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Date: Wed, 3 Apr 2024 18:07:52 -0700
From: Andrew Morton <akpm@linux-foundation.org>
To: syzbot <syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com>
Cc: cgroups@vger.kernel.org, hannes@cmpxchg.org,
 linux-kernel@vger.kernel.org, linux-mm@kvack.org, mhocko@kernel.org,
 muchun.song@linux.dev, roman.gushchin@linux.dev, shakeel.butt@linux.dev,
 syzkaller-bugs@googlegroups.com
Subject: Re: [syzbot] [cgroups?] [mm?] WARNING in __mod_memcg_lruvec_state
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On Tue, 02 Apr 2024 01:03:26 -0700 syzbot <syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com> wrote:

> 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+9319a4268a640e26b72b@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

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);
 		}
 	}
 
_