RFR: 8239559: Cgroups v2: Incorrect detection logic on some systems

[Bob Vandette]

Severin,

Don’t we need the contents of /proc/self/mountinfo in order to construct the path to the cgroup controllers?

On Thu, 2020-02-20 at 14:50 +0000, Baesken, Matthias wrote:
> Hi  Severin,
> 
> grep cgroup /proc/self/mountinfo 
> 
> returns  nothing.
> 
> Best Regards, Matthias
> 


Assuming your fix is correct, don’t we also need to apply the same change to the hotspot source cgroupSubsystem_linux.cpp?

Bob;


> On Feb 21, 2020, at 8:32 AM, Severin Gehwolf <sgehwolf at redhat.com> wrote:
> 
> Hi,
> 
> Could I please get a review of this fix to the detection heuristic of
> cgroup v1 vs cgroup v2? Matthias (in CC) discovered that on some old
> systems the JDK Metrics code throws InternalError caused by wrong
> detection logic when Metrics are being created on Linux.
> 
> The reason for this is that hierarchy IDs of 0 in /proc/cgroups is
> being used as a heuristic to detect cgroups v2 systems. Apparently some
> old systems like RHEL 6 and SLES 11 have no cgroups controllers
> mounted, thus, triggering a false positive.
> 
> The fix is to also look at /proc/self/mountinfo and correct logic in
> this case.
> 
> Bug: https://bugs.openjdk.java.net/browse/JDK-8239559
> webrev: http://cr.openjdk.java.net/~sgehwolf/webrevs/JDK-8239559/01/webrev/
> 
> Testing: docker/cgroups tests on hybrid (cgroups v1) and unified
> hierarchy (cgroups v2). New regression test. Looks good here.
> 
> Unfortunately, I wasn't able to reproduce this on an actual affected
> system. I somewhat reproduced via the derived regression test based on
> data from reporters. I'd appreciate any testing on systems where this
> reproduces.
> 
> Thanks,
> Severin
>