linux-ext4 - [PATCH -next] ext4: add an update to i_disksize in ext4_block_page

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Message-Id: <20250731140528.1554917-1-sunyongjian@huaweicloud.com>
Date: Thu, 31 Jul 2025 22:05:28 +0800
From: sunyongjian@...weicloud.com
To: linux-ext4@...r.kernel.org
Cc: linux-fsdevel@...r.kernel.org,
	yangerkun@...wei.com,
	yi.zhang@...wei.com,
	libaokun1@...wei.com,
	chengzhihao1@...wei.com,
	sunyongjian1@...wei.com
Subject: [PATCH -next] ext4: add an update to i_disksize in ext4_block_page_mkwrite

From: Yongjian Sun <sunyongjian1@...wei.com>

After running a stress test combined with fault injection,
we performed fsck -a followed by fsck -fn on the filesystem
image. During the second pass, fsck -fn reported:

Inode 131512, end of extent exceeds allowed value
	(logical block 405, physical block 1180540, len 2)

This inode was not in the orphan list. Analysis revealed the
following call chain that leads to the inconsistency:

                             ext4_da_write_end()
                              //does not update i_disksize
                             ext4_punch_hole()
                              //truncate folio, keep size
ext4_page_mkwrite()
 ext4_block_page_mkwrite()
  ext4_block_write_begin()
    ext4_get_block()
     //insert written extent without update i_disksize
journal commit
echo 1 > /sys/block/xxx/device/delete

da-write path updates i_size but does not update i_disksize. Then
ext4_punch_hole truncates the da-folio yet still leaves i_disksize
unchanged. Then ext4_page_mkwrite sees ext4_nonda_switch return 1
and takes the nodioread_nolock path, the folio about to be written
has just been punched out, and it’s offset sits beyond the current
i_disksize. This may result in a written extent being inserted, but
again does not update i_disksize. If the journal gets committed and
then the block device is yanked, we might run into this.

To fix this, we now check in ext4_block_page_mkwrite whether
i_disksize needs to be updated to cover the newly allocated blocks.

Signed-off-by: Yongjian Sun <sunyongjian1@...wei.com>
---
 fs/ext4/inode.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index ed54c4d0f2f9..050270b265ae 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -6666,8 +6666,18 @@ static int ext4_block_page_mkwrite(struct inode *inode, struct folio *folio,
 		goto out_error;

 	if (!ext4_should_journal_data(inode)) {
+		loff_t disksize = folio_pos(folio) + len;
 		block_commit_write(folio, 0, len);
 		folio_mark_dirty(folio);
+		if (disksize > READ_ONCE(EXT4_I(inode)->i_disksize)) {
+			down_write(&EXT4_I(inode)->i_data_sem);
+			if (disksize > EXT4_I(inode)->i_disksize)
+				EXT4_I(inode)->i_disksize = disksize;
+			up_write(&EXT4_I(inode)->i_data_sem);
+			ret = ext4_mark_inode_dirty(handle, inode);
+			if (ret)
+				goto out_error;
+		}
 	} else {
 		ret = ext4_journal_folio_buffers(handle, folio, len);
 		if (ret)
-- 
2.39.2