linux-kernel - Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe

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Message-ID: <20201005095351.GI425362@ulmo>
Date:   Mon, 5 Oct 2020 11:53:51 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     Nicolin Chen <nicoleotsuka@...il.com>, joro@...tes.org,
        vdumpa@...dia.com, jonathanh@...dia.com,
        linux-tegra@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()

On Fri, Oct 02, 2020 at 05:50:08PM +0300, Dmitry Osipenko wrote:
> 02.10.2020 17:22, Dmitry Osipenko пишет:
> >>  static int tegra_smmu_of_xlate(struct device *dev,
> >>  			       struct of_phandle_args *args)
> >>  {
> >> +	struct platform_device *iommu_pdev = of_find_device_by_node(args->np);
> >> +	struct tegra_mc *mc = platform_get_drvdata(iommu_pdev);
> >>  	u32 id = args->args[0];
> >>  
> >> +	of_node_put(args->np);
> >> +
> >> +	if (!mc || !mc->smmu)
> >> +		return -EPROBE_DEFER;
> > platform_get_drvdata(NULL) will crash.
> > 
> 
> Actually, platform_get_drvdata(NULL) can't happen. I overlooked this.

How so? It's technically possible for the iommus property to reference a
device tree node for which no platform device will ever be created, in
which case of_find_device_by_node() will return NULL. That's very
unlikely and perhaps worth just crashing on to make sure it gets fixed
immediately.

Thierry

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