btrfs: remove inode_dio_wait() calls when starting reflink operations

When starting a reflink operation we have these calls to inode_dio_wait()
which used to be needed because direct IO writes that don't cross the
i_size boundary did not take the inode's VFS lock, so we could race with
them and end up with ordered extents in target range after calling
btrfs_wait_ordered_range().

However that is not the case anymore, because the inode's VFS lock was
changed from a mutex to a rw semaphore, by commit 9902af79
("parallel lookups: actual switch to rwsem"), and several years later we
started to lock the inode's VFS lock in shared mode for direct IO writes
that don't cross the i_size boundary (commit e9adabb9 ("btrfs: use
shared lock for direct writes within EOF")).

So remove those inode_dio_wait() calls.
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/reflink.c

@@ -771,7 +771,6 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	struct inode *inode_in = file_inode(file_in);
 	struct inode *inode_out = file_inode(file_out);
 	u64 bs = BTRFS_I(inode_out)->root->fs_info->sb->s_blocksize;
-	bool same_inode = inode_out == inode_in;
 	u64 wb_len;
 	int ret;
 
@@ -809,15 +808,6 @@ static int btrfs_remap_file_range_prep(struct file *file_in, loff_t pos_in,
 	else
 		wb_len = ALIGN(*len, bs);
 
-	/*
-	 * Since we don't lock ranges, wait for ongoing lockless dio writes (as
-	 * any in progress could create its ordered extents after we wait for
-	 * existing ordered extents below).
-	 */
-	inode_dio_wait(inode_in);
-	if (!same_inode)
-		inode_dio_wait(inode_out);
-
 	/*
 	 * Workaround to make sure NOCOW buffered write reach disk as NOCOW.
 	 *