From 88f0787f93f097a125a0aa156eb9a5628adfc2c2 Mon Sep 17 00:00:00 2001
From: Alex Goins <agoins@nvidia.com>
Date: Thu, 12 Dec 2019 20:18:53 -0600
Subject: [PATCH xserver] modesetting: Fix msSharePixmapBacking Segfault
 Regression
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Commit cb1b1e184 modified msSharePixmapBacking() to derive modesettingPtr from
the 'screen' argument. Unfortunately, the name of the argument is misleading --
the screen is the slave screen. If the master is modesetting,
and the slave is not modesetting, it will segfault.

To fix the problem, this change derives modesettingPtr from
ppix->drawable.pScreen. This method is already used when calling
ms->glamor.shareable_fd_from_pixmap() later in the function.

To avoid future issues, this change also renames the 'screen' argument to
'slave'.

Signed-off-by: Alex Goins <agoins@nvidia.com>
Reviewed-by: Michel Dänzer <mdaenzer@redhat.com>
(cherry picked from commit 456dff1bf890459840718339279dcb84d36531eb)
---
 hw/xfree86/drivers/modesetting/driver.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/hw/xfree86/drivers/modesetting/driver.c b/hw/xfree86/drivers/modesetting/driver.c
index ce8bac9f5..0817fa470 100644
--- a/hw/xfree86/drivers/modesetting/driver.c
+++ b/hw/xfree86/drivers/modesetting/driver.c
@@ -1454,10 +1454,11 @@ CreateScreenResources(ScreenPtr pScreen)
 }
 
 static Bool
-msSharePixmapBacking(PixmapPtr ppix, ScreenPtr screen, void **handle)
+msSharePixmapBacking(PixmapPtr ppix, ScreenPtr slave, void **handle)
 {
 #ifdef GLAMOR_HAS_GBM
-    modesettingPtr ms = modesettingPTR(xf86ScreenToScrn(screen));
+    modesettingPtr ms =
+        modesettingPTR(xf86ScreenToScrn(ppix->drawable.pScreen));
     int ret;
     CARD16 stride;
     CARD32 size;
-- 
2.34.1