Re: [PATCH] iommu/arm-smmu-v3: Don't leak the CMDQV device on a bad #iommu-cells

[Mostafa Saleh <smostafa@google.com>]

On Thu, Nov 12, 2026 at 08:20:19AM +0000, Arun Iyengar via B4 Relay wrote:
> From: Arun Iyengar <aiyengar1990@gmail.com>
> 
> arm_smmu_device_dt_probe() only logs a missing or invalid #iommu-cells
> and carries on with ret = -EINVAL. For "nvidia,tegra264-smmu" it then
> calls tegra_cmdqv_dt_probe(), which takes a reference on the CMDQV
> platform device in smmu->impl_dev, and returns the error. That reference
> is only dropped by tegra241_cmdqv_probe() via arm_smmu_impl_probe(),
> which is never reached, so every failed probe leaks it.
> 
> Return the error as soon as #iommu-cells is found to be wrong, before

This is one of the things I came across a while ago when I passed
the whole driver to Sashiko [1] and IMHO, it shouldn’t be worth it
to fix as the FW can do many other harmful stuff to the kernel
leading to panics or memory corruption and the binding for the driver
is quite clear.

Thanks,
Mostafa

[1] https://lore.kernel.org/all/20260924085616.300650-1-smostafa@google.com/

> anything takes a reference.
> 
> Fixes: ea69dc4e207b ("iommu/arm-smmu-v3: Add device-tree support for CMDQV driver")
> Reported-by: Sashiko <sashiko-bot@kernel.org>
> Closes: https://lore.kernel.org/all/sashiko-outbox-206486@kernel.org/
> Signed-off-by: Arun Iyengar <aiyengar1990@gmail.com>
> ---
> The Sashiko AI review found this leak while reviewing my series
> "iommu/arm-smmu-v3: Keep the clock of the RK3588 PCIe SMMU running"
> [1]. It is not related to that series, so it is sent on its own.
> 
> Only compile-tested (arm64 allmodconfig, W=1): I have no Tegra264
> hardware.
> 
> This patch was developed with Claude (Anthropic) as a coding assistant:
> it wrote the code and the commit message, and I reviewed it.
> 
> [1] https://lore.kernel.org/r/20261110-smmu-v3-pcie-pd-v1-0-628819ca44b9@gmail.com
> ---
>  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 13 +++++++------
>  1 file changed, 7 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> index 6d4520c47308..f685ed0c01b3 100644
> --- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> +++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
> @@ -5661,14 +5661,15 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev,
>  {
>  	struct device *dev = &pdev->dev;
>  	u32 cells;
> -	int ret = -EINVAL;
>  
> -	if (of_property_read_u32(dev->of_node, "#iommu-cells", &cells))
> +	if (of_property_read_u32(dev->of_node, "#iommu-cells", &cells)) {
>  		dev_err(dev, "missing #iommu-cells property\n");
> -	else if (cells != 1)
> +		return -EINVAL;
> +	}
> +	if (cells != 1) {
>  		dev_err(dev, "invalid #iommu-cells value (%d)\n", cells);
> -	else
> -		ret = 0;
> +		return -EINVAL;
> +	}
>  
>  	parse_driver_options(smmu);
>  
> @@ -5680,7 +5681,7 @@ static int arm_smmu_device_dt_probe(struct platform_device *pdev,
>  		static_branch_enable(&arm_smmu_erratum_repeat_tlbi_cfgi_key);
>  	}
>  
> -	return ret;
> +	return 0;
>  }
>  
>  static unsigned long arm_smmu_resource_size(struct arm_smmu_device *smmu)
> 
> ---
> base-commit: 2cf4be57b301ed2d7af82e70cff5dfd96894d8de
> change-id: 20261112-smmu-cmdqv-leak-003f273b5e59
> 
> Best regards,
> --  
> Arun Iyengar <aiyengar1990@gmail.com>
> 
>