RFR(XS): 8143897 :Weblogic12medrec assert(handler_address == SharedRuntime::compute_compiled_exc_handler(nm, pc, exception, force_unwind, true)) failed: Must be the same

[Dean Long]

Jamsheed, it just occurred to me, why don't we need a LoadLoad barrier 
when we do the lock-free reads?

dl

On 2/4/2016 1:04 AM, Jamsheed C m wrote:
> Thanks Vladimir.
>
> Best Regards,
> Jamsheed
>
> On 2/3/2016 11:31 PM, Vladimir Kozlov wrote:
>> Looks good.
>>
>> Thanks,
>> Vladimir
>>
>> On 2/3/16 1:56 AM, Jamsheed C m wrote:
>>> Hi Vladimir, Chris,
>>>
>>> On 1/29/2016 6:22 AM, Vladimir Kozlov wrote:
>>>> On 1/28/16 12:29 PM, Jamsheed C m wrote:
>>>>>
>>>>>
>>>>> On 1/29/2016 12:15 AM, Christian Thalinger wrote:
>>>>>>     if (count() < cache_size) {
>>>>>>       set_pc_at(count(),addr);
>>>>>>       set_handler_at(count(), handler);
>>>>>>
>>>>>> Shouldn’t we read count() only once into a local variable to rule 
>>>>>> any odd race bugs down the road?
>>>>
>>>> +1. As I understand, Chris is suggesting to do it in addition to 
>>>> storestore barrier.
>>> I have made the suggested change.
>>> http://cr.openjdk.java.net/~thartmann/8143897/webrev.01/
>>>
>>> Best Regards,
>>> Jamsheed
>>>
>>>>
>>>> Do we have other similar code?
>>>>
>>>> Thanks,
>>>> Vladimir
>>>>
>>>>>
>>>>> write to cache is mutex lock protected. so this code is safe.
>>>>>
>>>>> Issue is seen in weak memory order machines.  lockless read of 
>>>>> exception cache values fails as writes in cache get
>>>>> reordered.
>>>>>
>>>>> Best Regards,
>>>>> Jamsheed
>>>>>>
>>>>>>> On Jan 28, 2016, at 5:16 PM, Jamsheed C m 
>>>>>>> <jamsheed.c.m at oracle.com> wrote:
>>>>>>>
>>>>>>> Hi,
>>>>>>>
>>>>>>> Please review the fix made for issue
>>>>>>>
>>>>>>> bug url: https://bugs.openjdk.java.net/browse/JDK-8143897
>>>>>>> web rev: http://cr.openjdk.java.net/~thartmann/8143897/webrev.00/
>>>>>>>
>>>>>>> Unit tests: As its hard, none
>>>>>>>
>>>>>>> Other tests: jprt.
>>>>>>>
>>>>>>> Description of the issue:
>>>>>>> A valid pc match in exception cache returning an invalid handler 
>>>>>>> makes assert to fail.
>>>>>>> This happens as  ExceptionCache reads are lock free access.
>>>>>>>
>>>>>>> As a fix for this i have put a storestore mem barrier before the 
>>>>>>> count is updated.
>>>>>>>
>>>>>>> Best Regards,
>>>>>>> Jamsheed
>>>>>
>>>
>