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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2014-03-17 at 12:20 +0000, Ian Campbell wrote:
> 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.

Done and pushed.

Ian.




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