[moderation] [kernel?] WARNING: ODEBUG bug in smpboot_thread_fn

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0138af2472df Merge tag 'erofs-for-7.0-rc6-fixes' of git://..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=10ae8eda580000
kernel config: https://syzkaller.appspot.com/x/.config?x=45cb3c58fd963c27
dashboard link: https://syzkaller.appspot.com/bug?extid=23b0ddccaae22336ab83
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
CC: [linux-...@vger.kernel.org pet...@infradead.org tg...@kernel.org]

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/21086fbd58ce/disk-0138af24.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/42a2ec9b755d/vmlinux-0138af24.xz
kernel image: https://storage.googleapis.com/syzbot-assets/744af7634ca1/bzImage-0138af24.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+23b0dd...@syzkaller.appspotmail.com

------------[ cut here ]------------
ODEBUG: free active (active state 0) object: ffff88805b513a78 object type: timer_list hint: br_ip6_multicast_port_query_expired+0x0/0x380 net/bridge/br_multicast.c:-1
WARNING: lib/debugobjects.c:632 at debug_print_object lib/debugobjects.c:629 [inline], CPU#0: rcuc/0/20
WARNING: lib/debugobjects.c:632 at __debug_check_no_obj_freed lib/debugobjects.c:1116 [inline], CPU#0: rcuc/0/20
WARNING: lib/debugobjects.c:632 at debug_check_no_obj_freed+0x405/0x550 lib/debugobjects.c:1146, CPU#0: rcuc/0/20
Modules linked in:
CPU: 0 UID: 0 PID: 20 Comm: rcuc/0 Tainted: G L syzkaller #0 PREEMPT_{RT,(full)}
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
RIP: 0010:debug_print_object lib/debugobjects.c:629 [inline]
RIP: 0010:__debug_check_no_obj_freed lib/debugobjects.c:1116 [inline]
RIP: 0010:debug_check_no_obj_freed+0x44a/0x550 lib/debugobjects.c:1146
Code: 89 44 24 20 e8 27 31 82 fd 48 8b 44 24 20 4c 8b 4d 00 4c 89 ef 48 c7 c6 40 74 a6 8b 48 c7 c2 c0 79 a6 8b 8b 0c 24 4d 89 f8 50 <67> 48 0f b9 3a 48 83 c4 08 4c 8b 6c 24 18 48 b9 00 00 00 00 00 fc
RSP: 0018:ffffc90000197a90 EFLAGS: 00010246
RAX: ffffffff89f27c60 RBX: ffffffff99848248 RCX: 0000000000000000
RDX: ffffffff8ba679c0 RSI: ffffffff8ba67440 RDI: ffffffff8f748ea0
RBP: ffffffff8b4f57e0 R08: ffff88805b513a78 R09: ffffffff8b4f6b20
R10: dffffc0000000000 R11: ffffffff81b0bab0 R12: ffff88805b513c00
R13: ffffffff8f748ea0 R14: ffff88805b513000 R15: ffff88805b513a78
FS: 0000000000000000(0000) GS:ffff888126339000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b2fc24000 CR3: 0000000068a94000 CR4: 00000000003526f0
Call Trace:
<TASK>
slab_free_hook mm/slub.c:2616 [inline]
slab_free mm/slub.c:6165 [inline]
kfree+0x13a/0x6c0 mm/slub.c:6483
kobject_cleanup lib/kobject.c:689 [inline]
kobject_release lib/kobject.c:720 [inline]
kref_put include/linux/kref.h:65 [inline]
kobject_put+0x228/0x560 lib/kobject.c:737
rcu_do_batch kernel/rcu/tree.c:2617 [inline]
rcu_core kernel/rcu/tree.c:2869 [inline]
rcu_cpu_kthread+0x99e/0x1470 kernel/rcu/tree.c:2957
smpboot_thread_fn+0x541/0xa50 kernel/smpboot.c:160
kthread+0x388/0x470 kernel/kthread.c:436
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
</TASK>
----------------
Code disassembly (best guess):
0: 89 44 24 20 mov %eax,0x20(%rsp)
4: e8 27 31 82 fd call 0xfd823130
9: 48 8b 44 24 20 mov 0x20(%rsp),%rax
e: 4c 8b 4d 00 mov 0x0(%rbp),%r9
12: 4c 89 ef mov %r13,%rdi
15: 48 c7 c6 40 74 a6 8b mov $0xffffffff8ba67440,%rsi
1c: 48 c7 c2 c0 79 a6 8b mov $0xffffffff8ba679c0,%rdx
23: 8b 0c 24 mov (%rsp),%ecx
26: 4d 89 f8 mov %r15,%r8
29: 50 push %rax
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 48 83 c4 08 add $0x8,%rsp
33: 4c 8b 6c 24 18 mov 0x18(%rsp),%r13
38: 48 rex.W
39: b9 00 00 00 00 mov $0x0,%ecx
3e: 00 fc add %bh,%ah


---
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 syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup