linux-kernel - Re: [PATCH v3 2/5] iommufd: Destroy vdevice on idevice destroy

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Message-ID: <aGzS57bGWtg8BpEU@yilunxu-OptiPlex-7050>
Date: Tue, 8 Jul 2025 16:12:23 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Nicolin Chen <nicolinc@...dia.com>
Cc: jgg@...dia.com, jgg@...pe.ca, kevin.tian@...el.com, will@...nel.org,
	aneesh.kumar@...nel.org, iommu@...ts.linux.dev,
	linux-kernel@...r.kernel.org, joro@...tes.org, robin.murphy@....com,
	shuah@...nel.org, aik@....com, dan.j.williams@...el.com,
	baolu.lu@...ux.intel.com, yilun.xu@...el.com
Subject: Re: [PATCH v3 2/5] iommufd: Destroy vdevice on idevice destroy

On Mon, Jun 30, 2025 at 12:34:03PM -0700, Nicolin Chen wrote:
> On Fri, Jun 27, 2025 at 11:38:06AM +0800, Xu Yilun wrote:
> > +static void iommufd_device_remove_vdev(struct iommufd_device *idev)
> > +{
> > +	struct iommufd_vdevice *vdev;
> > +
> > +	mutex_lock(&idev->igroup->lock);
> > +	/* vdev has been completely destroyed by userspace */
> > +	if (!idev->vdev)
> > +		goto out_unlock;
> > +
> > +	vdev = iommufd_get_vdevice(idev->ictx, idev->vdev->obj.id);
> > +	if (IS_ERR(vdev)) {
> > +		/*
> > +		 * vdev is removed from xarray by userspace, but is not
> > +		 * destroyed/freed. Since iommufd_vdevice_abort() is reentrant,
> > +		 * safe to destroy vdev here.
> > +		 */
> > +		iommufd_vdevice_abort(&idev->vdev->obj);
> > +		goto out_unlock;
> 
> This is the case #3, i.e. a racing vdev destory, in the commit log?
> 
> I think it is worth clarifying that there is a concurrent destroy:
> 		/*
> 		 * An ongoing vdev destroy ioctl has removed the vdev from the
> 		 * object xarray but has not finished iommufd_vdevice_destroy()
> 		 * yet, as it is holding the same mutex.

Applied this part.

>		 * Destroy the vdev here,
> 		 * i.e. the iommufd_vdevice_destroy() will be a NOP once it is
> 		 * unlocked.
> 		 */
> 
> > @@ -147,10 +183,12 @@ int iommufd_vdevice_alloc_ioctl(struct iommufd_ucmd *ucmd)
> >  	if (rc)
> >  		goto out_abort;
> >  	iommufd_object_finalize(ucmd->ictx, &vdev->obj);
> > -	goto out_put_idev;
> > +	goto out_unlock_igroup;
> >  
> >  out_abort:
> >  	iommufd_object_abort_and_destroy(ucmd->ictx, &vdev->obj);
> > +out_unlock_igroup:
> > +	mutex_unlock(&idev->igroup->lock);
> 
> Looks like we will have to partially revert the _ucmd allocator,
> in this function:
> https://lore.kernel.org/all/107b24a3b791091bb09c92ffb0081c56c413b26d.1749882255.git.nicolinc@nvidia.com/
> 
> Please try fixing the conflicts on top of Jason's for-next tree.

Yes, will rebase for next version.

Thanks,
Yilun

> 
> Thanks
> Nicolin