8<--- cut here ---
Unable to handle kernel NULL pointer dereference at virtual address 00000004
pgd = 80003000
[00000004] *pgd=80000080004003, *pmd=00000000
Internal error: Oops: 207 [#1] PREEMPT SMP ARM
Dumping ftrace buffer:
   (ftrace buffer empty)
Modules linked in:
CPU: 1 PID: 222 Comm: kworker/u4:5 Not tainted 5.12.0-rc2-syzkaller #0
Hardware name: ARM-Versatile Express
Workqueue: usbip_event event_handler
PC is at atomic_fetch_add_relaxed arch/arm/include/asm/atomic.h:223 [inline]
PC is at __refcount_add include/linux/refcount.h:193 [inline]
PC is at __refcount_inc include/linux/refcount.h:250 [inline]
PC is at refcount_inc include/linux/refcount.h:267 [inline]
PC is at get_task_struct include/linux/sched/task.h:104 [inline]
PC is at kthread_stop+0x60/0x4e4 kernel/kthread.c:616
LR is at __this_cpu_preempt_check+0x1c/0x20 lib/smp_processor_id.c:70
pc : [<8027397c>]    lr : [<82133164>]    psr: 60000113
sp : 846b1e48  ip : 846b1df8  fp : 846b1e64
r10: 847c6368  r9 : 82a9ab98  r8 : 00000100
r7 : 839e8768  r6 : 83822c98  r5 : 00000004  r4 : fffffffc
r3 : 00000000  r2 : 00000000  r1 : 5a91b000  r0 : 00000001
Flags: nZCv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 30c5387d  Table: 8906aa80  DAC: 00000000
Process kworker/u4:5 (pid: 222, stack limit = 0x846b0210)
Stack: (0x846b1e48 to 0x846b2000)
1e40:                   847c6360 839e8744 842cd4bc 839e8768 846b1eac 846b1e68
1e60: 81200fc8 80273928 846b1e94 811fcfd8 890f4840 00000000 890f4840 e6e5e17a
1e80: 842cd4bc 847c6360 839e8744 842cd4bc 839e8768 00000100 82a9ab98 847c6368
1ea0: 846b1edc 846b1eb0 811fd00c 81200f4c 811fcf3c 839e8770 845b8800 84420000
1ec0: 84f67400 83ac7572 83822c98 00000088 846b1f3c 846b1ee0 802696a4 811fcf48
1ee0: 00000001 00000000 802695e4 84420000 00000000 00000000 839e8770 83fed638
1f00: 00000000 82a9abf0 00000000 e6e5e17a 8213beb4 845b8800 84420000 845b8814
1f20: 84420038 83806d00 846b0000 00000088 846b1f74 846b1f40 80269dcc 802693dc
1f40: 846b1f74 83806d00 80271b6c 845b8b80 845bfc00 846b0000 00000000 80269d68
1f60: 845b8800 846c1e64 846b1fac 846b1f78 80271f40 80269d74 80258640 845b8bc4
1f80: 00000000 845bfc00 80271dbc 00000000 00000000 00000000 00000000 00000000
1fa0: 00000000 846b1fb0 80200114 80271dc8 00000000 00000000 00000000 00000000
1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
1fe0: 00000000 00000000 00000000 00000000 00000013 00000000 00000000 00000000
Backtrace: 
[<8027391c>] (kthread_stop) from [<81200fc8>] (vhci_shutdown_connection+0x88/0x3a0 drivers/usb/usbip/vhci_hcd.c:1023)
 r7:839e8768 r6:842cd4bc r5:839e8744 r4:847c6360
[<81200f40>] (vhci_shutdown_connection) from [<811fd00c>] (event_handler+0xd0/0x1c0 drivers/usb/usbip/usbip_event.c:78)
 r10:847c6368 r9:82a9ab98 r8:00000100 r7:839e8768 r6:842cd4bc r5:839e8744
 r4:847c6360
[<811fcf3c>] (event_handler) from [<802696a4>] (process_one_work+0x2d4/0x998 kernel/workqueue.c:2275)
 r10:00000088 r9:83822c98 r8:83ac7572 r7:84f67400 r6:84420000 r5:845b8800
 r4:839e8770 r3:811fcf3c
[<802693d0>] (process_one_work) from [<80269dcc>] (worker_thread+0x64/0x54c kernel/workqueue.c:2421)
 r10:00000088 r9:846b0000 r8:83806d00 r7:84420038 r6:845b8814 r5:84420000
 r4:845b8800
[<80269d68>] (worker_thread) from [<80271f40>] (kthread+0x184/0x1a4 kernel/kthread.c:292)
 r10:846c1e64 r9:845b8800 r8:80269d68 r7:00000000 r6:846b0000 r5:845bfc00
 r4:845b8b80
[<80271dbc>] (kthread) from [<80200114>] (ret_from_fork+0x14/0x20 arch/arm/kernel/entry-common.S:158)
Exception stack(0x846b1fb0 to 0x846b1ff8)
1fa0:                                     00000000 00000000 00000000 00000000
1fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
1fe0: 00000000 00000000 00000000 00000000 00000013 00000000
 r10:00000000 r9:00000000 r8:00000000 r7:00000000 r6:00000000 r5:80271dbc
 r4:845bfc00
Code: e3130001 1a000079 e2845008 f595f000 (e1953f9f) 
---[ end trace 9dad1eb9c36f8be4 ]---