Output of pstack for the process 1988(pid of the one of the child process that hanged)
pstack 1988

#1  0x000000317d8f0990 in PerlIOUnix_read () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#2  0x000000317d8f5055 in PerlIOBuf_fill () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#3  0x000000317d8ef8c8 in Perl_PerlIO_fill () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#4  0x000000317d8f4cbf in PerlIOBase_read () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#5  0x000000317d8f4dfb in PerlIO_getc () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#6  0x000000317d8a2a20 in Perl_sv_gets () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#7  0x000000317d88db93 in Perl_do_readline () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#8  0x000000317d88a33e in Perl_runops_standard () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#9  0x000000317d837e9c in perl_run () from /usr/lib64/perl5/5.8.8/x86_64-linux-thread-multi/CORE/libperl.so
#10 0x000000000040179c in main ()