ext4: update s_overhead_clusters in the superblock during an on-line resize

When doing an online resize, the on-disk superblock on-disk wasn't
updated.  This means that when the file system is unmounted and
remounted, and the on-disk overhead value is non-zero, this would
result in the results of statfs(2) to be incorrect.

This was partially fixed by Commits 10b01ee ("ext4: fix overhead
calculation to account for the reserved gdt blocks"), 85d825d
("ext4: force overhead calculation if the s_overhead_cluster makes no
sense"), and eb70542 ("ext4: update the cached overhead value in
the superblock").

However, since it was too expensive to forcibly recalculate the
overhead for bigalloc file systems at every mount, this didn't fix the
problem for bigalloc file systems.  This commit should address the
problem when resizing file systems with the bigalloc feature enabled.

Signed-off-by: Theodore Ts'o <[email protected]>
Cc: [email protected]
Reviewed-by: Andreas Dilger <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Theodore Ts'o <[email protected]>

Author: tytso

fs/ext4/resize.c

@@ -1484,6 +1484,7 @@ static void ext4_update_super(struct super_block *sb,
 	 * Update the fs overhead information
 	 */
 	ext4_calculate_overhead(sb);
+	es->s_overhead_clusters = cpu_to_le32(sbi->s_overhead);
 
 	if (test_opt(sb, DEBUG))
 		printk(KERN_DEBUG "EXT4-fs: added group %u:"