------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 3 PID: 19431 at lib/refcount.c:28 refcount_warn_saturate+0x14a/0x210 lib/refcount.c:28
Modules linked in:
CPU: 3 UID: 0 PID: 19431 Comm: kbnepd ÿÿÿÿ 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 f8 92 13 fd 84 db 0f 85 66 ff ff ff e8 0b 98 13 fd c6 05 9b de c2 0b 01 90 48 c7 c7 a0 35 f1 8b e8 57 1c d2 fc 90 <0f> 0b 90 90 e9 43 ff ff ff e8 e8 97 13 fd 0f b6 1d 76 de c2 0b 31
RSP: 0018:ffffc90002ebf988 EFLAGS: 00010286
RAX: 0000000000000000 RBX: 0000000000000000 RCX: ffffffff817b2e58
RDX: ffff88805ca0a480 RSI: ffffffff817b2e65 RDI: 0000000000000001
RBP: ffff88806062c878 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: ffff888020d0c800
R13: ffff88806062c878 R14: ffffffff85df0030 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff888097ae1000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000000c90611d CR3: 0000000061b69000 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+0x14f0/0x24c0 net/core/dev.c:12289
 unregister_netdevice_many net/core/dev.c:12317 [inline]
 unregister_netdevice_queue+0x305/0x3f0 net/core/dev.c:12161
 unregister_netdevice include/linux/netdevice.h:3389 [inline]
 unregister_netdev+0x1f/0x60 net/core/dev.c:12335
 bnep_session+0x224e/0x2d80 net/bluetooth/bnep/core.c:525
 kthread+0x3c5/0x780 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>