[PATCH] ext2: preserve IOMAP_F_DIRTY for extending direct writes

[Hungyu Lin]

ext2_iomap_begin() sets IOMAP_F_DIRTY for writes that may extend i_size,
but clears the flag after ext2_get_blocks(). When the write uses an
existing mapped block, iomap can then use FUA and skip
generic_write_sync(), even though ext2_dio_write_end_io() updates the
inode size. An O_DSYNC write can therefore return without persisting
the new size.

For example, on a FUA-capable device, a 512-byte O_DIRECT|O_DSYNC write
at offset 512 into a fsynced one-byte file returns successfully and
extends the in-memory size to 1024, while an immediate read of the
on-disk inode still shows size 1. An explicit fsync persists the new
size.

Move setting of IOMAP_F_DIRTY after the initialization.

Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hungyu Lin <dennylin0707@xxxxxxxxx>
Link: https://patch.msgid.link/20261029013616.97194-1-dennylin0707@xxxxxxxxx
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 fs/ext2/inode.c | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 12ac4cfe1500..51250717c70b 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -805,6 +805,12 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	    (first_block << blkbits) < i_size_read(inode))
 		create = 0;
 
+	ret = ext2_get_blocks(inode, first_block, max_blocks,
+			&bno, &new, &boundary, create);
+	if (ret < 0)
+		return ret;
+
+	iomap->flags = 0;
 	/*
 	 * Writes that span EOF might trigger an IO size update on completion,
 	 * so consider them to be dirty for the purposes of O_DSYNC even if
@@ -812,13 +818,6 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	 */
 	if ((flags & IOMAP_WRITE) && offset + length > i_size_read(inode))
 		iomap->flags |= IOMAP_F_DIRTY;
-
-	ret = ext2_get_blocks(inode, first_block, max_blocks,
-			&bno, &new, &boundary, create);
-	if (ret < 0)
-		return ret;
-
-	iomap->flags = 0;
 	iomap->offset = (u64)first_block << blkbits;
 	iomap->bdev = inode->i_sb->s_bdev;
 
-- 
2.53.0


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