I did a fresh install of Ubuntu 16.04. I am facing shutdown issues often.
It hangs in a terminal with the message (sometimes shutdown works):
soft lockup, cpu#4 struck for 22s
I installed Ubuntu alongside Windows 10 with secure login turned off (as it prompted to turn off secure login to install third party drivers).
(Laptop model is Dell Inspiron 7550)
Best Answer
I have Dell i7559 with i7-6700HQ and GTX 960M.
After a fresh install (boot directly to the installer with nomodeset, update all packages before logging in, # dpkg-reconfigure compiz), I got this cpu lockup issue.
Then I installed Nvidia driver 364.19 from https://launchpad.net/~graphics-drivers/+archive/ubuntu/ppa and everything (shutdown, reboot and suspend) works fine now.
Hope this helps.