On Thu, 5 Dec 2024 20:05:56 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 t... > > Sergey Chernyshev has updated the pull request with a new target base due to > a merge or a rebase. The pull request now contains 13 commits: > > - diverged after integration of JDK-8344177 > > # Conflicts: > # src/java.base/linux/classes/jdk/internal/platform/CgroupUtil.java > - update cgroup v1 in metrics > - Apply suggestions from code review > > Co-authored-by: Severin Gehwolf <jerb...@gmail.com> > - updated test (path is reduced) > - updated test (path is reduced) > - adjust path suffix in cgroup (v1) version specific code, when root != > cgroup > - Merge branch 'master' into JDK-8343191 > - warn wenn ../ encountered, update path adjustment > - Update src/hotspot/os/linux/cgroupV1Subsystem_linux.cpp > > Co-authored-by: Severin Gehwolf <jerb...@gmail.com> > - Merge branch 'master' into JDK-8343191 > - ... and 3 more: https://git.openjdk.org/jdk/compare/bd6d911c...2a7e9d82 FYI: I'll try to test and review this more thoroughly next week. src/hotspot/os/linux/cgroupV2Subsystem_linux.cpp line 322: > 320: } else { > 321: log_warning(os, container)("Cgroup cpu/memory controller path > includes '../', detected limits won't be accurate"); > 322: } Please move this warning to `CgroupUtil::adjust_controller` and abort the adjustment, we don't need to issue this warning multiple times, and we'd not be able to adjust it to a path that will work. Showing the warning once should be sufficient. We shouldn't see this path in any non-moved scenarios. It would perhaps help if we included some detail why this warning is being shown. I suggest: ```cgroup controller path seems to have moved (includes '.../'), detected limits won't be accurate``` ------------- PR Review: https://git.openjdk.org/jdk/pull/21808#pullrequestreview-2484225572 PR Review Comment: https://git.openjdk.org/jdk/pull/21808#discussion_r1872956609