On Thu, 10 Nov 2022 21:26:15 +0800
Zeng Heng <zengheng4@xxxxxxxxxx> wrote:
> There is warning reported by kobject lib in kobject_put():
>
> kobject: '(null)' (00000000be81a546): is not initialized, yet kobject_put() is being called.
> WARNING: CPU: 0 PID: 535 at lib/kobject.c:718 kobject_put+0x12c/0x180
> Call Trace:
> cdev_device_add
> __iio_device_register
> __devm_iio_device_register
> tmp117_probe
>
> If don't need to register chardev for most of IIO devices,
> we just register them with device_add() only, and use device_del()
> to unregister them.
>
> Otherwise, when device_add() fails in internal and calls kobject_put()
> in error handling path, it would report warning because the device
> never be registered as chardev and there is no release function for it.
>
> Fixes: 8ebaa3ff1e71 ("iio: core: register chardev only if needed")
> Signed-off-by: Zeng Heng <zengheng4@xxxxxxxxxx>
Interesting corner case. The cdev_device_add() call is fine with
!dev->devt which is what this code was taking advantage of. The exception
as you have highlighted is the error path of device_add().
So I think it should also cope with unwinding if device_add() fails
and not be calling cdev_del() Note that cdev_device_del() has the
appropriate guards to be safe whether or not (dev->devt) is true.
Perhaps change cdev_device_add() to have
rc = device_add(dev);
if (rc && dev->devt)
cdev_del(cdev);
return rc;
Jonathan
> ---
> drivers/iio/industrialio-core.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 151ff3993354..f4f48bda07f7 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -1982,7 +1982,11 @@ int __iio_device_register(struct iio_dev *indio_dev, struct module *this_mod)
> /* assign device groups now; they should be all registered now */
> indio_dev->dev.groups = iio_dev_opaque->groups;
>
> - ret = cdev_device_add(&iio_dev_opaque->chrdev, &indio_dev->dev);
> + if (iio_dev_opaque->attached_buffers_cnt || iio_dev_opaque->event_interface)
> + ret = cdev_device_add(&iio_dev_opaque->chrdev, &indio_dev->dev);
> + else
> + ret = device_add(&indio_dev->dev);
> +
> if (ret < 0)
> goto error_unreg_eventset;
>
> @@ -2008,7 +2012,10 @@ void iio_device_unregister(struct iio_dev *indio_dev)
> {
> struct iio_dev_opaque *iio_dev_opaque = to_iio_dev_opaque(indio_dev);
>
> - cdev_device_del(&iio_dev_opaque->chrdev, &indio_dev->dev);
> + if (iio_dev_opaque->chrdev.kobj.state_initialized)
> + cdev_device_del(&iio_dev_opaque->chrdev, &indio_dev->dev);
> + else
> + device_del(&indio_dev->dev);
>
> mutex_lock(&iio_dev_opaque->info_exist_lock);
>
