RFR: 8245543: Cgroups: Incorrect detection logic on some systems (still reproducible) [v3]

[Bob Vandette]

On Mon, 5 Oct 2020 10:16:49 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

>> 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:
> 
>   Fix typo in comment

src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java line 150:

> 148:         // find anyway in that case.
> 149:         try (Stream<String> mntInfo = CgroupUtil.readFilePrivileged(Paths.get(mountInfo))) {
> 150:             boolean anyCgroupMounted = mntInfo.anyMatch(CgroupSubsystemFactory::noSystemdCgroupLine);

I'd prefer a similar approach to the hotspot side where you do a positive check for controllers we are interested in
rather than a negative check for systemd.

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

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