linux-ext4 - [PATCH 1/2] ext4: update s_overhead_clusters in the superblock during an on-line resize

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Message-Id: <20220629040026.112371-1-tytso@mit.edu>
Date:   Wed, 29 Jun 2022 00:00:25 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     "Theodore Ts'o" <tytso@....edu>, stable@...nel.org
Subject: [PATCH 1/2] 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 10b01ee92df5 ("ext4: fix overhead
calculation to account for the reserved gdt blocks"), 85d825dbf489
("ext4: force overhead calculation if the s_overhead_cluster makes no
sense"), and eb7054212eac ("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 <tytso@....edu>
Cc: stable@...nel.org
---
 fs/ext4/resize.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 8b70a4701293..e5c2713aa11a 100644
--- a/fs/ext4/resize.c
+++ b/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:"
-- 
2.31.0