drivers: staging: rtl8192eu: Fix deadlock in rtw_joinbss_event_prehandle

In the Linux kernel, the following vulnerability has been resolved:

drivers: staging: rtl8192eu: Fix deadlock in rtw_joinbss_event_prehandle

There is a deadlock in rtw_joinbss_event_prehandle(), which is shown below:

(Thread 1) | (Thread 2)

| _set_timer()

rtw_joinbss_event_prehandle()| mod_timer()

spin_lock_bh() //(1) | (wait a time)

... | rtw_join_timeout_handler()

| _rtw_join_timeout_handler()

del_timer_sync() | spin_lock_bh() //(2)

(wait timer to stop) | ...

We hold pmlmepriv->lock in position (1) of thread 1 and

use del_timer_sync() to wait timer to stop, but timer handler

also need pmlmepriv->lock in position (2) of thread 2.

As a result, rtw_joinbss_event_prehandle() will block forever.

This patch extracts del_timer_sync() from the protection of

spin_lock_bh(), which could let timer handler to obtain

the needed lock. What`s more, we change spin_lock_bh() to

spin_lock_irq() in _rtw_join_timeout_handler() in order to

prevent deadlock.