diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 0df5ee1..464cff7 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1276,6 +1276,7 @@
 
 	unsigned int s_log_groups_per_flex;
 	struct flex_groups *s_flex_groups;
+	ext4_group_t s_flex_groups_allocated;
 
 	/* workqueue for dio unwritten */
 	struct workqueue_struct *dio_unwritten_wq;
@@ -2055,6 +2056,8 @@
 extern void *ext4_kvmalloc(size_t size, gfp_t flags);
 extern void *ext4_kvzalloc(size_t size, gfp_t flags);
 extern void ext4_kvfree(void *ptr);
+extern int ext4_alloc_flex_bg_array(struct super_block *sb,
+				    ext4_group_t ngroup);
 extern __printf(4, 5)
 void __ext4_error(struct super_block *, const char *, unsigned int,
 		  const char *, ...);
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 365d800..3f5c67b 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1503,6 +1503,10 @@
 	if (err)
 		goto out;
 
+	err = ext4_alloc_flex_bg_array(sb, input->group + 1);
+	if (err)
+		return err;
+
 	flex_gd.count = 1;
 	flex_gd.groups = input;
 	flex_gd.bg_flags = &bg_flags;
@@ -1662,7 +1666,7 @@
 	unsigned long n_desc_blocks;
 	unsigned long o_desc_blocks;
 	unsigned long desc_blocks;
-	int err = 0, flexbg_size = 1;
+	int err = 0, flexbg_size = 1 << sbi->s_log_groups_per_flex;
 
 	o_blocks_count = ext4_blocks_count(es);
 
@@ -1721,13 +1725,13 @@
 			goto out;
 	}
 
-	if (EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_FLEX_BG) &&
-	    es->s_log_groups_per_flex)
-		flexbg_size = 1 << es->s_log_groups_per_flex;
-
 	if (ext4_blocks_count(es) == n_blocks_count)
 		goto out;
 
+	err = ext4_alloc_flex_bg_array(sb, n_group + 1);
+	if (err)
+		return err;
+
 	flex_gd = alloc_flex_gd(flexbg_size);
 	if (flex_gd == NULL) {
 		err = -ENOMEM;
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index b875ff5..b8de488 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1925,15 +1925,45 @@
 	return res;
 }
 
+int ext4_alloc_flex_bg_array(struct super_block *sb, ext4_group_t ngroup)
+{
+	struct ext4_sb_info *sbi = EXT4_SB(sb);
+	struct flex_groups *new_groups;
+	int size;
+
+	if (!sbi->s_log_groups_per_flex)
+		return 0;
+
+	size = ext4_flex_group(sbi, ngroup - 1) + 1;
+	if (size <= sbi->s_flex_groups_allocated)
+		return 0;
+
+	size = roundup_pow_of_two(size * sizeof(struct flex_groups));
+	new_groups = ext4_kvzalloc(size, GFP_KERNEL);
+	if (!new_groups) {
+		ext4_msg(sb, KERN_ERR, "not enough memory for %d flex groups",
+			 size / (int) sizeof(struct flex_groups));
+		return -ENOMEM;
+	}
+
+	if (sbi->s_flex_groups) {
+		memcpy(new_groups, sbi->s_flex_groups,
+		       (sbi->s_flex_groups_allocated *
+			sizeof(struct flex_groups)));
+		ext4_kvfree(sbi->s_flex_groups);
+	}
+	sbi->s_flex_groups = new_groups;
+	sbi->s_flex_groups_allocated = size / sizeof(struct flex_groups);
+	return 0;
+}
+
 static int ext4_fill_flex_info(struct super_block *sb)
 {
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_group_desc *gdp = NULL;
-	ext4_group_t flex_group_count;
 	ext4_group_t flex_group;
 	unsigned int groups_per_flex = 0;
-	size_t size;
-	int i;
+	int i, err;
 
 	sbi->s_log_groups_per_flex = sbi->s_es->s_log_groups_per_flex;
 	if (sbi->s_log_groups_per_flex < 1 || sbi->s_log_groups_per_flex > 31) {
@@ -1942,17 +1972,9 @@
 	}
 	groups_per_flex = 1 << sbi->s_log_groups_per_flex;
 
-	/* We allocate both existing and potentially added groups */
-	flex_group_count = ((sbi->s_groups_count + groups_per_flex - 1) +
-			((le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks) + 1) <<
-			      EXT4_DESC_PER_BLOCK_BITS(sb))) / groups_per_flex;
-	size = flex_group_count * sizeof(struct flex_groups);
-	sbi->s_flex_groups = ext4_kvzalloc(size, GFP_KERNEL);
-	if (sbi->s_flex_groups == NULL) {
-		ext4_msg(sb, KERN_ERR, "not enough memory for %u flex groups",
-			 flex_group_count);
+	err = ext4_alloc_flex_bg_array(sb, sbi->s_groups_count);
+	if (err)
 		goto failed;
-	}
 
 	for (i = 0; i < sbi->s_groups_count; i++) {
 		gdp = ext4_get_group_desc(sb, i, NULL);