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SubjectRe: [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@linux.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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