Redirect logged in users at instance of login

add_filter( 'login_redirect', 'home_url' );

sORRY This didnt work I get 404 error after login and 404 after log out

Of course that woudln’t work. Try this:

function login_redirect_filter() {
	return home_url();
}
add_filter( 'login_redirect', 'login_redirect_filter' );

I would like to redirect to the referring page, ie the page the user was on when he clicked login button.