Xwayland fatal error when Wayland output disappears

[Pekka Paalanen]

On Thu, 26 Oct 2017 15:40:13 +0200
Michael Thayer <michael.thayer at oracle.com> wrote:

> Hello,
> 
> Reporting this here in case it is of interest.  I have been debugging
> regular desktop crashes on my new Ubuntu 17.10 systems.  One of them
> seems to happen when Xwayland FatalError-s out because a Wayland output
> disappears.  I have only investigated this so far, but hopefully this
> will be helpful to someone who knows it better: the error is
> "wl_registry at 2: error 0: invalid global wl_output (28)", which seems to
> be posted by wl_registry_bind in wayland-server.c, and get picked up in
> xwl_log_handler in Xwayland.  Xwayland exiting in turn causes GNOME
> Shell to panic.

Hi,

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.


Thanks,
pq
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