Re: [PATCH v3 07/10] iommu: Use right way to retrieve iommu_ops

Lu Baolu
2022-02-15T02:03:27Z

On 2/15/22 9:46 AM, Lu Baolu wrote:
> On 2/14/22 8:49 PM, Joerg Roedel wrote:
>> On Mon, Feb 14, 2022 at 09:55:35AM +0800, Lu Baolu wrote:
>>> +static inline const struct iommu_ops *dev_iommu_ops(struct device *dev)
>>> +{
>>> +    /*
>>> +     * Assume that valid ops must be installed if iommu_probe_device()
>>> +     * has succeeded. The device ops are essentially for internal use
>>> +     * within the IOMMU subsystem itself, so we should be able to trust
>>> +     * ourselves not to misuse the helper.
>>> +     */
>>> +    WARN_ON(!dev || !dev->iommu || !dev->iommu->iommu_dev ||
>>> +        !dev->iommu->iommu_dev->ops);
>>
>> There is no need for this WARN_ON, the code will oops anyway when one of
>> the pointers checked here is NULL.
>>
>
> We really don't need to WARN_ON intermediate null pointers. But I would
> argue that we could add a WARN() on null dev->iommu->iommu_dev->ops, so
> that callers have no need to check the returned ops.

Oh, sorry! We don't need to check null ops either. That will also result
in a null pointer reference oops in the caller.

So, yes. No need for this WARN_ON().

Best regards,
baolu