!!!  ;-)

							Thanx, Paul
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