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Re: [libvirt] libvirtd live-locking on CTX_LOCK when doing 'virsh <domid> save /tmp/blah' with guest corrupting memory (on purpose).



On Wed, Apr 08, 2015 at 04:45:24PM +0100, Andrew Cooper wrote:
> On 08/04/15 15:47, Konrad Rzeszutek Wilk wrote:
> > Hey Jim, Andrew, and Ian,
> >
> > This is libvirt v1.2.14 + three patches:
> > c82a59b libxl: drop virDomainObj lock when destroying a domain
> > a1c9d30 libxl: acquire a job when destroying a domain
> > 5bd5406 libxl: Move job acquisition in libxlDomainStart to callers
> >
> > For fun I've set up an guest with PCI passthrough and tried to save it
> > (HAHAH) with an disastrous result (xc_save_helper was stuck). Probably
> > due to outstanding DMA operations wreaking havoc.
> 
> Outstanding DMA wont make any difference.  It isn't (and can't) be
> reflected in the logdirty bitmap, so libxc simply wont know about it.
> 
> xc_save_helper is blocked because it has called back into the libxl with
> the suspend_and_state() callback.
> 
> i.e. libxc has requested that libxl pause the domain, and that request
> is still outstanding.
> 
> 
> The vcpu trace from the very bottom shows that the guest has not yet
> paused itself.  1 vcpu is blocked in the hypervisor while the other look
> to be in some spinlock code.

Except the guest is in '---ss- ' so it _should_ be paused by now. 
> 
> ~Andrew


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