[POWERPC] iSeries: don't printk with HV spinlock held

Printk was observed to hang during module unload due to a limited
window of characters that may be sent to the hypervisor.  The window
only reexpands when we receive an ack from the HV and the spinlock here
prevents us from ever processing that ack.  This fixes it by dropping
the lock before doing the printk, then looping back to the top to
reacquire the lock.
Signed-off-by: NStephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/platforms/iseries/lpevents.c

@@ -121,6 +121,7 @@ void process_hvlpevents(void)
 {
 	struct HvLpEvent * event;
 
+ restart:
 	/* If we have recursed, just return */
 	if (!spin_trylock(&hvlpevent_queue.hq_lock))
 		return;
@@ -146,8 +147,20 @@ void process_hvlpevents(void)
 			if (event->xType < HvLpEvent_Type_NumTypes &&
 					lpEventHandler[event->xType])
 				lpEventHandler[event->xType](event);
-			else
-				printk(KERN_INFO "Unexpected Lp Event type=%d\n", event->xType );
+			else {
+				u8 type = event->xType;
+
+				/*
+				 * Don't printk in the spinlock as printk
+				 * may require ack events form the HV to send
+				 * any characters there.
+				 */
+				hvlpevent_clear_valid(event);
+				spin_unlock(&hvlpevent_queue.hq_lock);
+				printk(KERN_INFO
+					"Unexpected Lp Event type=%d\n", type);
+				goto restart;
+			}
 
 			hvlpevent_clear_valid(event);
 		} else if (hvlpevent_queue.hq_overflow_pending)