RFR: 8349988: Change cgroup version detection logic to not depend on /proc/cgroups [v3]

[Thomas Fitzsimmons]

On Fri, 28 Feb 2025 12:39:37 GMT, Thomas Fitzsimmons <duke at openjdk.org> wrote:

>> You are right, that if any of the required controllers aren't enabled at the kernel level we fail with `NVALID_CGROUPS_GENERIC`. However, the `if` condition is within the cgroups v1 branch while it used to be outside a version specific branch.
>> 
>> Also note that `/proc/cgroup` containing (last digit `0`, indicating the enabled flag):
>> 
>> 
>> cpuset  3   1   0\n
>> 
>> 
>> ... is semantically equivalent to it being missing entirely from `proc/cgroup`. But keeping `if (i != PIDS_IDX && i != CPUSET_IDX) {` above, would keep `all_required_controllers_enabled == true` which is not correct. Yes, we should keep/add a test like you suggest, but amend the patch to something like this: https://github.com/jerboaa/jdk/commit/26f765db9fef6f1d7be79452da701987274117c5
>
> Makes sense, will do.  I will also simplify the test case as you suggest.

I configured my testing `RHEL 8` virtual machine to get a real example of how `cpuset` might be disabled.  I created a full test case from it.

Previously `determine_type` would return `INVALID_CGROUPS_V1` later in the function.  Here is a version of the test case that passes without my patch:

https://github.com/fitzsim/jdk/commit/a671c643f16c63c3091868197bee1fbcde81f57d

With my patch, and the removal of ` && i != CPUSET_IDX`, `determine_type` returns `INVALID_CGROUPS_GENERIC` earlier.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23811#discussion_r1978075381