refcount_t: increment on 0; use-after-free.
WARNING: CPU: 0 PID: 3785 at lib/refcount.c:153 refcount_inc_checked lib/refcount.c:153 [inline]
WARNING: CPU: 0 PID: 3785 at lib/refcount.c:153 refcount_inc_checked+0x61/0x70 lib/refcount.c:151
Kernel panic - not syncing: panic_on_warn set ...

CPU: 0 PID: 3785 Comm: syz-executor.1 Not tainted 4.19.55 #27
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x172/0x1f0 lib/dump_stack.c:113
 panic+0x263/0x507 kernel/panic.c:185
 __warn.cold+0x20/0x4a kernel/panic.c:540
 report_bug+0x263/0x2b0 lib/bug.c:186
 fixup_bug arch/x86/kernel/traps.c:178 [inline]
 fixup_bug arch/x86/kernel/traps.c:173 [inline]
 do_error_trap+0x204/0x360 arch/x86/kernel/traps.c:296
 do_invalid_op+0x1b/0x20 arch/x86/kernel/traps.c:316
 invalid_op+0x14/0x20 arch/x86/entry/entry_64.S:1013
RIP: 0010:refcount_inc_checked lib/refcount.c:153 [inline]
RIP: 0010:refcount_inc_checked+0x61/0x70 lib/refcount.c:151
Code: 1d 1d 80 12 06 31 ff 89 de e8 1b 6e 47 fe 84 db 75 dd e8 d2 6c 47 fe 48 c7 c7 c0 93 81 87 c6 05 fd 7f 12 06 01 e8 0d 46 1b fe <0f> 0b eb c1 90 66 2e 0f 1f 84 00 00 00 00 00 55 48 89 e5 41 57 41
RSP: 0018:ffff8880a5bb7888 EFLAGS: 00010282
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 0000000000000000
RDX: 0000000000012cf8 RSI: ffffffff8155b1c6 RDI: ffffed1014b76f03
RBP: ffff8880a5bb7898 R08: ffff88808eb52140 R09: ffffed1015d04fe9
R10: ffffed1015d04fe8 R11: ffff8880ae827f47 R12: ffff88821ade1978
R13: ffff8880a9747b20 R14: ffff8880a9747b18 R15: ffff88821ade18f8
 kref_get include/linux/kref.h:47 [inline]
 kobject_get+0x66/0xc0 lib/kobject.c:613
 kset_get include/linux/kobject.h:213 [inline]
 kobj_kset_join lib/kobject.c:186 [inline]
 kobject_add_internal lib/kobject.c:238 [inline]
 kobject_add_internal+0x14f/0x380 lib/kobject.c:217
 kobject_add_varg lib/kobject.c:382 [inline]
 kobject_add+0x150/0x1c0 lib/kobject.c:426
 class_dir_create_and_add drivers/base/core.c:1560 [inline]
 get_device_parent.isra.0+0x415/0x570 drivers/base/core.c:1615
 device_add+0x2f4/0x1760 drivers/base/core.c:1871
 hci_register_dev+0x304/0x880 net/bluetooth/hci_core.c:3198
 hci_uart_register_dev drivers/bluetooth/hci_ldisc.c:676 [inline]
 hci_uart_set_proto drivers/bluetooth/hci_ldisc.c:700 [inline]
 hci_uart_tty_ioctl+0x761/0xaf0 drivers/bluetooth/hci_ldisc.c:754
 tty_ioctl+0x8b5/0x1510 drivers/tty/tty_io.c:2678
 vfs_ioctl fs/ioctl.c:46 [inline]
 file_ioctl fs/ioctl.c:501 [inline]
 do_vfs_ioctl+0xd5f/0x1380 fs/ioctl.c:688
 ksys_ioctl+0xab/0xd0 fs/ioctl.c:705
 __do_sys_ioctl fs/ioctl.c:712 [inline]
 __se_sys_ioctl fs/ioctl.c:710 [inline]
 __x64_sys_ioctl+0x73/0xb0 fs/ioctl.c:710
 do_syscall_64+0xfd/0x620 arch/x86/entry/common.c:293
 entry_SYSCALL_64_after_hwframe+0x49/0xbe
RIP: 0033:0x4592c9
Code: fd b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00 00 66 90 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 0f 83 cb b7 fb ff c3 66 2e 0f 1f 84 00 00 00 00
RSP: 002b:00007f7b05056c78 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 0000000000000003 RCX: 00000000004592c9
RDX: 0000000000000000 RSI: 00000000400455c8 RDI: 0000000000000003
RBP: 000000000075bf20 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 00007f7b050576d4
R13: 00000000004c1f52 R14: 00000000004d4df0 R15: 00000000ffffffff
Kernel Offset: disabled
Rebooting in 86400 seconds..