Process may be in “D” state. It is “uninterruptable sleep”, it usually means “io-wait”
You can’t trace them or kill them (reboot just kills ) as they are “uninterruptable”.
You observe app slowness or performance issues due to processes waiting stuck io.

 

You may observe iowait processes with command “ps auxwww “ in Linux.
Then below command is vital for iowai t troubleshooting as it logs full kernel stack trace to /var/log/messages.
 “echo w > /proc/sysrq-trigger”

 

We solved an Algo CCR application NFS4 hang problem on RHEL 7.4 server due to this troubleshooting method.

Solutions were applications of all below 3 articles.
 https://access.redhat.com/solutions/3164451
 https://access.redhat.com/solutions/1583803
 NFS share hangs on NFS clients when tcp_timestamps disabled (MOS Doc ID 2286691.1)