[PATCH 4/5] drm: Don't compute obj counts expensively in get_resources

Daniel Vetter daniel.vetter at ffwll.ch
Fri Dec 9 19:12:31 UTC 2016


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_mode_config.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/drm_mode_config.c b/drivers/gpu/drm/drm_mode_config.c
index 2735a5847ffa..64c2971478db 100644
--- a/drivers/gpu/drm/drm_mode_config.c
+++ b/drivers/gpu/drm/drm_mode_config.c
@@ -90,10 +90,10 @@ 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;
@@ -131,15 +131,6 @@ 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;
@@ -179,6 +170,9 @@ 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;
@@ -186,6 +180,7 @@ int drm_mode_getresources(struct drm_device *dev, void *data,
 			}
 			copied++;
 		}
+		connector_count = copied;
 	}
 	card_res->count_connectors = connector_count;
 
-- 
2.10.2



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