INFO: rcu detected stall in lapb_t1timer_expiry (2)

Status: upstream: reported C repro on 2026/06/29 08:22
Reported-by: syzbot+0cdc91244b02fa9ade5f@syzkaller.appspotmail.com
First crash: 82d, last: 2d06h
▶ ▼ Similar bugs (5)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
linux-6.1 INFO: rcu detected stall in lapb_t1timer_expiry 1 1 70d 70d 0/3 upstream: reported on 2026/07/11 10:32
upstream INFO: rcu detected stall in lapb_t1timer_expiry kvm 1 1 1607d 1607d 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 295d 306d 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 209d 791d 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 inconclusive 1 235d 235d 0/2 upstream: reported C repro on 2026/01/27 05:10

Sample crash report:
rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 	0-....: (1 GPs behind) idle=129/1/0x4000000000000000 softirq=6557/6558 fqs=5029 
	(t=10500 jiffies g=7061 q=159318)
NMI backtrace for cpu 0
CPU: 0 PID: 4386 Comm: syz.2.19 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <IRQ>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_single_cpu_backtrace include/linux/nmi.h:166 [inline]
 rcu_dump_cpu_stacks+0x22d/0x380 kernel/rcu/tree_stall.h:349
 print_cpu_stall+0x31f/0x5f0 kernel/rcu/tree_stall.h:633
 check_cpu_stall kernel/rcu/tree_stall.h:727 [inline]
 rcu_pending kernel/rcu/tree.c:3936 [inline]
 rcu_sched_clock_irq+0x6ec/0x1120 kernel/rcu/tree.c:2619
 update_process_times+0x193/0x200 kernel/time/timer.c:2021
 tick_sched_handle kernel/time/tick-sched.c:254 [inline]
 tick_sched_timer+0x37d/0x560 kernel/time/tick-sched.c:1473
 __run_hrtimer kernel/time/hrtimer.c:1685 [inline]
 __hrtimer_run_queues+0x4b0/0xb60 kernel/time/hrtimer.c:1749
 hrtimer_interrupt+0x397/0x8b0 kernel/time/hrtimer.c:1811
 local_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1097 [inline]
 __sysvec_apic_timer_interrupt+0x137/0x4a0 arch/x86/kernel/apic/apic.c:1114
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0x4d/0xc0 arch/x86/kernel/apic/apic.c:1108
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:check_region_inline mm/kasan/generic.c:-1 [inline]
RIP: 0010:kasan_check_range+0xb/0x290 mm/kasan/generic.c:189
Code: 31 c0 c3 0f 0b b8 ea ff ff ff c3 0f 0b b8 ea ff ff ff c3 00 00 cc cc 00 00 cc cc 00 00 cc cc b0 01 48 85 f6 0f 84 ac 01 00 00 <55> 41 57 41 56 41 54 53 49 89 f8 49 01 f0 0f 82 0e 02 00 00 49 89
RSP: 0018:ffffc90000007188 EFLAGS: 00000202
RAX: 0000000000000001 RBX: 0000000000000010 RCX: ffffffff81352823
RDX: 0000000000000001 RSI: 0000000000000010 RDI: ffffc90000007298
RBP: 0000000000000000 R08: 0000000000000001 R09: 000000000000000e
R10: dffffc0000000000 R11: fffff52000000e55 R12: 1ffffffff1c0b472
R13: 1ffffffff1c0b472 R14: ffffc90000007298 R15: ffffffff8e05a394
 memset+0x1e/0x40 mm/kasan/shadow.c:44
 unwind_next_frame+0x9e3/0x1cf0 arch/x86/kernel/unwind_orc.c:547
 arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track mm/kasan/common.c:46 [inline]
 set_alloc_info mm/kasan/common.c:434 [inline]
 __kasan_slab_alloc+0x92/0xc0 mm/kasan/common.c:467
 kasan_slab_alloc include/linux/kasan.h:254 [inline]
 slab_post_alloc_hook+0x4c/0x380 mm/slab.h:519
 slab_alloc_node mm/slub.c:3225 [inline]
 slab_alloc mm/slub.c:3233 [inline]
 kmem_cache_alloc+0x15d/0x280 mm/slub.c:3238
 skb_clone+0x1bd/0x350 net/core/skbuff.c:1527
 dev_queue_xmit_nit+0x2db/0xae0 net/core/dev.c:2354
 xmit_one net/core/dev.c:3657 [inline]
