urandom device created on LVM doesn't work, why?

We can create a new urandom device on a normal directory (test_urandom in below example), and it works as expected. E.g.

test_urandom$ sudo mknod -m 0444 ./urandom c 1 9
test_urandom$ ls -l
total 0
cr--r--r-- 1 root root 1, 9 Jun  9 09:06 urandom
test_urandom$ head -c 10 ./urandom 
�׫O1�9�^

However, if the directory is in a LVM (Logical Volume Management) filesystem, it failed and system complained with permission denied.

test_urandom_lvm$ sudo mknod -m 0444 ./urandom c 1 9
test_urandom_lvm$ ls -l
total 0
cr--r--r-- 1 root root 1, 9 Jun  9 09:06 urandom
test_urandom_lvm$ head -c 10 ./urandom
head: cannot open ‘./urandom’ for reading: Permission denied

Is this a limitation of LVM? or there is other configuration needed to make it work?