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

[syzbot <syzbot+ae231e0552fa77b26ea1@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    6d35786de281 Merge tag 'for-linus' of git://git.kernel.org..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=126bf21f980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f2e8ebfec4636d32
dashboard link: https://syzkaller.appspot.com/bug?extid=ae231e0552fa77b26ea1
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/b3ab34c4c807/disk-6d35786d.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/03f465478178/vmlinux-6d35786d.xz
kernel image: https://storage.googleapis.com/syzbot-assets/29d261604425/bzImage-6d35786d.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+ae231e0552fa77b26ea1@syzkaller.appspotmail.com

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ODEBUG: free active (active state 0) object: ffff888033a47278 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#1: rcuc/1/28
WARNING: lib/debugobjects.c:632 at __debug_check_no_obj_freed lib/debugobjects.c:1116 [inline], CPU#1: rcuc/1/28
WARNING: lib/debugobjects.c:632 at debug_check_no_obj_freed+0x405/0x550 lib/debugobjects.c:1146, CPU#1: rcuc/1/28
Modules linked in:
CPU: 1 UID: 0 PID: 28 Comm: rcuc/1 Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
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 81 7f fd 48 8b 44 24 20 4c 8b 4d 00 4c 89 ef 48 c7 c6 a0 53 a7 8b 48 c7 c2 20 59 a7 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:ffffc90000a2fa90 EFLAGS: 00010246
RAX: ffffffff89f32240 RBX: ffffffff99a8edc0 RCX: 0000000000000000
RDX: ffffffff8ba75920 RSI: ffffffff8ba753a0 RDI: ffffffff8f933740
RBP: ffffffff8b4f5380 R08: ffff888033a47278 R09: ffffffff8b4f6700
R10: dffffc0000000000 R11: ffffffff81b0c180 R12: ffff888033a47400
R13: ffffffff8f933740 R14: ffff888033a47000 R15: ffff888033a47278
FS:  0000000000000000(0000) GS:ffff888126279000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb873a4da08 CR3: 000000004cc78000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 slab_free_hook mm/slub.c:2620 [inline]
 slab_free mm/slub.c:6250 [inline]
 kfree+0x13e/0x6c0 mm/slub.c:6565
 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+0x514/0xb70 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 81 7f fd       	call   0xfd7f8130
   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 a0 53 a7 8b 	mov    $0xffffffff8ba753a0,%rsi
  1c:	48 c7 c2 20 59 a7 8b 	mov    $0xffffffff8ba75920,%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


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