RFR: 8149085: IntegrationTest1.java fails intermittently due to use of semi-initialized TLAB

[Stefan Johansson]

On 2016-06-08 15:57, Mikael Gerdin wrote:
> Hi,
>
> On 2016-06-08 13:56, Erik Helin wrote:
>> On 2016-05-24, Stefan Johansson wrote:
>>> Hi,
>>>
>>> Please review this fix for:
>>> https://bugs.openjdk.java.net/browse/JDK-8149085
>>>
>>> Webrev:
>>> http://cr.openjdk.java.net/~sjohanss/8149085/hotspot.00/
>>
>> Looks reasonable, it is better than the current check. Reviewed.
>
> +1
>
Thanks guys for being reasonable :)

Stefan
> /Mikael
>
>>
>> Thanks,
>> Erik
>>
>>> Summary:
>>> Thread::cooked_allocated_bytes() tries to give a good estimation of 
>>> how much
>>> has been allocated by a given thread. It does this by adding the stored
>>> _allocated_bytes valued, incremented when a TLAB is retired, with 
>>> the used
>>> bytes from the currently active TLAB. This works fine when
>>> cooked_allocated_bytes() is called by the current thread, but when 
>>> called to
>>> query a different thread there is a risk that the thread is in the 
>>> middle of
>>> retiring its TLAB. In such case there was risk that a bad 
>>> used_bytes() value
>>> was used and in turn caused the test in question to fail.
>>>
>>> A similar issue seems to have been semi-fixed before, the removed code
>>> suggests that making sure that the signed used bytes size is more 
>>> than zero
>>> is enough to make it a valid TLAB, but it turns out this is not enough.
>>> Instead making sure that the used bytes value is less than the max 
>>> allowed
>>> TLAB-size should ensure that the TLAB has been fully initialized.
>>>
>>> As the added comment suggests there is still a race present in this 
>>> code,
>>> and I don't intend to fix this now because I see this more as a fast
>>> sampling function than something that we should rely on.
>>>
>>> Testing:
>>> Verified fix locally. RBT run for G1 and Parallel is ongoing.
>>>
>>> Thanks,
>>> Stefan
>>>