drm/vkms: No need for ->pages_lock in crc work anymore

We're now guaranteed to no longer race against prepare_fb/cleanup_fb,
which means we can access ->vaddr without having to hold a lock.

Before the previous patches it was fairly easy to observe the cursor
->vaddr being invalid, but that's now gone, so we can upgrade to a
full WARN_ON.

Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606222751.32567-11-daniel.vetter@ffwll.ch

drivers/gpu/drm/vkms/vkms_crc.c

@@ -97,16 +97,10 @@ static void compose_cursor(struct vkms_crc_data *cursor_crc,
 	cursor_obj = drm_gem_fb_get_obj(&cursor_crc->fb, 0);
 	cursor_vkms_obj = drm_gem_to_vkms_gem(cursor_obj);
 
-	mutex_lock(&cursor_vkms_obj->pages_lock);
-	if (!cursor_vkms_obj->vaddr) {
-		DRM_WARN("cursor plane vaddr is NULL");
-		goto out;
-	}
+	if (WARN_ON(!cursor_vkms_obj->vaddr))
+		return;
 
 	blend(vaddr_out, cursor_vkms_obj->vaddr, primary_crc, cursor_crc);
-
-out:
-	mutex_unlock(&cursor_vkms_obj->pages_lock);
 }
 
 static uint32_t _vkms_get_crc(struct vkms_crc_data *primary_crc,
@@ -123,15 +117,12 @@ static uint32_t _vkms_get_crc(struct vkms_crc_data *primary_crc,
 		return 0;
 	}
 
-	mutex_lock(&vkms_obj->pages_lock);
 	if (WARN_ON(!vkms_obj->vaddr)) {
-		mutex_unlock(&vkms_obj->pages_lock);
 		kfree(vaddr_out);
 		return crc;
 	}
 
 	memcpy(vaddr_out, vkms_obj->vaddr, vkms_obj->gem.size);
-	mutex_unlock(&vkms_obj->pages_lock);
 
 	if (cursor_crc)
 		compose_cursor(cursor_crc, primary_crc, vaddr_out);