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

[Yu, Fenghua]

>this paramter mean use all physical memory and about 1GB swap space.
>Could you expand swap space?

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.

Actually we though of this issue before releasing the ptcg patch and
wrote some non-sleeping versions of ptcg patches. But since we couldn't
see the sleeping issue during our testing, we didn't release a
non-sleeping ptcg patch. If replacing the ptcg patch in -mm1 tree with
one of our non-sleeping ptcg patches, the issue goes away.

Tony and I are working on releasing a final ptcg patch to solve the
issue.

Thanks.

-Fenghua
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