 dev_hard_start_xmit+0x140/0x7d0 net/core/dev.c:3678
 sch_direct_xmit+0x24d/0x4a0 net/sched/sch_generic.c:345
 __dev_xmit_skb net/core/dev.c:3897 [inline]
 __dev_queue_xmit+0x1694/0x2e50 net/core/dev.c:4266
 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+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x56c/0x810 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:finish_lock_switch+0x12f/0x290 kernel/sched/core.c:4804
Code: 83 c7 18 be ff ff ff ff e8 8e da 6c 08 85 c0 74 46 4d 85 ff 75 62 0f 1f 44 00 00 48 89 df e8 78 4a 76 08 e8 93 e3 2a 00 fb 5b <41> 5c 41 5d 41 5e 41 5f 5d c3 48 89 df e8 2f 0e fe ff 43 80 3c 2c
RSP: 0018:ffffc9000347f618 EFLAGS: 00000282
RAX: 3894a668f2fd9b00 RBX: ffff888018fbd940 RCX: 3894a668f2fd9b00
RDX: dffffc0000000000 RSI: ffffffff8a2b2be0 RDI: ffffffff8a7a48c0
RBP: 1ffff11017207613 R08: ffff8880b903b30b R09: 1ffff11017207661
R10: dffffc0000000000 R11: ffffed1017207662 R12: 1ffff110172075c1
R13: dffffc0000000000 R14: ffff8880b903ae08 R15: 0000000000000000
 finish_task_switch+0x12f/0x650 kernel/sched/core.c:4921
 context_switch kernel/sched/core.c:5052 [inline]
 __schedule+0x11cb/0x4350 kernel/sched/core.c:6395
 preempt_schedule_irq+0xbb/0x160 kernel/sched/core.c:6799
 irqentry_exit+0x63/0x70 kernel/entry/common.c:435
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:arch_stack_walk+0x100/0x140 arch/x86/kernel/stacktrace.c:27
Code: d6 6a 08 00 83 bd 78 ff ff ff 00 74 32 4c 8d bd 78 ff ff ff 4c 89 ff e8 8e 4b 08 00 48 85 c0 74 1e 48 89 df 48 89 c6 41 ff d6 <84> c0 74 11 4c 89 ff e8 94 4c 08 00 83 bd 78 ff ff ff 00 75 d5 65
RSP: 0018:ffffc9000347f9e8 EFLAGS: 00000292
RAX: 0000000000000001 RBX: ffffc9000347faa0 RCX: 0000000080000001
RDX: dffffc0000000000 RSI: ffffffff89c0fd9c RDI: ffffc9000347faa0
RBP: ffffc9000347fa70 R08: ffffc9000347fab0 R09: 0000000000000007
R10: dffffc0000000000 R11: fffff5200068ff49 R12: ffff88802c5c1dc0
R13: dffffc0000000000 R14: ffffffff816782a0 R15: ffffc9000347f9e8
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 kasan_save_stack+0x35/0x60 mm/kasan/common.c:38
 kasan_record_aux_stack+0xb8/0x100 mm/kasan/generic.c:348
 task_work_add+0x2f/0x1d0 kernel/task_work.c:38
 fput_many+0xde/0x1a0 fs/file_table.c:367
 filp_close+0x10e/0x150 fs/open.c:1371
 __range_close fs/file.c:692 [inline]
 __close_range+0x24f/0x510 fs/file.c:747
 __do_sys_close_range fs/open.c:1410 [inline]
 __se_sys_close_range fs/open.c:1407 [inline]
 __x64_sys_close_range+0x76/0x80 fs/open.c:1407
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f7d62673159
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:00007ffc05e96a98 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: ffffffffffffffda RBX: 00007ffc05e96b80 RCX: 00007f7d62673159
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 0000000000016bfc R08: 0000000000000001 R09: 0000000000000000
R10: 0000001b31520000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f7d628fafac R14: 00007f7d628fafa8 R15: 00007f7d628fafa0
 </TASK>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/09/17 06:27 linux-5.15.y 0248c33e835e 95928915 .config console log report syz / log C [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in lapb_t1timer_expiry
2026/06/29 08:21 linux-5.15.y eceeec79dbc6 fb92f11c .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan-perf INFO: rcu detected stall in lapb_t1timer_expiry
* Struck through repros no longer work on HEAD.