On Mon, 23 May 2022 22:11:47 GMT, Ioi Lam <ik...@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).
src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java
line 155:
> 153: // There are some controllers (such as freezer) that
> Java doesn't
> 154: // care about. Just ignore them. These are not
> considered in the
> 155: // anyCgroupsV1Controller/anyCgroupsV1Controller checks.
It's not clear why this `default` is necessary. Could we just add the comment
like so:
// Intentional fall-through. There are controllers (such as freezer) that
// Java doesn't care about. Just ignore them. Only listed controllers are
// considered in the anyCgroupsV1Controller/anyCgroupsV2Controller checks.
src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java
line 229:
> 227: String name = tokens[1];
> 228: if (!name.equals("")) {
> 229: // This is probably a v1 controller that we have ignored
> (e.g., freezer)
Could we add an assertion that the controller isn't in the `infos` map?
if (!name.equals("")) {
// This must be a v1 controller that we have ignored (e.g., freezer)
assert infos.get(name) == null;
return;
}
-------------
PR: https://git.openjdk.java.net/jdk/pull/8858
