Bug#789118: Cannot unlock screen after upgrading GNOME if locked before upgrade

[Simon McVittie]

On Wed, 25 Jan 2017 at 12:52:13 +0000, Simon McVittie wrote:
> With that incompatibility out of the way, there's another one:
> 
>     Jan 25 12:28:31 host gdm-session-worker.really[11355]: pam_unix(gdm-password:auth): conversation failed
>     Jan 25 12:28:31 host gdm-session-worker.really[11355]: pam_unix(gdm-password:auth): auth could not identify password for [user]

I think this might be caused by gnome-shell raising an exception when
it fails to load an animation, with the traceback below, and the PAM
conversation not proceeding because gnome-shell is no longer talking
to the gdm-session-worker as a result of that exception.

>     Jan 25 12:28:14 host gnome-session[5143]: (gnome-shell:5342): Gjs-WARNING **: JS
>      ERROR: Exception in callback for signal: next: Error: can't convert this._frame
>      to an integer
>     Jan 25 12:28:14 host gnome-session[5143]: Animation<._showFrame at resource:///org/
>     gnome/shell/ui/animation.js:59
>     Jan 25 12:28:14 host gnome-session[5143]: wrapper at resource:///org/gnome/gjs/modules/lang.js:169
>     Jan 25 12:28:14 host gnome-session[5143]: Animation<.play at resource:///org/gnome/shell/ui/animation.js:34
>     Jan 25 12:28:14 host gnome-session[5143]: wrapper at resource:///org/gnome/gjs/modules/lang.js:169
>     Jan 25 12:28:14 host gnome-session[5143]: AuthPrompt<.setActorInDefaultButtonWell at resource:///org/gnome/shell/gdm/authPrompt.js:313
>     Jan 25 12:28:14 host gnome-session[5143]: wrapper at resource:///org/gnome/gjs/modules/lang.js:169
>     Jan 25 12:28:14 host gnome-session[5143]: AuthPrompt<.startSpinning at resource:///org/gnome/shell/gdm/authPrompt.js:329
>     Jan 25 12:28:14 host gnome-session[5143]: wrapper at resource:///org/gnome/gjs/modules/lang.js:169
>     Jan 25 12:28:14 host gnome-session[5143]: AuthPrompt<._init/<@resource:///org/gnome/shell/gdm/authPrompt.js:67
>     Jan 25 12:28:14 host gnome-session[5143]: _emit at resource:///org/gnome/gjs/modules/signals.js:124
>     Jan 25 12:28:14 host gnome-session[5143]: AuthPrompt<._initButtons/<@resource:///org/gnome/shell/gdm/authPrompt.js:191

That looks like https://bugzilla.redhat.com/show_bug.cgi?id=1350303
which is some sort of install-order issue, or possibly the existing
gnome-shell trying to use the old pixbuf loader cache that has been
invalidated in the meantime by upgrading.

There is a workaround for that bug in stretch's gnome-shell, added
by <https://bugzilla.gnome.org/show_bug.cgi?id=774805>;
but of course during a live upgrade we're still dealing with jessie's
gnome-shell, not stretch's, so we can't fix bugs.

    S