------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28, CPU#3: swapper/3/0
Modules linked in:
CPU: 3 UID: 0 PID: 0 Comm: swapper/3 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:refcount_warn_saturate+0xf4/0x130 lib/refcount.c:28
Code: 06 e8 10 a5 ec fc 48 8d 3d 09 01 10 0c 67 48 0f b9 3a e8 ff a4 ec fc 5b 5d c3 cc cc cc cc e8 f3 a4 ec fc 48 8d 3d fc 00 10 0c <67> 48 0f b9 3a e8 e2 a4 ec fc 5b 5d e9 9b 39 9f 06 e8 d6 a4 ec fc
RSP: 0018:ffffc900006f8d98 EFLAGS: 00010046
RAX: 0000000000010002 RBX: ffff88801463c998 RCX: ffffffff851d371b
RDX: ffff88801eeea540 RSI: ffffffff851d37ad RDI: ffffffff912d38b0
RBP: 0000000000000003 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: 0000000000000000 R12: ffff88801463c998
R13: ffff888051a41c00 R14: 000000000000000b R15: 1ffff11005c1280c
FS:  0000000000000000(0000) GS:ffff8880d60ea000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fe9986e1ff8 CR3: 000000002cff8000 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:281
 req_done+0x1dc/0x2e0 net/9p/trans_virtio.c:147
 vring_interrupt+0x2ef/0x660 drivers/virtio/virtio_ring.c:3297
 __handle_irq_event_percpu+0x232/0x880 kernel/irq/handle.c:209
 handle_irq_event_percpu kernel/irq/handle.c:246 [inline]
 handle_irq_event+0xab/0x1e0 kernel/irq/handle.c:263
 handle_edge_irq+0x34c/0x950 kernel/irq/chip.c:859
 generic_handle_irq_desc include/linux/irqdesc.h:188 [inline]
 handle_irq arch/x86/kernel/irq.c:209 [inline]
 call_irq_handler arch/x86/kernel/irq.c:265 [inline]
 __common_interrupt+0xd8/0x2f0 arch/x86/kernel/irq.c:280
 common_interrupt+0xb9/0xe0 arch/x86/kernel/irq.c:273
 </IRQ>
 <TASK>
 asm_common_interrupt+0x26/0x40 arch/x86/include/asm/idtentry.h:665
RIP: 0010:pv_native_safe_halt+0xf/0x20 arch/x86/kernel/paravirt.c:64
Code: 96 8d 02 c3 cc cc cc cc 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 c3 59 12 00 fb f4 <e9> bc 48 03 00 66 2e 0f 1f 84 00 00 00 00 00 66 90 90 90 90 90 90
RSP: 0018:ffffc90000197e00 EFLAGS: 00000206
RAX: 00000000008beeeb RBX: ffff88801eeea540 RCX: ffffffff8bb942d5
RDX: 0000000000000000 RSI: ffffffff8e1a3656 RDI: ffffffff8c400f80
RBP: ffffed1003ddd4a8 R08: 0000000000000001 R09: ffffed100d4e678d
R10: ffff88806a733c6b R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: 1ffff92000032fc4 R15: dffffc0000000000
 arch_safe_halt arch/x86/include/asm/paravirt.h:62 [inline]
 default_idle+0x9/0x10 arch/x86/kernel/process.c:768
 default_idle_call+0x6c/0xb0 kernel/sched/idle.c:122
 cpuidle_idle_call kernel/sched/idle.c:199 [inline]
 do_idle+0x3a7/0x5b0 kernel/sched/idle.c:355
 cpu_startup_entry+0x4f/0x60 kernel/sched/idle.c:454
 start_secondary+0x21d/0x2d0 arch/x86/kernel/smpboot.c:312
 common_startup_64+0x13e/0x158
 </TASK>
----------------
Code disassembly (best guess), 1 bytes skipped:
   0:	e8 10 a5 ec fc       	call   0xfceca515
   5:	48 8d 3d 09 01 10 0c 	lea    0xc100109(%rip),%rdi        # 0xc100115
   c:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  11:	e8 ff a4 ec fc       	call   0xfceca515
  16:	5b                   	pop    %rbx
  17:	5d                   	pop    %rbp
  18:	c3                   	ret
  19:	cc                   	int3
  1a:	cc                   	int3
  1b:	cc                   	int3
  1c:	cc                   	int3
  1d:	e8 f3 a4 ec fc       	call   0xfceca515
  22:	48 8d 3d fc 00 10 0c 	lea    0xc1000fc(%rip),%rdi        # 0xc100125
* 29:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2e:	e8 e2 a4 ec fc       	call   0xfceca515
  33:	5b                   	pop    %rbx
  34:	5d                   	pop    %rbp
  35:	e9 9b 39 9f 06       	jmp    0x69f39d5
  3a:	e8 d6 a4 ec fc       	call   0xfceca515