------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 46 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 0 UID: 0 PID: 46 Comm: kworker/u32:2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: netns cleanup_net
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 b8 c9 13 fd 84 db 0f 85 66 ff ff ff e8 cb ce 13 fd c6 05 c9 de c3 0b 01 90 48 c7 c7 e0 22 f1 8b e8 87 57 d2 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 a8 ce 13 fd 0f b6 1d a4 de c3 0b 31
RSP: 0018:ffffc90000007bd8 EFLAGS: 00010086
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff817a5ed8
RDX: ffff88801ff74900 RSI: ffffffff817a5ee5 RDI: 0000000000000001
RBP: ffff88804d898778 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88804d898778
R13: ffff88805f468000 R14: 0000000000000015 R15: 1ffff110083fc00c
FS:  0000000000000000(0000) GS:ffff8880977e7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000008001b000 CR3: 000000005959e000 CR4: 0000000000352ef0
DR0: 000000000000007f DR1: 000000000000f971 DR2: 0000000000000d6d
DR3: 0000000080000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 __refcount_sub_and_test include/linux/refcount.h:400 [inline]
 __refcount_dec_and_test include/linux/refcount.h:432 [inline]
 refcount_dec_and_test include/linux/refcount.h:450 [inline]
 p9_req_put+0x1ec/0x250 net/9p/client.c:404
 req_done+0x1dc/0x2e0 net/9p/trans_virtio.c:147
 vring_interrupt drivers/virtio/virtio_ring.c:2718 [inline]
 vring_interrupt+0x31e/0x400 drivers/virtio/virtio_ring.c:2693
 __handle_irq_event_percpu+0x236/0x920 kernel/irq/handle.c:203
 handle_irq_event_percpu kernel/irq/handle.c:240 [inline]
 handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:257
 handle_edge_irq+0x3ca/0x9e0 kernel/irq/chip.c:855
 generic_handle_irq_desc include/linux/irqdesc.h:173 [inline]
 handle_irq arch/x86/kernel/irq.c:254 [inline]
 call_irq_handler arch/x86/kernel/irq.c:310 [inline]
 __common_interrupt+0xcd/0x2f0 arch/x86/kernel/irq.c:325
 common_interrupt+0x61/0xe0 arch/x86/kernel/irq.c:318
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:693
RIP: 0010:handle_softirqs+0x1dd/0x8e0 kernel/softirq.c:608
Code: 88 6c 24 26 4c 89 7c 24 18 48 c7 c7 20 be 8b 8b e8 78 90 e5 09 65 66 c7 05 26 35 27 12 00 00 e8 19 69 47 00 fb bb ff ff ff ff <49> c7 c7 c0 c0 00 8e 41 0f bc dc 83 c3 01 0f 85 a4 00 00 00 e9 b1
RSP: 0018:ffffc90000007f28 EFLAGS: 00000212
RAX: 0000000000aabe80 RBX: 00000000ffffffff RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffffffff8daff475 RDI: ffffffff8bf1d540
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: ffffffff908358d7 R11: 0000000000000000 R12: 0000000000000382
R13: 000000000000000a R14: 1ffff92000000fed R15: ffffed1003fee920
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0x109/0x170 kernel/softirq.c:723
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1052 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1052
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:lockdep_unregister_key+0xe9/0x140 kernel/locking/lockdep.c:6616
Code: 48 89 ef e8 b9 e5 ff ff 48 83 2d 09 ec 2b 14 01 89 c3 e8 da ee ff ff 9c 58 f6 c4 02 75 52 41 f7 c4 00 02 00 00 74 01 fb 84 db <75> 1b 5b 5d 41 5c e9 4c 77 0a 00 8b 05 6a 1b ec 0e 31 db 85 c0 74
RSP: 0018:ffffc900006df7a8 EFLAGS: 00000246
RAX: 0000000000000046 RBX: 0000000000000000 RCX: 0000000000000001
RDX: 0000000000000000 RSI: ffffffff8dbf1802 RDI: ffffffff8bf1d540
RBP: ffffffff972a5a88 R08: 00000000000379b9 R09: ffffffff95ca4d92
R10: 0000000000000004 R11: 0000000000000000 R12: 0000000000000246
R13: ffff88804c368000 R14: ffff88804c3684c0 R15: 0000000000000008
 __qdisc_destroy+0x11a/0x4d0 net/sched/sch_generic.c:1083
 qdisc_put+0xab/0xe0 net/sched/sch_generic.c:1109
 shutdown_scheduler_queue+0xa5/0x160 net/sched/sch_generic.c:1162
 netdev_for_each_tx_queue include/linux/netdevice.h:2664 [inline]
 dev_shutdown+0xb8/0x430 net/sched/sch_generic.c:1494
 unregister_netdevice_many_notify+0xb2c/0x24c0 net/core/dev.c:12242
 unregister_netdevice_many net/core/dev.c:12317 [inline]
 default_device_exit_batch+0x853/0xaf0 net/core/dev.c:12821
 ops_exit_list net/core/net_namespace.c:205 [inline]
 ops_undo_list+0x363/0xab0 net/core/net_namespace.c:252
 cleanup_net+0x41b/0x8b0 net/core/net_namespace.c:695
 process_one_work+0x9cf/0x1b70 kernel/workqueue.c:3263
 process_scheduled_works kernel/workqueue.c:3346 [inline]
 worker_thread+0x6c8/0xf10 kernel/workqueue.c:3427
 kthread+0x3c2/0x780 kernel/kthread.c:463
 ret_from_fork+0x675/0x7d0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
----------------
Code disassembly (best guess):
   0:	88 6c 24 26          	mov    %ch,0x26(%rsp)
   4:	4c 89 7c 24 18       	mov    %r15,0x18(%rsp)
   9:	48 c7 c7 20 be 8b 8b 	mov    $0xffffffff8b8bbe20,%rdi
  10:	e8 78 90 e5 09       	call   0x9e5908d
  15:	65 66 c7 05 26 35 27 	movw   $0x0,%gs:0x12273526(%rip)        # 0x12273545
  1c:	12 00 00
  1f:	e8 19 69 47 00       	call   0x47693d
  24:	fb                   	sti
  25:	bb ff ff ff ff       	mov    $0xffffffff,%ebx
* 2a:	49 c7 c7 c0 c0 00 8e 	mov    $0xffffffff8e00c0c0,%r15 <-- trapping instruction
  31:	41 0f bc dc          	bsf    %r12d,%ebx
  35:	83 c3 01             	add    $0x1,%ebx
  38:	0f 85 a4 00 00 00    	jne    0xe2
  3e:	e9                   	.byte 0xe9
  3f:	b1                   	.byte 0xb1