linux-kernel - Re: [PATCH v2 1/4] iommufd: Add iommufd_object_tombstone

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Message-ID: <aFukMWTmupyHXCxw@yilunxu-OptiPlex-7050>
Date: Wed, 25 Jun 2025 15:24:33 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...dia.com>
Cc: 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,
	baolu.lu@...ux.intel.com, yilun.xu@...el.com
Subject: Re: [PATCH v2 1/4] iommufd: Add iommufd_object_tombstone_user()
 helper

On Tue, Jun 24, 2025 at 10:35:20AM -0300, Jason Gunthorpe wrote:
> On Mon, Jun 23, 2025 at 05:49:43PM +0800, Xu Yilun wrote:
> > @@ -251,16 +252,30 @@ static int iommufd_fops_release(struct inode *inode, struct file *filp)
> >  	 */
> >  	while (!xa_empty(&ictx->objects)) {
> >  		unsigned int destroyed = 0;
> > -		unsigned long index;
> >  
> > -		xa_for_each(&ictx->objects, index, obj) {
> > -			if (!refcount_dec_if_one(&obj->users))
> > -				continue;
> 
> I don't think you need all these changes..
> 
> xa_for_each will skip the XA_ZERO_ENTRIES because it won't return NULL
> 
> xa_empty() will fail, but just remove it.
> 
> @@ -288,6 +288,7 @@ static int iommufd_fops_release(struct inode *inode, struct file *filp)
>         struct iommufd_sw_msi_map *next;
>         struct iommufd_sw_msi_map *cur;
>         struct iommufd_object *obj;
> +       bool empty;
>  
>         /*
>          * The objects in the xarray form a graph of "users" counts, and we have
> @@ -298,11 +299,13 @@ static int iommufd_fops_release(struct inode *inode, struct file *filp)
>          * until the entire list is destroyed. If this can't progress then there
>          * is some bug related to object refcounting.
>          */
> -       while (!xa_empty(&ictx->objects)) {
> +       do {
>                 unsigned int destroyed = 0;
>                 unsigned long index;
>  
> +               empty = true;
>                 xa_for_each(&ictx->objects, index, obj) {
> +                       empty = false;
>                         if (!refcount_dec_if_one(&obj->users))
>                                 continue;
>                         destroyed++;
> @@ -313,8 +316,13 @@ static int iommufd_fops_release(struct inode *inode, struct file *filp)
>                 /* Bug related to users refcount */
>                 if (WARN_ON(!destroyed))
>                         break;
> -       }
> -       WARN_ON(!xa_empty(&ictx->groups));
> +       } while (!empty);
> +
> +       /*
> +        * There may be some tombstones left over from
> +        * iommufd_object_tombstone_user()
> +        */
> +       xa_destroy(&ictx->groups);

I'm good to it. I was obsessed to ensure the xarray super clean.

Thanks,
Yilun

> 
> 
> Jason