------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 0 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 0 UID: 0 PID: 0 Comm: swapper/0 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
RIP: 0010:refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Code: ff 89 de e8 18 e5 d9 fc 84 db 0f 85 66 ff ff ff e8 2b ea d9 fc c6 05 fe e8 b2 0b 01 90 48 c7 c7 40 a6 15 8c e8 57 e1 98 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 08 ea d9 fc 0f b6 1d d9 e8 b2 0b 31
RSP: 0018:ffffc90000007be0 EFLAGS: 00010082
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff817a02f8
RDX: ffffffff8e2977c0 RSI: ffffffff817a0305 RDI: 0000000000000001
RBP: ffff888050c1b988 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888050c1b988
R13: ffff88804bb13800 R14: 0000000000000015 R15: 1ffff1100889680c
FS:  0000000000000000(0000) GS:ffff8880974ba000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3aec8d8e9c CR3: 000000005b537000 CR4: 0000000000352ef0
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:2719 [inline]
 vring_interrupt+0x31b/0x400 drivers/virtio/virtio_ring.c:2694
 __handle_irq_event_percpu+0x22c/0x7d0 kernel/irq/handle.c:158
 handle_irq_event_percpu kernel/irq/handle.c:193 [inline]
 handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:210
 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+0xd0/0x2f0 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:565
Code: 88 6c 24 26 4c 89 7c 24 18 48 c7 c7 e0 a8 ab 8b e8 68 b6 15 0a 65 66 c7 05 c6 62 5a 12 00 00 e8 69 f2 46 00 fb bb ff ff ff ff <49> c7 c7 c0 c0 20 8e 41 0f bc dc 83 c3 01 0f 85 a4 00 00 00 e9 b1
RSP: 0018:ffffc90000007f28 EFLAGS: 00000206
RAX: 0000000001bf8f96 RBX: 00000000ffffffff RCX: ffffffff81c2eedf
RDX: 0000000000000000 RSI: ffffffff8de4f55a RDI: ffffffff8c163780
RBP: 0000000000000000 R08: 0000000000000001 R09: 0000000000000001
R10: ffffffff90abab97 R11: 0000000000000000 R12: 0000000000000282
R13: 000000000000000a R14: 1ffff92000000fed R15: fffffbfff1c52ef8
 __do_softirq kernel/softirq.c:613 [inline]
 invoke_softirq kernel/softirq.c:453 [inline]
 __irq_exit_rcu+0x109/0x170 kernel/softirq.c:680
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:696
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1050 [inline]
 sysvec_apic_timer_interrupt+0xa4/0xc0 arch/x86/kernel/apic/apic.c:1050
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:702
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:82
Code: 2d 64 02 e9 13 0a 03 00 0f 1f 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 f3 0f 1e fa eb 07 0f 00 2d 53 65 18 00 fb f4 <c3> cc cc cc cc 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffffff8e207e08 EFLAGS: 00000286
RAX: 0000000001bf8f91 RBX: 0000000000000000 RCX: ffffffff8b91ab29
RDX: 0000000000000000 RSI: ffffffff8de4f55a RDI: ffffffff8c163780
RBP: fffffbfff1c52ef8 R08: 0000000000000001 R09: ffffed1005646655
R10: ffff88802b2332ab R11: 0000000000000000 R12: 0000000000000000
R13: ffffffff8e2977c0 R14: ffffffff90abab90 R15: 0000000000000000
 arch_safe_halt arch/x86/include/asm/paravirt.h:107 [inline]
 default_idle+0x13/0x20 arch/x86/kernel/process.c:757
 default_idle_call+0x6d/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:190 [inline]
 do_idle+0x391/0x510 kernel/sched/idle.c:330
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:428
 rest_init+0x16b/0x2b0 init/main.c:744
 start_kernel+0x3ee/0x4d0 init/main.c:1097
 x86_64_start_reservations+0x18/0x30 arch/x86/kernel/head64.c:307
 x86_64_start_kernel+0x130/0x190 arch/x86/kernel/head64.c:288
 common_startup_64+0x13e/0x148
 </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 e0 a8 ab 8b 	mov    $0xffffffff8baba8e0,%rdi
  10:	e8 68 b6 15 0a       	call   0xa15b67d
  15:	65 66 c7 05 c6 62 5a 	movw   $0x0,%gs:0x125a62c6(%rip)        # 0x125a62e5
  1c:	12 00 00
  1f:	e8 69 f2 46 00       	call   0x46f28d
  24:	fb                   	sti
  25:	bb ff ff ff ff       	mov    $0xffffffff,%ebx
* 2a:	49 c7 c7 c0 c0 20 8e 	mov    $0xffffffff8e20c0c0,%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