If drm_dev_register() fails after registering a minor (e.g. render minor
registered, primary minor fails), userspace could have opened the first
minor and entered a drm_dev_enter() critical section. Since the
unplugged flag was never set, the ioctl proceeds while the error path
tears down device resources.
Fix this by introducing drm_dev_synchronize_unplug(), which sets the
unplugged flag and waits for the SRCU barrier, ensuring all in-flight
drm_dev_enter() critical sections complete before cleanup proceeds; call
it on the error path of drm_dev_register().
Fixes: bee330f3d672 ("drm: Use srcu to protect drm_device.unplugged")
Cc: [email protected]
Reported-by: [email protected]
Closes: https://lore.kernel.org/all/[email protected]/
Signed-off-by: Danilo Krummrich <[email protected]>
---
drivers/gpu/drm/drm_drv.c | 34 +++++++++++++++++++++++++---------
1 file changed, 25 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
index 675675480da4..e890052061f3 100644
--- a/drivers/gpu/drm/drm_drv.c
+++ b/drivers/gpu/drm/drm_drv.c
@@ -473,6 +473,22 @@ void drm_dev_exit(int idx)
}
EXPORT_SYMBOL(drm_dev_exit);
+/*
+ * Mark the device as unplugged and wait for any in-flight drm_dev_enter()
+ * critical sections to complete.
+ */
+static void drm_dev_synchronize_unplug(struct drm_device *dev)
+{
+ /*
+ * After synchronizing any critical read section is guaranteed to see
+ * the new value of ->unplugged, and any critical section which might
+ * still have seen the old value of ->unplugged is guaranteed to have
+ * finished.
+ */
+ dev->unplugged = true;
+ synchronize_srcu(&drm_unplug_srcu);
+}
+
/**
* drm_dev_unplug - unplug a DRM device
* @dev: DRM device
@@ -485,15 +501,7 @@ EXPORT_SYMBOL(drm_dev_exit);
*/
void drm_dev_unplug(struct drm_device *dev)
{
- /*
- * After synchronizing any critical read section is guaranteed to see
- * the new value of ->unplugged, and any critical section which might
- * still have seen the old value of ->unplugged is guaranteed to have
- * finished.
- */
- dev->unplugged = true;
- synchronize_srcu(&drm_unplug_srcu);
-
+ drm_dev_synchronize_unplug(dev);
drm_dev_unregister(dev);
/* Clear all CPU mappings pointing to this device */
@@ -1091,6 +1099,7 @@ int drm_dev_register(struct drm_device *dev, unsigned
long flags)
goto err_minors;
dev->registered = true;
+ dev->unplugged = false;
if (driver->load) {
ret = driver->load(dev, flags);
@@ -1118,6 +1127,13 @@ int drm_dev_register(struct drm_device *dev, unsigned
long flags)
if (dev->driver->unload)
dev->driver->unload(dev);
err_minors:
+ /*
+ * If a minor was registered before the failure, userspace could have
+ * opened it and entered a drm_dev_enter() critical section. Ensure all
+ * such sections complete before we clean up.
+ */
+ drm_dev_synchronize_unplug(dev);
+
remove_compat_control_link(dev);
drm_minor_unregister(dev, DRM_MINOR_ACCEL);
drm_minor_unregister(dev, DRM_MINOR_PRIMARY);
--
2.54.0
