[PATCH] drm: Don't compute obj counts expensively in get_resources

[Daniel Vetter]

Looping when we keep track of this is silly. Only thing we have to
be careful is with sampling the connector count. To avoid inconsisten
results due to gcc re-computing this, use READ_ONCE.

And to avoid surprising userspace, make sure we don't copy more
connectors than planned, and report the actual number of connectors
copied. That way any racing hot-add/remove will be handled.

v2: Actually try to not blow up, somehow I lost the hunk that checks
we don't copy too much. Noticed by Chris.

Cc: Chris Wilson <chris at chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/drm_crtc.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_crtc.c b/drivers/gpu/drm/drm_crtc.c
index 28c109ff7330..59c5261a309c 100644
--- a/drivers/gpu/drm/drm_crtc.c
+++ b/drivers/gpu/drm/drm_crtc.c
@@ -1842,10 +1842,10 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
 	struct drm_crtc *crtc;
 	struct drm_encoder *encoder;
 	int ret = 0;
-	int connector_count = 0;
-	int crtc_count = 0;
+	int connector_count = READ_ONCE(dev->mode_config.num_connector);
+	int crtc_count = dev->mode_config.num_crtc;
 	int fb_count = 0;
-	int encoder_count = 0;
+	int encoder_count = dev->mode_config.num_encoder;
 	int copied = 0;
 	uint32_t __user *fb_id;
 	uint32_t __user *crtc_id;
@@ -1883,15 +1883,6 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
 	/* mode_config.mutex protects the connector list against e.g. DP MST
 	 * connector hot-adding. CRTC/Plane lists are invariant. */
 	mutex_lock(&dev->mode_config.mutex);
-	drm_for_each_crtc(crtc, dev)
-		crtc_count++;
-
-	drm_for_each_connector(connector, dev)
-		connector_count++;
-
-	drm_for_each_encoder(encoder, dev)
-		encoder_count++;
-
 	card_res->max_height = dev->mode_config.max_height;
 	card_res->min_height = dev->mode_config.min_height;
 	card_res->max_width = dev->mode_config.max_width;
@@ -1931,6 +1922,9 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
 		copied = 0;
 		connector_id = (uint32_t __user *)(unsigned long)card_res->connector_id_ptr;
 		drm_for_each_connector(connector, dev) {
+			if (copied >= connector_count)
+				break;
+
 			if (put_user(connector->base.id,
 				     connector_id + copied)) {
 				ret = -EFAULT;
@@ -1938,6 +1932,7 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
 			}
 			copied++;
 		}
+		connector_count = copied;
 	}
 	card_res->count_connectors = connector_count;
 
-- 
2.8.1