RFR(xxs): 8176140: Crashes or timeouts during error reporting may lead to infinitely repeated error logs until ErrorLogTimeout is hit

[Thomas Stüfe]

Hi all,

please review this tiny fix.

Issue: https://bugs.openjdk.java.net/browse/JDK-8176140

Webrev:
http://cr.openjdk.java.net/~stuefe/webrevs/8176140-Crashes-or-timeouts-during-error-reporting-may-lead-to-infinitely-repeated-error-logs-until-ErrorLogTimeout-is-hit/jdk10-webrev.00/webrev/

Basically, the error reporting had this bug where a secondary crash (or,
after JDK-8166944, a timeout) could lead to an error log with infinitely
repeated content. In practice, one would hit either the maximum stack depth
of the reporting thread or the ErrorLogTimeout.

This would happen if the crash were to happen inside
VMError::report_and_die(), after the reporting is done
|VMError::report(&log, true)| and before the |log_done| flag is set. This
is a very small window, but Chris was able to trigger this bug by
introducing an error inside an ubiquitous base function (malloc), so it is
not just theoretical.

The fix is simply to set log_done right after the VMError::report() call.

Thanks & Kind Regards, Thomas