linux-kernel - Re: [PATCH v2 4/4] iommu: Get DT/ACPI parsing into the proper probe path

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Message-ID: <20250422190036.GA1213339@ziepe.ca>
Date: Tue, 22 Apr 2025 16:00:36 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: William McVicker <willmcvicker@...gle.com>
Cc: Robin Murphy <robin.murphy@....com>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Sudeep Holla <sudeep.holla@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, Russell King <linux@...linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Stuart Yoder <stuyoder@...il.com>,
	Laurentiu Tudor <laurentiu.tudor@....com>,
	Nipun Gupta <nipun.gupta@....com>,
	Nikhil Agarwal <nikhil.agarwal@....com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, devicetree@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Charan Teja Kalla <quic_charante@...cinc.com>
Subject: Re: [PATCH v2 4/4] iommu: Get DT/ACPI parsing into the proper probe
 path

On Mon, Apr 21, 2025 at 02:19:35PM -0700, William McVicker wrote:
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 1813cfd0c4bd..6d124447545c 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1440,8 +1440,8 @@ static void platform_shutdown(struct device *_dev)
>  
>  static int platform_dma_configure(struct device *dev)
>  {
> -       struct platform_driver *drv = to_platform_driver(dev->driver);
>         struct fwnode_handle *fwnode = dev_fwnode(dev);
> +       struct platform_driver *drv;
>         enum dev_dma_attr attr;
>         int ret = 0;
>  
> @@ -1451,8 +1451,12 @@ static int platform_dma_configure(struct device *dev)
>                 attr = acpi_get_dma_attr(to_acpi_device_node(fwnode));
>                 ret = acpi_dma_configure(dev, attr);
>         }
> -       /* @drv may not be valid when we're called from the IOMMU layer */
> -       if (ret || !dev->driver || drv->driver_managed_dma)
> +       /* @dev->driver may not be valid when we're called from the IOMMU layer */
> +       if (ret || !dev->driver)
> +               return ret;
> +
> +       drv = to_platform_driver(dev->driver);
> +       if (drv->driver_managed_dma)
>                 return ret;
>  
>         ret = iommu_device_use_default_domain(dev);

The diagnosis looks right to me, but pedantically I think it should
have a READ_ONCE():

struct driver *drv = READ_ONCE(dev->driver);

And then never touch dev->driver again in the function.

Send a proper patch?

Jason