[V2] modesetting: Fix X crash in ms_dirty_update()

[Jim Qu]

On some Intel iGPU + AMD dGPU platform, when connect extern display
from dGPU, X will crash, show the log like:

randr: falling back to unsynchronized pixmap sharing
(EE)
(EE) Backtrace:
(EE) 0: /usr/lib/xorg/Xorg (xorg_backtrace+0x4e)
(EE) 1: /usr/lib/xorg/Xorg (0x55cb0151a000+0x1b5ce9)
(EE) 2: /lib/x86_64-linux-gnu/libpthread.so.0 (0x7f1587a1d000+0x11390)
(EE)
(EE) Segmentation fault at address 0x0
(EE)

There is NULL pointer accessing on ent->slave_dst->drawable.pScreen->
SharedPixmapNotifyDamage.

On the platform, since the dGPU is GPU device, so that the iGPU is
output master device. SharedPixmapNotifyDamage() should be called when
current device is output master.

Change-Id: I8fa6922a4f75b5e068970fc4d362f778052379f2
Signed-off-by: Jim Qu <Jim.Qu at amd.com>
---
 hw/xfree86/drivers/modesetting/driver.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/hw/xfree86/drivers/modesetting/driver.c b/hw/xfree86/drivers/modesetting/driver.c
index 9362370..37fafb1 100644
--- a/hw/xfree86/drivers/modesetting/driver.c
+++ b/hw/xfree86/drivers/modesetting/driver.c
@@ -640,19 +640,21 @@ ms_dirty_update(ScreenPtr screen, int *timeout)
     xorg_list_for_each_entry(ent, &screen->pixmap_dirty_list, ent) {
         region = DamageRegion(ent->damage);
         if (RegionNotEmpty(region)) {
-            msPixmapPrivPtr ppriv =
-                msGetPixmapPriv(&ms->drmmode, ent->slave_dst);
+            if (!screen->isGPU) {
+                    msPixmapPrivPtr ppriv =
+                        msGetPixmapPriv(&ms->drmmode, ent->slave_dst->master_pixmap);
 
-            if (ppriv->notify_on_damage) {
-                ppriv->notify_on_damage = FALSE;
+                    if (ppriv->notify_on_damage) {
+                        ppriv->notify_on_damage = FALSE;
 
-                ent->slave_dst->drawable.pScreen->
-                    SharedPixmapNotifyDamage(ent->slave_dst);
-            }
+                        ent->slave_dst->drawable.pScreen->
+                            SharedPixmapNotifyDamage(ent->slave_dst);
+                    }
 
-            /* Requested manual updating */
-            if (ppriv->defer_dirty_update)
-                continue;
+                    /* Requested manual updating */
+                    if (ppriv->defer_dirty_update)
+                        continue;
+            }
 
             redisplay_dirty(screen, ent, timeout);
             DamageEmpty(ent->damage);
-- 
2.7.4