[11u] RFR: 8257746: Regression introduced with JDK-8250984 - memory might be null in some machines

[Baesken, Matthias]

Hi Severin,  thanks for backporting this.
Looks good to me .

Best regards, Matthias


>Please review this backport which adds necessary null checks before
>actually using the memory controller which might be null in some cases.
>JDK-8250984 introduced this regression and has been backported to
>11.0.10. There have been reports where an NPE happens. For example on
>an old SLES 11 system (cgroups v1) which only has the cpu controller
>mounted and a jtreg test is attempted to be run. jtreg itselfs as some
>initialization logic that uses OperatingSystemMXBean which has been
>made container aware via JDK-8226575.
>
>The JDK head patch doesn't apply since it has cgroups v2 support. It's
>a rather simple rewrite though.
>
>Bug: https://bugs.openjdk.java.net/browse/JDK-8257746
>webrev: https://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8257746/jdk11/01/webrev/
>
>Testing:
>Container tests on Linux (cgroups v1). Mattias Baesken reports that on
>a system which reproduces the issue it's fixed with the proposed patch.