Xwayland fatal error when Wayland output disappears
Pekka Paalanen
ppaalanen at gmail.com
Fri Oct 27 08:39:28 UTC 2017
On Fri, 27 Oct 2017 09:54:39 +0200
Michael Thayer <michael.thayer at oracle.com> wrote:
> Hello Pekka,
>
> On 27.10.2017 08:01, Pekka Paalanen wrote:
> > On Thu, 26 Oct 2017 15:40:13 +0200 Michael Thayer
> > <michael.thayer at oracle.com> wrote:
> [ Discussion of a global Wayland object disappearing triggering a fatal
> error in xwl_log_handler in Xwayland.]
> >
> > there is a known race around Wayland globals. If the Wayland server
> > adds and removes a global in a very short time, it may succeed to
> > remove the global (wl_output) before all clients have processed the
> > add. If a client process an add after the server removed, you hit
> > exactly this fatal error.
> >
> > It's a design flaw in Wayland, gone unnoticed for years until it was
> > too late to fix properly.
> >
> > This issue is recorded: https://phabricator.freedesktop.org/T7722
> >
> > There is a suggested mitigation, but I am not aware of anyone
> > working on it.
>
> Trigger warning: a person who does not know the code base is about to
> make suggestions.
>
> I am wondering why Xwayland has to call FatalError in that log handler.
Because the Wayland connection is already dead and disconnected due to
the error it is reporting.
Thanks,
pq
> From my naive point of view, the race you mentioned is not a design
> flaw in Wayland but part of the real world that Wayland and its clients
> ought to deal with. Other than that call in the log handler, I see no
> reason why Xwayland should not just notice that the object has gone away
> again and get on with life.
>
> As I said, I do not know the code base well. But for the sake of the
> argument, and since it is not likely to make things worse, I will try
> removing that locally and see what happens.
>
> Regards and thanks.
> Michael
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