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

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Message-ID: <CADhLXY7FJqRLjX7X2yJfa0=iDbUAMwhS35cOEExW+qBJWAnt+A@mail.gmail.com>
Date: Sun, 18 Jan 2026 12:31:43 +0530
From: Deepanshu Kartikey <kartikey406@...il.com>
To: Andrew Morton <akpm@...ux-foundation.org>
Cc: syzbot <syzbot+079a3b213add54dd18a7@...kaller.appspotmail.com>, 
	cgroups@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org, 
	mhocko@...nel.org, roman.gushchin@...ux.dev, shakeel.butt@...ux.dev, 
	syzkaller-bugs@...glegroups.com, Johannes Weiner <hannes@...xchg.org>, 
	Muchun Song <muchun.song@...ux.dev>, Minchan Kim <minchan@...nel.org>
Subject: Re: [syzbot] [cgroups?] [mm?] WARNING in memcg1_swapout

On Sun, Jan 18, 2026 at 9:51 AM Deepanshu Kartikey
<kartikey406@...il.com> wrote:
>
> On Sun, Jan 18, 2026 at 6:27 AM Andrew Morton <akpm@...ux-foundation.org> wrote:
> >
> > 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.
> >
>
> Hi Andrew,
>
> I checked the git blame output for commit 0f853ca2a798:
>
> Line 763: memcg1_swapout(folio, swap);
> Line 764: __swap_cache_del_folio(ci, folio, swap, shadow);
>                     (d7a7b2f91f36b - Kairui Song, 2026-01-13 02:33:36 +0800)
>
> Kairui's reordering patch appears to have been merged on Jan 13.
> The syzbot report is also from Jan 13, likely from earlier in the
> day before the reordering patch was merged.
>
> So this report is from before the fix. The warning should not appear
> in linux-next builds after Jan 13.
>
> Thanks,
>
> Deepanshu

Hi Andrew,

I tested with the latest linux-next in sysbot. It is working fine

Thanks

Deepanshu