[syzbot] [mm?] WARNING in set_mm_walk

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 562bfb501c54 Merge tag 'integrity-v7.2-rc7' of git://git.k..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=11a8cbb9580000
kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
dashboard link: https://syzkaller.appspot.com/bug?extid=12ee2725d5fde63a9c96
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-562bfb50.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/9cbf6ef0490e/vmlinux-562bfb50.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7ee52864c79a/bzImage-562bfb50.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+12ee27...@syzkaller.appspotmail.com

------------[ cut here ]------------
current_is_kswapd()
WARNING: mm/vmscan.c:3800 at set_mm_walk+0x210/0x270 mm/vmscan.c:3800, CPU#1: kswapd0/110
Modules linked in:
CPU: 1 UID: 0 PID: 110 Comm: kswapd0 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:set_mm_walk+0x210/0x270 mm/vmscan.c:3800
Code: 13 00 00 4d 8d 7d 08 e9 f7 fe ff ff e8 79 f5 2a 00 e9 b7 fe ff ff e8 7f 6b ba ff 90 0f 0b 90 e9 d2 fe ff ff e8 71 6b ba ff 90 <0f> 0b 90 e9 74 ff ff ff 4c 89 ff e8 80 f5 2a 00 e9 4e fe ff ff 48
RSP: 0018:ffffc900027772b8 EFLAGS: 00010293
RAX: 0000000000000000 RBX: ffff888024934a80 RCX: ffffffff824ff8e8
RDX: ffff888024934a80 RSI: ffffffff824ff96f RDI: ffff888024934a80
RBP: 0000000000020000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000020000 R11: 0000000000000000 R12: 0000000000000000
R13: ffffc90002777c38 R14: 0000000000000001 R15: ffffc90002777c40
FS: 0000000000000000(0000) GS:ffff8880d5ed8000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b31923ffc CR3: 0000000109695000 CR4: 0000000000352ef0
DR0: 0000000000000005 DR1: 0000000000000005 DR2: 0000000020040004
DR3: 0000000000000056 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
try_to_inc_max_seq+0xf0/0x1090 mm/vmscan.c:4023
try_to_shrink_lruvec+0x4bd/0x6b0 mm/vmscan.c:4977
lru_gen_shrink_lruvec mm/vmscan.c:5128 [inline]
shrink_lruvec+0x31e/0x25b0 mm/vmscan.c:5888
mem_cgroup_shrink_node+0x227/0x6a0 mm/vmscan.c:6753
mem_cgroup_soft_reclaim mm/memcontrol-v1.c:312 [inline]
memcg1_soft_limit_reclaim+0x2d5/0x830 mm/memcontrol-v1.c:362
balance_pgdat+0xa11/0x1f00 mm/vmscan.c:7177
kswapd+0x556/0xb50 mm/vmscan.c:7462
kthread+0x370/0x450 kernel/kthread.c:436
ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>


---
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[Andrew Morton]

On Mon, 10 Aug 2026 17:13:29 -0700 syzbot <syzbot+12ee27...@syzkaller.appspotmail.com> wrote:

> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: 562bfb501c54 Merge tag 'integrity-v7.2-rc7' of git://git.k..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11a8cbb9580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
> dashboard link: https://syzkaller.appspot.com/bug?extid=12ee2725d5fde63a9c96
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

Thanks. One for the MGLRU develoeprs, it seems.

https://share.gemini.google/Wg4a5ns7E0LF might save a bit of time figuring this out.

[Shakeel Butt]

On Mon, Aug 10, 2026 at 05:48:52PM -0700, Andrew Morton wrote:
> On Mon, 10 Aug 2026 17:13:29 -0700 syzbot <syzbot+12ee27...@syzkaller.appspotmail.com> wrote:
>
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit: 562bfb501c54 Merge tag 'integrity-v7.2-rc7' of git://git.k..
> > git tree: upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=11a8cbb9580000
> > kernel config: https://syzkaller.appspot.com/x/.config?x=145fa60d73086782
> > dashboard link: https://syzkaller.appspot.com/bug?extid=12ee2725d5fde63a9c96
> > compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
>
> Thanks. One for the MGLRU develoeprs, it seems.
>
> https://share.gemini.google/Wg4a5ns7E0LF might save a bit of time figuring this out.
>

This is memcg-v1's soft limit which is deprecated. I am more inclined to simply
remove this code instead of fixing it.

I will take a stab at removal.

[Lorenzo Stoakes (ARM)]

On Mon, Aug 10, 2026 at 09:39:08PM -0700, Shakeel Butt wrote:
> This is memcg-v1's soft limit which is deprecated. I am more inclined to simply
> remove this code instead of fixing it.

Love it :)

The best code is no code (sadly we have to have _some_ code :)