[vbox-dev] [SPAM] Re: Fix to #13789

[a.urakov at drweb.com]

Hello Klaus,

yes, we already upgraded to new version. At the moment I have not 
encountered other problems, but if I find them then I will let you know 
necessarily.

Thanks again,
Alexander

17.02.2015 18:45, Klaus Espenlaub пишет:
> Alexander,
>
> all your fixes (including the relevant subset of this one) are 
> included in 4.3.22. Would be great if you could provide feedback if 
> any deadlocks or other quirks are left.
>
> Regards,
> Klaus
> On 12.02.2015 12:42, a.urakov at drweb.com wrote:
>> 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, a.urakov at drweb.com wrote:
>>>> Diffs attached
>>>>
>>>> 30.01.2015 17:49, a.urakov at drweb.com 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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