On Sat, Jan 07, 2012 at 05:35:25PM +0100, Peter Zijlstra wrote:
> On Sat, 2012-01-07 at 22:56 +0800, Wu Fengguang wrote:
> > Subject:
> > Date: Sat Jan 07 22:50:45 CST 2012
> >
> > The uninitilized shift may lead to denominator=0 in
> > prop_fraction_percpu() and divide error in bdi_dirty_limit().
>
> I'm not seeing how, only proc_change_shift() can change ->index, and it
> does that after it writes ->pg[index]->shift.
Then I lose the clue why bdi_dirty_limit() will divide error at all.
prop_change_shift() does
change ->pg[index]->shift
smp_wmb()
change ->index
Will the read side prop_fraction_percpu() need some read memory barrier?
Thanks,
Fengguang
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