Bug#897975: [gdm3]

[Iain Lane]

Hi,

Sorry for the delay. Niels pointed me at this bug, which is suspiciously
similar to one we saw on Ubuntu around the same time ...

On Wed, Jun 13, 2018 at 01:43:18PM +0200, rastersoft wrote:
> After several tests, I started to suspect that the problem could be in the
> firmware loading: my hypothesis is that when I use my SSD hard disk, the
> loading is so fast that the graphic card is still not available when GDM
> tries to boot in Wayland mode, so it fails and tries again in X11 mode. At
> this moment it has ended loading the firmware as is available, so this mode
> succeeds, but without offering Wayland because that failed before. If I
> enter a session and exit, GDM is reloaded and this time the Wayland mode
> works because the graphics card's firmware is already loaded.
> 
> To test this I renamed /usr/sbin/gdm3 to /usr/sbin/gdm3_bin, and created a
> little script at /usr/sbin/gdm3 that waits 3 seconds before launching the
> true gdm3. With this quick and dirty hack everything works fine: GDM3 is
> always shown after booting, and I have Wayland available.
> 
> Of course, this is not a true solution: the system should wait until the
> graphics card is fully available before continuing loading, and not just
> "add a delay". But I think it proofs that there is some kind of race
> condition during boot.

Your theory is right - GDM is starting up before the DRM devices that it
needs are available, and it doesn't handle that very well. We have a
workaround in place in Ubuntu which seems to have fixed the bug.  There
is actually a logind boolean property "CanGraphical" for this, that was
introduced so display managers like GDM can wait before they start up.
But the branch to make GDM respect this property[0] isn't yet merged
because it is a bit unreliable so far.

So I cherry-picked the Ubuntu workaround to a branch on salsa. Would you
be able to try it please? (Test built but not tried it myself yet, so
sorry if there's some stupid mistake.)

  https://salsa.debian.org/gnome-team/gdm/commits/wip/gdm-wait-for-drm

I can't test this myself. Apparently none of my machines are capable of
tickling this bug. :(

Cheers,

-- 
Iain Lane                                  [ iain at orangesquash.org.uk ]
Debian Developer                                   [ laney at debian.org ]
Ubuntu Developer                                   [ laney at ubuntu.com ]

[0] https://gitlab.gnome.org/GNOME/gdm/merge_requests/37
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