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xen-devel
Re: [Xen-devel] Detecting deadlocks with hypervisor..
From: Anthony Liguori <aliguori@xxxxxxxxxx>
To: T S <thileepan_@xxxxxxxxxxx>
CC: xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] Detecting deadlocks with hypervisor..
Date: Fri, 24 Mar 2006 13:24:46 -0600
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.
Thank you for the reply. Do you mean to say that the canonicalize..()
functions in the xc_linux_save.c are actually invoked in the guest OS'
context?
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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