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

On 13.02.20 10:01, Julien Grall wrote:

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?


I can rephrase that part to make it clear.


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