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Re: [Xen-devel] [PATCH v2] xen: arm: increase priority of SGIs used as IPIs

On Mon, 2014-03-17 at 12:11 +0000, Julien Grall wrote:
> Hi Ian,
> On 03/17/2014 11:31 AM, Ian Campbell wrote:
> > Code such as on_selected_cpus expects/requires that an IPI can preempt a
> > processor which is just handling a normal interrupt. Lacking this property 
> > can
> > result in a deadlock between two CPUs trying to IPI each other from 
> > interrupt
> > context.
> > 
> > For the time being there is only two priorities, IRQ and IPI, although it is
> > also conceivable that in the future some IPIs might be higher priority than
> > others. This could be used to implement a better BUG() than we have now, 
> > but I
> > haven't tackled that yet.
> > 
> > Tested with a debug patch which sends a local IPI from a keyhandler, which 
> > is
> > run in serial interrupt context.
> > 
> > This should also fix the issue reported by Oleksandr in "xen/arm:
> > maintenance_interrupt SMP fix" without resorting to trylock.
> Sorry, I didn't notice it before. If you plan to keep the last
> paragraph, can you add a link to the patch?

I'll drop the para, I don't think it is useful anymore.

> Regards,

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