"Variable $foo will not stay shared" Warning/Error in Perl While Calling Subroutine

Update3: If you like this posting please don't upvote me but upvote the genius answer by DVK below.

I have the following subroutines:

 use warnings;
#Input
 my @pairs = (
    "fred bill",
    "hello bye",
    "hello fred",
    "foo bar",
    "fred foo");

#calling the subroutine
my @ccomp = connected_component(@pairs);

use Data::Dumper;
print Dumper \@ccomp;

sub connected_component {

    my  @arr    = @_;
    my %links;

    foreach my $arrm (  @arr ) {
        my ($x,$y) = split(/\s+/,$arrm);;
        $links{$x}{$y} = $links{$y}{$x} = 1;

    }

    my %marked;  # nodes we have already visited
    my @stack;

    my @all_ccomp;

    for my $node (sort keys %links) {
        next if exists $marked{$node};
        @stack = ();
        connected($node);
        print "@stack\n";
        push @all_ccomp, [@stack];
    }

    sub connected {
        no warnings 'recursion';
        my $node = shift;
        return if exists $marked{$node};  # Line 43
        $marked{$node} = 1;
        push @stack, $node;   # Line 45
        my $children = $links{$node};  # Line 46
        connected($_) for keys %$children;
    }


    return @all_ccomp;
}

But why it gives this message:

Variable "%marked" will not stay shared at mycode.pl line 43.
Variable "@stack" will not stay shared at mycode.pl line 45.
Variable "%links" will not stay shared at mycode.pl line 46.

Is it harmful? Error? How can fix my code so that it get rid of that message?

Update1: I update the code that runs as is with the actuall error message

Update2: I tried to modify using sub as DVK suggested. And it WORKED!

use warnings;
#Input
 my @pairs = (
    "fred bill",
    "hello bye",
    "hello fred",
    "foo bar",
    "fred foo");

#calling the subroutine
my @ccomp = connected_component(@pairs);

use Data::Dumper;
print Dumper \@ccomp;

sub