ext4: try all groups in ext4_mb_new_blocks_simple

[ Upstream commit 19a043bb1f ]

ext4_mb_new_blocks_simple ignores the group before goal, so it will fail
if free blocks reside in group before goal. Try all groups to avoid
unexpected failure.
Search finishes either if any free block is found or if no available
blocks are found. Simpliy check "i >= max" to distinguish the above
cases.

Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Suggested-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Link: https://lore.kernel.org/r/20230603150327.3596033-8-shikemeng@huaweicloud.com
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Stable-dep-of: 3f4830abd236 ("ext4: fix potential unnitialized variable")
Signed-off-by: Sasha Levin <sashal@kernel.org>

fs/ext4/mballoc.c

@@ -5887,7 +5887,7 @@ static ext4_fsblk_t ext4_mb_new_blocks_simple(handle_t *handle,
 	struct buffer_head *bitmap_bh;
 	struct super_block *sb = ar->inode->i_sb;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
-	ext4_group_t group;
+	ext4_group_t group, nr;
 	ext4_grpblk_t blkoff;
 	ext4_grpblk_t max = EXT4_CLUSTERS_PER_GROUP(sb);
 	ext4_grpblk_t i = 0;
@@ -5901,7 +5901,7 @@ static ext4_fsblk_t ext4_mb_new_blocks_simple(handle_t *handle,
 
 	ar->len = 0;
 	ext4_get_group_no_and_offset(sb, goal, &group, &blkoff);
-	for (; group < ext4_get_groups_count(sb); group++) {
+	for (nr = ext4_get_groups_count(sb); nr > 0; nr--) {
 		bitmap_bh = ext4_read_block_bitmap(sb, group);
 		if (IS_ERR(bitmap_bh)) {
 			*errp = PTR_ERR(bitmap_bh);
@@ -5925,10 +5925,13 @@ static ext4_fsblk_t ext4_mb_new_blocks_simple(handle_t *handle,
 		if (i < max)
 			break;
 
+		if (++group >= ext4_get_groups_count(sb))
+			group = 0;
+
 		blkoff = 0;
 	}
 
-	if (group >= ext4_get_groups_count(sb) || i >= max) {
+	if (i >= max) {
 		*errp = -ENOSPC;
 		return 0;
 	}