[BUG] net: bluetooth: a possible sleep-in-atomic-context bug in disconnect_all_peers()

The kernel module may sleep while holding a spinlock.
The function call path (from bottom to top) in Linux 4.19 is:

net/bluetooth/l2cap_core.c, 840:
     mutex_lock in l2cap_get_ident
net/bluetooth/l2cap_core.c, 1402:
     l2cap_get_ident in l2cap_send_disconn_req
net/bluetooth/l2cap_core.c, 736:
     l2cap_send_disconn_req in l2cap_chan_close
net/bluetooth/6lowpan.c, 1053:
     l2cap_chan_close in disconnect_all_peers
net/bluetooth/6lowpan.c, 1051:
     spin_lock in disconnect_all_peers

mutex_lock() can sleep at runtime.

I am not sure how to properly fix this possible bug, so I only report it.

This bug is found by a static analysis tool STCheck written by myself.


Best wishes,
Jia-Ju Bai