[PATCH 1/2] ext4: fix DAX write locking

[Christoph Hellwig <hch@lst.de>]

Unlike O_DIRECT DAX is not an optional opt-in feature selected by the
application, so we'll have to provide the traditional synchronіzation
of overlapping writes as we do for buffered writes.

This was broken historically for DAX, but got fixed for ext2 and XFS
as part of the iomap conversion.  Fix up ext4 as well.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/ext4/file.c | 10 +---------
 1 file changed, 1 insertion(+), 9 deletions(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index d663d3d..a1e88aa 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -175,7 +175,6 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct inode *inode = file_inode(iocb->ki_filp);
 	ssize_t ret;
-	bool overwrite = false;
 
 	inode_lock(inode);
 	ret = ext4_write_checks(iocb, from);
@@ -188,16 +187,9 @@ ext4_dax_write_iter(struct kiocb *iocb, struct iov_iter *from)
 	if (ret)
 		goto out;
 
-	if (ext4_overwrite_io(inode, iocb->ki_pos, iov_iter_count(from))) {
-		overwrite = true;
-		downgrade_write(&inode->i_rwsem);
-	}
 	ret = dax_iomap_rw(iocb, from, &ext4_iomap_ops);
 out:
-	if (!overwrite)
-		inode_unlock(inode);
-	else
-		inode_unlock_shared(inode);
+	inode_unlock(inode);
 	if (ret > 0)
 		ret = generic_write_sync(iocb, ret);
 	return ret;
-- 
2.1.4