syzbot

 sign-in | mailing list | source | docs
🐞 Open [460]
🐞 Fixed [21]
🐞 Invalid [130]
⬇ Missing Backports [18]
≡ Crashes
Kernel Health Bugs/Month Bug Lifetimes Fuzzing
💬 Send us feedback

INFO: rcu detected stall in lapb_t1timer_expiry

Status: upstream: reported C repro on 2026/01/27 05:10
Bug presence: origin:lts-only
[Documentation on labels]
Reported-by: syzbot+d026d1f61fedf7893450@syzkaller.appspotmail.com
First crash: 17h12m, last: 17h12m
▶ ▼ Bug presence (2)
Date Name Commit Repro Result
2026/01/27 linux-6.6.y (ToT) cbb31f77b879 C [report] INFO: rcu detected stall in addrconf_rs_timer
2026/01/27 upstream (ToT) fcb70a56f4d8 C Didn't crash
▶ ▼ Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: rcu detected stall in lapb_t1timer_expiry kvm 1 1 1372d 1372d 0/29 auto-closed as invalid on 2022/06/25 00:02
linux-5.15 INFO: rcu detected stall in lapb_t1timer_expiry 1 2 61d 71d 0/3 upstream: reported on 2025/11/17 07:08
upstream INFO: rcu detected stall in lapb_t1timer_expiry (2) usb x25 1 C error error 21 55d 556d 0/29 upstream: reported C repro on 2024/07/20 04:25
▶ ▼ Fix bisection attempts (1)
Created Duration User Patch Repo Result
2026/01/27 15:00 8m fix candidate upstream error job log

Sample crash report:
hrtimer: interrupt took 57693 ns
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	1-...!: (1 GPs behind) idle=9a8c/1/0x4000000000000000 softirq=10363/10366 fqs=0
rcu: 	(t=10500 jiffies g=9465 q=118 ncpus=2)
rcu: rcu_preempt kthread starved for 10500 jiffies! g9465 f0x0 RCU_GP_WAIT_FQS(5) ->state=0x0 ->cpu=0
rcu: 	Unless rcu_preempt kthread gets sufficient CPU time, OOM is now expected behavior.
rcu: RCU grace-period kthread stack dump:
task:rcu_preempt     state:R  running task     stack:27656 pid:17    ppid:2      flags:0x00004000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5381 [inline]
 __schedule+0x1553/0x45a0 kernel/sched/core.c:6700
 schedule+0xbd/0x170 kernel/sched/core.c:6774
 schedule_timeout+0x188/0x2d0 kernel/time/timer.c:2168
 rcu_gp_fqs_loop+0x313/0x1590 kernel/rcu/tree.c:1667
 rcu_gp_kthread+0x9d/0x3b0 kernel/rcu/tree.c:1866
 kthread+0x2fa/0x390 kernel/kthread.c:388
 ret_from_fork+0x48/0x80 arch/x86/kernel/process.c:152
 ret_from_fork_asm+0x11/0x20 arch/x86/entry/entry_64.S:293
 </TASK>
rcu: Stack dump where RCU GP kthread last ran:
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5794 Comm: syz-executor166 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:on_stack arch/x86/include/asm/stacktrace.h:60 [inline]
RIP: 0010:stack_access_ok arch/x86/kernel/unwind_orc.c:393 [inline]
RIP: 0010:deref_stack_reg arch/x86/kernel/unwind_orc.c:403 [inline]
RIP: 0010:unwind_next_frame+0xf1b/0x2970 arch/x86/kernel/unwind_orc.c:585
Code: 15 00 00 8b 6d 00 31 ff 89 ee e8 b0 d1 4b 00 85 ed 0f 95 c0 4c 39 f3 0f 96 c1 20 c1 4d 39 f7 0f 97 c0 84 c1 0f 84 fd 01 00 00 <49> 8d 46 08 48 39 d8 0f 97 c1 4c 39 f8 0f 96 c0 84 c1 48 8b 6c 24
RSP: 0018:ffffc90000006eb0 EFLAGS: 00000002
RAX: ffffffff813b4501 RBX: ffffc90000000000 RCX: 0000000000000101
RDX: ffff88802ced9e00 RSI: 0000000000000002 RDI: 0000000000000000
RBP: 0000000000000002 R08: ffff88802ced9e00 R09: 0000000000000003
R10: 0000000000000004 R11: 0000000000000100 R12: 1ffff92000000dfd
R13: 1ffff92000000dfe R14: ffffc90000007bb8 R15: ffffc90000008000
FS:  000055557ede33c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000007d3ea000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 perf_callchain_kernel+0x42e/0x690 arch/x86/events/core.c:2780
 get_perf_callchain+0x235/0x4f0 kernel/events/callchain.c:204
