RE: [2.6.25-rc5-mm1][regression] ia64: hackbench doesn't finish >12 hour

[Luck, Tony]

> We can reproduce the soft lockup issue now and root cause the issue as
well.
>
> Since the ptc.g patch uses semaphore ptcg_sem to serialize multiple
> ptc.g instructions in ia64_global_tlb_purge(). This requires the code
> path should be safe to sleep in down(). But the code path can not
> sleep during swap because it holds some spin locks (e.g.
anon_vma_lock).
> Going to sleep finally causes soft lockup.

I've just pushed a new version of this patch into my test tree (so
it will show up in -mm and linux-next when they pull and rebuild).
It now uses the Piggin/Wilcox "spinaphore" primitives.  It passes
all my tests, and some runs of "hackbench" that tried to match the
tests that failed before at Fujitsu by forcing moderate amounts of
swapping.

-Tony
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