Bug#741464: grub-pc-bin: hangs after displaying boot menu

[Bernhard Übelacker]

Hello,
I tried if I could reproduce this issue.
(In my setup there is a tftp delivering grub installed by grub-mknetdir)

I could not get it to hang by "terminal_input at_keyboard".
But similar to what Jeroen Dekkers described I was not able anymore to
enter sane text with the keyboard. It feels like only every ~10th key
appears in grub.
(In virtualbox, qemu and on a real machine, with grub from testing
and/or a build from upstream git.)

I could track it down to calls into the PXE stack.
By avoiding these calls normal keyboard input is then still possible
when having at_keyboard loaded. (Unfortunately being then not able to
load anything via network).

By using a test function which does only the protected to real mode
switch and back without the actual PXE call, I assume the problem is
only with the mode switch itself - somehow resetting keyboard states.

------------

Attached patch (against upstream) should help in debugging the problem:
- if environment no_nic_poll is set to 1, avoid the problematic PXE call
- if environment no_nic_poll is set to 1 make only the switch from
  protected mode to real and back (and avoids the problematic PXE call)

That way the keyboard input stays fluid when using this sequence:
  set no_nic_poll=1
  terminal_input at_keyboard

When you now unset the environment the keyboard reacts broken again:
  unset no_nic_poll

(Booting would still be possible if the environment is reset just before
downloading any files)

------------

Unfortunately I was not able to reproduce it on a plain from harddisk
loaded grub.

That leaves a couple of questions open:
- have the submitter and commenter also a setup involving PXE?
- or do we have 2 or 3 different problems?

Kind regards,
Bernhard
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