state: fix race condition when reading cgroup

[giuseppe]

by the time crun attempts to read from the cgroup, systemd might have
already cleaned it up. When using systemd, on ENOENT state reports
the container as "stopped" instead of an error.

Closes: containers/podman#7148

Signed-off-by: Giuseppe Scrivano [email protected]

[edsantiago]

LGTM

I had to quickly crash-course on crun_error_release(), ..._get_errno() and look for the possibility of a constant instead of "stopped" (none found, not worth fixing for this PR). The logic looks sound. Thanks @giuseppe !

[rhatdan]

@giuseppe Can you cut a release? Is this something we should race into stable, IE RHEL8 (8.3)? Or can we wait until RHEL8.3.1?

[edsantiago]

Does RHEL even ship crun? (EDIT: I checked the module. Yes, crun 0.14.1-2 is in the container-tools rhel8-rhel-8.3.0 module. But is it used?)

[giuseppe]

@giuseppe Can you cut a release? Is this something we should race into stable, IE RHEL8 (8.3)? Or can we wait until RHEL8.3.1?

I think we can wait for 8.3.1. The race just causes an error message to be reported but no functionality is affected.

Does RHEL even ship crun? (EDIT: I checked the module. Yes, crun 0.14.1-2 is in the container-tools rhel8-rhel-8.3.0 module. But is it used?)

It is tech preview. Who is interested in the additional crun functionalities will have the opportunity to try it out.

[edsantiago]

The race just causes an error message to be reported but no functionality is affected.

Well, to be fully honest, podman build does fail at that step. It usually succeeds on rerun. But it's not just a spurious error message, it does lead to failure.

It is tech preview.

Aha, thank you. So presumably cgroups v2 is also tech preview then, and users would need to enable it explicitly?

[giuseppe]

Aha, thank you. So presumably cgroups v2 is also tech preview then, and users would need to enable it explicitly?

yes, AFAIK cgroup v1 is still the default for RHEL 8.x.

[rhatdan]

cgroup V1 will always be the default in RHEL8. Not even supported until RHEL8.4. crun is shipping for the first time in RHEL 8.3 as I understand it.