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[Xen-devel] Re: [PATCH] fix pgd_lock deadlock

On Tue, Feb 15, 2011 at 09:26:35PM +0100, Thomas Gleixner wrote:
> Another thing. You check for in_interrupt(), but what makes sure that
> the code which takes pgd_lock is never taken with interrupts disabled
> except during early boot ?

It's perfectly fine to take pgd_lock with irq disabled, as long as you
don't pretend to take the page_table_lock too after that. So that's
not a concern.

I removed _irqsave from all pgd_lock, and I doubt there's any code
protected by pgd_lock that runs with irq disabled, but if there is,
it's still ok and it especially shouldn't have used _irqsave.

The only real issue here to sort out, is if pgd_lock is ever taken
from irq or not, and to me it looks like in_interrupt() should trigger
if it is ever taken from irq, so it won't go unnoticed for long if
this isn't ok.

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