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

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Message-ID: <aHFocHh3kB0/wJ7H@Asurada-Nvidia>
Date: Fri, 11 Jul 2025 12:39:28 -0700
From: Nicolin Chen <nicolinc@...dia.com>
To: Xu Yilun <yilun.xu@...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>, <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

On Fri, Jul 11, 2025 at 11:02:53PM +0800, Xu Yilun wrote:
> > 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?

They are. Just nicer to pick one for consistency.

Typo was "tomestones", any way..

Thanks
Nicolin