Re: [RFC PATCH] driver core: platform: Call iommu_release_device in dma_cleanup

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Aug 29, 2024 at 12:05:04PM +0000, Sachin Parekh wrote:
> Installing a kernel module that has an iommu node in its
> device tree increments corresponding iommu kernel module
> reference count during driver_register.
> Removing the same kernel module doesn't decrement the
> iommu reference count resulting in error while
> removing the iommu kernel module

Please wrap kernel changelog text at 72 columns like your editor asked
you to :)

>     $ modprobe arm-smmu-v3
>     $ modprobe test_module
>     $ modprobe -r test_module
>     $ modprobe -r arm-smmu-v3
>     modprobe: can't unload module arm_smmu_v3: Resource temporarily unavailable

Does this happen for any in-kernel driver?

Why has this not been noticed before?

> 
> Cause:
>     platform_driver_register
>         ...
>         -> platform_dma_configure
>             ...
>             -> iommu_probe_device (Increments reference count)
> 
>     platform_driver_unregister
>         ...
>         -> platform_dma_cleanup
>             ...
>             -> No corresponding iommu_release_device call
> 
> Fix:
>     Call iommu_release_device in platform_dma_cleanup to remove the
>     iommu from the corresponding kernel module
> 
> Signed-off-by: Sachin Parekh <sachinparekh@google.com>

What commit id does this fix?

> ---
>  drivers/base/platform.c | 3 +++
>  drivers/iommu/iommu.c   | 3 +--
>  include/linux/iommu.h   | 1 +
>  3 files changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 4c3ee6521ba5..c8125325a5e9 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -1467,6 +1467,9 @@ static void platform_dma_cleanup(struct device *dev)
>  
>  	if (!drv->driver_managed_dma)
>  		iommu_device_unuse_default_domain(dev);
> +
> +	if (dev_of_node(dev))
> +		iommu_release_device(dev);

Are you sure that all devices that pass this should have this call made?
How well was this tested on different systems?

thanks,

greg k-h