INFO: rcu detected stall in lapb_t1timer_expiry

Status: upstream: reported on 2026/07/11 10:32
Reported-by: syzbot+d0bd5b1ae5241ae44bd7@syzkaller.appspotmail.com
First crash: 19d, last: 19d
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-5.15 INFO: rcu detected stall in lapb_t1timer_expiry (2) 1 1 31d 31d 0/3 upstream: reported on 2026/06/29 08:22
upstream INFO: rcu detected stall in lapb_t1timer_expiry kvm 1 1 1557d 1557d 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 245d 255d 0/3 auto-obsoleted due to no activity on 2026/03/07 17:20
upstream INFO: rcu detected stall in lapb_t1timer_expiry (2) usb x25 1 syz, C error error 22 159d 741d 0/29 auto-obsoleted due to no activity on 2026/06/01 15:08
linux-6.6 INFO: rcu detected stall in lapb_t1timer_expiry origin:lts-only 1 syz, C error 1 185d 185d 0/2 upstream: reported C repro on 2026/01/27 05:10

Sample crash report:
rcu: INFO: rcu_preempt detected expedited stalls on CPUs/tasks: { 0-.... } 2690 jiffies s: 8169 root: 0x1/.
rcu: blocking rcu_node structures (internal RCU debug):
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 5053 Comm: syz.2.211 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
RIP: 0010:orc_ip arch/x86/kernel/unwind_orc.c:30 [inline]
RIP: 0010:__orc_find arch/x86/kernel/unwind_orc.c:52 [inline]
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:178 [inline]
RIP: 0010:unwind_next_frame+0x1212/0x1fd0 arch/x86/kernel/unwind_orc.c:448
Code: c1 48 c1 f9 02 48 c1 e8 3f 48 01 c8 48 83 e0 fe 4c 8d 7c 45 00 4c 89 f8 48 c1 e8 03 48 b9 00 00 00 00 00 fc ff df 0f b6 04 08 <84> c0 75 27 49 63 07 4c 01 f8 49 8d 4f 04 4c 39 f0 48 0f 46 e9 49
RSP: 0018:ffffc90000006678 EFLAGS: 00000803
RAX: 0000000000000000 RBX: ffffc90000006780 RCX: dffffc0000000000
RDX: ffffffff8f3c16d0 RSI: ffffffff8e987a60 RDI: 0000000000000001
RBP: ffffffff8e987a7c R08: 0000000000000008 R09: ffffc900000067d0
R10: dffffc0000000000 R11: fffff52000000cfc R12: ffffffff8e987a78
R13: ffffffff8e987a7c R14: ffffffff8a3a66ec R15: ffffffff8e987a7c
FS:  00007f45977256c0(0000) GS:ffff8880b8e00000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000100000000 CR3: 0000000024f31000 CR4: 00000000003506f0
DR0: 0000200000000300 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <IRQ>
 perf_callchain_kernel+0x42a/0x690 arch/x86/events/core.c:2805
 get_perf_callchain+0x236/0x490 kernel/events/callchain.c:204
 perf_callchain kernel/events/core.c:7512 [inline]
 perf_prepare_sample+0x399/0x2020 kernel/events/core.c:7545
 __perf_event_output kernel/events/core.c:7730 [inline]
 perf_event_output_forward+0x197/0x2f0 kernel/events/core.c:7750
 __perf_event_overflow+0x457/0x630 kernel/events/core.c:9496
 perf_swevent_overflow+0x19b/0x230 kernel/events/core.c:9579
 perf_swevent_event+0x458/0x570 kernel/events/core.c:-1
 perf_tp_event+0x36b/0xc10 kernel/events/core.c:10064
 perf_trace_run_bpf_submit+0xf3/0x1c0 kernel/events/core.c:10032
 perf_trace_preemptirq_template+0x268/0x320 include/trace/events/preemptirq.h:14
 trace_irq_disable include/trace/events/preemptirq.h:36 [inline]
 trace_hardirqs_off_finish+0x13f/0x180 kernel/trace/trace_preemptirq.c:67
 irqentry_enter+0x33/0x50 kernel/entry/common.c:382
 sysvec_apic_timer_interrupt+0xa/0xc0 arch/x86/kernel/apic/apic.c:1118
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:691
RIP: 0010:__raw_spin_unlock_irqrestore include/linux/spinlock_api_smp.h:152 [inline]
RIP: 0010:_raw_spin_unlock_irqrestore+0xbc/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> 4f 57 1e f7 65 8b 05 50 08 c8 75 85 c0 74 3c 48 c7 04 24 0e 36
RSP: 0018:ffffc900000071e0 EFLAGS: 00000206
RAX: dffffc0000000004 RBX: 0000000000000a06 RCX: ecbe0449f5e13c00
RDX: dffffc0000000000 RSI: ffffffff8a8c17a0 RDI: 0000000000000001
RBP: ffffc90000007268 R08: ffffffff90b10307 R09: 1ffffffff2162060
R10: dffffc0000000000 R11: fffffbfff2162061 R12: dffffc0000000000
R13: ffff88804bfb3560 R14: ffffffff8d1dd2f0 R15: 1ffff92000000e3c
 __stack_depot_save+0x439/0x480 lib/stackdepot.c:502
 kasan_save_stack mm/kasan/common.c:47 [inline]
 kasan_set_track+0x60/0x70 mm/kasan/common.c:53
