linux-kernel - Re: [PATCH v3 07/10] iommu: Use right way to retrieve iommu

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Message-ID: <YgpP7AhY5hd/DX/C@8bytes.org>
Date:   Mon, 14 Feb 2022 13:49:48 +0100
From:   Joerg Roedel <joro@...tes.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Ben Skeggs <bskeggs@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Eric Auger <eric.auger@...hat.com>,
        Liu Yi L <yi.l.liu@...el.com>,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v3 07/10] iommu: Use right way to retrieve iommu_ops

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.