[Bug]: container-toolkit DaemonSet: containerd-socket hostPath volume lacks mountPropagation: HostToContainer, pins host ZFS mounts and blocks zfs destroy ("dataset is busy") #3083

Problem

The nvidia-container-toolkit-daemonset in GPU Operator v26.7.1 mounts these hostPath volumes:

The toolkit container's own rootfs lives under /run/containerd. Its /host sub-mount carries every host mount, including all ZFS datasets. Because containerd-socket is a private recursive bind, the whole mount tree is copied into the container's mount namespace when the container starts. After that, the copy never receives unmount events from the host.

Impact

• Any ZFS dataset that is mounted on the host when the toolkit container starts stays pinned in the container's mount namespace.
• Later, the host unmounts the dataset, and it reports mounted=no. But zfs destroy still fails with cannot destroy '': dataset is busy.
• The dataset stays undeletable until the toolkit container restarts. The restart re-pins every dataset that exists at that moment.
• This affects every container restart, including node reboots. Datasets created after the container starts are not affected.

Evidence

After the dataset is unmounted on the host, its mount entries are still found in the toolkit process's mount namespace:
$ grep -l /proc/[0-9]*/mountinfo
/proc//mountinfo # comm=nvidia-toolkit
.../runtime/sock-dir/io.containerd.runtime.v2.task/k8s.io//rootfs/host/ - zfs

Environment

• NVIDIA GPU Operator v26.7.1 (Helm chart gpu-operator-v26.7.1)
• OS: Ubuntu 24.04
• Kernel Version: 6.8.0-142-generic
• Container Runtime Version: containerd v2.1.4
• Container-toolkit image: nvcr.io/nvidia/k8s/container-toolkit:v1.20.1
• GPU Driver: 580.105.08
• Host filesystems: ZFS datasets mounted on the host
• Kubernetes Distro and Version: Kubelet v1.33.5

Steps to reproduce

1. Create and mount a ZFS dataset on a GPU node.
2. Restart the nvidia-container-toolkit pod on that node, or reboot the node.
3. Unmount the dataset on the host and run zfs destroy -r .
4. The destroy fails with dataset is busy. The dataset's mount is still listed in the toolkit process's /proc//mountinfo.

Requested fix

Set mountPropagation: HostToContainer on the containerd-socket volume, the same as host-root and driver-install-dir, so that host unmounts propagate into the container. A setting in ClusterPolicy to configure it would also work. Patching the DaemonSet by hand isn't a durable workaround because the operator reconciles it back.