Re: [PATCH v4 2/7] iommufd: Add iommufd_object_tombstone_user() helper

[Jason Gunthorpe <jgg@nvidia.com>]

On Fri, Jul 11, 2025 at 11:02:53PM +0800, Xu Yilun wrote:
> > With one nit:
> > 
> > > -	while (!xa_empty(&ictx->objects)) {
> > > +	for (;;) {

Actually just leave this, if xa_empty does work out then the loop
exits quickly, otherwise the break will deal with the tombstones
 it.

> > >  		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?

Maybe:

 We can't use xa_empty() to end the loop as the tombstones are stored
 as XA_ZERO_ENTRY in the xarray. However xa_for_each() automatically
 converts them to NULL and skips them causing xa_empty() to be kept
 false. Thus once xa_for_each() finds no further !NULL entries the
 loop is done.

?

Jason