[PATCH] ext2: preserve IOMAP_F_DIRTY for extending direct writes

[Hungyu Lin <dennylin0707@gmail.com>]

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.

Initialize iomap->flags before setting IOMAP_F_DIRTY so that the flag
survives and the required metadata synchronization takes place.

Fixes: fb5de4358e1a ("ext2: Move direct-io to use iomap")
Cc: stable@vger.kernel.org
Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
 fs/ext2/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/ext2/inode.c b/fs/ext2/inode.c
index 12ac4cfe1500..ba23cadb157b 100644
--- a/fs/ext2/inode.c
+++ b/fs/ext2/inode.c
@@ -805,6 +805,7 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	    (first_block << blkbits) < i_size_read(inode))
 		create = 0;
 
+	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
@@ -818,7 +819,6 @@ static int ext2_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	if (ret < 0)
 		return ret;
 
-	iomap->flags = 0;
 	iomap->offset = (u64)first_block << blkbits;
 	iomap->bdev = inode->i_sb->s_bdev;
 
-- 
2.43.0