[vbox-dev] [SPAM] Re: Fix to #13789
a.urakov at drweb.com
a.urakov at drweb.com
Thu Feb 12 11:42:01 UTC 2015
you are right, if approved Medium lock order is "from parent to child",
then there is nothing wrong in original VirtualBoxImpl.cpp code. Thanks
12.02.2015 14:22, Klaus Espenlaub пишет:
> Hi Alexander,
> this patch (the VirtualBoxImpl.cpp part) is loosening up
> synchronization a bit too much for my taste. The approved lock order
> for Medium instances is "from parent to child", which is why your
> MachineImpl.cpp change is a perfect catch (and solution, because the
> child lock is held unnecessarily).
> The VirtualBoxImpl.cpp part on the other hand uses the correct lock
> order, so I'm wondering if you have any evidence that this is actually
> solving any deadlock. Not disputing that the code should still work
> properly after the change (with a tiny bit less atomicity which isn't
> strictly required), but I suspect there was nothing wrong with it
> initially. If it played part of a deadlock then it's most likely the
> other party where the lock order is wrong. If you're running a debug
> build then the lock validator in the runtime is active and should
> catch anything fishy (unless it involves event semapshores as they
> have no owner).
> Feedback appreciated :-)
> On 30.01.2015 15:50, a.urakov at drweb.com wrote:
>> Diffs attached
>> 30.01.2015 17:49, a.urakov at drweb.com пишет:
>>> We would like to contribute to VirtualBox under MIT license. We send
>>> our changes to fix bug described at
>>> https://www.virtualbox.org/ticket/13789 .
>>> The idea is that functions /Medium::removeRegistry()/ and
>>> /Medium::addRegistry()/ themselves take write locks on mediums, so
>>> we get read lock only for /Medium::getAnyMachineBackref()/ call in
>>> /VirtualBox::unregisterMachine()/ function. Also we release read
>>> lock on medium after we got its parent and before we are going to
>>> iterate through parents in /Machine::detachAllMedia()/ function.
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