RFR (XS) 8010723 - possible deadlock with SystemDictionary_lock

[Coleen Phillimore]

Hi Ioi,

I think the fact that this class is in the placeholder table with 
LOAD_INSTANCE key is what makes this remove_unshareable_info() thread 
safe, not the SystemDictionary_lock->wait() call. Since we remove the 
LOAD_INSTANCE entry below, changing the comment to say this will prevent 
someone from rearranging this code.
Also we shouldn't put bug numbers in the code, except for very rare 
cases, so this one should be removed.

The logic looks correct.
Thanks,
Coleen



On 3/29/2013 10:00 AM, Karen Kinnear wrote:
> Ioi,
>
> I take it back, this fix works fine. A bootstrap class loading is 
> waiting on
> the SystemDictionary_lock and the oldprobe->instance_load_in_progress().
>
> So, the remove_unshareable_info and restore_unshareable_info today
> are safe because they are single-threaded within the 
> instance_load_in_progress
> specifically for the boot loader.
>
> Might want to add that to the comment. Other parallel class loaders 
> have to be
> multi-threaded through load_instance to prevent deadlocks so if we use 
> a shared
> archive for them, we would need a different solution.
>
> thanks,
> Karen
>
> On Mar 29, 2013, at 9:06 AM, Karen Kinnear wrote:
>
>> Ioi,
>>
>> Thank you for jumping on this so quickly. I totally appreciate the 
>> detailed comments
>> in the code.
>>
>> The comment about the the other threads waiting on the SD_lock is not 
>> accurate -
>> there is a wait above, but there is a notify in find_or_define which 
>> means that other
>> threads will get through.
>>
>> Does the solution depend on this?
>>
>> thanks,
>> Karen
>>
>> On Mar 28, 2013, at 6:17 PM, Ioi Lam wrote:
>>
>>> Please review:
>>>
>>> http://cr.openjdk.java.net/~iklam/8010723/sysdic_lock_001/
>>>
>>> Bug: fatal error: acquiring lock Metaspace allocation lock/5 out
>>> of order with lock SystemDictionary_lock/4 -- possible deadlock
>>>
>>> http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=8010723
>>> https://jbs.oracle.com/bugs/browse/JDK-8010723
>>>
>>> Summary of fix:
>>>
>>>     This crash is caused by the patch in JDK-8007725
>>> http://hg.openjdk.java.net/hsx/hsx25/hotspot/rev/1fc4d4768b90
>>>
>>>     The code was calling Klass::remove_unshareable_info()(from within
>>> SystemDictionary::clean_up_shared_class)while
>>>     holding SystemDictionary_lock. This is unnecessary and possibly
>>>     unsafe.
>>>
>>>     I changed the code to call Klass::remove_unshareable_info() outside
>>>     of the SystemDictionary_lock. This is OK
>>>     because Klass::restore_unshareable_info()is also being called 
>>> outside
>>>     of SystemDictionary_lock.
>>>
>>> Tests:
>>>
>>>     I am running the UTE stress tests now.
>>>
>>> Thanks
>>> - Ioi
>>>
>>
>

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