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List:       linux-ext4
Subject:    [PATCH 2/2] ext4: avoid resizing to a partial cluster size
From:       "Kiselev, Oleg" <okiselev () amazon ! com>
Date:       2022-06-30 2:17:22
Message-ID: 9CDF7393-5645-4E8A-9D68-01CF7F4C4955 () amazon ! com
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This patch avoids an attempt to resize the filesystem to an
unaligned cluster boundary.  An online resize to a size that is not
integral to cluster size results in the last iteration attempting to
grow the fs by a negative amount, which trips a BUG_ON and leaves the fs
with a corrupted in-memory superblock.

Signed-off-by: Oleg Kiselev <okiselev@amazon.com>
---
 fs/ext4/resize.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 2acc9fca99ea..8803905907de 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1624,7 +1624,8 @@ static int ext4_setup_next_flex_gd(struct super_block *sb,

 	o_blocks_count = ext4_blocks_count(es);

-	if (o_blocks_count == n_blocks_count)
+	if ((o_blocks_count == n_blocks_count) ||
+	    ((n_blocks_count - o_blocks_count) < sbi->s_cluster_ratio))
 		return 0;

 	ext4_get_group_no_and_offset(sb, o_blocks_count, &group, &last);
--
2.32.0


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