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

Kairui Song
2024-12-15T17:45:18Z

On Sun, Dec 15, 2024 at 3:43 AM Kairui Song <ryncsn@gmail.com> wrote:
>
> On Sat, Dec 14, 2024 at 2:06 PM Yu Zhao <yuzhao@google.com> wrote:
> >
> > On Fri, Dec 13, 2024 at 8:56 PM syzbot
> > <syzbot+38a0cbd267eff2d286ff@syzkaller.appspotmail.com> wrote:
> > >
> > > Hello,
> > >
> > > syzbot found the following issue on:
> > >
> > > HEAD commit: 7cb1b4663150 Merge tag 'locking_urgent_for_v6.13_rc3' of g..
> > > git tree: upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=16e96b30580000
> > > kernel config: https://syzkaller.appspot.com/x/.config?x=fee25f93665c89ac
> > > dashboard link: https://syzkaller.appspot.com/bug?extid=38a0cbd267eff2d286ff
> > > compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> > >
> > > Unfortunately, I don't have any reproducer for this issue yet.
> > >
> > > Downloadable assets:
> > > disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-7cb1b466.raw.xz
> > > vmlinux: https://storage.googleapis.com/syzbot-assets/13e083329dab/vmlinux-7cb1b466.xz
> > > kernel image: https://storage.googleapis.com/syzbot-assets/fe3847d08513/bzImage-7cb1b466.xz
> > >
> > > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > > Reported-by: syzbot+38a0cbd267eff2d286ff@syzkaller.appspotmail.com
> > >
> > > ------------[ cut here ]------------
> > > WARNING: CPU: 0 PID: 80 at mm/list_lru.c:97 lock_list_lru_of_memcg+0x395/0x4e0 mm/list_lru.c:97
> > > Modules linked in:
> > > CPU: 0 UID: 0 PID: 80 Comm: kswapd0 Not tainted 6.13.0-rc2-syzkaller-00018-g7cb1b4663150 #0
> > > Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
> > > RIP: 0010:lock_list_lru_of_memcg+0x395/0x4e0 mm/list_lru.c:97
> > > Code: e9 22 fe ff ff e8 9b cc b6 ff 4c 8b 7c 24 10 45 84 f6 0f 84 40 ff ff ff e9 37 01 00 00 e8 83 cc b6 ff eb 05 e8 7c cc b6 ff 90 <0f> 0b 90 eb 97 89 e9 80 e1 07 80 c1 03 38 c1 0f 8c 7a fd ff ff 48
> > > RSP: 0018:ffffc9000105e798 EFLAGS: 00010093
> > > RAX: ffffffff81e891c4 RBX: 0000000000000000 RCX: ffff88801f53a440
> > > RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> > > RBP: ffff888042e70054 R08: ffffffff81e89156 R09: 1ffffffff2032cae
> > > R10: dffffc0000000000 R11: fffffbfff2032caf R12: ffffffff81e88e5e
> > > R13: ffffffff9a3feb20 R14: 0000000000000000 R15: ffff888042e70000
> > > FS: 0000000000000000(0000) GS:ffff88801fc00000(0000) knlGS:0000000000000000
> > > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > > CR2: 0000000020161000 CR3: 0000000032d12000 CR4: 0000000000352ef0
> > > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > > Call Trace:
> > > <TASK>
> > > list_lru_add+0x59/0x270 mm/list_lru.c:164
> > > list_lru_add_obj+0x17b/0x250 mm/list_lru.c:187
> > > workingset_update_node+0x1af/0x230 mm/workingset.c:634
> > > xas_update lib/xarray.c:355 [inline]
> > > update_node lib/xarray.c:758 [inline]
> > > xas_store+0xb8f/0x1890 lib/xarray.c:845
> > > page_cache_delete mm/filemap.c:149 [inline]
> > > __filemap_remove_folio+0x4e9/0x670 mm/filemap.c:232
> > > __remove_mapping+0x86f/0xad0 mm/vmscan.c:791
> > > shrink_folio_list+0x30a6/0x5ca0 mm/vmscan.c:1467
> > > evict_folios+0x3c86/0x5800 mm/vmscan.c:4593
> > > try_to_shrink_lruvec+0x9a6/0xc70 mm/vmscan.c:4789
> > > shrink_one+0x3b9/0x850 mm/vmscan.c:4834
> > > shrink_many mm/vmscan.c:4897 [inline]
> > > lru_gen_shrink_node mm/vmscan.c:4975 [inline]
> > > shrink_node+0x37c5/0x3e50 mm/vmscan.c:5956
> > > kswapd_shrink_node mm/vmscan.c:6785 [inline]
> > > balance_pgdat mm/vmscan.c:6977 [inline]
> > > kswapd+0x1ca9/0x36f0 mm/vmscan.c:7246
> > > kthread+0x2f0/0x390 kernel/kthread.c:389
> > > ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:147
> > > ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
> > > </TASK>
> >
> > This one seems to be related to "mm/list_lru: split the lock to
> > per-cgroup scope".
> >
> > Kairui, can you please take a look? Thanks.
>
> Thanks for pinging, yes that's a new sanity check added by me.
>
> Which is supposed to mean, a list_lru is being reparented while the
> memcg it belongs to isn't dying.
>
> More concretely, list_lru is marked dead by memcg_offline_kmem ->
> memcg_reparent_list_lrus, if the function is called for one memcg, but
> now the memcg is not dying, this WARN triggers. I'm not sure how this
> is caused. One possibility is if alloc_shrinker_info() in
> mem_cgroup_css_online failed, then memcg_offline_kmem is called early?
> Doesn't seem to fit this case though.. Or maybe just sync issues with
> the memcg dying flag so the user saw the list_lru dying before seeing
> memcg dying? The object might be leaked to the parent cgroup, seems
> not too terrible though.
>
> I'm not sure how to reproduce this. I will keep looking.

Managed to boot the image and using the kernel config provided by bot,
so far local tests didn't trigger any issue. Is there any way I can
reproduce what the bot actually did? Or provide some patch for the bot
to test?