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

[Ingo Molnar <mingo@elte.hu>]

* 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