RFR: 8245543: Cgroups: Incorrect detection logic on some systems (still reproducible) [v4]

[Severin Gehwolf]

> An issue similar to [JDK-8239559](https://bugs.openjdk.java.net/browse/JDK-8239559) has been discovered. On the
> affected system, `/proc/self/mountinfo` contains a line such as this one:
> 
> 35 26 0:26 / /sys/fs/cgroup/systemd rw,nosuid,nodev,noexec,relatime - cgroup systemd rw,name=systemd
>  
> 
> Note that `/proc/cgroups` looks like this:
> 
> #subsys_name	hierarchy	num_cgroups	enabled
> cpuset	0	1	1
> cpu	0	1	1
> cpuacct	0	1	1
> blkio	0	1	1
> memory	0	1	1
> devices	0	1	1
> freezer	0	1	1
> net_cls	0	1	1
> perf_event	0	1	1
> net_prio	0	1	1
> hugetlb	0	1	1
> pids	0	1	1
> 
> This is in fact a cgroups v1 system with systemd put into a separate namespace via FS type `cgroup`. That mountinfo
> line confuses the cgroups version detection heuristic. It only looked whether or not there is **any** entry in
> mountinfo of FS-type `cgroup` . That's wrong. A better heuristic would be looking at controllers we care about: `cpu`,
> `cpuacct`, `memory`, `cpuset` for hotspot and some more for the Java side. The proposed fix on the hotspot side is to
> set `any_cgroup_mounts_found` to true only if one of those controllers show up in mountinfo. Otherwise, we know it's
> cgroup v2 due to the zero hierarchy ids.  For the Java side the proposal is to add some parsing for mountinfo lines and
> look for `cgroup` FS-type lines which aren't also mounted purely for systemd.
> **Testing**
> 
>  - [x] Linux x86_64 container tests on cgroup v1 (fastdebug)
>  - [x] Linux x86_64 container tests on cgroup v2 (fastdebug)
>  - [x] Added regression test which fails prior the patch and passes after
>  - [x] Submit testing

Severin Gehwolf has updated the pull request incrementally with one additional commit since the last revision:

  8245543: Cgroups: Incorrect detection logic on some systems (still reproducible)

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/485/files
  - new: https://git.openjdk.java.net/jdk/pull/485/files/d334ac60..5e2ca2dc

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=485&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=485&range=02-03

  Stats: 548 lines in 5 files changed: 284 ins; 193 del; 71 mod
  Patch: https://git.openjdk.java.net/jdk/pull/485.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/485/head:pull/485

PR: https://git.openjdk.java.net/jdk/pull/485