ocfs2: fix NULL dereference for moving extents

We can't dereference "bg" before it has been assigned.  GCC should have
warned about this but "bg" was initialized to NULL.  I've fixed that as
well.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJie Liu <jeff.liu@oracle.com>
Reviewed-by: NJie Liu <jeff.liu@oracle.com>
Cc: Mark Fasheh <mfasheh@suse.com>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

fs/ocfs2/move_extents.c

@@ -471,7 +471,7 @@ static int ocfs2_validate_and_adjust_move_goal(struct inode *inode,
 	int ret, goal_bit = 0;
 
 	struct buffer_head *gd_bh = NULL;
-	struct ocfs2_group_desc *bg = NULL;
+	struct ocfs2_group_desc *bg;
 	struct ocfs2_super *osb = OCFS2_SB(inode->i_sb);
 	int c_to_b = 1 << (osb->s_clustersize_bits -
 					inode->i_sb->s_blocksize_bits);
@@ -481,13 +481,6 @@ static int ocfs2_validate_and_adjust_move_goal(struct inode *inode,
 	 */
 	range->me_goal = ocfs2_block_to_cluster_start(inode->i_sb,
 						      range->me_goal);
-	/*
-	 * moving goal is not allowd to start with a group desc blok(#0 blk)
-	 * let's compromise to the latter cluster.
-	 */
-	if (range->me_goal == le64_to_cpu(bg->bg_blkno))
-		range->me_goal += c_to_b;
-
 	/*
 	 * validate goal sits within global_bitmap, and return the victim
 	 * group desc
@@ -501,6 +494,13 @@ static int ocfs2_validate_and_adjust_move_goal(struct inode *inode,
 
 	bg = (struct ocfs2_group_desc *)gd_bh->b_data;
 
+	/*
+	 * moving goal is not allowd to start with a group desc blok(#0 blk)
+	 * let's compromise to the latter cluster.
+	 */
+	if (range->me_goal == le64_to_cpu(bg->bg_blkno))
+		range->me_goal += c_to_b;
+
 	/*
 	 * movement is not gonna cross two groups.
 	 */