 perf_callchain kernel/events/core.c:7740 [inline]
 perf_sample_save_callchain include/linux/perf_event.h:1232 [inline]
 perf_prepare_sample+0x390/0x1ca0 kernel/events/core.c:7784
 __perf_event_output kernel/events/core.c:7972 [inline]
 perf_event_output_forward+0x187/0x3e0 kernel/events/core.c:7993
 __perf_event_overflow+0x447/0x630 kernel/events/core.c:9718
 perf_swevent_overflow kernel/events/core.c:9794 [inline]
 perf_swevent_event+0x324/0x630 kernel/events/core.c:-1
 perf_tp_event+0x54f/0x1450 kernel/events/core.c:10344
 perf_trace_run_bpf_submit+0xf4/0x1c0 kernel/events/core.c:10268
 perf_trace_preemptirq_template+0x269/0x330 include/trace/events/preemptirq.h:14
 trace_irq_enable+0xbb/0xe0 include/trace/events/preemptirq.h:40
 trace_hardirqs_on+0x18/0x40 kernel/trace/trace_preemptirq.c:56
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xc0/0x120 kernel/locking/spinlock.c:194
Code: c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f7 44 24 20 00 02 00 00 41 c6 04 07 f8 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> bb ca ce f6 65 8b 05 ac 00 76 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc900000079a0 EFLAGS: 00000206
RAX: dffffc0000000004 RBX: 0000000000000a02 RCX: 44e425f313173900
RDX: dffffc0000000000 RSI: ffffffff8acac900 RDI: 0000000000000001
RBP: ffffc90000007a28 R08: ffffffff911be5c7 R09: 1ffffffff2237cb8
R10: dffffc0000000000 R11: fffffbfff2237cb9 R12: dffffc0000000000
R13: ffff88802d1c0118 R14: ffffffff975872b0 R15: 1ffff92000000f34
 debug_object_assert_init+0x1f1/0x2f0 lib/debugobjects.c:900
 debug_timer_assert_init kernel/time/timer.c:792 [inline]
 debug_assert_init kernel/time/timer.c:837 [inline]
 __mod_timer+0x55/0xdb0 kernel/time/timer.c:1020
 lapb_start_t1timer net/lapb/lapb_timer.c:44 [inline]
 lapb_t1timer_expiry+0x745/0xab0 net/lapb/lapb_timer.c:202
 call_timer_fn+0x189/0x540 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x542/0x800 kernel/time/timer.c:2023
 run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xd3/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:generic_exec_single+0x481/0x4f0 kernel/smp.c:418
Code: 75 11 e8 02 02 0b 00 48 85 db 75 16 e8 f8 01 0b 00 eb 15 e8 f1 01 0b 00 e8 8c fa 07 09 48 85 db 74 ea e8 e2 01 0b 00 fb 31 c0 <48> c7 44 24 20 0e 36 e0 45 4b c7 04 2c 00 00 00 00 43 c7 44 2c 08
RSP: 0018:ffffc9000481f860 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000200 RCX: ffff88802ced9e00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000481f930 R08: ffffffff911be5df R09: 1ffffffff2237cbb
R10: dffffc0000000000 R11: fffffbfff2237cbc R12: 1ffff92000903f10
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff92000903f31
 smp_call_function_single+0x36d/0x5a0 kernel/smp.c:647
 task_function_call kernel/events/core.c:120 [inline]
 event_function_call+0x359/0x650 kernel/events/core.c:305
 _perf_event_period kernel/events/core.c:5904 [inline]
 _perf_ioctl kernel/events/core.c:5973 [inline]
 perf_ioctl+0x1fdc/0x24a0 kernel/events/core.c:6074
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa536b1e649
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff87d4c308 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fa536b1e649
RDX: 00002000000001c0 RSI: 0000000040082404 RDI: 0000000000000004
RBP: 0000000000000000 R08: 000055557ede4730 R09: 000055557ede4730
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>
INFO: NMI handler (nmi_cpu_backtrace_handler) took too long to run: 2.589 msecs
CPU: 1 PID: 5793 Comm: syz-executor166 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xc0/0x120 kernel/locking/spinlock.c:194
