RFR 8234613: JavaThread can escape back to Java from an ongoing handshake

[Patricio Chilano]

Thanks Coleen!

Patricio

On 11/22/19 5:15 PM, coleen.phillimore at oracle.com wrote:
>
> This fix looks good to me, from your explanations offline and in the 
> bug report.
> Coleen
>
> On 11/22/19 1:25 PM, Patricio Chilano wrote:
>> Hi,
>>
>> This patch aims to address a current bug where, given the right 
>> combination of handshakes and external suspend/resume, a JavaThread 
>> can transition from a safe state back to Java without blocking for a 
>> still-in-progress handshake. In the description of the bug I added an 
>> example, tracing the state changes of the JavaThread as it goes 
>> through the different transitions until it escapes the handshake. 
>> Currently, the window of time for this issue to happen is so small 
>> that we do not see actual failures running tests. Running test 
>> SuspendAtExit.java and adding some small delay before restoring the 
>> JavaThread state in java_suspend_self_with_safepoint_check() can 
>> demonstrate the issue.
>> The proposed fix is to check again if we have a pending/in-progress 
>> handshake operation after executing ~ThreadInVMForHandshake().
>>
>> Tested with mach5, tiers1-6 on all platforms (Linux, macOS, Windows 
>> and Solaris).
>>
>> Bug: https://bugs.openjdk.java.net/browse/JDK-8234613
>> Webrev: http://cr.openjdk.java.net/~pchilanomate/8234613/v01/webrev/
>>
>> Thanks,
>> Patricio
>