ring-buffer: Add missing unlock

In some error handling cases the lock is not unlocked.  The return is
converted to a goto, to share the unlock at the end of the function.

A simplified version of the semantic patch that finds this problem is as
follows: (http://coccinelle.lip6.fr/)

// <smpl>
@r exists@
expression E1;
identifier f;
@@

f (...) { <+...
* spin_lock_irq (E1,...);
... when != E1
* return ...;
...+> }
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
LKML-Reference: <Pine.LNX.4.64.1003291736440.21896@ask.diku.dk>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

kernel/trace/ring_buffer.c

@@ -1209,18 +1209,19 @@ rb_remove_pages(struct ring_buffer_per_cpu *cpu_buffer, unsigned nr_pages)
 
 	for (i = 0; i < nr_pages; i++) {
 		if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
-			return;
+			goto out;
 		p = cpu_buffer->pages->next;
 		bpage = list_entry(p, struct buffer_page, list);
 		list_del_init(&bpage->list);
 		free_buffer_page(bpage);
 	}
 	if (RB_WARN_ON(cpu_buffer, list_empty(cpu_buffer->pages)))
-		return;
+		goto out;
 
 	rb_reset_cpu(cpu_buffer);
 	rb_check_pages(cpu_buffer);
 
+out:
 	spin_unlock_irq(&cpu_buffer->reader_lock);
 }
 
@@ -1237,7 +1238,7 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
 
 	for (i = 0; i < nr_pages; i++) {
 		if (RB_WARN_ON(cpu_buffer, list_empty(pages)))
-			return;
+			goto out;
 		p = pages->next;
 		bpage = list_entry(p, struct buffer_page, list);
 		list_del_init(&bpage->list);
@@ -1246,6 +1247,7 @@ rb_insert_pages(struct ring_buffer_per_cpu *cpu_buffer,
 	rb_reset_cpu(cpu_buffer);
 	rb_check_pages(cpu_buffer);
 
+out:
 	spin_unlock_irq(&cpu_buffer->reader_lock);
 }