linux-kernel - Re: [syzbot] [cgroups?] WARNING in css_rstat

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Message-ID: <e938953c-8735-4276-8f45-543ade5cc515@gmail.com>
Date: Mon, 21 Jul 2025 17:29:01 -0700
From: JP Kobryn <inwardvessel@...il.com>
To: Shakeel Butt <shakeel.butt@...ux.dev>, Michal Koutný
 <mkoutny@...e.com>
Cc: syzbot <syzbot+8d052e8b99e40bc625ed@...kaller.appspotmail.com>,
 cgroups@...r.kernel.org, hannes@...xchg.org, linux-kernel@...r.kernel.org,
 syzkaller-bugs@...glegroups.com, tj@...nel.org
Subject: Re: [syzbot] [cgroups?] WARNING in css_rstat_exit

Thanks Michal and Shakeel for the input on this. I will be sending out a
series to harden css_create(). I was able to open a small window for the
placement of css_rstat_init() that satisfies existing constraints and
allows for error handling before refcounts come into play.

On 7/17/25 11:46 AM, Shakeel Butt wrote:
> On Thu, Jul 17, 2025 at 03:28:27PM +0200, Michal Koutný wrote:
>> Thanks for looking into this JP.
>> You seem to tracked down the cause with uncleaned rstat, beware that the
>> approach in the patch would leave reference imbalance after
>> init_and_link_css() though.
> 
> Yeah I discussed the same with JP and I think JP is planning to move the
> css_rstat_init() before init_and_link_css() and a second param to
> css_rstat_init() to differentiate between css_is_self() or not.