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: Kemeng 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: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index dab4627..535a8fb 100644 (file)
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -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;
 }