From: Thierry Reding <thierry.reding@gmail.com>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: Nicolin Chen <nicoleotsuka@gmail.com>,
joro@8bytes.org, vdumpa@nvidia.com, jonathanh@nvidia.com,
linux-tegra@vger.kernel.org, iommu@lists.linux-foundation.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()
Date: Mon, 5 Oct 2020 13:15:47 +0200 [thread overview]
Message-ID: <20201005111547.GQ425362@ulmo> (raw)
In-Reply-To: <ae48aaaf-fe10-6de4-06bb-2afbde799168@gmail.com>
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On Mon, Oct 05, 2020 at 01:36:55PM +0300, Dmitry Osipenko wrote:
> 05.10.2020 12:53, Thierry Reding пишет:
> > 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.
>
> The tegra_smmu_ops are registered from the SMMU driver itself and MC
> driver sets platform data before SMMU is initialized, hence device is
> guaranteed to exist and mc can't be NULL.
Yes, but that assumes that args->np points to the memory controller's
device tree node. It's obviously a mistake to do this, but I don't think
anyone will prevent you from doing this:
iommus = <&{/chosen} 0>;
In that case, since no platform device is created for the /chosen node,
iommu_pdev will end up being NULL and platform_get_drvdata() will crash.
That said, I'm fine with not adding a check for that. If anyone really
does end up messing this up they deserve the crash.
I'm still a bit undecided about the mc->smmu check because I haven't
convinced myself yet that it can't happen.
Thierry
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WARNING: multiple messages have this Message-ID (diff)
From: Thierry Reding <thierry.reding@gmail.com>
To: Dmitry Osipenko <digetx@gmail.com>
Cc: linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
jonathanh@nvidia.com, linux-tegra@vger.kernel.org
Subject: Re: [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device()
Date: Mon, 5 Oct 2020 13:15:47 +0200 [thread overview]
Message-ID: <20201005111547.GQ425362@ulmo> (raw)
In-Reply-To: <ae48aaaf-fe10-6de4-06bb-2afbde799168@gmail.com>
[-- Attachment #1.1: Type: text/plain, Size: 1930 bytes --]
On Mon, Oct 05, 2020 at 01:36:55PM +0300, Dmitry Osipenko wrote:
> 05.10.2020 12:53, Thierry Reding пишет:
> > 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.
>
> The tegra_smmu_ops are registered from the SMMU driver itself and MC
> driver sets platform data before SMMU is initialized, hence device is
> guaranteed to exist and mc can't be NULL.
Yes, but that assumes that args->np points to the memory controller's
device tree node. It's obviously a mistake to do this, but I don't think
anyone will prevent you from doing this:
iommus = <&{/chosen} 0>;
In that case, since no platform device is created for the /chosen node,
iommu_pdev will end up being NULL and platform_get_drvdata() will crash.
That said, I'm fine with not adding a check for that. If anyone really
does end up messing this up they deserve the crash.
I'm still a bit undecided about the mc->smmu check because I haven't
convinced myself yet that it can't happen.
