On Thu, 31 Oct 2024 15:00:25 GMT, Sergey Chernyshev <schernys...@openjdk.org> wrote:
> Cgroup V1 subsustem fails to initialize mounted controllers properly in > certain cases, that may lead to controllers left undetected/inactive. We > observed the behavior in CloudFoundry deployments, it affects also host > systems. > > The relevant /proc/self/mountinfo line is > > > 2207 2196 0:43 > /system.slice/garden.service/garden/good/2f57368b-0eda-4e52-64d8-af5c > /sys/fs/cgroup/cpu,cpuacct ro,nosuid,nodev,noexec,relatime master:25 - cgroup > cgroup rw,cpu,cpuacct > > > /proc/self/cgroup: > > > 11:cpu,cpuacct:/system.slice/garden.service/garden/bad/2f57368b-0eda-4e52-64d8-af5c > > > Here, Java runs inside containerized process that is being moved cgroups due > to load balancing. > > Let's examine the condition at line 64 here > https://github.com/openjdk/jdk/blob/55a7cf14453b6cd1de91362927b2fa63cba400a1/src/hotspot/os/linux/cgroupV1Subsystem_linux.cpp#L59-L72 > It is always FALSE and the branch is never taken. The issue was spotted > earlier by @jerboaa in > [JDK-8288019](https://bugs.openjdk.org/browse/JDK-8288019). > > The original logic was intended to find the common prefix of `_root`and > `cgroup_path` and concatenate the remaining suffix to the `_mount_point` > (lines 67-68). That could lead to the following results: > > Example input > > _root = "/a" > cgroup_path = "/a/b" > _mount_point = "/sys/fs/cgroup/cpu,cpuacct" > > > result _path > > "/sys/fs/cgroup/cpu,cpuacct/b" > > > Here, cgroup_path comes from /proc/self/cgroup 3rd column. The man page > (https://man7.org/linux/man-pages/man7/cgroups.7.html#NOTES) for control > groups states: > > > ... > /proc/pid/cgroup (since Linux 2.6.24) > This file describes control groups to which the process > with the corresponding PID belongs. The displayed > information differs for cgroups version 1 and version 2 > hierarchies. > For each cgroup hierarchy of which the process is a > member, there is one entry containing three colon- > separated fields: > > hierarchy-ID:controller-list:cgroup-path > > For example: > > 5:cpuacct,cpu,cpuset:/daemons > ... > [3] This field contains the pathname of the control group > in the hierarchy to which the process belongs. This > pathname is relative to the mount point of the > hierarchy. > > > This explicitly states the "pathname is relative to the mount point of the > hierarchy". Hence, the correct result could have been > > > /sys/fs/cgroup/cpu,cpuacct/a/b > > > Howe... This pull request has now been integrated. Changeset: de29ef3b Author: Sergey Chernyshev <schernys...@openjdk.org> Committer: Dmitry Chuyko <dchu...@openjdk.org> URL: https://git.openjdk.org/jdk/commit/de29ef3bf3a029f99f340de9f093cd20544217fd Stats: 491 lines in 9 files changed: 449 ins; 3 del; 39 mod 8343191: Cgroup v1 subsystem fails to set subsystem path Co-authored-by: Severin Gehwolf <sgehw...@openjdk.org> Reviewed-by: sgehwolf, mbaesken ------------- PR: https://git.openjdk.org/jdk/pull/21808
