Re: [PATCH v8 4/5] iommu/arm-smmu: Add the device_link between masters and smmu

[Robin Murphy <robin.murphy@arm.com>]

On 02/03/18 10:10, Vivek Gautam wrote:
> From: Sricharan R <sricharan@codeaurora.org>
> 
> Finally add the device link between the master device and
> smmu, so that the smmu gets runtime enabled/disabled only when the
> master needs it. This is done from add_device callback which gets
> called once when the master is added to the smmu.
> 
> Signed-off-by: Sricharan R <sricharan@codeaurora.org>
> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
> ---
>   drivers/iommu/arm-smmu.c | 21 +++++++++++++++++++++
>   1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 3d6a1875431f..bb1ea82c1003 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -217,6 +217,9 @@ struct arm_smmu_device {
>   
>   	/* IOMMU core code handle */
>   	struct iommu_device		iommu;
> +
> +	/* runtime PM link to master */
> +	struct device_link *link;

Just the one?

>   };
>   
>   enum arm_smmu_context_fmt {
> @@ -1470,10 +1473,26 @@ static int arm_smmu_add_device(struct device *dev)
>   
>   	iommu_device_link(&smmu->iommu, dev);
>   
> +	/*
> +	 * Establish the link between smmu and master, so that the
> +	 * smmu gets runtime enabled/disabled as per the master's
> +	 * needs.
> +	 */
> +	smmu->link = device_link_add(dev, smmu->dev, DL_FLAG_PM_RUNTIME);

Maybe I've misunderstood how the API works, but AFAICS the second and 
subsequent devices are all just going to overwrite (and leak) the link 
of the previous one...

> +	if (!smmu->link) {
> +		dev_warn(smmu->dev, "Unable to create device link between %s and %s\n",
> +			 dev_name(smmu->dev), dev_name(dev));
> +		ret = -ENODEV;
> +		goto out_unlink;
> +	}
> +
>   	arm_smmu_rpm_put(smmu);
>   
>   	return 0;
>   
> +out_unlink:
> +	iommu_device_unlink(&smmu->iommu, dev);
> +	arm_smmu_master_free_smes(fwspec);
>   out_rpm_put:
>   	arm_smmu_rpm_put(smmu);
>   out_cfg_free:
> @@ -1496,6 +1515,8 @@ static void arm_smmu_remove_device(struct device *dev)
>   	cfg  = fwspec->iommu_priv;
>   	smmu = cfg->smmu;
>   
> +	device_link_del(smmu->link);

...and equivalently you end up with a double-free (or more) here of a 
link which may not have belonged to dev anyway.

Robin.

> +
>   	ret = arm_smmu_rpm_get(smmu);
>   	if (ret < 0)
>   		return;
>