Hi Klaus,
you are right, if approved Medium lock order is "from parent to child",
then there is nothing wrong in original VirtualBoxImpl.cpp code. Thanks
a lot!
Regards,
Alexander
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 :-)
Klaus
On 30.01.2015 15:50, [email protected] wrote:
Diffs attached
30.01.2015 17:49, [email protected] пишет:
Hello!
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.
Regards,
Alexander
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