[mutter] gpu/kms: Use correct DRM event context version

[Jonas Ådahl <jadahl src gnome org>]

commit 177d0c2d63679df771aead70ff5ecd6f6951b213
Author: Daniel Stone <daniels collabora com>
Date:   Wed Jan 2 15:44:52 2019 +0100

    gpu/kms: Use correct DRM event context version
    
    DRM_EVENT_CONTEXT_VERSION is the latest context version supported by
    whatever version of libdrm is present. Mutter was blindly asserting it
    supported whatever version that may be, even if it actually didn't.
    
    With libdrm 2.4.78, setting a higher context version than 2 will attempt
    to call the page_flip_handler2 vfunc if it was non-NULL, which being a
    random chunk of stack memory, it might well have been.
    
    Set the version as 2, which should be bumped only with the appropriate
    version checks.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=781034

 src/backends/native/meta-gpu-kms.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/src/backends/native/meta-gpu-kms.c b/src/backends/native/meta-gpu-kms.c
index 974f8f425..5b1ee107f 100644
--- a/src/backends/native/meta-gpu-kms.c
+++ b/src/backends/native/meta-gpu-kms.c
@@ -371,7 +371,7 @@ meta_gpu_kms_wait_for_flip (MetaGpuKms *gpu_kms,
     }
 
   memset (&evctx, 0, sizeof evctx);
-  evctx.version = DRM_EVENT_CONTEXT_VERSION;
+  evctx.version = 2;
   evctx.page_flip_handler = page_flip_handler;
 
   while (TRUE)