syzbot


WARNING: ODEBUG bug in smpboot_thread_fn

Status: moderation: reported on 2026/03/26 22:05
Subsystems: kernel
[Documentation on labels]
Reported-by: syzbot+23b0ddccaae22336ab83@syzkaller.appspotmail.com
First crash: 7d11h, last: 3d16h

Sample crash report:
------------[ 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

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/03/26 16:36 upstream 0138af2472df fca8d360 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: ODEBUG bug in smpboot_thread_fn
2026/03/22 21:56 upstream 8d8bd2a5aa98 5b92003d .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-kasan-gce-smack-root WARNING: ODEBUG bug in smpboot_thread_fn
* Struck through repros no longer work on HEAD.