linux-kernel - Re: [RFC 08/14] vfio/nvgrace-egm: Expose EGM region as char device

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Message-ID: <20250905133434.GE616306@nvidia.com>
Date: Fri, 5 Sep 2025 10:34:34 -0300
From: Jason Gunthorpe <jgg@...dia.com>
To: ankita@...dia.com
Cc: alex.williamson@...hat.com, yishaih@...dia.com, skolothumtho@...dia.com,
	kevin.tian@...el.com, yi.l.liu@...el.com, zhiw@...dia.com,
	aniketa@...dia.com, cjia@...dia.com, kwankhede@...dia.com,
	targupta@...dia.com, vsethi@...dia.com, acurrid@...dia.com,
	apopple@...dia.com, jhubbard@...dia.com, danw@...dia.com,
	anuaggarwal@...dia.com, mochs@...dia.com, kjaju@...dia.com,
	dnigam@...dia.com, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 08/14] vfio/nvgrace-egm: Expose EGM region as char device

On Thu, Sep 04, 2025 at 04:08:22AM +0000, ankita@...dia.com wrote:
> +static struct chardev *
> +setup_egm_chardev(struct nvgrace_egm_dev *egm_dev)
> +{
> +	struct chardev *egm_chardev;
> +	int ret;
> +
> +	egm_chardev = kvzalloc(sizeof(*egm_chardev), GFP_KERNEL);
> +	if (!egm_chardev)
> +		goto create_err;
> +
> +	device_initialize(&egm_chardev->device);
> +
> +	/*
> +	 * Use the proximity domain number as the device minor
> +	 * number. So the EGM corresponding to node X would be
> +	 * /dev/egmX.
> +	 */
> +	egm_chardev->device.devt = MKDEV(MAJOR(dev), egm_dev->egmpxm);
> +	egm_chardev->device.class = class;
> +	egm_chardev->device.release = egm_chardev_release;
> +	egm_chardev->device.parent = &egm_dev->aux_dev.dev;
> +	cdev_init(&egm_chardev->cdev, &file_ops);
> +	egm_chardev->cdev.owner = THIS_MODULE;
> +
> +	ret = dev_set_name(&egm_chardev->device, "egm%lld", egm_dev->egmpxm);
> +	if (ret)
> +		goto error_exit;
> +
> +	ret = cdev_device_add(&egm_chardev->cdev, &egm_chardev->device);
> +	if (ret)
> +		goto error_exit;
> +
> +	return egm_chardev;
> +
> +error_exit:
> +	kvfree(egm_chardev);

After calling init you have to use put_device not kvfree.

Why kvalloc anyhow? Struct chardev is not big

>  static void egm_driver_remove(struct auxiliary_device *aux_dev)
>  {
> +	struct nvgrace_egm_dev *egm_dev =
> +		container_of(aux_dev, struct nvgrace_egm_dev, aux_dev);
> +	struct chardev *egm_chardev = xa_erase(&egm_chardevs, egm_dev->egmpxm);
> +
> +	if (!egm_chardev)
> +		return;
> +
> +	del_egm_chardev(egm_chardev);
>  }

This proceeds even if files are left open which is not going to be any
good..

Jason