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

[Lu Baolu]

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.

Best regards,
baolu