tty: Fix BKL taken under a spinlock bug introduced in the BKL split

The fasync path takes the BKL (it probably doesn't need to in fact)
while holding the file_list spinlock.  You can't do that with the kernel
lock: it causes lock inversions and deadlocks.

Leave the BKL over that bit for the moment.

Identified by AKPM.
Signed-off-by: NAlan Cox <alan@linux.intel.com>
Acked-and-Tested-by: NThomas Gleixner <tglx@linutronix.de>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/char/tty_io.c

@@ -516,7 +516,6 @@ static void do_tty_hangup(struct work_struct *work)
 	/* inuse_filps is protected by the single kernel lock */
 	lock_kernel();
 	check_tty_count(tty, "do_tty_hangup");
-	unlock_kernel();
 
 	file_list_lock();
 	/* This breaks for file handles being sent over AF_UNIX sockets ? */
@@ -531,7 +530,6 @@ static void do_tty_hangup(struct work_struct *work)
 	}
 	file_list_unlock();
 
-	lock_kernel();
 	tty_ldisc_hangup(tty);
 
 	read_lock(&tasklist_lock);