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Re: [libvirt] [PATCH] Fix deadlock in QEMU close callback APIs



On Thu, Feb 28, 2013 at 02:50:34PM +0100, Jiri Denemark wrote:
> On Thu, Feb 28, 2013 at 13:33:31 +0000, Daniel P. Berrange wrote:
> > From: "Daniel P. Berrange" <berrange redhat com>
> > 
> > There is a lock ordering problem in the QEMU close callback
> > APIs.
> > 
> > When starting a guest we have a lock on the VM. We then
> > set a autodestroy callback, which acquires a lock on the
> > close callbacks.
> > 
> > When running auto-destroy, we obtain a lock on the close
> > callbacks, then run each callbacks - which obtains a lock
> > on the VM.
> > 
> > This causes deadlock if anyone tries to start a VM, while
> > autodestroy is taking place.
> > 
> > The fix is to do autodestroy in 2 phases. First obtain
> > all the callbacks and remove them from the list under
> > the close callback lock. Then invoke each callback
> > from outside the close callback lock.
> 
> Looks like we can just remove 568a6cda277f04ab9baaeb97490e548b7b608aa6
> then, can't we?

Quite possibly. I'll investigate that further, and test what happens.

Daniel
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