Re: [PATCH 01/10] iommu: Remove useless group refcounting

From: Jason Gunthorpe <jgg@nvidia.com>
To: "Tian, Kevin" <kevin.tian@intel.com>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>,
	Lu Baolu <baolu.lu@linux.intel.com>,
	David Woodhouse <dwmw2@infradead.org>,
	Heiko Stuebner <heiko@sntech.de>,
	"iommu@lists.linux.dev" <iommu@lists.linux.dev>,
	Jernej Skrabec <jernej.skrabec@gmail.com>,
	Joerg Roedel <joro@8bytes.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>,
	"linux-rockchip@lists.infradead.org"
	<linux-rockchip@lists.infradead.org>,
	"linux-sunxi@lists.linux.dev" <linux-sunxi@lists.linux.dev>,
	Orson Zhai <orsonzhai@gmail.com>,
	Robin Murphy <robin.murphy@arm.com>,
	Samuel Holland <samuel@sholland.org>,
	Chen-Yu Tsai <wens@csie.org>, Will Deacon <will@kernel.org>,
	Chunyan Zhang <zhang.lyra@gmail.com>,
	Alex Williamson <alex.williamson@redhat.com>
Subject: Re: [PATCH 01/10] iommu: Remove useless group refcounting
Date: Mon, 24 Jul 2023 15:06:11 -0300	[thread overview]
Message-ID: <ZL69k24VQdH0LFHk@nvidia.com> (raw)
In-Reply-To: <BN9PR11MB527621E6E7D464982B8730118C02A@BN9PR11MB5276.namprd11.prod.outlook.com>

On Mon, Jul 24, 2023 at 02:11:44AM +0000, Tian, Kevin wrote:
> > From: Jason Gunthorpe <jgg@nvidia.com>
> > Sent: Friday, July 21, 2023 8:02 PM
> > 
> > On Fri, Jul 21, 2023 at 07:10:57AM +0000, Tian, Kevin wrote:
> > > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > > Sent: Wednesday, July 19, 2023 3:06 AM
> > > >
> > > >  int iommu_device_use_default_domain(struct device *dev)
> > > >  {
> > > > -	struct iommu_group *group = iommu_group_get(dev);
> > > > +	/* Caller must be a probed driver on dev */
> > > > +	struct iommu_group *group = dev->iommu_group;
> > > >  	int ret = 0;
> > >
> > > this is called in the probing path by .dma_configure().
> > >
> > > the driver hasn't been probed yet hence the rationale to not
> > > refcount is due to device_lock() instead?
> > 
> > At this point the driver core has partially attached/detached a driver
> > so I'm considering it part of the probed driver explanation.
> > 
> > Really during anything protected by the driver core probe path is
> > assured that the group cannot change.
> > 
> 
> Probably this worths a slightly different comment then?

How about

	/* Caller is the driver core during the post-probe path */

Jason