fix spinlock recursion in hvc_console

commit 611e097d7707741a336a0677d9d69bec40f29f3d
Author: Christian Borntraeger <borntraeger@de.ibm.com>
hvc_console: rework setup to replace irq functions with callbacks
introduced a spinlock recursion problem.

request_irq tries to call the handler if the IRQ is shared.
The irq handler of hvc_console calls hvc_poll and hvc_kill
which might take the hvc_struct spinlock. Therefore, we have
to call request_irq outside the spinlock.

We can move the notifier_add safely outside the spinlock as ->data must
not be changed by the backend. Otherwise, tty_hangup would fail anyway.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

drivers/char/hvc_console.c

@@ -322,11 +322,10 @@ static int hvc_open(struct tty_struct *tty, struct file * filp)
 
 	hp->tty = tty;
 
-	if (hp->ops->notifier_add)
-		rc = hp->ops->notifier_add(hp, hp->data);
-
 	spin_unlock_irqrestore(&hp->lock, flags);
 
+	if (hp->ops->notifier_add)
+		rc = hp->ops->notifier_add(hp, hp->data);
 
 	/*
 	 * If the notifier fails we return an error.  The tty layer