linux-kernel - Re: [PATCH v4 3/7] iommufd: Add a pre

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aHDbsFvzHl1UnQiZ@yilunxu-OptiPlex-7050>
Date: Fri, 11 Jul 2025 17:38:56 +0800
From: Xu Yilun <yilun.xu@...ux.intel.com>
To: "Tian, Kevin" <kevin.tian@...el.com>
Cc: Jason Gunthorpe <jgg@...dia.com>, "will@...nel.org" <will@...nel.org>,
	"aneesh.kumar@...nel.org" <aneesh.kumar@...nel.org>,
	"iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"joro@...tes.org" <joro@...tes.org>,
	"robin.murphy@....com" <robin.murphy@....com>,
	"shuah@...nel.org" <shuah@...nel.org>,
	"nicolinc@...dia.com" <nicolinc@...dia.com>,
	"aik@....com" <aik@....com>,
	"Williams, Dan J" <dan.j.williams@...el.com>,
	"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
	"Xu, Yilun" <yilun.xu@...el.com>
Subject: Re: [PATCH v4 3/7] iommufd: Add a pre_destroy() op for objects

On Fri, Jul 11, 2025 at 03:16:38AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@...dia.com>
> > Sent: Friday, July 11, 2025 1:15 AM
> > 
> > On Thu, Jul 10, 2025 at 07:40:58AM +0000, Tian, Kevin wrote:
> > > > From: Xu Yilun <yilun.xu@...ux.intel.com>
> > > > Sent: Wednesday, July 9, 2025 12:03 PM
> > > >
> > > > Add a pre_destroy() op which gives objects a chance to clear their
> > > > short term users references before destruction. This op is intended for
> > > > external driver created objects (e.g. idev) which does deterministic
> > > > destruction.
> > > >
> > > > In order to manage the lifecycle of interrelated objects as well as the
> > > > deterministic destruction (e.g. vdev can't outlive idev, and idev
> > > > destruction can't fail), short term users references are allowed to
> > > > live out of an ioctl execution. An immediate use case is, vdev holds
> > > > idev's short term user reference until vdev destruction completes, idev
> > > > leverages existing wait_shortterm mechanism to ensure it is destroyed
> > > > after vdev.
> > > >
> > > > This extended usage makes the referenced object unable to just wait for
> > > > its reference gone. It needs to actively trigger the reference removal,
> > > > as well as prevent new references before wait. Should implement these
> > > > work in pre_destroy().
> > > >
> > > > Suggested-by: Jason Gunthorpe <jgg@...dia.com>
> > > > Signed-off-by: Xu Yilun <yilun.xu@...ux.intel.com>
> > >
> > > Reviewed-by: Kevin Tian <kevin.tian@...el.com>
> > >
> > > btw is it clearer to rename 'shortterm_users' as 'wait_cnt', as the
> > > meaning now is beyond shortterm and is really about the need of
> > > waiting?
> > 
> > Probably so, as a followup change would be fine if we don't need a v5

We have some comments to quick fix. Let me make a v5 and include this
change.

> > 
> > /*
> >  * Destroy will sleep and wait for wait_cnt to go to zero. This
> >  * allows concurrent users of the ID to reliably avoid causing a
> >  * spurious destroy failure. Incrementing this count should either be
> >  * short lived or be revoked and blocked during pre_destroy
> >  */
> > refcount_t wait_cnt;
> > 
> > ?
> 
> Looks good