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

[Aleksandr Nogikh]

On Tue, Oct 10, 2023 at 4:20 PM Johannes Weiner <hannes@xxxxxxxxxxx> wrote:
>
> This is the earlier version of the hugetlb cgroup accounting patches
> that trigger on an uncharged hugetlbfs:
>
>   7547          /*
>   7548           * Note that it is normal to see !memcg for a hugetlb folio.
>   7549           * It could have been allocated when memory_hugetlb_accounting was not
>   7550           * selected, for e.g.
>   7551           */
>   7552          VM_WARN_ON_ONCE_FOLIO(!memcg, old);
>
> It's been fixed in the revision that's in the latest next release:
>
>   7539          /*
>   7540           * Note that it is normal to see !memcg for a hugetlb folio.
>   7541           * For e.g, itt could have been allocated when memory_hugetlb_accounting
>   7542           * was not selected.
>   7543           */
>   7544          VM_WARN_ON_ONCE_FOLIO(!folio_test_hugetlb(old) && !memcg, old);
>   7545          if (!memcg)
>   7546                  return;
>
> > Modules linked in:
> > CPU: 1 PID: 5208 Comm: syz-executor.1 Not tainted 6.6.0-rc4-next-20231005-syzkaller #0
> > Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/06/2023
> > RIP: 0010:mem_cgroup_migrate+0x2fa/0x390 mm/memcontrol.c:7552
> > Code: f7 ff e9 36 ff ff ff 80 3d 84 b2 d1 0c 00 0f 85 54 ff ff ff 48 c7 c6 a0 9e 9b 8a 48 89 ef e8 0d 5c df ff c6 05 68 b2 d1 0c 01 <0f> 0b e9 37 ff ff ff 48 c7 c6 e0 9a 9b 8a 48 89 df e8 f0 5b df ff
> > RSP: 0018:ffffc90004b2fa38 EFLAGS: 00010246
> > RAX: 0000000000040000 RBX: ffffea0005338000 RCX: ffffc90005439000
> > RDX: 0000000000040000 RSI: ffffffff81e76463 RDI: ffffffff8ae96da0
> > RBP: ffffea0001d98000 R08: 0000000000000000 R09: fffffbfff1d9db9a
> > R10: ffffffff8ecedcd7 R11: 0000000000000000 R12: 0000000000000000
> > R13: 0000000000000200 R14: 0000000000000000 R15: ffffea0001d98018
> > FS:  00007fc15e89d6c0(0000) GS:ffff8880b9900000(0000) knlGS:0000000000000000
> > CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> > CR2: 0000001b31820000 CR3: 000000007f5e1000 CR4: 00000000003506f0
> > DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> > DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> > Call Trace:
> >  <TASK>
> >  hugetlbfs_migrate_folio fs/hugetlbfs/inode.c:1066 [inline]
> >  hugetlbfs_migrate_folio+0xd0/0x120 fs/hugetlbfs/inode.c:1049
> >  move_to_new_folio+0x183/0x690 mm/migrate.c:966
> >  unmap_and_move_huge_page mm/migrate.c:1428 [inline]
> >  migrate_hugetlbs mm/migrate.c:1546 [inline]
> >  migrate_pages+0x16ac/0x27c0 mm/migrate.c:1900
> >  migrate_to_node mm/mempolicy.c:1072 [inline]
> >  do_migrate_pages+0x43e/0x690 mm/mempolicy.c:1171
> >  kernel_migrate_pages+0x59b/0x780 mm/mempolicy.c:1682
> >  __do_sys_migrate_pages mm/mempolicy.c:1700 [inline]
> >  __se_sys_migrate_pages mm/mempolicy.c:1696 [inline]
> >  __x64_sys_migrate_pages+0x96/0x100 mm/mempolicy.c:1696
> >  do_syscall_x64 arch/x86/entry/common.c:51 [inline]
> >  do_syscall_64+0x38/0xb0 arch/x86/entry/common.c:81
> >  entry_SYSCALL_64_after_hwframe+0x63/0xcd
> > RIP: 0033:0x7fc15da7cae9
> > 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:00007fc15e89d0c8 EFLAGS: 00000246 ORIG_RAX: 0000000000000100
> > RAX: ffffffffffffffda RBX: 00007fc15db9bf80 RCX: 00007fc15da7cae9
> > RDX: 0000000020000340 RSI: 0000000000000080 RDI: 0000000000000000
> > RBP: 00007fc15dac847a R08: 0000000000000000 R09: 0000000000000000
> > R10: 00000000200003c0 R11: 0000000000000246 R12: 0000000000000000
> > R13: 000000000000000b R14: 00007fc15db9bf80 R15: 00007ffd87d7c058
> >  </TASK>
> >
> >
> > ---
> > This report is generated by a bot. It may contain errors.
> > See https://goo.gl/tpsmEJ for more information about syzbot.
> > syzbot engineers can be reached at syzkaller@xxxxxxxxxxxxxxxx.
> >
> > syzbot will keep track of this issue. See:
> > https://goo.gl/tpsmEJ#status for how to communicate with syzbot.
> >
> > If the bug is already fixed, let syzbot know by replying with:
> > #syz fix: exact-commit-title
>
> #syz fix: next-20231010
>

Thanks for sharing the info and updating the issue!

If there's no fixing commit (the faulty series is dropped or
replaced), it's better to just invalidate the report:

#syz invalid

Otherwise, as in this case, syzbot would start looking for the
"next-20231010" commit (and won't find it because it's a tag) and,
after some time, start complaining that no such commit is reachable
from any of the master branches of the tested trees.

-- 
Aleksandr