[RFC] Fix attempt for Mesa + X-Server 1.20 + modesetting-ddx hangs on KDE5.

[Adam Jackson]

On Fri, 2018-05-04 at 15:45 +0200, Mario Kleiner wrote:

> The real problem, if i understand it correctly, is the way the life-time
> of dri3_drawables and loader_dri3_drawables is managed atm. by Mesa's
> bindContext() functions. Whenever glXMakeCurrent() etc. are called to
> assign new/different GLXDrawables to the same context (ie. one context
> reused for drawing into many different drawables, as opposed to using
> one dedicated context for each drawable), we destroy the underlying
> DRIDrawables/dri3_drawables_loader_dri3_drawables and they lose all
> state wrt. pending bufferswaps, msc, sbc, ust.

That's utterly, utterly, utterly broken.

> Therefore one of these patches is either a good enough fix for the KDE
> hang problems atm. or a diagnosis of the problem as a starting point for
> brighter people to deal with the root cause ;-)

I'll see what I can come up with. I'm not sure there's a great fix for
this that doesn't involve a few more roundtrips at MakeCurrent time,
since we can lose drawables asynchronously, but such is life.

- ajax