In a future patch, a read lock on drm_device.master_rwsem is held in the ioctl handler before the check for ioctl permissions. However, this inverts the lock hierarchy of drm_global_mutex --> master_rwsem.
To avoid this, we do some prep work to grab the drm_global_mutex before checking for ioctl permissions.
Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com Reviewed-by: Daniel Vetter daniel.vetter@ffwll.ch --- drivers/gpu/drm/drm_ioctl.c | 21 ++++++++++++--------- 1 file changed, 12 insertions(+), 9 deletions(-)
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index d25713b09b80..59c5aa850dd5 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -767,24 +767,27 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata, { struct drm_file *file_priv = file->private_data; struct drm_device *dev = file_priv->minor->dev; + bool locked_ioctl; int retcode;
if (drm_dev_is_unplugged(dev)) return -ENODEV;
+ /* Enforce sane locking for modern driver ioctls. */ + locked_ioctl = (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)) && + !(flags & DRM_UNLOCKED)); + if (locked_ioctl) + mutex_lock(&drm_global_mutex); + retcode = drm_ioctl_permit(flags, file_priv); if (unlikely(retcode)) - return retcode; + goto out;
- /* Enforce sane locking for modern driver ioctls. */ - if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) || - (flags & DRM_UNLOCKED)) - retcode = func(dev, kdata, file_priv); - else { - mutex_lock(&drm_global_mutex); - retcode = func(dev, kdata, file_priv); + retcode = func(dev, kdata, file_priv); + +out: + if (locked_ioctl) mutex_unlock(&drm_global_mutex); - } return retcode; } EXPORT_SYMBOL(drm_ioctl_kernel);