WARNING: refcount bug in do_enable_set

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit:    8f3d9f35 Linux 5.7-rc1
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1182b24fe00000
kernel config:  https://syzkaller.appspot.com/x/.config?x=11f10cc27c63cade
dashboard link: https://syzkaller.appspot.com/bug?extid=2e9900a1e1b3c9c96a77
compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+2e9900a1e1b3c9c96a77@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ cut here ]------------
refcount_t: underflow; use-after-free.
WARNING: CPU: 0 PID: 10817 at lib/refcount.c:28 refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28
Kernel panic - not syncing: panic_on_warn set ...
CPU: 0 PID: 10817 Comm: kworker/0:7 Not tainted 5.7.0-rc1-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
Workqueue: events do_enable_set
Call Trace:
 __dump_stack lib/dump_stack.c:77 [inline]
 dump_stack+0x1e9/0x30e lib/dump_stack.c:118
 panic+0x264/0x7a0 kernel/panic.c:221
 __warn+0x209/0x210 kernel/panic.c:582
 report_bug+0x1ac/0x2d0 lib/bug.c:195
 fixup_bug arch/x86/kernel/traps.c:175 [inline]
 do_error_trap+0xca/0x1c0 arch/x86/kernel/traps.c:267
 do_invalid_op+0x32/0x40 arch/x86/kernel/traps.c:286
 invalid_op+0x23/0x30 arch/x86/entry/entry_64.S:1027
RIP: 0010:refcount_warn_saturate+0x15b/0x1a0 lib/refcount.c:28
Code: c7 9a a9 f2 88 31 c0 e8 a3 fb ac fd 0f 0b eb 85 e8 5a e7 da fd c6 05 10 48 cf 05 01 48 c7 c7 c6 a9 f2 88 31 c0 e8 85 fb ac fd <0f> 0b e9 64 ff ff ff e8 39 e7 da fd c6 05 f0 47 cf 05 01 48 c7 c7
RSP: 0000:ffffc900016d7c48 EFLAGS: 00010246
RAX: 8e9964d9ee901300 RBX: 0000000000000003 RCX: ffff888089a0e5c0
RDX: 0000000000000000 RSI: 0000000080000000 RDI: 0000000000000000
RBP: 0000000000000003 R08: ffffffff815cbca9 R09: ffffed1015d06660
R10: ffffed1015d06660 R11: 0000000000000000 R12: ffffffff895f43c8
R13: dffffc0000000000 R14: ffff88809365b018 R15: ffff8880ae83b400
 do_enable_set+0x63a/0x8d0 net/bluetooth/6lowpan.c:1075
 process_one_work+0x76e/0xfd0 kernel/workqueue.c:2268
 worker_thread+0xa7f/0x1450 kernel/workqueue.c:2414
 kthread+0x353/0x380 kernel/kthread.c:268
 ret_from_fork+0x24/0x30 arch/x86/entry/entry_64.S:352
Kernel Offset: disabled
Rebooting in 86400 seconds..


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