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xen-devel
Re: [Xen-devel] [PATCH] Fix locking bug in vcpu_migrate
Nice that empirical evidence supports the patch, however, I'm being dense
and don't understand why order of lock release matters.
I was taught long ago to release them in order, but as I think about it,
I agree with you that there doesn't seem to be a scenario when the
release would matter.
It's odd that it seemed to lead to such a big difference for me, then.
I'll do some further tests -- maybe I changed something else to cause
the behavior, or the problem is more random than I thought and just
hasn't occurred for me yet in all the new tests.
perhaps you've merely perturbed a fragile pos code that's
broken in some other way.
That's entirely possible.
Also the last hunk of your patch is broken -- in the final else clause you
call spin_unlock_irqrestore on the wrong lock. This is very definitely a
bug, as irqs should never be enabled while any schedule_lock is held.
Definitely. I had fixed that here but sent an old version of the patch
-- a boneheaded mistake.
-John
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