linux-kernel - Re: [syzbot] [cgroups?] [mm?] WARNING in memcg1

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Message-Id: <20260117165722.6dc25d72fd58254cb89e711b@linux-foundation.org>
Date: Sat, 17 Jan 2026 16:57:22 -0800
From: Andrew Morton <akpm@...ux-foundation.org>
To: syzbot <syzbot+079a3b213add54dd18a7@...kaller.appspotmail.com>
Cc: cgroups@...r.kernel.org, hannes@...xchg.org,
 linux-kernel@...r.kernel.org, linux-mm@...ck.org, mhocko@...nel.org,
 muchun.song@...ux.dev, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev,
 syzkaller-bugs@...glegroups.com, Johannes Weiner <hannes@...xchg.org>,
 Muchun Song <muchun.song@...ux.dev>, Deepanshu Kartikey
 <kartikey406@...il.com>, Minchan Kim <minchan@...nel.org>
Subject: Re: [syzbot] [cgroups?] [mm?] WARNING in memcg1_swapout

On Sat, 17 Jan 2026 01:30:25 -0800 syzbot <syzbot+079a3b213add54dd18a7@...kaller.appspotmail.com> wrote:

> Hello,
> 
> syzbot found the following issue on:
> 
> HEAD commit:    0f853ca2a798 Add linux-next specific files for 20260113
> git tree:       linux-next
> console output: https://syzkaller.appspot.com/x/log.txt?x=14f7259a580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=8d6e5303d96e21b5
> dashboard link: https://syzkaller.appspot.com/bug?extid=079a3b213add54dd18a7
> compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
> syz repro:      https://syzkaller.appspot.com/x/repro.syz?x=167ef922580000
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=16d295fa580000
> 
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/480cd223f3f6/disk-0f853ca2.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/1ca2f0dbb7cc/vmlinux-0f853ca2.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/60a0fef5805b/bzImage-0f853ca2.xz
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+079a3b213add54dd18a7@...kaller.appspotmail.com

Thanks.

> ------------[ cut here ]------------
> WARNING: mm/memcontrol-v1.c:642 at memcg1_swapout+0x6c2/0x8d0 mm/memcontrol-v1.c:642, CPU#0: syz.4.233/6746

That's

	VM_WARN_ON_ONCE(oldid != 0);

which was added by Deepanshu's "mm/swap_cgroup: fix kernel BUG in
swap_cgroup_record".

This patch has Fixes: 1a4e58cce84e ("mm: introduce MADV_PAGEOUT"),
which is six years old.  For some reason it has no cc:stable.

Deepanshu's patch has no reviews.

So can I please do the memcg maintainer summoning dance here?  We have a
repeatable BUG happening in mainline Linux.