Re: [Xen-devel] Detecting deadlocks with hypervisor..

[Anthony Liguori <aliguori@xxxxxxxxxx>]

T S wrote:
> This may sound a silly question (pardon me because i am relatively new 
> to linux kernel) .. will it be possible to continue running reboot.c 
> (or for that matter any kernel thread) when the kernel is deadlocked ? 
> In Linux, is the kernel a single process or a bunch of parallelly 
> executing entities? If later, then during a kernel deadlock (eg: by 
> loading a faulty module that disables interrupts and do something 
> silly) there can still be some other processes/threads run, right?
Sorry for not making this more clear previously.  You cannot restore a 
dead-locked domain if a normal xm save doesn't work.  One thing that 
makes Xen unique is that guests actually are aware of what physical 
pages are assigned to them.  When one does a save/restore, the guest has 
to canonicalize all of it's internal references to physical pages.  When 
it's restored, it then remaps it's newly assigned physical pages to all 
the old places where it needed to know about them for some reason or 
another.
If the guest isn't responsive when you do a save, then it will never 
canonicalize itself and there is no way to restore the domain.
Regards,

Anthony Liguori

> thanks
> TS
>
> > If a suspend completes correctly, Xend will see it (another watch 
> > will fire),
> > and xc_linux_save will be free to complete the save.
> >
> > > Also, does it seem viable to clone a copy of a deadlocked guest OS 
> > in the
> > > first place?
> >
> > If you have a byte-for-byte copy of a deadlocked guest, even if you 
> > could
> > suspend it, surely it will be deadlocked when it is resumed.  How do you
> > intend to break the deadlock, and how is it easier to do that from 
> > outside
> > than it is to perform deadlock detection in the guest?
> >
> > Ewan.
> >
> >
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