[Bug 1711358] Re: 20170817 - ISO hangs on boot on qemu with splash screen enabled and qxl graphics driver

[Stefan Bader]

So I think I can now at least explain the weirdness. Booting from the
ISO as well as the first boot in OEM mode seem to be in a way where grub
does not use graphics mode and hands that off to a vt. In that case,
when the kernels starts there will be no VESA framebuffer which later
gets switched over to qxl framebuffer.

So what I think broke is the init of the framebuffer drawing context.
Which potentially is not needed when it is switched over from VESA to
qxl. As soon as there was one successful boot in OEM mode, it looks like
graphics handoff is used. So after that both 4.12 and 4.14 (and likely
4.13 as well) will successfully boot as well.

One way I was able to make this work immediately was to interrupt the
boot and replace $vt_handoff by vt.handoff=7 (or =1). And then boot on
with that setting. In the crashed boots this was not set at all.

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Title:
  20170817 - ISO hangs on boot on qemu with splash screen enabled and
  qxl graphics driver

Status in linux package in Ubuntu:
  Confirmed
Status in plymouth package in Ubuntu:
  Confirmed
Status in ubiquity package in Ubuntu:
  Confirmed

Bug description:
  Test Case
  1. Boot artful desktop 20170817 under qemu with qxl
  2. Wait until ubiquity-dm is displayed

  Expected result
  It boots

  Actual result
  It hangs on the splash screen and the dots below the Ubuntu logo are not blinking. If the option 'splash' is removed from the boot command line it boots successfully.

  It also boots successfully with -vga std but in this case the splash
  screen is in text mode not graphical unlike with the qxl driver.

  - It started with kernel 4.12.
  - It is still happening with kernel 4.13.
  - It only happens when booting from an ISO and not on an installed system.
  - It works with cirrus/vga, but not qxl
  - It works if nosplash is set (or splash removed from the boot command line)
  - It works on Xenial but not on Artful

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