EXA: ExaDoPrepareAccess return value fixes.

Only return TRUE if the GPU copy is being accessed, and preserve the return
value on repeated / nested calls for the same pixmap.

exaPrepareAccessReg_mixed could get inconsistent return values e.g. when the
same pixmap is both the destination and source of an operation, potentially
resulting in a crash.

Signed-off-by: Michel Dänzer <daenzer@vmware.com>
Acked-by: Maarten Maathuis <madman2003@gmail.com>
Signed-off-by: Keith Packard <keithp@keithp.com>

2 files changed, 20 insertions, 11 deletions

diff --git a/exa/exa.c b/exa/exa.c
index 023288c12..b3c5bfffe 100644
--- a/exa/exa.c
+++ b/exa/exa.c
@@ -283,7 +283,7 @@ exaGetOffscreenPixmap (DrawablePtr pDrawable, int *xp, int *yp)
 }
 
 /**
- * Returns TRUE if pixmap can be accessed offscreen.
+ * Returns TRUE if the pixmap GPU copy is being accessed.
  */
 Bool
 ExaDoPrepareAccess(PixmapPtr pPixmap, int index)
@@ -291,7 +291,7 @@ ExaDoPrepareAccess(PixmapPtr pPixmap, int index)
     ScreenPtr pScreen = pPixmap->drawable.pScreen;
     ExaScreenPriv (pScreen);
     ExaPixmapPriv(pPixmap);
-    Bool has_gpu_copy;
+    Bool has_gpu_copy, ret;
     int i;
 
     if (!(pExaScr->info->flags & EXA_OFFSCREEN_PIXMAPS))
@@ -304,7 +304,7 @@ ExaDoPrepareAccess(PixmapPtr pPixmap, int index)
     for (i = 0; i < EXA_NUM_PREPARE_INDICES; i++) {
 	if (pExaScr->access[i].pixmap == pPixmap) {
 	    pExaScr->access[i].count++;
-	    return TRUE;
+	    return pExaScr->access[i].retval;
 	}
     }
 
@@ -323,29 +323,33 @@ ExaDoPrepareAccess(PixmapPtr pPixmap, int index)
 
     has_gpu_copy = exaPixmapHasGpuCopy(pPixmap);
 
-    if (has_gpu_copy && pExaPixmap->fb_ptr)
+    if (has_gpu_copy && pExaPixmap->fb_ptr) {
 	pPixmap->devPrivate.ptr = pExaPixmap->fb_ptr;
-    else
+	ret = TRUE;
+    } else {
 	pPixmap->devPrivate.ptr = pExaPixmap->sys_ptr;
+	ret = FALSE;
+    }
 
     /* Store so we can handle repeated / nested calls. */
     pExaScr->access[index].pixmap = pPixmap;
     pExaScr->access[index].count = 1;
 
     if (!has_gpu_copy)
-	return FALSE;
+	goto out;
 
     exaWaitSync (pScreen);
 
     if (pExaScr->info->PrepareAccess == NULL)
-	return TRUE;
+	goto out;
 
     if (index >= EXA_PREPARE_AUX_DEST &&
 	!(pExaScr->info->flags & EXA_SUPPORTS_PREPARE_AUX)) {
 	if (pExaPixmap->score == EXA_PIXMAP_SCORE_PINNED)
 	    FatalError("Unsupported AUX indices used on a pinned pixmap.\n");
 	exaMoveOutPixmap (pPixmap);
-	return FALSE;
+	ret = FALSE;
+	goto out;
     }
 
     if (!(*pExaScr->info->PrepareAccess) (pPixmap, index)) {
@@ -353,11 +357,15 @@ ExaDoPrepareAccess(PixmapPtr pPixmap, int index)
 	    !(pExaScr->info->flags & EXA_MIXED_PIXMAPS))
 	    FatalError("Driver failed PrepareAccess on a pinned pixmap.\n");
 	exaMoveOutPixmap (pPixmap);
-
-	return FALSE;
+	ret = FALSE;
+	goto out;
     }
 
-    return TRUE;
+    ret = TRUE;
+
+out:
+    pExaScr->access[index].retval = ret;
+    return ret;
 }
 
 /**
diff --git a/exa/exa_priv.h b/exa/exa_priv.h
index 69c0d241d..085235524 100644
--- a/exa/exa_priv.h
+++ b/exa/exa_priv.h
@@ -194,6 +194,7 @@ typedef struct {
     struct {
 	PixmapPtr pixmap;
 	int count;
+	Bool retval;
     } access[EXA_NUM_PREPARE_INDICES];
 
     /* Holds information on fallbacks that cannot be relayed otherwise. */