Thierry
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next prev parent reply other threads:[~2020-10-05 11:15 UTC|newest]
Thread overview: 92+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-02 6:08 [PATCH v4 0/3] iommu/tegra-smmu: Add PCI support Nicolin Chen
2020-10-02 6:08 ` Nicolin Chen
2020-10-02 6:08 ` [PATCH v4 1/3] iommu/tegra-smmu: Use fwspec in tegra_smmu_(de)attach_dev Nicolin Chen
2020-10-02 6:08 ` Nicolin Chen
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:52 ` Dmitry Osipenko
2020-10-02 14:52 ` Dmitry Osipenko
2020-10-02 19:56 ` Nicolin Chen
2020-10-02 19:56 ` Nicolin Chen
2020-10-02 14:26 ` Dmitry Osipenko
2020-10-02 14:26 ` Dmitry Osipenko
2020-10-02 14:41 ` Dmitry Osipenko
2020-10-02 14:41 ` Dmitry Osipenko
2020-10-02 19:45 ` Nicolin Chen
2020-10-02 19:45 ` Nicolin Chen
2020-10-02 20:12 ` Dmitry Osipenko
2020-10-02 20:12 ` Dmitry Osipenko
2020-10-02 23:53 ` Nicolin Chen
2020-10-02 23:53 ` Nicolin Chen
2020-10-03 4:01 ` Dmitry Osipenko
2020-10-03 4:01 ` Dmitry Osipenko
2020-10-02 6:08 ` [PATCH v4 2/3] iommu/tegra-smmu: Rework tegra_smmu_probe_device() Nicolin Chen
2020-10-02 6:08 ` Nicolin Chen
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:58 ` Dmitry Osipenko
2020-10-02 14:58 ` Dmitry Osipenko
2020-10-02 19:53 ` Nicolin Chen
2020-10-02 19:53 ` Nicolin Chen
2020-10-05 9:47 ` Thierry Reding
2020-10-05 9:47 ` Thierry Reding
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:22 ` Dmitry Osipenko
2020-10-02 14:50 ` Dmitry Osipenko
2020-10-02 14:50 ` Dmitry Osipenko
2020-10-05 9:53 ` Thierry Reding
2020-10-05 9:53 ` Thierry Reding
2020-10-05 10:36 ` Dmitry Osipenko
2020-10-05 10:36 ` Dmitry Osipenko
2020-10-05 11:15 ` Thierry Reding [this message]
2020-10-05 11:15 ` Thierry Reding
2020-10-05 13:28 ` Dmitry Osipenko
2020-10-05 13:28 ` Dmitry Osipenko
2020-10-05 14:22 ` Thierry Reding
2020-10-05 14:22 ` Thierry Reding
2020-10-05 9:51 ` Thierry Reding
2020-10-05 9:51 ` Thierry Reding
2020-10-02 14:23 ` Dmitry Osipenko
2020-10-02 14:23 ` Dmitry Osipenko
2020-10-02 18:01 ` Nicolin Chen
2020-10-02 18:01 ` Nicolin Chen
2020-10-02 18:20 ` Dmitry Osipenko
2020-10-02 18:20 ` Dmitry Osipenko
2020-10-02 15:02 ` Dmitry Osipenko
2020-10-02 15:02 ` Dmitry Osipenko
2020-10-02 18:58 ` Nicolin Chen
2020-10-02 18:58 ` Nicolin Chen
2020-10-05 9:57 ` Thierry Reding
2020-10-05 9:57 ` Thierry Reding
2020-10-06 1:05 ` Nicolin Chen
2020-10-06 1:05 ` Nicolin Chen
2020-10-08 9:53 ` Thierry Reding
2020-10-08 9:53 ` Thierry Reding
2020-10-08 21:12 ` Nicolin Chen
2020-10-08 21:12 ` Nicolin Chen
2020-10-09 12:25 ` Thierry Reding
2020-10-09 12:25 ` Thierry Reding
2020-10-09 15:54 ` Nicolin Chen
2020-10-09 15:54 ` Nicolin Chen
2020-10-02 15:23 ` Dmitry Osipenko
2020-10-02 15:23 ` Dmitry Osipenko
2020-10-02 16:00 ` Dmitry Osipenko
2020-10-02 16:00 ` Dmitry Osipenko
2020-10-02 16:37 ` Dmitry Osipenko
2020-10-02 16:37 ` Dmitry Osipenko
2020-10-02 16:50 ` Dmitry Osipenko
2020-10-02 16:50 ` Dmitry Osipenko
2020-10-02 6:08 ` [PATCH v4 3/3] iommu/tegra-smmu: Add PCI support Nicolin Chen
2020-10-02 6:08 ` Nicolin Chen
2020-10-02 14:35 ` Dmitry Osipenko
2020-10-02 14:35 ` Dmitry Osipenko
2020-10-02 17:45 ` Nicolin Chen
2020-10-02 17:45 ` Nicolin Chen
2020-10-02 18:04 ` Dmitry Osipenko
2020-10-02 18:04 ` Dmitry Osipenko
2020-10-02 18:04 ` Dmitry Osipenko
2020-10-02 18:04 ` Dmitry Osipenko
2020-10-05 10:04 ` Thierry Reding
2020-10-05 10:04 ` Thierry Reding
2020-10-06 0:54 ` Nicolin Chen
2020-10-06 0:54 ` Nicolin Chen
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