[PATCH] ext4: fix credit calculation in ext4_ext_calc_credits_for_insert

Fix a nit in ext4_ext_calc_credits_for_insert().  Besides, credits for the
new root are already added in the index split accounting.

Signed-off-by: Johann Lombardi <johann.lombardi@bull.net>
Signed-off-by: Alex Tomas <alex@clusterfs.com>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

fs/ext4/extents.c

@@ -1531,16 +1531,17 @@ int inline ext4_ext_calc_credits_for_insert(struct inode *inode,
 
 	/*
 	 * tree can be full, so it would need to grow in depth:
-	 * allocation + old root + new root
+	 * we need one credit to modify old root, credits for
+	 * new root will be added in split accounting
 	 */
-	needed += 2 + 1 + 1;
+	needed += 1;
 
 	/*
 	 * Index split can happen, we would need:
 	 *    allocate intermediate indexes (bitmap + group)
 	 *  + change two blocks at each level, but root (already included)
 	 */
-	needed = (depth * 2) + (depth * 2);
+	needed += (depth * 2) + (depth * 2);
 
 	/* any allocation modifies superblock */
 	needed += 1;