linux-kernel - Re: [PATCH v5 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20201004215731.GA21420@Asurada-Nvidia>
Date:   Sun, 4 Oct 2020 14:57:31 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Dmitry Osipenko <digetx@...il.com>
Cc:     thierry.reding@...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 v5 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()

On Sat, Oct 03, 2020 at 05:06:42PM +0300, Dmitry Osipenko wrote:
> 03.10.2020 09:59, Nicolin Chen 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];
> >  
> > +	put_device(&iommu_pdev->dev);
> > +
> > +	if (!mc || !mc->smmu)
> > +		return -EPROBE_DEFER;
> 
> I'm not very excited by seeing code in the patches that can't be
> explained by the patch authors and will appreciate if you could provide
> a detailed explanation about why this NULL checking is needed because I
> think it is unneeded, especially given that other IOMMU drivers don't
> have such check.

This function could be called from of_iommu_configure(), which is
a part of other driver's probe(). So I think it's safer to have a
check. Yet, given mc driver is added to the "arch_initcall" stage,
you are probably right that there's no really need at this moment
because all clients should be called after mc/smmu are inited. So
I'll resend a v6, if that makes you happy.

> I'm asking this question second time now, please don't ignore review
> comments next time.

I think I missed your reply or misunderstood it.