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

* 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 ;-)

Ingo


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