WP Edit post page with WP_Query problem

// --> In functions.php

// Build Arrays

$artistList =  array();
$genresList = array();

add_action('init', 'getArtists');
add_action('init', 'getGenres');

function getArtists()
{
    global $artistList;
    $loop = new WP_Query( array( 'post_type' => 'artists' ) );
    while ( $loop->have_posts() ) : $loop->the_post();
    array_push($artistList, get_the_title());
    endwhile;
}


function getGenres()
{
    global $genresList;
    $terms = get_terms('genres', array( 'hide_empty' => 0));
    $count = count($terms);
    if ( $count > 0 ){
        foreach ( $terms as $term ) {
            array_push($genresList, $term->name);
        }
    }
}

// --> In custom plugin file

add_action( 'add_meta_boxes', 'tracks_meta_box_add' );
add_action( 'save_post', 'tracks_meta_box_save' );

function tracks_meta_box_add()
{
    add_meta_box( 'tracks-artist-mb', 'Artist', 'initTracksArtistMb', 'tracks', 'normal', 'high' );
    add_meta_box( 'tracks-genre-mb', 'Genre', 'initTracksGenreMb', 'tracks', 'normal', 'high' );
    add_meta_box( 'tracks-position-mb', 'Chart Position', 'initTracksPositionMb', 'tracks', 'normal', 'high' );
    add_meta_box( 'tracks-vimeoLink-mb', 'Vimeo Link', 'initTracksVimeoMb', 'tracks', 'normal', 'high' );
    add_meta_box( 'tracks-youtubeLink-mb', 'YouTube Link', 'initTracksYoutubeMb', 'tracks', 'normal', 'high' );

}

function initTracksArtistMb($post)
{
    global $artistList;
    $values = get_post_custom( $post->ID );
    $selected = isset( $values['track_artist'] ) ? esc_attr( $values['track_artist'][0] ) : '';
    //wp_nonce_field( 'artist_nonce', 'meta_box_nonce' );

    echo '<p><em>&bull; Choose an existing artist</em></p>';
    echo '<label for="track_artist"></label>';
    echo '<select name="track_artist" id="track_artist">';
    echo '<option>Select an Artist...</option>';
    foreach ($artistList as $artist)
    {
        ?>
        <option value="<?php echo $artist; ?>" <?php selected($selected, $artist); ?>><?php echo $artist; ?></option>
        <?php
    }
    echo '</select>';
    echo '<p><em>&bull; Or add a new artist</em></p>';
    echo '<p><a href="#">Add new Artist</a></p>';
}

function initTracksGenreMb($post)
{
    //wp_nonce_field( 'genre_nonce', 'meta_box_nonce' );
    global $genresList;
    $values = get_post_custom( $post->ID );
    $check = isset( $values['track_genres'] ) ? esc_attr( $values['track_genres'] ) : '';
    $count = sizeof($genresList);
    echo '<p><em>&bull; Choose from existing genres</em></p>';
    echo '<div id="genre-check-list" class="sl-node">';
    for($i=0; $i<$count; $i++)
    {
        echo '<div class="genre-check-item sl-node">';
        echo '<input type="checkbox" id="track_genres" name="track_genres" ', checked( $check, 'on' ), '/>';
        echo '<label for="', $genresList[$i], '">', $genresList[$i], '</label>';
        echo '</div>';
    }
    echo '</div>';
    echo '<p><em>&bull; Or add a new genre</em></p>';
    echo '<p><a href="#">Add New Genre</a></p>';
}

function tracks_meta_box_save($post_id)
{
    // Save the data
}