ext4: fix DAX write locking

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>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Reviewed-by: Jan Kara <jack@suse.cz>

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index ff3f6107b0ba34cdf3614d6584f3b461d4e812b5..87e11dfe3cde883c0bdd47c9b43fa6461ab4323d 100644 (file)
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -178,7 +178,6 @@ 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);
@@ -191,16 +190,9 @@ 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;