Linux kernel allows access to some of /proc/<pid>/* entries where the
process <pid> is in the zombie state. To follow Linux behavior add
a new p_lockreap counter which is intended to hold process vmspace
from release in proc_reap(). Use new facility in pseudofs code to hold
process when needed if node has PFS_ZOMBIE flag set.
We discussed this a while ago, I did.
However, the kern.wait_dequeue_sigchld knob does not allow to get CLD_KILLED.
I see it's not easy to do. If you point me in the right direction, I'll try.