linux-ext4 - [PATCH 2/3] ext4: force overhead calculation if the s_overhead

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Date:   Thu, 14 Apr 2022 22:54:39 -0400
From:   "Theodore Ts'o" <tytso@....edu>
To:     Ext4 Developers List <linux-ext4@...r.kernel.org>
Cc:     Fariya F <fariya.fatima03@...il.com>,
        "Theodore Ts'o" <tytso@....edu>, stable@...nel.org
Subject: [PATCH 2/3] ext4: force overhead calculation if the s_overhead_cluster makes no sense

If the file system does not use bigalloc, calculating the overhead is
cheap, so force the recalculation of the overhead so we don't have to
trust the precalculated overhead in the superblock.

Signed-off-by: Theodore Ts'o <tytso@....edu>
Cc: stable@...nel.org
---
 fs/ext4/super.c | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 23a9b2c086ed..d08820fdfdee 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -5289,9 +5289,18 @@ static int __ext4_fill_super(struct fs_context *fc, struct super_block *sb)
 	 * Get the # of file system overhead blocks from the
 	 * superblock if present.
 	 */
-	if (es->s_overhead_clusters)
-		sbi->s_overhead = le32_to_cpu(es->s_overhead_clusters);
-	else {
+	sbi->s_overhead = le32_to_cpu(es->s_overhead_clusters);
+	/* ignore the precalculated value if it is ridiculous */
+	if (sbi->s_overhead > ext4_blocks_count(es))
+		sbi->s_overhead = 0;
+	/*
+	 * If the bigalloc feature is not enabled recalculating the
+	 * overhead doesn't take long, so we might as well just redo
+	 * it to make sure we are using the correct value.
+	 */
+	if (!ext4_has_feature_bigalloc(sb))
+		sbi->s_overhead = 0;
+	if (sbi->s_overhead == 0) {
 		err = ext4_calculate_overhead(sb);
 		if (err)
 			goto failed_mount_wq;
-- 
2.31.0