Re: [Xen-devel] [PATCH] xen: make sure stop_machine_run() is always called in a tasklet

[Julien Grall <julien@xxxxxxx>]

Hi,

On 13/02/2020 11:01, Jürgen Groß wrote:
> On 13.02.20 10:01, Julien Grall wrote:
> > Hi,
> >
> > On 11/02/2020 10:35, Juergen Gross wrote:
> > > With core scheduling active it is mandatory for stop_machine_run() to
> > > be called in a tasklet only, as otherwise a scheduling deadlock would
> > > occur: stop_machine_run() does a cpu rendezvous by activating a tasklet
> > > on all other cpus. In case stop_machine_run() was not called in an idle
> > > vcpu it would block scheduling the idle vcpu on its siblings with core
> > > scheduling being active, resulting in a hang.
> > This suggests it is not safe to call stop_machine_run() outside a 
> > tasklet but still under "idle vCPU" context. However, alternative 
> > patching on Arm during boot will not be in a tasklet. Is it going to 
> > be safe?
> Yes.
>
> I can rephrase that part to make it clear.
That would nice. Thank you!

Cheers,

--
Julien Grall

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