[PATCH] xfree86: belately init RandR12 if xinerama fails. (#24627)

[Peter Hutterer]

On Tue, Dec 08, 2009 at 05:24:06PM -0800, Aaron Plattner wrote:
> On Tue, Dec 08, 2009 at 03:52:27PM -0800, Peter Hutterer wrote:
> > Xorg +xinerama crashes immediately due to whacky dependency between Xinerama
> > and RandR12. The latter doesn't initialize if Xinerama is enabled, but if
> > only one screen is found, Xinerama is disabled again and RandR12 tries to
> > access data it never initialized.
> > 
> > Dependency chain is:
> > - ProcessCommandLine sets noPanoramiXExtension to FALSE
> > - xf86RandR12Init() is a noop
> > - PanoramiXExtensionInit sets noPanoramiXExtension to TRUE
> > - xf86RandR12CreateScreenResources tries to use the devPrivates key it never
> >   initialized.
> > 
> > This hack checks if the key was initialized if noPanoramiXExtension is TRUE.
> > If not, re-initialize RandR12, this time for reals.
> > 
> > X.Org Bug 24627 <http://bugs.freedesktop.org/show_bug.cgi?id=24627>
> > 
> > Signed-off-by: Peter Hutterer <peter.hutterer at who-t.net>
> > ---
> > 
> > Don't know if there are any side-effects of doing this.
> > 
> >  hw/xfree86/modes/xf86RandR12.c |    2 ++
> >  1 files changed, 2 insertions(+), 0 deletions(-)
> > 
> > diff --git a/hw/xfree86/modes/xf86RandR12.c b/hw/xfree86/modes/xf86RandR12.c
> > index 6ea9d26..dd80ee0 100644
> > --- a/hw/xfree86/modes/xf86RandR12.c
> > +++ b/hw/xfree86/modes/xf86RandR12.c
> > @@ -767,6 +767,8 @@ xf86RandR12CreateScreenResources (ScreenPtr pScreen)
> >      /* XXX disable RandR when using Xinerama */
> >      if (!noPanoramiXExtension)
> >  	return TRUE;
> > +    else if (!xf86RandR12Key)
> > +        xf86RandR12Init(pScreen);
> 
> This makes me nervous because it starts calling a big chain of
> ScreenInit-style functions at CreateScreenResources time.  I can't find any
> concrete examples of things that would fail, but it perturbs the init order
> pretty drastically, but only in obscure Xinerama cases.  Would it be
> acceptable to just bail out without doing anything if (!xf86RandR12Key)?

that'd be the following patch then which - afaict - works too. Though the
same predicament stands, I don't know if there are any side-effects. Keith,
any comments?