linux-kernel - Re: [PATCH v4 2/7] iommufd: Add iommufd_object_tombstone

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Message-ID: <aHEnnesvLL5te5rf@yilunxu-OptiPlex-7050>
Date: Fri, 11 Jul 2025 23:02:53 +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 v4 2/7] iommufd: Add iommufd_object_tombstone_user()
 helper

> With one nit:
> 
> > -	while (!xa_empty(&ictx->objects)) {
> > +	for (;;) {
> >  		unsigned int destroyed = 0;
> >  		unsigned long index;
> > +		bool empty = true;
> >  
> > +		/*
> > +		 * xa_for_each() will not return tomestones (zeroed entries),
> > +		 * which prevent the xarray being empty. So use an empty flags
> 
> Since the first "empty" and the second "empty" are different things,
> 
> > +		 * instead of xa_empty() to indicate all entries are either
> > +		 * NULLed or tomestoned.
> > +		 */
> 
> let's write something like this (correcting typos too):
> 
> 		/*
> 		 * We can't use xa_empty(), as a tombstone (NULLed entry) would
                                                            ^
> 		 * prevent it returning true, unlike xa_for_each() ignoring the
> 		 * NULLed entries. So use an empty flag instead of xa_empty() to
                   ^
s/NULLed/zeroed, are they?

Thanks,
Yilun

> 		 * indicate all entries are either NULLed or tombstoned.
> 		 */