trivial: radix-tree: document wrap-around issue of radix_tree_next_hole()

And some 80-line cleanups.
Signed-off-by: Wu Fengguang <wfg@linux.intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

lib/radix-tree.c

@@ -640,13 +640,14 @@ EXPORT_SYMBOL(radix_tree_tag_get);
  *
  *	Returns: the index of the hole if found, otherwise returns an index
  *	outside of the set specified (in which case 'return - index >= max_scan'
- *	will be true).
+ *	will be true). In rare cases of index wrap-around, 0 will be returned.
  *
  *	radix_tree_next_hole may be called under rcu_read_lock. However, like
- *	radix_tree_gang_lookup, this will not atomically search a snapshot of the
- *	tree at a single point in time. For example, if a hole is created at index
- *	5, then subsequently a hole is created at index 10, radix_tree_next_hole
- *	covering both indexes may return 10 if called under rcu_read_lock.
+ *	radix_tree_gang_lookup, this will not atomically search a snapshot of
+ *	the tree at a single point in time. For example, if a hole is created
+ *	at index 5, then subsequently a hole is created at index 10,
+ *	radix_tree_next_hole covering both indexes may return 10 if called
+ *	under rcu_read_lock.
  */
 unsigned long radix_tree_next_hole(struct radix_tree_root *root,
 				unsigned long index, unsigned long max_scan)