[v5.15] INFO: rcu detected stall in lapb_t1timer_expiry

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc5ec8769306 Linux 5.15.196
git tree: linux-5.15.y
console output: https://syzkaller.appspot.com/x/log.txt?x=160d7212580000
kernel config: https://syzkaller.appspot.com/x/.config?x=e1bb6d24ef2164eb
dashboard link: https://syzkaller.appspot.com/bug?extid=72e9568c3431cf1fb5e6
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/ed7568bc5bb4/disk-cc5ec876.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e343e0aaac77/vmlinux-cc5ec876.xz
kernel image: https://storage.googleapis.com/syzbot-assets/089870f2a980/bzImage-cc5ec876.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+72e956...@syzkaller.appspotmail.com

rcu: INFO: rcu_preempt self-detected stall on CPU
rcu: 0-....: (10501 ticks this GP) idle=395/1/0x4000000000000000 softirq=10876/10876 fqs=5205
(t=10502 jiffies g=13973 q=1094)
NMI backtrace for cpu 0
CPU: 0 PID: 5696 Comm: syz.3.382 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/02/2025
Call Trace:
<IRQ>
dump_stack_lvl+0x168/0x230 lib/dump_stack.c:106
nmi_cpu_backtrace+0x397/0x3d0 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+0x22f/0x380 kernel/rcu/tree_stall.h:349
print_cpu_stall+0x31d/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+0x6d8/0x1110 kernel/rcu/tree.c:2619
update_process_times+0x193/0x200 kernel/time/timer.c:1818
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+0x4fe/0xc40 kernel/time/hrtimer.c:1749
hrtimer_interrupt+0x3bb/0x8d0 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:dev_queue_xmit_nit+0x621/0xb00 net/core/dev.c:2324
Code: c8 04 66 41 89 06 4c 8b 74 24 28 48 8b 5c 24 10 4c 89 e8 48 c1 e8 03 42 80 3c 38 00 74 08 4c 89 ef e8 93 99 e6 f9 4d 8b 6d 00 <49> 39 dd 0f 84 43 02 00 00 e8 61 31 a2 f9 e9 d9 fa ff ff e8 57 31
RSP: 0000:ffffc900000076a8 EFLAGS: 00000246
RAX: 1ffff1100fce712f RBX: ffff8880221c4080 RCX: ffff88807c2a0000
RDX: 0000000000000100 RSI: 0000000000000002 RDI: 0000000000000001
RBP: ffff888029db83d8 R08: dffffc0000000000 R09: ffffed10053b70bc
R10: ffffed10053b70bc R11: 1ffff110053b70bb R12: ffff888029db8500
R13: ffff8880221c4080 R14: ffff88807e738940 R15: dffffc0000000000
xmit_one net/core/dev.c:3644 [inline]
dev_hard_start_xmit+0x13e/0x7e0 net/core/dev.c:3665
sch_direct_xmit+0x24e/0x4a0 net/sched/sch_generic.c:342
__dev_xmit_skb net/core/dev.c:3884 [inline]
__dev_queue_xmit+0x170e/0x2ed0 net/core/dev.c:4253
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+0x652/0xa70 net/lapb/lapb_timer.c:-1
call_timer_fn+0x16c/0x530 kernel/time/timer.c:1451
expire_timers kernel/time/timer.c:1496 [inline]
__run_timers+0x525/0x7c0 kernel/time/timer.c:1767
run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1780
handle_softirqs+0x328/0x820 kernel/softirq.c:576
__do_softirq kernel/softirq.c:610 [inline]
invoke_softirq kernel/softirq.c:450 [inline]
__irq_exit_rcu+0x12f/0x220 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:schedule_debug kernel/sched/core.c:5601 [inline]
RIP: 0010:__schedule+0x138/0x4390 kernel/sched/core.c:6286
Code: 74 08 48 89 df e8 48 c4 0a f8 48 8b 1b 48 89 d8 48 c1 e8 03 42 80 3c 28 00 74 08 48 89 df e8 2f c4 0a f8 48 81 3b 9d 6e ac 57 <0f> 85 53 13 00 00 83 7c 24 50 00 75 42 49 8d 5f 18 48 89 d8 48 c1
RSP: 0000:ffffc900033dfd00 EFLAGS: 00000246
RAX: 1ffff9200067b000 RBX: ffffc900033d8000 RCX: 0000000000000000
RDX: 0000000000000010 RSI: 0000000000000000 RDI: ffffc900033dfe70
RBP: ffffc900033dfed0 R08: dffffc0000000000 R09: ffffc900033dfe60
R10: fffff5200067bfce R11: 1ffff9200067bfcc R12: ffffc900033dfe60
R13: dffffc0000000000 R14: ffff8880b9000000 R15: ffff88807c2a0000
schedule+0x11b/0x1e0 kernel/sched/core.c:6478
exit_to_user_mode_loop+0x47/0x130 kernel/entry/common.c:169
exit_to_user_mode_prepare+0xee/0x180 kernel/entry/common.c:214
irqentry_exit_to_user_mode+0x5/0x30 kernel/entry/common.c:320
asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0033:0x7fa5877e2190
Code: f6 48 8b 0f 31 c0 56 48 8d 35 14 9a 19 00 ff 77 18 4c 8b 4f 10 4c 8b 47 08 48 8d 3d ec e7 1b 00 e8 45 ac ff ff 0f 1f 44 00 00 <48> 89 f0 48 83 ec 08 4c 8b 4a 28 4c 8b 42 20 48 8b 4a 18 4c 8b 5a
RSP: 002b:00007fa585b84058 EFLAGS: 00000246
RAX: 00007fa587b076e8 RBX: 00007fa587b73fa0 RCX: 00007fa5879b646e
RDX: 00007fa587b73fd0 RSI: 0000000000000000 RDI: 000000000000002e
RBP: 00007fa58799ff91 R08: 0000000000000077 R09: 002bdc193e2b0674
R10: 0000003f53c38af3 R11: 00000000000056f4 R12: 0000000000000000
R13: 00007fa587b74038 R14: 00007fa587b73fa0 R15: 00007ffeca242108
</TASK>


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