Hi,

I've been fiddling around with this for a while. Booting with init=/bin/bash 
allowed poweroff -f to work.
So I then booted into full userspace and started to rip modules out with rmmod.

It appears that the laptop has a Synopsys DesignWare controller embedded in it.
This makes the kernel load the dw_dmac_core and dw_dmac modules.
An rmmod of dw_dmac produces an instant lockup.
I think it is the same lockup happening at shutdown and reboot.
Blacklisting both modules makes shutdown and reboot work correctly for me.

I suspect that some sort of DMI based blacklist will be required in the kernel.
Exposing the hardware to user space probably isn't the best idea anyway.

Cheers,
Scott

** Changed in: linux (Ubuntu)
       Status: Incomplete => Confirmed

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https://bugs.launchpad.net/bugs/1319149

Title:
  [HP Pavilion 11-n038ca x360 PC] Boots very unreliably

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