[PATCH 2/3] drm/exynos: avoid race condition when adding a drm component

[Gustavo Padovan]

From: Gustavo Padovan <gustavo.padovan at collabora.co.uk>

exynos_drm_component_add() correctly checks if a component is present on
drm_component_list however it release the lock right after the check
and before we add the new component to the list. That just creates room
to add the same component more than once to the list.

The lock should be held for the whole journey while adding a new
component.

Signed-off-by: Gustavo Padovan <gustavo.padovan at collabora.co.uk>
---
 drivers/gpu/drm/exynos/exynos_drm_drv.c | 16 +++++-----------
 1 file changed, 5 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/exynos/exynos_drm_drv.c b/drivers/gpu/drm/exynos/exynos_drm_drv.c
index cb3ed9b..230573d 100644
--- a/drivers/gpu/drm/exynos/exynos_drm_drv.c
+++ b/drivers/gpu/drm/exynos/exynos_drm_drv.c
@@ -402,10 +402,8 @@ int exynos_drm_component_add(struct device *dev,
 			 * added already just return.
 			 */
 			if (cdev->dev_type_flag == (EXYNOS_DEVICE_TYPE_CRTC |
-						EXYNOS_DEVICE_TYPE_CONNECTOR)) {
-				mutex_unlock(&drm_component_lock);
-				return 0;
-			}
+						EXYNOS_DEVICE_TYPE_CONNECTOR))
+				goto unlock;
 
 			if (dev_type == EXYNOS_DEVICE_TYPE_CRTC) {
 				cdev->crtc_dev = dev;
@@ -417,14 +415,11 @@ int exynos_drm_component_add(struct device *dev,
 				cdev->dev_type_flag |= dev_type;
 			}
 
-			mutex_unlock(&drm_component_lock);
-			return 0;
+			goto unlock;
 		}
 	}
 
-	mutex_unlock(&drm_component_lock);
-
-	cdev = kzalloc(sizeof(*cdev), GFP_KERNEL);
+	cdev = kzalloc(sizeof(*cdev), GFP_ATOMIC);
 	if (!cdev)
 		return -ENOMEM;
 
@@ -436,10 +431,9 @@ int exynos_drm_component_add(struct device *dev,
 	cdev->out_type = out_type;
 	cdev->dev_type_flag = dev_type;
 
-	mutex_lock(&drm_component_lock);
 	list_add_tail(&cdev->list, &drm_component_list);
+unlock:
 	mutex_unlock(&drm_component_lock);
-
 	return 0;
 }
 
-- 
1.9.3