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

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 10/04/15 16:44, Konrad Rzeszutek Wilk wrote:
> 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. 

You cannot trust this line for an HVM guest.  It simply means that the
toolstack has performed the remote_shutdown hypercall, not that the
guest has finally stopped.

~Andrew

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