[Xen-devel] Re: [PATCH 08/13] xen/pvticketlock: disable interrupts while blocking

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 09/02/2011 07:47 AM, Peter Zijlstra wrote:
> On Thu, 2011-09-01 at 17:55 -0700, Jeremy Fitzhardinge wrote:
>> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>
>>
>> We need to make sure interrupts are disabled while we're relying on the
>> contents of the per-cpu lock_waiting values, otherwise an interrupt
>> handler could come in, try to take some other lock, block, and overwrite
>> our values.
> Would this make it illegal to take a spinlock from NMI context?

That would be problematic.  But a Xen domain wouldn't be getting NMIs -
at least not standard x86 ones - so that's moot.

> I know that its generally considered bad form, but there's at least one
> spinlock that's only taken from NMI context and thus hasn't got any
> deadlock potential.

Which one?

    J

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