RFR: 8287107: CgroupSubsystemFactory.setCgroupV2Path asserts with freezer controller

[Mikhailo Seledtsov]

On Mon, 23 May 2022 22:11:47 GMT, Ioi Lam <iklam at openjdk.org> wrote:

> This PR fixes a bug found on an Ubuntu host that's mostly running with cgroupv2, but there's a controller (freezer) that is mounted in cgroupv1 mode.
> 
> The container support code in the VM and JDK checks if we have simultaneously mounted v1 and v2 containers. If so, we revert to "hybrid" mode (which is essentially v1).
> 
> However, the "hybrid checks" only considers the following controllers that Java cares about:
> 
> - cpu
> - cpuacct
> - cpuset
> - blkio
> - memory
> - pids
> 
> If only "freezer" is mounted in v1 mode, Java will start in V2 mode. Later, when `setCgroupV2Path()` sees the first line in /proc/self/cgroup, it runs into the assert.
> 
> 
> $ cat /proc/self/cgroup
> 1:freezer:/
> 0::/user.slice/user-1001.slice/session-85.scope
> 
> 
> The fix is simple -- when we get to `setCgroupV2Path()`, we have already decided that the system has not mounted any v1 controllers that we care about, so we should just ignore all the v1 controllers (which has a non-empty name).

Marked as reviewed by mseledtsov (Committer).

Change looks good to me. Thanks for the fix.

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PR: https://git.openjdk.java.net/jdk/pull/8858