Commit 68e294dc authored by Kemeng Shi's avatar Kemeng Shi Committed by Theodore Ts'o
Browse files

ext4: improve inode table blocks counting in ext4_num_overhead_clusters 



As inode table blocks are contiguous, inode table blocks inside the
block_group can be represented as range [itbl_cluster_start,
itbl_cluster_last]. Then we can simply account inode table cluters and
check cluster overlap with [itbl_cluster_start, itbl_cluster_last]
instead of traverse each block of inode table.

By the way, this patch fixes code style problem of comment for
ext4_num_overhead_clusters.

[ Merged fix-up patch which fixed potentially access to an
  uninitialzied stack variable. --TYT ]

Signed-off-by: default avatarKemeng Shi <shikemeng@huaweicloud.com>
Link: https://lore.kernel.org/r/20230221115919.1918161-8-shikemeng@huaweicloud.com
Link: https://lore.kernel.org/r/202303171446.eLEhZzAu-lkp@intel.com/


Reported-by: default avatarkernel test robot <lkp@intel.com>
Reported-by: default avatarDan Carpenter <error27@gmail.com>
Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
parent cefa74d0

fs/ext4/balloc.c

+47 −43
Original line number Diff line number Diff line
@@ -80,32 +80,56 @@ static inline int ext4_block_in_group(struct super_block *sb, 
	return (actual_group == block_group) ? 1 : 0;

}



/* Return the number of clusters used for file system metadata; this

/*

 * Return the number of clusters used for file system metadata; this

 * represents the overhead needed by the file system.

 */

static unsigned ext4_num_overhead_clusters(struct super_block *sb,

					   ext4_group_t block_group,

					   struct ext4_group_desc *gdp)

{

	unsigned num_clusters;

	int block_cluster = -1, inode_cluster = -1, itbl_cluster = -1, i, c;

	unsigned base_clusters, num_clusters;

	int block_cluster = -1, inode_cluster;

	int itbl_cluster_start = -1, itbl_cluster_end = -1;

	ext4_fsblk_t start = ext4_group_first_block_no(sb, block_group);

	ext4_fsblk_t itbl_blk;

	ext4_fsblk_t end = start + EXT4_BLOCKS_PER_GROUP(sb) - 1;

	ext4_fsblk_t itbl_blk_start, itbl_blk_end;

	struct ext4_sb_info *sbi = EXT4_SB(sb);



	/* This is the number of clusters used by the superblock,

	 * block group descriptors, and reserved block group

	 * descriptor blocks */

	num_clusters = ext4_num_base_meta_clusters(sb, block_group);

	base_clusters = ext4_num_base_meta_clusters(sb, block_group);

	num_clusters = base_clusters;



	/*

	 * For the allocation bitmaps and inode table, we first need

	 * to check to see if the block is in the block group.  If it

	 * is, then check to see if the cluster is already accounted

	 * for in the clusters used for the base metadata cluster, or

	 * if we can increment the base metadata cluster to include

	 * that block.  Otherwise, we will have to track the cluster

	 * used for the allocation bitmap or inode table explicitly.

	 * Account and record inode table clusters if any cluster

	 * is in the block group, or inode table cluster range is

	 * [-1, -1] and won't overlap with block/inode bitmap cluster

	 * accounted below.

	 */

	itbl_blk_start = ext4_inode_table(sb, gdp);

	itbl_blk_end = itbl_blk_start + sbi->s_itb_per_group - 1;

	if (itbl_blk_start <= end && itbl_blk_end >= start) {

		itbl_blk_start = itbl_blk_start >= start ?

			itbl_blk_start : start;

		itbl_blk_end = itbl_blk_end <= end ?

			itbl_blk_end : end;



		itbl_cluster_start = EXT4_B2C(sbi, itbl_blk_start - start);

		itbl_cluster_end = EXT4_B2C(sbi, itbl_blk_end - start);



		num_clusters += itbl_cluster_end - itbl_cluster_start + 1;

		/* check if border cluster is overlapped */

		if (itbl_cluster_start == base_clusters - 1)

			num_clusters--;

	}



	/*

	 * For the allocation bitmaps, we first need to check to see

	 * if the block is in the block group.  If it is, then check

	 * to see if the cluster is already accounted for in the clusters

	 * used for the base metadata cluster and inode tables cluster.

	 * Normally all of these blocks are contiguous, so the special

	 * case handling shouldn't be necessary except for *very*

	 * unusual file system layouts.
@@ -113,46 +137,26 @@ static unsigned ext4_num_overhead_clusters(struct super_block *sb, 
	if (ext4_block_in_group(sb, ext4_block_bitmap(sb, gdp), block_group)) {

		block_cluster = EXT4_B2C(sbi,

					 ext4_block_bitmap(sb, gdp) - start);

		if (block_cluster < num_clusters)

			block_cluster = -1;

		else if (block_cluster == num_clusters) {

		if (block_cluster >= base_clusters &&

		    (block_cluster < itbl_cluster_start ||

		    block_cluster > itbl_cluster_end))

			num_clusters++;

			block_cluster = -1;

		}

	}



	if (ext4_block_in_group(sb, ext4_inode_bitmap(sb, gdp), block_group)) {

		inode_cluster = EXT4_B2C(sbi,

					 ext4_inode_bitmap(sb, gdp) - start);

		if (inode_cluster < num_clusters)

			inode_cluster = -1;

		else if (inode_cluster == num_clusters) {

			num_clusters++;

			inode_cluster = -1;

		}

	}



	itbl_blk = ext4_inode_table(sb, gdp);

	for (i = 0; i < sbi->s_itb_per_group; i++) {

		if (ext4_block_in_group(sb, itbl_blk + i, block_group)) {

			c = EXT4_B2C(sbi, itbl_blk + i - start);

			if ((c < num_clusters) || (c == inode_cluster) ||

			    (c == block_cluster) || (c == itbl_cluster))

				continue;

			if (c == num_clusters) {

				num_clusters++;

				continue;

			}

		/*

		 * Additional check if inode bitmap is in just accounted

		 * block_cluster

		 */

		if (inode_cluster != block_cluster &&

		    inode_cluster >= base_clusters &&

		    (inode_cluster < itbl_cluster_start ||

		    inode_cluster > itbl_cluster_end))

			num_clusters++;

			itbl_cluster = c;

		}

	}



	if (block_cluster != -1)

		num_clusters++;

	if (inode_cluster != -1)

		num_clusters++;



	return num_clusters;

}