ocfs2: fix BUG when calculate new backup super

commit 5c9ee4cb upstream.

When resizing, it firstly extends the last gd.  Once it should backup
super in the gd, it calculates new backup super and update the
corresponding value.

But it currently doesn't consider the situation that the backup super is
already done.  And in this case, it still sets the bit in gd bitmap and
then decrease from bg_free_bits_count, which leads to a corrupted gd and
trigger the BUG in ocfs2_block_group_set_bits:

    BUG_ON(le16_to_cpu(bg->bg_free_bits_count) < num_bits);

So check whether the backup super is done and then do the updates.
Signed-off-by: Joseph Qi <joseph.qi@huawei.com>
Reviewed-by: Jiufei Xue <xuejiufei@huawei.com>
Reviewed-by: Yiwen Jiang <jiangyiwen@huawei.com>
Cc: Mark Fasheh <mfasheh@suse.de>
Cc: Joel Becker <jlbec@evilplan.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

fs/ocfs2/resize.c

@@ -54,11 +54,12 @@
 static u16 ocfs2_calc_new_backup_super(struct inode *inode,
 				       struct ocfs2_group_desc *gd,
 				       u16 cl_cpg,
+				       u16 old_bg_clusters,
 				       int set)
 {
 	int i;
 	u16 backups = 0;
-	u32 cluster;
+	u32 cluster, lgd_cluster;
 	u64 blkno, gd_blkno, lgd_blkno = le64_to_cpu(gd->bg_blkno);
 
 	for (i = 0; i < OCFS2_MAX_BACKUP_SUPERBLOCKS; i++) {
@@ -71,6 +72,12 @@ static u16 ocfs2_calc_new_backup_super(struct inode *inode,
 		else if (gd_blkno > lgd_blkno)
 			break;
 
+		/* check if already done backup super */
+		lgd_cluster = ocfs2_blocks_to_clusters(inode->i_sb, lgd_blkno);
+		lgd_cluster += old_bg_clusters;
+		if (lgd_cluster >= cluster)
+			continue;
+
 		if (set)
 			ocfs2_set_bit(cluster % cl_cpg,
 				      (unsigned long *)gd->bg_bitmap);
@@ -99,6 +106,7 @@ static int ocfs2_update_last_group_and_inode(handle_t *handle,
 	u16 chain, num_bits, backups = 0;
 	u16 cl_bpc = le16_to_cpu(cl->cl_bpc);
 	u16 cl_cpg = le16_to_cpu(cl->cl_cpg);
+	u16 old_bg_clusters;
 
 	trace_ocfs2_update_last_group_and_inode(new_clusters,
 						first_new_cluster);
@@ -112,6 +120,7 @@ static int ocfs2_update_last_group_and_inode(handle_t *handle,
 
 	group = (struct ocfs2_group_desc *)group_bh->b_data;
 
+	old_bg_clusters = le16_to_cpu(group->bg_bits) / cl_bpc;
 	/* update the group first. */
 	num_bits = new_clusters * cl_bpc;
 	le16_add_cpu(&group->bg_bits, num_bits);
@@ -125,7 +134,7 @@ static int ocfs2_update_last_group_and_inode(handle_t *handle,
 				     OCFS2_FEATURE_COMPAT_BACKUP_SB)) {
 		backups = ocfs2_calc_new_backup_super(bm_inode,
 						     group,
-						     cl_cpg, 1);
+						     cl_cpg, old_bg_clusters, 1);
 		le16_add_cpu(&group->bg_free_bits_count, -1 * backups);
 	}
 
@@ -163,7 +172,7 @@ static int ocfs2_update_last_group_and_inode(handle_t *handle,
 	if (ret < 0) {
 		ocfs2_calc_new_backup_super(bm_inode,
 					    group,
-					    cl_cpg, 0);
+					    cl_cpg, old_bg_clusters, 0);
 		le16_add_cpu(&group->bg_free_bits_count, backups);
 		le16_add_cpu(&group->bg_bits, -1 * num_bits);
 		le16_add_cpu(&group->bg_free_bits_count, -1 * num_bits);