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Subject: Re: [PATCH v4 12/22] iommu: introduce device fault report API
To: Jacob Pan <jacob.jun.pan@linux.intel.com>,
 "iommu@lists.linux-foundation.org" <iommu@lists.linux-foundation.org>,
 LKML <linux-kernel@vger.kernel.org>, Joerg Roedel <joro@8bytes.org>,
 David Woodhouse <dwmw2@infradead.org>,
 Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
 Alex Williamson <alex.williamson@redhat.com>
Cc: Rafael Wysocki <rafael.j.wysocki@intel.com>,
 "Liu, Yi L" <yi.l.liu@intel.com>, "Tian, Kevin" <kevin.tian@intel.com>,
 Raj Ashok <ashok.raj@intel.com>, Christoph Hellwig <hch@infradead.org>,
 Lu Baolu <baolu.lu@linux.intel.com>
References: <1523915351-54415-1-git-send-email-jacob.jun.pan@linux.intel.com>
 <1523915351-54415-13-git-send-email-jacob.jun.pan@linux.intel.com>
From: Jean-Philippe Brucker <jean-philippe.brucker@arm.com>
Message-ID: <b9175586-e638-c807-3ef0-f0e0bc1b8243@arm.com>
Date: Mon, 30 Apr 2018 17:53:52 +0100
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List-ID: <linux-kernel.vger.kernel.org>

Hi,

I noticed a couple issues when testing

On 16/04/18 22:49, Jacob Pan wrote:
> +int iommu_register_device_fault_handler(struct device *dev,
> +					iommu_dev_fault_handler_t handler,
> +					void *data)
> +{
> +	struct iommu_param *param = dev->iommu_param;
> +
> +	/*
> +	 * Device iommu_param should have been allocated when device is
> +	 * added to its iommu_group.
> +	 */
> +	if (!param)
> +		return -EINVAL;
> +
> +	/* Only allow one fault handler registered for each device */
> +	if (param->fault_param)
> +		return -EBUSY;

Should this be inside the param lock? We probably don't expect
concurrent register/unregister but it seems cleaner

> +
> +	mutex_lock(&param->lock);
> +	get_device(dev);
> +	param->fault_param =
> +		kzalloc(sizeof(struct iommu_fault_param), GFP_ATOMIC);
> +	if (!param->fault_param) {
> +		put_device(dev);
> +		mutex_unlock(&param->lock);
> +		return -ENOMEM;
> +	}
> +	mutex_init(&param->fault_param->lock);
> +	param->fault_param->handler = handler;
> +	param->fault_param->data = data;
> +	INIT_LIST_HEAD(&param->fault_param->faults);
> +
> +	mutex_unlock(&param->lock);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(iommu_register_device_fault_handler);
> +
> +/**
> + * iommu_unregister_device_fault_handler() - Unregister the device fault handler
> + * @dev: the device
> + *
> + * Remove the device fault handler installed with
> + * iommu_register_device_fault_handler().
> + *
> + * Return 0 on success, or an error.
> + */
> +int iommu_unregister_device_fault_handler(struct device *dev)
> +{
> +	struct iommu_param *param = dev->iommu_param;
> +	int ret = 0;
> +
> +	if (!param)
> +		return -EINVAL;
> +
> +	mutex_lock(&param->lock);

We should return EINVAL here, if fault_param is NULL. That way users can
call unregister_fault_handler unconditionally in their cleanup paths

> +	/* we cannot unregister handler if there are pending faults */
> +	if (list_empty(&param->fault_param->faults)) {

if (!list_empty(...))

> +		ret = -EBUSY;
> +		goto unlock;
> +	}
> +
> +	list_del(&param->fault_param->faults);

faults is the list head, no need for list_del

> +	kfree(param->fault_param);
> +	param->fault_param = NULL;
> +	put_device(dev);
> +
> +unlock:
> +	mutex_unlock(&param->lock);
> +
> +	return 0;

return ret

Thanks,
Jean