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Re: [Xen-devel] CONFIG_SMP required for save/restore and migration: bug?

On Tue, 2013-08-27 at 01:09 +0200, Luca Lesinigo wrote:
> So: with my config, non-SMP kernels will freeze after restore, while
> activating CONFIG_SMP and nothing else will make this problem
> disappear. Maybe non-SMP kernels are supposed to migrate but there's a
> software problem, or maybe SMP is a requirement but is not documented
> (or at least I wasn't able to find it). Maybe it's not CONFIG_SMP but
> one of its dependencies.

I can't see any explicit CONFIG_SMP so I think it must be one of its
dependencies (or something even more complex). Perhaps we implicitly
rely on CPU hotplug support or something similar.

Can you diff the working and non-working configs to see if anything has
become implicitly (de)activated by changing the CONFIG_SMP setting?

The easiest way to get to the bottom of this is probably to do printk
instrumentation of drivers/xen/manage.c:do_suspend(). For some of the
really early bits you might want to use xen_raw_printk() rather than
regular printk (to avoid problems with the console not being restored
yet). That will require a debug hypervisor build though (or perhaps
guest_loglvl=all on your h/v command line)

Turning on CONFIG_PM_DEBUG might also be interesting.


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