linux-kernel - Re: [syzbot] [cgroups?] general protection fault in __cgroup_rstat

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Message-ID: <p32ytuin2hmxacacroykhtfxf6l5l7sji33dt4xknnojqm4xh2@hrldb5d6fgfj>
Date: Mon, 2 Jun 2025 16:15:56 +0200
From: Michal Koutný <mkoutny@...e.com>
To: syzbot <syzbot+31eb4d4e7d9bc1fc1312@...kaller.appspotmail.com>, 
	inwardvessel@...il.com
Cc: akpm@...ux-foundation.org, andrii@...nel.org, ast@...nel.org, 
	axboe@...nel.dk, bpf@...r.kernel.org, cgroups@...r.kernel.org, 
	daniel@...earbox.net, eddyz87@...il.com, hannes@...xchg.org, haoluo@...gle.com, 
	hawk@...nel.org, john.fastabend@...il.com, jolsa@...nel.org, josef@...icpanda.com, 
	kpsingh@...nel.org, linux-block@...r.kernel.org, linux-kernel@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, linux-mm@...ck.org, martin.lau@...ux.dev, mhocko@...nel.org, 
	muchun.song@...ux.dev, mykolal@...com, netdev@...r.kernel.org, roman.gushchin@...ux.dev, 
	sdf@...ichev.me, shakeel.butt@...ux.dev, shuah@...nel.org, song@...nel.org, 
	syzkaller-bugs@...glegroups.com, tj@...nel.org, yonghong.song@...ux.dev
Subject: Re: [syzbot] [cgroups?] general protection fault in
 __cgroup_rstat_lock

On Sun, Jun 01, 2025 at 09:21:02AM -0700, syzbot <syzbot+31eb4d4e7d9bc1fc1312@...kaller.appspotmail.com> wrote:
> syzbot suspects this issue was fixed by commit:
> 
> commit a97915559f5c5ff1972d678b94fd460c72a3b5f2
> Author: JP Kobryn <inwardvessel@...il.com>
> Date:   Fri Apr 4 01:10:48 2025 +0000
> 
>     cgroup: change rstat function signatures from cgroup-based to css-based

It says: "This non-functional change serves..."

However, it moves the *_rstat_init in cgroup_create() after kernfs dir
creation and given the reproducer has a fault injected:
	mkdir(&(0x7f0000000000)='./cgroup/file0\x00', 0xd0939199c36b4d28) (fail_nth: 8)

I'd say this might be relevant (although I don't see the possibly
incorrect error handlnig path) but it doesn't mean this commit fixes it,
it'd rather require the reproducer to adjust the N on this path.

0.02€,
Michal

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