linux-kernel - Re: [PATCH 0/5 cgroup/for-6.16-fixes] harden css_create() for safe placement of call to css_rstat

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Message-ID: <cughucmlrkwe3unwwmtx3yrqyrqwsedrbh2ck5feqs6cr36j3z@fhrnw6nfnyte>
Date: Fri, 25 Jul 2025 19:23:43 +0200
From: Michal Koutný <mkoutny@...e.com>
To: JP Kobryn <inwardvessel@...il.com>
Cc: tj@...nel.org, shakeel.butt@...ux.dev, yosryahmed@...gle.com, 
	hannes@...xchg.org, akpm@...ux-foundation.org, linux-kernel@...r.kernel.org, 
	cgroups@...r.kernel.org, kernel-team@...a.com
Subject: Re: [PATCH 0/5 cgroup/for-6.16-fixes] harden css_create() for safe
 placement of call to css_rstat_init()

Hi.

On Mon, Jul 21, 2025 at 06:40:25PM -0700, JP Kobryn <inwardvessel@...il.com> wrote:
...

Thanks for the instructive summary!

> If any of the three goto jumps are taken, async cleanup will begin and
> css_rstat_exit() will be invoked. But since css_rstat_init() would not have
> succeeded, the warning will eventually be reached.

First thought is why not simply add a flag that'd guide whether
css_rstat_exit() has work to do.

This is meant as a fix, so it should have some metadata, I'd consider this one:
Fixes: 5da3bfa029d68 ("cgroup: use separate rstat trees for each subsystem")

(that's when css_rstat_init was moved to css_create)

and likely this
Reported-by: syzbot+8d052e8b99e40bc625ed@...kaller.appspotmail.com

(Sorry for being such a bureaucrat.)

It's most appropriate in your 4/5 but do you think it'd be possible to
reshuffle the series to put the fix in front (to ease it for stable
kernels) and refactorings after?

Regards,
Michal

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