WARNING: ODEBUG bug in mcheck_cpu_init

Status: moderation: reported on 2026/10/09 13:58
Subsystems: edac
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+fcc0b3f9f99f26c710d7@syzkaller.appspotmail.com
First crash: 4d02h, last: 4d02h
▶ ▼ ✨ AI Jobs (2)
ID Workflow Result Correct Bug Created Started Finished Revision
d0a7f796 repro-c 💥 WARNING: ODEBUG bug in mcheck_cpu_init 2026/10/08 02:56 2026/10/08 02:56 2026/10/08 03:40 f8f239cf
4856b5bd assessment-security DenialOfService: ✅ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ WARNING: ODEBUG bug in mcheck_cpu_init 2026/10/07 00:00 2026/10/07 00:00 2026/10/07 01:05 f7710056

Sample crash report:
------------[ cut here ]------------
ODEBUG: init active (active state 0) object: ffff88802b523440 object type: timer_list hint: mce_timer_fn+0x0/0x2e0 arch/x86/kernel/cpu/mce/core.c:2717
WARNING: lib/debugobjects.c:629 at debug_print_object+0x198/0x2b0 lib/debugobjects.c:629, CPU#3: swapper/3/0
Modules linked in:
CPU: 3 UID: 0 PID: 0 Comm: swapper/3 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:debug_print_object+0x1a5/0x2b0 lib/debugobjects.c:629
Code: b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 80 3c 02 00 75 4f 48 8d 3d d8 b1 1c 0c 41 56 48 8b 14 ed 40 52 62 8c 4c 89 e6 <67> 48 0f b9 3a 58 83 05 e2 e1 11 0c 01 48 83 c4 18 5b 5d 41 5c 41
RSP: 0000:ffffc9000049fc78 EFLAGS: 00010046
RAX: dffffc0000000000 RBX: ffffc9000049fd20 RCX: 0000000000000000
RDX: ffffffff8c625180 RSI: ffffffff8c624ce0 RDI: ffffffff91508dd0
RBP: 0000000000000003 R08: ffff88802b523440 R09: ffffffff8bf31240
R10: ffffffff9bc2e87b R11: 0000000000000000 R12: ffffffff8c624ce0
R13: ffffffff8bf31280 R14: ffffffff81b2b0a0 R15: ffffc9000049fd38
FS:  0000000000000000(0000) GS:ffff888096c52000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000000eb96000 CR4: 0000000000350eb0
Call Trace:
 <TASK>
 __debug_object_init+0x229/0x3d0 lib/debugobjects.c:818
 debug_timer_init kernel/time/timer.c:788 [inline]
 debug_init kernel/time/timer.c:836 [inline]
 timer_init_key+0x35/0x310 kernel/time/timer.c:880
 __mcheck_cpu_setup_timer arch/x86/kernel/cpu/mce/core.c:2087 [inline]
 mcheck_cpu_init+0x273/0x4d0 arch/x86/kernel/cpu/mce/core.c:2262
 identify_cpu+0xe84/0x1c40 arch/x86/kernel/cpu/common.c:2126
 identify_secondary_cpu+0x178/0x270 arch/x86/kernel/cpu/common.c:2187
 ap_starting arch/x86/kernel/smpboot.c:190 [inline]
 start_secondary+0xcf/0x2d0 arch/x86/kernel/smpboot.c:280
 common_startup_64+0x13e/0x158
 </TASK>
----------------
Code disassembly (best guess):
   0:	b8 00 00 00 00       	mov    $0x0,%eax
   5:	00 fc                	add    %bh,%ah
   7:	ff                   	lcall  (bad)
   8:	df 48 89             	fisttps -0x77(%rax)
   b:	fa                   	cli
   c:	48 c1 ea 03          	shr    $0x3,%rdx
  10:	80 3c 02 00          	cmpb   $0x0,(%rdx,%rax,1)
  14:	75 4f                	jne    0x65
  16:	48 8d 3d d8 b1 1c 0c 	lea    0xc1cb1d8(%rip),%rdi        # 0xc1cb1f5
  1d:	41 56                	push   %r14
  1f:	48 8b 14 ed 40 52 62 	mov    -0x739dadc0(,%rbp,8),%rdx
  26:	8c
  27:	4c 89 e6             	mov    %r12,%rsi
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	58                   	pop    %rax
  30:	83 05 e2 e1 11 0c 01 	addl   $0x1,0xc11e1e2(%rip)        # 0xc11e219
  37:	48 83 c4 18          	add    $0x18,%rsp
  3b:	5b                   	pop    %rbx
  3c:	5d                   	pop    %rbp
  3d:	41 5c                	pop    %r12
  3f:	41                   	rex.B

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/05 13:46 upstream a90ee4305c4a 1995e6c7 .config console log report info [disk image (non-bootable)] [vmlinux] [kernel image] ci-qemu-upstream-386 WARNING: ODEBUG bug in mcheck_cpu_init
* Struck through repros no longer work on HEAD.