The bug is in Perl itself, and seems to be fixed in 5.15.5.

The following code, which is the simplest I have found to trigger the problem, causes a segmentation fault for versions up to 5.14.2, but not in 5.15.5 or bleadperl:

#!/usr/bin/perl

use strict;
use warnings;

use Scalar::Util 'weaken';

# the number of iteration that causes a segmentation fault varies
# on my machine, 5.14.2 18700, 5.12.4 20147, blead 
# at these values, the bug shows up most of the time but not always

my $ITER= $ARGV[0] || 18700;

my $head= {};
my $tail= $head;

foreach (1..$ITER)
  { my $new_tail= { p => $tail };
    weaken( $new_tail->{p});
    $tail->{n}=  $new_tail;
    $tail= $new_tail;
  }

print "done\n";
[download]