Code: c7 44 24 20 00 00 00 00 9c 8f 44 24 20 f7 44 24 20 00 02 00 00 41 c6 04 07 f8 75 4b f7 c3 00 02 00 00 74 01 fb bf 01 00 00 00 <e8> bb ca ce f6 65 8b 05 ac 00 76 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc900001f0880 EFLAGS: 00000206
RAX: dffffc0000000004 RBX: 0000000000000a02 RCX: d2b4958df9dc4900
RDX: dffffc0000000000 RSI: ffffffff8acac900 RDI: 0000000000000001
RBP: ffffc900001f0910 R08: ffffffff911be5cf R09: 1ffffffff2237cb9
R10: dffffc0000000000 R11: fffffbfff2237cba R12: dffffc0000000000
R13: 0000000000000a02 R14: ffffffff9761d960 R15: 1ffff9200003e110
FS:  000055557ede33c0(0000) GS:ffff8880b8f00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 000000001bbf2000 CR4: 00000000003506e0
Call Trace:
 <IRQ>
 spin_unlock_irqrestore include/linux/spinlock.h:406 [inline]
 __wake_up_common_lock kernel/sched/wait.c:140 [inline]
 __wake_up+0x132/0x1a0 kernel/sched/wait.c:160
 aoenet_xmit+0x13b/0x190 drivers/block/aoe/aoenet.c:124
 aoecmd_cfg+0x9ca/0xa50 drivers/block/aoe/aoecmd.c:1375
 call_timer_fn+0x189/0x540 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x542/0x800 kernel/time/timer.c:2023
 run_timer_softirq+0x67/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x280/0x820 kernel/softirq.c:578
 __do_softirq kernel/softirq.c:612 [inline]
 invoke_softirq kernel/softirq.c:452 [inline]
 __irq_exit_rcu+0xd3/0x190 kernel/softirq.c:661
 irq_exit_rcu+0x9/0x20 kernel/softirq.c:673
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1088 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1088
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:687
RIP: 0010:generic_exec_single+0x481/0x4f0 kernel/smp.c:418
Code: 75 11 e8 02 02 0b 00 48 85 db 75 16 e8 f8 01 0b 00 eb 15 e8 f1 01 0b 00 e8 8c fa 07 09 48 85 db 74 ea e8 e2 01 0b 00 fb 31 c0 <48> c7 44 24 20 0e 36 e0 45 4b c7 04 2c 00 00 00 00 43 c7 44 2c 08
RSP: 0018:ffffc9000480f860 EFLAGS: 00000246
RAX: 0000000000000000 RBX: 0000000000000200 RCX: ffff88802f515a00
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: ffffc9000480f930 R08: ffffffff911be5df R09: 1ffffffff2237cbb
R10: dffffc0000000000 R11: fffffbfff2237cbc R12: 1ffff92000901f10
R13: dffffc0000000000 R14: 0000000000000000 R15: 1ffff92000901f31
 smp_call_function_single+0x36d/0x5a0 kernel/smp.c:647
 task_function_call kernel/events/core.c:120 [inline]
 event_function_call+0x359/0x650 kernel/events/core.c:305
 _perf_event_period kernel/events/core.c:5904 [inline]
 _perf_ioctl kernel/events/core.c:5973 [inline]
 perf_ioctl+0x1fdc/0x24a0 kernel/events/core.c:6074
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:871 [inline]
 __se_sys_ioctl+0xfd/0x170 fs/ioctl.c:857
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x55/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7fa536b1e649
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 d0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fff87d4c308 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00007fa536b1e649
RDX: 00002000000001c0 RSI: 0000000040082404 RDI: 0000000000000004
RBP: 0000000000000000 R08: 000055557ede4730 R09: 000055557ede4730
R10: 0000000000000002 R11: 0000000000000246 R12: 0000000000000000
R13: 0000000000000000 R14: 0000000000000000 R15: 0000000000000000
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/01/27 05:09 linux-6.6.y cbb31f77b879 efb3e894 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-6-6-kasan-perf INFO: rcu detected stall in lapb_t1timer_expiry
* Struck through repros no longer work on HEAD.