[syzbot] [cgroups?] [mm?] WARNING in __mod_memcg_lruvec_state

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 317c7bc0ef03 Merge tag 'mmc-v6.9-rc1' of git://git.kernel...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15fd40c5180000
kernel config: https://syzkaller.appspot.com/x/.config?x=f64ec427e98bccd7
dashboard link: https://syzkaller.appspot.com/bug?extid=9319a4268a640e26b72b
compiler: gcc (Debian 12.2.0-14) 12.2.0, 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/7bc7510fe41f/non_bootable_disk-317c7bc0.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/efab473d72c0/vmlinux-317c7bc0.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5ba3f56d362d/bzImage-317c7bc0.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+9319a4...@syzkaller.appspotmail.com

------------[ cut here ]------------
WARNING: CPU: 0 PID: 30105 at mm/memcontrol.c:865 __mod_memcg_lruvec_state+0x3fa/0x550 mm/memcontrol.c:865
Modules linked in:
CPU: 0 PID: 30105 Comm: syz-executor.2 Not tainted 6.9.0-rc1-syzkaller-00178-g317c7bc0ef03 #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:__mod_memcg_lruvec_state+0x3fa/0x550 mm/memcontrol.c:865
Code: 45 85 e4 75 1d 48 83 c4 18 5b 5d 41 5c 41 5d 41 5e 41 5f c3 cc cc cc cc b8 00 04 00 00 e9 80 fd ff ff 89 c6 e9 a0 fd ff ff 90 <0f> 0b 90 e9 a7 fc ff ff 48 c7 c7 18 43 e1 8f e8 32 51 f8 ff e9 5e
RSP: 0018:ffffc900034beef8 EFLAGS: 00010202
RAX: 0000000000000292 RBX: 0000000000000001 RCX: 1ffffffff1fc2863
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffff888024b92bc8
RBP: ffff888024b92000 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000001
R13: ffff88801c326000 R14: 0000000000000001 R15: ffff888024b92000
FS: 00007f0811bf96c0(0000) GS:ffff88806b000000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000cfff1dd CR3: 000000003e4e2000 CR4: 0000000000350ef0
DR0: 0000000000000031 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
__update_lru_size include/linux/mm_inline.h:47 [inline]
lru_gen_update_size include/linux/mm_inline.h:199 [inline]
lru_gen_add_folio+0x62d/0xe80 include/linux/mm_inline.h:262
lruvec_add_folio include/linux/mm_inline.h:323 [inline]
lru_add_fn+0x3fc/0xd80 mm/swap.c:215
folio_batch_move_lru+0x243/0x400 mm/swap.c:233
lru_add_drain_cpu+0x534/0x860 mm/swap.c:667
lru_add_drain+0x109/0x440 mm/swap.c:767
__folio_batch_release+0x68/0xb0 mm/swap.c:1091
folio_batch_release include/linux/pagevec.h:101 [inline]
mpage_prepare_extent_to_map+0x112b/0x14b0 fs/ext4/inode.c:2505
ext4_do_writepages+0xa9e/0x3250 fs/ext4/inode.c:2632
ext4_writepages+0x303/0x730 fs/ext4/inode.c:2768
do_writepages+0x1a3/0x7f0 mm/page-writeback.c:2612
filemap_fdatawrite_wbc mm/filemap.c:397 [inline]
filemap_fdatawrite_wbc+0x148/0x1c0 mm/filemap.c:387
__filemap_fdatawrite_range+0xba/0x100 mm/filemap.c:430
file_write_and_wait_range+0xd0/0x140 mm/filemap.c:788
ext4_sync_file+0x296/0xf30 fs/ext4/fsync.c:158
vfs_fsync_range+0x141/0x230 fs/sync.c:188
generic_write_sync include/linux/fs.h:2793 [inline]
ext4_buffered_write_iter+0x2e6/0x3d0 fs/ext4/file.c:305
ext4_file_write_iter+0x874/0x1a40 fs/ext4/file.c:698
call_write_iter include/linux/fs.h:2108 [inline]
new_sync_write fs/read_write.c:497 [inline]
vfs_write+0x6db/0x1100 fs/read_write.c:590
ksys_write+0x12f/0x260 fs/read_write.c:643
do_syscall_x64 arch/x86/entry/common.c:52 [inline]
do_syscall_64+0xd2/0x260 arch/x86/entry/common.c:83
entry_SYSCALL_64_after_hwframe+0x6d/0x75
RIP: 0033:0x7f0810e7dda9
Code: 28 00 00 00 75 05 48 83 c4 28 c3 e8 e1 20 00 00 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 b0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f0811bf90c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f0810fabf80 RCX: 00007f0810e7dda9
RDX: 0000000000002000 RSI: 0000000020000180 RDI: 0000000000000007
RBP: 00007f0810eca47a R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 000000000000000b R14: 00007f0810fabf80 R15: 00007ffd57bcc8d8
</TASK>


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[Andrew Morton]

Well it beats me. I assume we failed to update for a new case. I'll
toss this into -next to perhaps shed a bit of light.

--- a/mm/memcontrol.c~__mod_memcg_lruvec_state-enhance-diagnostics
+++ a/mm/memcontrol.c
@@ -860,10 +860,12 @@ void __mod_memcg_lruvec_state(struct lru
case NR_ANON_THPS:
case NR_SHMEM_PMDMAPPED:
case NR_FILE_PMDMAPPED:
- WARN_ON_ONCE(!in_task());
+ if (WARN_ON_ONCE(!in_task()))
+ pr_warn("stat item index: %d\n", idx);
break;
default:
- VM_WARN_ON_IRQS_ENABLED();
+ if (VM_WARN_ON_IRQS_ENABLED())
+ pr_warn("stat item index: %d\n", idx);
}
}

_

[Yosry Ahmed]

Line 865 from this commit should be this warning (i.e. warning because
IRQs are enabled). This also makes sense because __update_lru_size()
should not be updating any of the above stats.

folio_batch_move_lru() in the above call stack should be acquiring the
lock with IRQs disabled though, so I am not sure what's going on from
a quick look.

Adding Yu Zhao here.

[Yu Zhao]

Probably an RT build where _irqsave doesn't disable IRQ?

[Yosry Ahmed]

Yeah, that's possible. I don't have enough familiarity with RT to know
for sure. Perhaps lruvec->lru_lock needs to be changed to a
raw_spinlock_t? I am not sure if that's the correct course of action.

[Shakeel Butt]

On Thu, Apr 04, 2024 at 09:47:34PM -0700, Yosry Ahmed wrote:
[...]

> >
> > Probably an RT build where _irqsave doesn't disable IRQ?
>
> Yeah, that's possible. I don't have enough familiarity with RT to know
> for sure. Perhaps lruvec->lru_lock needs to be changed to a
> raw_spinlock_t? I am not sure if that's the correct course of action.

The kernel config does not have CONFIG_PREEMPT_RT enabled. However I
have not idea how irqs are getting enabled to raise this warning.