linux-kernel - Re: [PATCH v3 1/5] iommufd: Add iommufd_object_tombstone

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Message-ID: <aGI7nHgYNtXhiet9@yilunxu-OptiPlex-7050>
Date: Mon, 30 Jun 2025 15:24:12 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Baolu Lu <baolu.lu@...ux.intel.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, nicolinc@...dia.com, aik@....com,
	dan.j.williams@...el.com, yilun.xu@...el.com
Subject: Re: [PATCH v3 1/5] iommufd: Add iommufd_object_tombstone_user()
 helper

> > -	while (!xa_empty(&ictx->objects)) {
> > +	for (;;) {
> >   		unsigned int destroyed = 0;
> >   		unsigned long index;
> > +		empty = true;
> >   		xa_for_each(&ictx->objects, index, obj) {
> > +			empty = false;
> 
> People like me, who don't know the details of how xa_for_each() and
> xa_empty() work, will ask why "empty = xa_empty()" isn't used here. So
> it's better to add some comments to make it more readable.
> 
> /* XA_ZERO_ENTRY is treated as a null entry by xa_for_each(). */

Yes. I try to make it more elaborate:

+               /*
+                * xa_for_each() will not return tomestones (zeroed entries),
+                * which prevent the xarray being empty. So use an empty flag
+                * instead of xa_empty() to indicate all entries are either
+                * NULLed or tomestoned.
+                */
                empty = true;

Thanks,
Yilun

> 
> Others look good to me.
> 
> Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>