Re: [PATCH v5 03/13] iommufd: Add iommufd_verify_unfinalized_object

[Nicolin Chen]

On Tue, Oct 29, 2024 at 03:55:58PM -0300, Jason Gunthorpe wrote:
> On Tue, Oct 29, 2024 at 09:18:05AM -0700, Nicolin Chen wrote:
> > I think we'd need the same change in iommufd_object_abort() too.
> 
> Makes sense

I found xa_cmpxchg() does xas_result to its returning value, which
turns XA_ZERO_ENTRY into NULL failing our intended verifications.

So, I replaced that further with xas_store:
-----------------------------------------------------------------
@@ -41,20 +41,26 @@ static struct miscdevice vfio_misc_dev;
 void iommufd_object_finalize(struct iommufd_ctx *ictx,
                             struct iommufd_object *obj)
 {
+       XA_STATE(xas, &ictx->objects, obj->id);
        void *old;

-       old = xa_store(&ictx->objects, obj->id, obj, GFP_KERNEL);
-       /* obj->id was returned from xa_alloc() so the xa_store() cannot fail */
-       WARN_ON(old);
+       xa_lock(&ictx->objects);
+       old = xas_store(&xas, obj);
+       xa_unlock(&ictx->objects);
+       /* obj->id was returned from xa_alloc() so the xas_store() cannot fail */
+       WARN_ON(old != XA_ZERO_ENTRY);
 }

 /* Undo _iommufd_object_alloc() if iommufd_object_finalize() was not called */
 void iommufd_object_abort(struct iommufd_ctx *ictx, struct iommufd_object *obj)
 {
+       XA_STATE(xas, &ictx->objects, obj->id);
        void *old;

-       old = xa_erase(&ictx->objects, obj->id);
-       WARN_ON(old);
+       xa_lock(&ictx->objects);
+       old = xas_store(&xas, NULL);
+       xa_unlock(&ictx->objects);
+       WARN_ON(old != XA_ZERO_ENTRY);
        kfree(obj);
 }
-----------------------------------------------------------------

Thanks
Nicolin