Re: [REGRESSION] Re: [PATCH 6.1 033/219] memcg: drop kmem.limit_in_bytes

Michal Hocko
2023-09-20T08:44:05Z

On Wed 20-09-23 01:11:01, Jeremi Piotrowski wrote:
> On Sun, Sep 17, 2023 at 09:12:40PM +0200, Greg Kroah-Hartman wrote:
> > 6.1-stable review patch. If anyone has any objections, please let me know.
> >
> > ------------------
>
> Hi Greg/Michal,
>
> This commit breaks userspace which makes it a bad commit for mainline and an
> even worse commit for stable.
>
> We ingested 6.1.54 into our nightly testing and found that runc fails to gather
> cgroup statistics (when reading kmem.limit_in_bytes). The same code is vendored
> into kubelet and kubelet fails to start if this operation fails. 6.1.53 is
> fine.

Could you expand some more on why is the file read? It doesn't support
writing to it for some time so how does reading it helps in any sense?

Anyway, I do agree that the stable backport should be reverted.

> > Address this by wiping out the file completely and effectively get back to
> > pre 4.5 era and CONFIG_MEMCG_KMEM=n configuration.
>
> On reads, the runc code checks for MEMCG_KMEM=n by checking
> kmem.usage_in_bytes. If it is present then runc expects the other cgroup files
> to be there (including kmem.limit_in_bytes). So this change is not effectively
> the same.
>
> Here's a link to the PR that would be needed to handle this change in userspace
> (not merged yet and would need to be propagated through the ecosystem):
>
> https://github.com/opencontainers/runc/pull/4018.

Thanks. Does that mean the revert is still necessary for the Linus tree
or do you expect that the fix can be merged and propagated in a
reasonable time?

--
Michal Hocko
SUSE Labs