 kasan_save_free_info+0x27/0x40 mm/kasan/generic.c:516
 ____kasan_slab_free+0x126/0x1f0 mm/kasan/common.c:237
 kasan_slab_free include/linux/kasan.h:177 [inline]
 slab_free_hook mm/slub.c:1729 [inline]
 slab_free_freelist_hook+0x133/0x1b0 mm/slub.c:1755
 slab_free mm/slub.c:3687 [inline]
 __kmem_cache_free+0xb6/0x200 mm/slub.c:3700
 skb_free_head net/core/skbuff.c:762 [inline]
 skb_release_data+0x5e9/0x7e0 net/core/skbuff.c:791
 skb_release_all net/core/skbuff.c:856 [inline]
 __kfree_skb net/core/skbuff.c:870 [inline]
 consume_skb+0xa2/0x100 net/core/skbuff.c:1035
 ifb_xmit+0x1d3/0x5a0 drivers/net/ifb.c:345
 __netdev_start_xmit include/linux/netdevice.h:4894 [inline]
 netdev_start_xmit include/linux/netdevice.h:4908 [inline]
 xmit_one net/core/dev.c:3695 [inline]
 dev_hard_start_xmit+0x292/0x8b0 net/core/dev.c:3711
 sch_direct_xmit+0x24d/0x4a0 net/sched/sch_generic.c:345
 __dev_xmit_skb net/core/dev.c:3932 [inline]
 __dev_queue_xmit+0x180d/0x3810 net/core/dev.c:4337
 lapb_data_transmit+0x86/0xa0 net/lapb/lapb_iface.c:447
 lapb_transmit_buffer+0x15f/0x1f0 net/lapb/lapb_out.c:149
 lapb_t1timer_expiry+0x65b/0xa50 net/lapb/lapb_timer.c:-1
 call_timer_fn+0x1ac/0x670 kernel/time/timer.c:1701
 expire_timers kernel/time/timer.c:1752 [inline]
 __run_timers+0x56c/0x810 kernel/time/timer.c:2023
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:2036
 handle_softirqs+0x291/0x910 kernel/softirq.c:596
 __do_softirq kernel/softirq.c:630 [inline]
 invoke_softirq kernel/softirq.c:470 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:679
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:691
 instr_sysvec_irq_work arch/x86/kernel/irq_work.c:17 [inline]
 sysvec_irq_work+0x9d/0xc0 arch/x86/kernel/irq_work.c:17
 </IRQ>
 <TASK>
 asm_sysvec_irq_work+0x16/0x20 arch/x86/include/asm/idtentry.h:728
RIP: 0010:finish_task_switch+0x267/0x8e0 kernel/sched/core.c:5124
Code: d6 08 85 c0 0f 84 38 01 00 00 48 85 db 0f 85 57 01 00 00 0f 1f 44 00 00 4c 89 e7 e8 d3 e3 e0 08 e8 8e 04 2f 00 fb 4c 8b 65 b8 <49> 8d bc 24 f8 15 00 00 48 89 f8 48 c1 e8 03 42 0f b6 04 30 84 c0
RSP: 0018:ffffc900048bf880 EFLAGS: 00000282
RAX: ecbe0449f5e13c00 RBX: 0000000000000000 RCX: ecbe0449f5e13c00
RDX: dffffc0000000000 RSI: ffffffff8a8c17a0 RDI: ffffffff8adf42e0
RBP: ffffc900048bf8d0 R08: ffff8880b8e3ad03 R09: 1ffff110171c75a0
R10: dffffc0000000000 R11: ffffed10171c75a1 R12: ffff888024fbda00
R13: 1ffff110171c76fa R14: dffffc0000000000 R15: ffff8880b8e3b7d0
 context_switch kernel/sched/core.c:5248 [inline]
 __schedule+0x1087/0x4030 kernel/sched/core.c:6562
 preempt_schedule_common+0x82/0xd0 kernel/sched/core.c:6731
 preempt_schedule+0xbc/0xd0 kernel/sched/core.c:6755
 preempt_schedule_thunk+0x16/0x18 arch/x86/entry/thunk_64.S:34
 try_to_wake_up+0x6c1/0x10b0 kernel/sched/core.c:4234
 wake_up_process kernel/sched/core.c:4362 [inline]
 wake_up_q+0x78/0xc0 kernel/sched/core.c:1010
 futex_wake+0x426/0x4f0 kernel/futex/waitwake.c:184
 do_futex+0x2e2/0x320 kernel/futex/syscalls.c:139
 __do_sys_futex kernel/futex/syscalls.c:211 [inline]
 __se_sys_futex+0x381/0x410 kernel/futex/syscalls.c:192
 do_syscall_x64 arch/x86/entry/common.c:46 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:76
 entry_SYSCALL_64_after_hwframe+0x68/0xd2
RIP: 0033:0x7f459679de59
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 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 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f45977250e8 EFLAGS: 00000246 ORIG_RAX: 00000000000000ca
RAX: ffffffffffffffda RBX: 00007f4596a25fa8 RCX: 00007f459679de59
RDX: 00000000000f4240 RSI: 0000000000000081 RDI: 00007f4596a25fac
RBP: 00007f4596a25fa0 R08: 00011d0e352a43f2 R09: 0000000000000000
R10: 000000000000000e R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4596a26038 R14: 00007ffda1bdc510 R15: 00007ffda1bdc5f8
 </TASK>

Crashes (1):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/07/11 10:32 linux-6.1.y 090666d3cc90 d78ea535 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-6-1-kasan-perf INFO: rcu detected stall in lapb_t1timer_expiry
* Struck through repros no longer work on HEAD.