Comment 8 for bug 811823

> You're right that this is not atomic; however, I believe the worst-case
> scenario is that the kernel fs will be mounted twice at the same mount
> point, which should not cause significant problems. (I have seen this
> outcome in practice on my machine while testing.)

Hm, that's not the behavior that I see. If I try to mount rpc_pipefs twice, mount exits with an error on the second attempt.

root@satwelltest1:~# mount -t rpc_pipefs rpc_pipefs /var/lib/nfs/rpc_pipefs
root@satwelltest1:~# mount -t rpc_pipefs rpc_pipefs /var/lib/nfs/rpc_pipefs
mount: rpc_pipefs already mounted or /var/lib/nfs/rpc_pipefs busy
mount: according to mtab, rpc_pipefs is already mounted on /var/lib/nfs/rpc_pipefs
root@satwelltest1:~# echo $?
32