------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: lib/refcount.c:28 at 0x0, CPU#2: kbnepd bnep0/12322
Modules linked in:
CPU: 2 UID: 0 PID: 12322 Comm: kbnepd bnep0 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~bpo12+1 04/01/2014
RIP: 0010:refcount_warn_saturate+0xc9/0x120 lib/refcount.c:28
Code: 5d e9 8b 0c 13 fd e8 86 0c 13 fd 48 8d 3d 9f 91 e5 0b 67 48 0f b9 3a 5b 5d e9 73 0c 13 fd e8 6e 0c 13 fd 48 8d 3d 97 91 e5 0b <67> 48 0f b9 3a 5b 5d e9 5b 0c 13 fd e8 56 0c 13 fd 48 8d 3d 8f 91
RSP: 0018:ffffc9000ccef918 EFLAGS: 00010293
RAX: 0000000000000000 RBX: 0000000000000003 RCX: ffffffff84abd79c
RDX: ffff88803f6ec980 RSI: ffffffff84abd802 RDI: ffffffff909169a0
RBP: ffff8880550e8c78 R08: 0000000000000005 R09: 0000000000000004
R10: 0000000000000003 R11: ffff88803f6ed4b0 R12: ffff888033e67800
R13: ffff8880550e8c78 R14: ffffffff85e596c0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8880d6b09000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f317c573460 CR3: 000000002a70c000 CR4: 0000000000352ef0
Call Trace:
 <TASK>
 __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]
 kref_put include/linux/kref.h:64 [inline]
 klist_dec_and_del lib/klist.c:206 [inline]
 klist_put+0x11b/0x1b0 lib/klist.c:217
 device_del+0x1d8/0x9f0 drivers/base/core.c:3855
 unregister_netdevice_many_notify+0x151e/0x2590 net/core/dev.c:12416
 unregister_netdevice_many net/core/dev.c:12444 [inline]
 unregister_netdevice_queue net/core/dev.c:12258 [inline]
 unregister_netdevice_queue+0x305/0x3c0 net/core/dev.c:12248
 unregister_netdevice include/linux/netdevice.h:3405 [inline]
 unregister_netdev+0x1f/0x60 net/core/dev.c:12462
 bnep_session+0x22db/0x2e10 net/bluetooth/bnep/core.c:525
 kthread+0x3c5/0x780 kernel/kthread.c:463
 ret_from_fork+0x983/0xb10 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
 </TASK>
----------------
Code disassembly (best guess):
   0:	5d                   	pop    %rbp
   1:	e9 8b 0c 13 fd       	jmp    0xfd130c91
   6:	e8 86 0c 13 fd       	call   0xfd130c91
   b:	48 8d 3d 9f 91 e5 0b 	lea    0xbe5919f(%rip),%rdi        # 0xbe591b1
  12:	67 48 0f b9 3a       	ud1    (%edx),%rdi
  17:	5b                   	pop    %rbx
  18:	5d                   	pop    %rbp
  19:	e9 73 0c 13 fd       	jmp    0xfd130c91
  1e:	e8 6e 0c 13 fd       	call   0xfd130c91
  23:	48 8d 3d 97 91 e5 0b 	lea    0xbe59197(%rip),%rdi        # 0xbe591c1
* 2a:	67 48 0f b9 3a       	ud1    (%edx),%rdi <-- trapping instruction
  2f:	5b                   	pop    %rbx
  30:	5d                   	pop    %rbp
  31:	e9 5b 0c 13 fd       	jmp    0xfd130c91
  36:	e8 56 0c 13 fd       	call   0xfd130c91
  3b:	48                   	rex.W
  3c:	8d                   	.byte 0x8d
  3d:	3d                   	.byte 0x3d
  3e:	8f                   	(bad)
  3f:	91                   	xchg   %eax,%ecx