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

Yosry Ahmed
2024-05-06T14:12:03Z

On Mon, May 06, 2024 at 06:03:29AM -0700, syzbot wrote:
> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: 2b84edefcad1 Add linux-next specific files for 20240506
> git tree: linux-next
> console+strace: https://syzkaller.appspot.com/x/log.txt?x=1164931f180000
> kernel config: https://syzkaller.appspot.com/x/.config?x=b499929e4aaba1af
> dashboard link: https://syzkaller.appspot.com/bug?extid=9319a4268a640e26b72b
> compiler: Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=123d5d1f180000
> C reproducer: https://syzkaller.appspot.com/x/repro.c?x=16527450980000
>
> Downloadable assets:
> disk image: https://storage.googleapis.com/syzbot-assets/6a22cf95ee14/disk-2b84edef.raw.xz
> vmlinux: https://storage.googleapis.com/syzbot-assets/f5c45b515282/vmlinux-2b84edef.xz
> kernel image: https://storage.googleapis.com/syzbot-assets/9bf98258a662/bzImage-2b84edef.xz
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+9319a4268a640e26b72b@syzkaller.appspotmail.com
>
> ------------[ cut here ]------------
> __mod_memcg_lruvec_state: missing stat item 25
> WARNING: CPU: 0 PID: 5091 at mm/memcontrol.c:999 __mod_memcg_lruvec_state+0x18c/0x430 mm/memcontrol.c:999

This doesn't seem to be the same issue as the original one syzbot
reported. It's the same function but a different warning. I am not sure
how to tell syzbot that.

Anyway, this warning is the one newly introduced by Shakeel. It is
firing because NR_SHMEM_PMDMAPPED and/or NR_FILE_PMDMAPPED are being
updated using __lruvec_stat_mod_folio(), which also updates the memcg
stats. However, these stats are not exported per-memcg.

I think the following should fix it.

#syz test

diff --git a/mm/rmap.c b/mm/rmap.c
index 12be4241474ab..d3a26ea4dbae2 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1441,7 +1441,7 @@ static __always_inline void __folio_add_file_rmap(struct folio *folio,

nr = __folio_add_rmap(folio, page, nr_pages, level, &nr_pmdmapped);
if (nr_pmdmapped)
- __lruvec_stat_mod_folio(folio, folio_test_swapbacked(folio) ?
+ __mod_node_page_state(folio, folio_test_swapbacked(folio) ?
NR_SHMEM_PMDMAPPED : NR_FILE_PMDMAPPED, nr_pmdmapped);
if (nr)
__lruvec_stat_mod_folio(folio, NR_FILE_MAPPED, nr);

> Modules linked in:
> CPU: 0 PID: 5091 Comm: syz-executor374 Not tainted 6.9.0-rc7-next-20240506-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 03/27/2024
> RIP: 0010:__mod_memcg_lruvec_state+0x18c/0x430 mm/memcontrol.c:999
> Code: ad 35 94 0d 00 0f 85 a4 01 00 00 c6 05 a0 35 94 0d 01 90 48 c7 c7 80 53 d7 8b 48 c7 c6 54 27 b8 8d 44 89 fa e8 55 f1 54 ff 90 <0f> 0b 90 90 e9 7c 01 00 00 4c 8d 7c 24 60 4c 89 fb 48 c1 eb 03 42
> RSP: 0018:ffffc9000338f1e0 EFLAGS: 00010246
> RAX: 38a0635190e19e00 RBX: ffffffff8fad3cb9 RCX: ffff8880221f0000
> RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
> RBP: ffffc9000338f2c0 R08: ffffffff815846c2 R09: fffffbfff1c3995c
> R10: dffffc0000000000 R11: fffffbfff1c3995c R12: 0000000000000200
> R13: dffffc0000000000 R14: 1ffff92000671e40 R15: 0000000000000019
> FS: 00005555900be380(0000) GS:ffff8880b9400000(0000) knlGS:0000000000000000
> CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> CR2: 000000000061cca0 CR3: 0000000075f1c000 CR4: 00000000003506f0
> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> Call Trace:
> <TASK>
> __mod_lruvec_state mm/memcontrol.c:1055 [inline]
> __lruvec_stat_mod_folio+0x1a4/0x300 mm/memcontrol.c:1075
> __folio_add_file_rmap mm/rmap.c:1444 [inline]
> folio_add_file_rmap_pmd+0x29c/0x700 mm/rmap.c:1485
> do_set_pmd+0x767/0xc40 mm/memory.c:4650
> set_huge_pmd+0x28a/0x710 mm/khugepaged.c:1452
> collapse_pte_mapped_thp+0x5c7/0x10b0 mm/khugepaged.c:1655
> madvise_collapse+0x661/0xcc0 mm/khugepaged.c:2762
> madvise_vma_behavior mm/madvise.c:1094 [inline]
> madvise_walk_vmas mm/madvise.c:1268 [inline]
> do_madvise+0xc5f/0x44d0 mm/madvise.c:1464
> __do_sys_madvise mm/madvise.c:1481 [inline]
> __se_sys_madvise mm/madvise.c:1479 [inline]
> __x64_sys_madvise+0xa6/0xc0 mm/madvise.c:1479
> do_syscall_x64 arch/x86/entry/common.c:52 [inline]
> do_syscall_64+0xf5/0x240 arch/x86/entry/common.c:83
> entry_SYSCALL_64_after_hwframe+0x77/0x7f
> RIP: 0033:0x7f1421be72a9
> Code: 48 83 c4 28 c3 e8 37 17 00 00 0f 1f 80 00 00 00 00 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 b8 ff ff ff f7 d8 64 89 01 48
> RSP: 002b:00007fffb7f38b78 EFLAGS: 00000246 ORIG_RAX: 000000000000001c
> RAX: ffffffffffffffda RBX: 00007fffb7f38d58 RCX: 00007f1421be72a9
> RDX: 0000000000000019 RSI: 0000000000800018 RDI: 0000000020000000
> RBP: 00007f1421c5a610 R08: 0000000000000000 R09: 0000000000000000
> R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
> R13: 00007fffb7f38d48 R14: 0000000000000001 R15: 0000000000000001
> </TASK>
>
>
> ---
> If you want syzbot to run the reproducer, reply with:
> #syz test: git://repo/address.git branch-or-commit-hash
> If you attach or paste a git patch, syzbot will apply it before testing.