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SubjectRe: [PATCH 2/2] mm: page allocator: Do not drain per-cpu lists via IPI from page allocator context
On Thu, Jan 12, 2012 at 04:18:12PM +0100, Peter Zijlstra wrote:
> On Wed, 2012-01-11 at 10:11 +0000, Mel Gorman wrote:
> > At least one bug report has
> > been seen on ppc64 against a 3.0 era kernel that looked like a bug
> > receiving interrupts on a CPU being offlined.
> Got details on that Mel? The preempt_disable() in on_each_cpu() should
> serialize against the stop_machine() crap in unplug.

I might have added 2 and 2 together and got 5.

The stack trace clearly was while sending IPIs in on_each_cpu() and
always when under memory pressure and stuck in direct reclaim. This was
on !PREEMPT kernels where preempt_disable() is a no-op. That is why I
thought get_online_cpu() would be necessary.

Mel Gorman

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