RFR(S): 8200450: Analysis and fix for JDK-8200366 (SIGSEGV in print_names())

[Vladimir Kozlov]

Thank you, Lutz

I agree with this approach with additional safeguarding checks. It has less affects on other code.

I start testing of these changes.

Thanks,
Vladimir

On 4/17/18 8:49 AM, Schmidt, Lutz wrote:
> Dear all,
> 
> may I please request your comments on this topic.
> 
> I have invested quite some time in testing, reproducing, analyzing, and fixing the effects that caused the CodeHeap State Analytics function print_names() to SIGSEGV (very rare, intermittent). Please refer to my description in the bug for the details (I did not want to duplicate it here).
> 
> I have prepared an preliminary webrev as a basis for further discussions. The webrev is preliminary at least with respect to the debugging/tracing output which is still in there intentionally. I thought it might be helpful for you to see how I tested that the changes actually hardened the code. A potential push candidate would have all #ifdef JDK8200450_TRACE sections removed. All #ifndef JDK8200450_REMEDY sections would be gone as well.
> 
> As workload I ran SPECjvm2008. From a separate process, I hammered sets of
>   - ${jcmd} ${testPID} Compiler.CodeHeap_Analytics discard
>   - ${jcmd} ${testPID} Compiler.CodeHeap_Analytics aggregate
>   - ${jcmd} ${testPID} Compiler.CodeHeap_Analytics MethodNames (50 repetitions)
>   - start over
> against the JVM. The pace was only limited by system capabilities. I scanned the output for marker strings to find handled issues which previously would have caused a SIGSEGV. Platforms tested are bsd_x86, linux_x86, linux_ppc, linux_s390. A handled issue was reported less frequently than 1 in 10,000. Unhandled issued were not encountered at all.
> 
> In addition, I cleaned the format strings a bit, replacing "%p" by INTPTR_FORMAT.
> 
> Bug:    https://bugs.openjdk.java.net/browse/JDK-8200450
> Webrev: http://cr.openjdk.java.net/~lucy/webrevs/8200450.00/
> 
> Thanks for having a look!
> Lutz
>   
>