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Date:   Wed, 20 Sep 2023 10:43:56 +0200
From:   Michal Hocko <mhocko@suse.com>
To:     Jeremi Piotrowski <jpiotrowski@linux.microsoft.com>
Cc:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        stable@vger.kernel.org, patches@lists.linux.dev,
        Shakeel Butt <shakeelb@google.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Muchun Song <muchun.song@linux.dev>, Tejun Heo <tj@kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        linux-kernel@vger.kernel.org, regressions@lists.linux.dev,
        mathieu.tortuyaux@gmail.com
Subject: Re: [REGRESSION] Re: [PATCH 6.1 033/219] memcg: drop
 kmem.limit_in_bytes
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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