syzbot


WARNING in stub_timer (2)

Status: upstream: reported on 2026/06/15 07:39
Subsystems: kernel
Labels: prio:high
[Documentation on labels]
Reported-by: syzbot+5e8dda76ca21dae314b6@syzkaller.appspotmail.com
First crash: 5d11h, last: 5d11h
✨ AI Jobs (1)
ID Workflow Result Correct Bug Created Started Finished Revision Error
f207d35a-c78e-47cd-bf83-542d686994e3 assessment-security DenialOfService: ✅ Exploitable: ✅ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ✅ UserNamespace: ✅ VMGuestTrigger: ❌ VMHostTrigger: ❌ WARNING in stub_timer (2) 2026/06/13 00:00 2026/06/13 00:00 2026/06/13 00:50 1d2f35898f2e0325486423250d5303b6bc05adcd

			
		
Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [kernel?] WARNING in stub_timer (2) 0 (1) 2026/06/15 07:39
Similar bugs (2)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 WARNING in stub_timer -1 1 56d 56d 0/3 upstream: reported on 2026/04/21 11:32
upstream WARNING in stub_timer kernel prio:normal -1 209 106d 158d 0/29 auto-obsoleted due to no activity on 2026/05/28 02:15

Sample crash report:
------------[ cut here ]------------
1
WARNING: kernel/time/hrtimer.c:443 at stub_timer+0xa/0x20 kernel/time/timer.c:716, CPU#0: udevd/4706
Modules linked in:
CPU: 0 UID: 0 PID: 4706 Comm: udevd 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:stub_timer+0xa/0x20 kernel/time/timer.c:716
Code: cc 66 66 66 66 66 66 2e 0f 1f 84 00 00 00 00 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa e8 d7 1a 13 00 90 <0f> 0b 90 31 c0 c3 cc cc cc cc cc 66 66 2e 0f 1f 84 00 00 00 00 00
RSP: 0018:ffffc90000007dd0 EFLAGS: 00010006
RAX: ffffffff81b2ac39 RBX: 1ffff11000046617 RCX: ffff888000232540
RDX: 0000000000010000 RSI: ffffffff8c28d0c0 RDI: ffffc9000255fb20
RBP: ffffc9000255fb20 R08: ffffffff90305bf7 R09: 1ffffffff2060b7e
R10: dffffc0000000000 R11: ffffffff81b2ac30 R12: ffff8880002330b8
R13: 1ffff11003f8506a R14: dffffc0000000000 R15: ffffffff81b2ac30
FS:  00007f6e41fb1880(0000) GS:ffff88808c894000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005589b464e660 CR3: 00000000128d0000 CR4: 0000000000352ef0
Call Trace:
 <IRQ>
 __run_hrtimer kernel/time/hrtimer.c:1930 [inline]
 __hrtimer_run_queues+0x3c0/0xa20 kernel/time/hrtimer.c:1994
 hrtimer_interrupt+0x44b/0x950 kernel/time/hrtimer.c:2113
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 __sysvec_apic_timer_interrupt+0x102/0x430 arch/x86/kernel/apic/apic.c:1067
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1061 [inline]
 sysvec_apic_timer_interrupt+0xa1/0xc0 arch/x86/kernel/apic/apic.c:1061
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:179 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0x47/0x80 kernel/locking/spinlock.c:198
Code: f7 e8 ad 28 f6 f5 f7 c3 00 02 00 00 74 05 e8 20 d2 21 f6 9c 58 a9 00 02 00 00 75 27 f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> c4 a7 e7 f5 65 8b 05 8d 9d 8c 07 85 c0 74 18 5b 41 5e c3 cc cc
RSP: 0018:ffffc9000255fac8 EFLAGS: 00000206
RAX: 0000000000000006 RBX: 0000000000000246 RCX: 0000000080000001
RDX: 0000000000000000 RSI: ffffffff8dfa9d91 RDI: 0000000000000001
RBP: ffffc9000255fbf0 R08: ffffffff90305bf7 R09: 1ffffffff2060b7e
R10: dffffc0000000000 R11: fffffbfff2060b7f R12: 1ffff920004abfae
R13: 1ffff920004abf60 R14: ffff88801fc28280 R15: dffffc0000000000
 schedule_hrtimeout_range_clock+0x142/0x330 kernel/time/sleep_timeout.c:213
 ep_poll fs/eventpoll.c:2030 [inline]
 do_epoll_wait+0xd36/0xf60 fs/eventpoll.c:2464
 __do_sys_epoll_wait fs/eventpoll.c:2472 [inline]
 __se_sys_epoll_wait fs/eventpoll.c:2467 [inline]
 __x64_sys_epoll_wait+0x1d7/0x230 fs/eventpoll.c:2467
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x174/0x580 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f6e418a7407
Code: 48 89 fa 4c 89 df e8 38 aa 00 00 8b 93 08 03 00 00 59 5e 48 83 f8 fc 74 1a 5b c3 0f 1f 84 00 00 00 00 00 48 8b 44 24 10 0f 05 <5b> c3 0f 1f 80 00 00 00 00 83 e2 39 83 fa 08 75 de e8 23 ff ff ff
RSP: 002b:00007ffe8bec5c00 EFLAGS: 00000202 ORIG_RAX: 00000000000000e8
RAX: ffffffffffffffda RBX: 00007f6e41fb1880 RCX: 00007f6e418a7407
RDX: 0000000000000008 RSI: 00007ffe8bec5d60 RDI: 000000000000000b
RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000bb8 R11: 0000000000000202 R12: 0000000000000000
R13: 0000556a1ef48100 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
----------------
Code disassembly (best guess):
   0:	f7 e8                	imul   %eax
   2:	ad                   	lods   %ds:(%rsi),%eax
   3:	28 f6                	sub    %dh,%dh
   5:	f5                   	cmc
   6:	f7 c3 00 02 00 00    	test   $0x200,%ebx
   c:	74 05                	je     0x13
   e:	e8 20 d2 21 f6       	call   0xf621d233
  13:	9c                   	pushf
  14:	58                   	pop    %rax
  15:	a9 00 02 00 00       	test   $0x200,%eax
  1a:	75 27                	jne    0x43
  1c:	f7 c3 00 02 00 00    	test   $0x200,%ebx
  22:	74 01                	je     0x25
  24:	fb                   	sti
  25:	bf 01 00 00 00       	mov    $0x1,%edi
* 2a:	e8 c4 a7 e7 f5       	call   0xf5e7a7f3 <-- trapping instruction
  2f:	65 8b 05 8d 9d 8c 07 	mov    %gs:0x78c9d8d(%rip),%eax        # 0x78c9dc3
  36:	85 c0                	test   %eax,%eax
  38:	74 18                	je     0x52
  3a:	5b                   	pop    %rbx
  3b:	41 5e                	pop    %r14
  3d:	c3                   	ret
  3e:	cc                   	int3
  3f:	cc                   	int3

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/06/11 07:37 upstream 9716c086c8e8 b754d2d8 .config console log report [disk image (non-bootable)] [vmlinux] [kernel image] ci-snapshot-upstream-root WARNING in stub_timer
* Struck through repros no longer work on HEAD.