James Peach created MESOS-9319:
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Summary: Create all container devices at isolation time
Key: MESOS-9319
URL: https://issues.apache.org/jira/browse/MESOS-9319
Project: Mesos
Issue Type: Bug
Components: containerization
Environment: When using a custom user namespace isolator, the task
fails at launch because opening devices fails with a {{EPERM}} error. This
problem is described in [this system
issue|https://github.com/systemd/systemd/pull/9483] and this [lxd
issue|https://github.com/lxc/lxd/issues/4950].
The problem arises in the Mesos containerizer due to the order of operations:
# Clone the containerizer with CLONE_NEWNS
# Mount a tmpfs for the devices
# mknod for the various device nodes
Referring back to the lxc issue, because we do (1) before (2), the tmpfs on
/dev is marked SB_I_NODEV. Due to the new 4.18 behavior, the mkdir in (3) now
succeeds (see commit
[55956b59df33|https://github.com/torvalds/linux/commit/55956b59df336f6738da916dbb520b6e37df9fbd]).
Previously it would fail and we would fall back to bind mounting the device.
However, even though we created the device, we can't actually open it due to
the SB_I_NODEV flag on the tmpfs mount. It appears that the purpose of allowing
mknod is to that containers can create overlayfs whiteouts.
One approach to deal with this in the Mesos containerizer is to complete the
device node cleanup that was begun in with the linux/devices isolator. This
approach involves moving all the responsibility for creating devices back to
the isolators. Then, at containerization time, we simply bind-mount the whole
of /dev from the per-container staging area. Since the isolators create the
devices in the host namespace and on the Mesos work directory, none of the
conditions that trigger the failure would be invoked.
Reporter: James Peach
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