documentclass[border=1cm]{standalone}

usepackage{tikz}
usetikzlibrary{decorations.markings}

begin{document}
begin{tikzpicture}

coordinate (A) at (0,0);
coordinate (B) at (1, 3);
coordinate (C) at (2, -1);
coordinate (D) at (3, 0.5);

draw plot [smooth] coordinates { (A) (B) (C) (D) };
path [
   postaction={decorate},
     decoration={
       markings,
       mark = at position {0.1dimexprpgfdecoratedpathlengthrelax} with {fill = red circle (0.5cm)}
  }
] plot [smooth] coordinates { (A) (B) (C) (D) };

end{tikzpicture}
end{document}

! Dimension too large.
<to be read again>
                   relax