[jdk17u-dev] RFR: 8349988: Change cgroup version detection logic to not depend on /proc/cgroups

[Thomas Fitzsimmons]

On Mon, 16 Feb 2026 20:27:31 GMT, Severin Gehwolf <sgehwolf at openjdk.org> wrote:

> Please review this backport of the cgroup version detection logic which affects JDK 17 as well. Newer systems which are affected, like Ubuntu 2025-XX, get more commonly used. Therefore, I propose to backport it there too. The JDK 21 backport got shipped with the 21.0.10 update in January. The patch is not clean due to `nullptr` vs `NULL` differences and more context changes (e.g. [JDK-8261242](https://bugs.openjdk.org/browse/JDK-8261242) not in JDK 17). Since the patch is not clean anyway, I've included the one-liner of [JDK-8354878](https://bugs.openjdk.org/browse/JDK-8354878) right away.
> 
> Testing:
> - [x] GHA
> - [x] Container tests on cg v1 and cg v2 on Linux x86_64 (RHEL 8 and Fedora 42). Manual testing on an affected cg v2 system that container limits are detected.

This looks good to me.  I no longer have the virtual machines at hand to test, so I didn't test it.  I confirmed the changes versus the original patch seem fine though:

- copyright date updated, OK
- `fclose` addition per JDK-8354878, good fix
- context differences around `match_mount_info`, expected
- double-space to single-space change in comment, fine
- comment differences due to JDK-8261242 not having been backported, expected

At least `make test TEST=test/hotspot/jtreg/containers/cgroup/CgroupSubsystemFactory.java` succeeds for me on `Fedora 43 x86-64`.

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PR Comment: https://git.openjdk.org/jdk17u-dev/pull/4271#issuecomment-3915886556