Re: [PATCH v2] vhost-vdpa: initialize state before publishing cdev

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] vhost_vdpa: spurious -EBUSY on open() due to uevent race during probe
--

commit cef3a58744e8aa0a22f86fbbe577797fa0a78e31
Author: Linfeng Sun <linfeng.sun.dev@gmail.com>

vhost-vdpa: initialize state before publishing cdev

Initialize the completion and as hash buckets before cdev_device_add()
makes the device accessible.

> diff --git a/drivers/vhost/vdpa.c b/drivers/vhost/vdpa.c
> index ff7d907191712..6cff1ed2004ee 100644
> --- a/drivers/vhost/vdpa.c
> +++ b/drivers/vhost/vdpa.c
> @@ -1655,7 +1655,7 @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
>  		return minor;
>  	}
>  
> -	atomic_set(&v->opened, 0);
> +	atomic_set(&v->opened, 1);
>  	spin_lock_init(&v->config_lock);
>  	v->minor = minor;
>  	v->vdpa = vdpa;
> @@ -1678,16 +1678,17 @@ static int vhost_vdpa_probe(struct vdpa_device *vdpa)
>  
>  	cdev_init(&v->cdev, &vhost_vdpa_fops);
>  	v->cdev.owner = THIS_MODULE;
> +	init_completion(&v->completion);
> +	for (i = 0; i < VHOST_VDPA_IOTLB_BUCKETS; i++)
> +		INIT_HLIST_HEAD(&v->as[i]);
>  
>  	r = cdev_device_add(&v->cdev, &v->dev);
>  	if (r)
>  		goto err;
>  
> -	init_completion(&v->completion);
>  	vdpa_set_drvdata(vdpa, v);
>  
> -	for (i = 0; i < VHOST_VDPA_IOTLB_BUCKETS; i++)
> -		INIT_HLIST_HEAD(&v->as[i]);
> +	atomic_set_release(&v->opened, 0);

[Severity: Medium]
Will this cause a spurious -EBUSY for userspace orchestration tools like udev?

When cdev_device_add() registers the character device, it fires a KOBJ_ADD
uevent. If userspace reacts immediately by calling open(), it will hit
vhost_vdpa_open():

drivers/vhost/vdpa.c:vhost_vdpa_open() {
	...
	opened = atomic_cmpxchg(&v->opened, 0, 1);
	if (opened)
		return -EBUSY;
	...
}

Since v->opened was artificially set to 1 earlier in probe, open() will be
rejected with -EBUSY until atomic_set_release() clears it, which might
break normal userspace orchestration that attempts to open the device right
after the uevent.

>  
>  	return 0;
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20261011-fix-null-pointer-in-vhost_vdpa_release-v2-1-66ba929971ce@gmail.com?part=1