Run strace ls /var/www/ and see what it hangs on. It’s certainly hung on I/O — that’s what the D state in your ps output means (and since kill doesn’t help, it’s one of the uninterruptible I/O syscalls). Most hangs involve an NFS server that’s gone to god, but based on your df that isn’t the case here. A quick check of dmesg for anything related to filesystems or disks might be worthwhile, just in case.
