RFR(XXS): 8227117: normal interpreter table is not restored after single stepping with TLH

[David Holmes]

Looks good!

Thanks,
David

On 6/07/2019 6:24 am, Daniel D. Daugherty wrote:
> Greetings,
> 
> Here's the new webrev URLs after CR0:
> 
> Full:
> 
> http://cr.openjdk.java.net/~dcubed/8227117-webrev/1_for_jdk14.full/
> 
> Inc:
> 
> http://cr.openjdk.java.net/~dcubed/8227117-webrev/1_for_jdk14.inc/
> 
> Only src/hotspot/share/prims/jvmtiEventController.cpp changed in this
> round. The only code change was this:
> 
>   VM_ChangeSingleStep::VM_ChangeSingleStep(bool on)
> -  : _on(on != 0)
> +  : _on(on)
>   {
>   }
> 
> The other change is a header comment block rewrite...
> 
> Thanks, in advance, for questions, comments or suggestions.
> 
> Dan
> 
> 
> 
> On 7/3/19 10:04 PM, Daniel D. Daugherty wrote:
>> Greetings,
>>
>> Robbin recently discovered this issue with Thread Local Handshakes. Since
>> he's not available at the moment, I'm handling the issue:
>>
>>     JDK-8227117 normal interpreter table is not restored after single 
>> stepping with TLH
>>     https://bugs.openjdk.java.net/browse/JDK-8227117
>>
>> When using Thread Local Handshakes, the normal interpreter table is
>> not restored after single stepping. This issue is caused by the
>> VM_ChangeSingleStep VM-op relying on SafepointSynchronize::end() to
>> restore the normal interpreter table for the "off" case.
>>
>> Prior to Thread Local Handshakes, this was a valid assumption to make.
>> SafepointSynchronize::end() has been refactored into
>> disarm_safepoint() and it only calls Interpreter::ignore_safepoints()
>> on the global safepoint branch. That matches up with the call to
>> Interpreter::notice_safepoints() that is also on the global safepoint
>> branch.
>>
>> The solution is for the VM_ChangeSingleStep VM-op for the "off" case
>> to call Interpreter::ignore_safepoints() directly.
>>
>> Here's the webrev URL:
>>
>> http://cr.openjdk.java.net/~dcubed/8227117-webrev/0_for_jdk14/
>>
>> The fix is just a small addition to VM_ChangeSingleStep::doit():
>>
>>    if (_on) {
>>      Interpreter::notice_safepoints();
>> +  } else {
>> +    Interpreter::ignore_safepoints();
>>    }
>>
>> Everything else is just new logging support for future debugging of
>> interpreter table management and single stepping.
>>
>> Tested this fix with Mach5 Tier[1-3] on the standard Oracle platforms.
>> Mach5 Tier[4-6] on standard Oracle platforms is running now.
>>
>> Thanks, in advance, for questions, comments or suggestions.
>>
>> Dan
>>
>>
>