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

[serguei.spitsyn at oracle.com]

Hi Dan,

Thank you and Robbin for discovering and fixing this!
The fix looks good to me.
It is nice to have this new logging.

Should we fix this bug in 13 first, or you consider it risky?

Thanks,
Serguei


On 7/3/19 7:04 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
>