sna: Do not enlarge the read back region if there is already CPU damage

We enlarge the read back into to minimise the number of times we have to
migrate pixmap data. However, if we then enlarge the read so that it
overwrites CPU dirty data, then we can introduce corruption.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

1 files changed, 5 insertions, 1 deletions

diff --git a/src/sna/sna_accel.c b/src/sna/sna_accel.c
index 1663fe3c..5d96ac57 100644
--- a/src/sna/sna_accel.c
+++ b/src/sna/sna_accel.c
@@ -2451,7 +2451,11 @@ sna_drawable_move_region_to_cpu(DrawablePtr drawable,
 			if (flags & MOVE_WRITE) {
 				int n = RegionNumRects(region), i;
 				BoxPtr boxes = RegionRects(region);
-				BoxPtr blocks = malloc(sizeof(BoxRec) * RegionNumRects(region));
+				BoxPtr blocks;
+
+				blocks = NULL;
+				if (priv->cpu_damage == NULL)
+					blocks = malloc(sizeof(BoxRec) * RegionNumRects(region));
 				if (blocks) {
 					for (i = 0; i < n; i++) {
 						blocks[i].x1 = boxes[i].x1 & ~31;