Re: [syzbot] [mm?] WARNING in set_mm_walk

[Andrew Morton]

On Wed, 12 Aug 2026 05:26:24 -0700 syzbot <syzbot+12ee2725d5fde63a9c96@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:

> syzbot has found a reproducer for the following issue on:
> 
> HEAD commit:    f5bbbfec59b4 Merge tag 'probes-fixes-v7.2-rc7' of git://gi..
> git tree:       upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=11f44c79580000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=c44651ea7dd2f307
> 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
> C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=10d11149580000
> 
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+12ee2725d5fde63a9c96@xxxxxxxxxxxxxxxxxxxxxxxxx
> 
> ------------[ cut here ]------------
> current_is_kswapd()
> WARNING: mm/vmscan.c:3800 at set_mm_walk+0x210/0x270 mm/vmscan.c:3800, CPU#2: kswapd0/111

Thanks.  Shakeel is working on a series which will fix this by removing
the calling code.  But it isn't a minor patch.

Shakeel, it would be good to have a backportable quick-fix to make this
warning go away?

> Modules linked in:
> CPU: 2 UID: 0 PID: 111 Comm: kswapd0 Not tainted syzkaller #0 PREEMPT(full) 
> 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 19 f7 2a 00 e9 b7 fe ff ff e8 7f 68 ba ff 90 0f 0b 90 e9 d2 fe ff ff e8 71 68 ba ff 90 <0f> 0b 90 e9 74 ff ff ff 4c 89 ff e8 20 f7 2a 00 e9 4e fe ff ff 48
> RSP: 0018:ffffc9000272f2b8 EFLAGS: 00010293
> RAX: 0000000000000000 RBX: ffff888023f04a80 RCX: ffffffff82500a88
> RDX: ffff888023f04a80 RSI: ffffffff82500b0f RDI: ffff888023f04a80
> RBP: 0000000000020000 R08: 0000000000000005 R09: 0000000000000000
> R10: 0000000000020000 R11: 0000000000000000 R12: 0000000000000000
> R13: ffffc9000272fc38 R14: 0000000000000001 R15: ffffc9000272fc40
> FS:  0000000000000000(0000) GS:ffff8880d5fec000(0000) knlGS:0000000000000000
> CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 00005643a2ed4168 CR3: 000000003c7ec000 CR4: 0000000000352ef0
> 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>