fuse: fix copy_file_range cache issues

a) Dirty cache needs to be written back not just in the writeback_cache
case, since the dirty pages may come from memory maps.

b) The fuse_writeback_range() helper takes an inclusive interval, so the
end position needs to be pos+len-1 instead of pos+len.

Fixes: 88bc7d5 ("fuse: add support for copy_file_range()")
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>

fs/fuse/file.c

@@ -3325,25 +3325,21 @@ static ssize_t __fuse_copy_file_range(struct file *file_in, loff_t pos_in,
 	if (file_inode(file_in)->i_sb != file_inode(file_out)->i_sb)
 		return -EXDEV;
 
-	if (fc->writeback_cache) {
-		inode_lock(inode_in);
-		err = fuse_writeback_range(inode_in, pos_in, pos_in + len);
-		inode_unlock(inode_in);
-		if (err)
-			return err;
-	}
+	inode_lock(inode_in);
+	err = fuse_writeback_range(inode_in, pos_in, pos_in + len - 1);
+	inode_unlock(inode_in);
+	if (err)
+		return err;
 
 	inode_lock(inode_out);
 
 	err = file_modified(file_out);
 	if (err)
 		goto out;
 
-	if (fc->writeback_cache) {
-		err = fuse_writeback_range(inode_out, pos_out, pos_out + len);
-		if (err)
-			goto out;
-	}
+	err = fuse_writeback_range(inode_out, pos_out, pos_out + len - 1);
+	if (err)
+		goto out;
 
 	if (is_unstable)
 		set_bit(FUSE_I_SIZE_UNSTABLE, &fi_out->state);