linux-kernel - Re: [PATCH] iommu/tegra-smmu: fix error checking for debugfs_create

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Message-ID: <CABGWkvrG8OWKpkY3g46XEje196zSXZ5rfekMRRDWMtp-uMrw-g@mail.gmail.com>
Date:   Tue, 31 Oct 2023 08:54:31 +0100
From:   Dario Binacchi <dario.binacchi@...rulasolutions.com>
To:     Thierry Reding <thierry.reding@...il.com>
Cc:     Baolu Lu <baolu.lu@...ux.intel.com>, linux-kernel@...r.kernel.org,
        Joerg Roedel <joro@...tes.org>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Krishna Reddy <vdumpa@...dia.com>,
        Robin Murphy <robin.murphy@....com>,
        Will Deacon <will@...nel.org>, iommu@...ts.linux.dev,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH] iommu/tegra-smmu: fix error checking for debugfs_create_dir()

Hello Thierry,

On Mon, Oct 30, 2023 at 4:30 PM Thierry Reding <thierry.reding@...il.com> wrote:
>
> On Wed, Oct 25, 2023 at 07:25:50PM +0800, Baolu Lu wrote:
> > On 2023/10/25 19:01, Dario Binacchi wrote:
> > > The return value of debugfs_create_dir() should be checked using the
> > > IS_ERR() function.
> > >
> > > Signed-off-by: Dario Binacchi <dario.binacchi@...rulasolutions.com>
> > > ---
> > >
> > >   drivers/iommu/tegra-smmu.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> > > index e445f80d0226..cd1d80c4c673 100644
> > > --- a/drivers/iommu/tegra-smmu.c
> > > +++ b/drivers/iommu/tegra-smmu.c
> > > @@ -1056,7 +1056,7 @@ DEFINE_SHOW_ATTRIBUTE(tegra_smmu_clients);
> > >   static void tegra_smmu_debugfs_init(struct tegra_smmu *smmu)
> > >   {
> > >     smmu->debugfs = debugfs_create_dir("smmu", NULL);
> > > -   if (!smmu->debugfs)
> > > +   if (IS_ERR(smmu->debugfs))
> > >             return;
> >
> > This check can be removed, as debugfs_create_file() can handle the case
> > where @parent is an error pointer.
>
> A patch for this has been in linux-next for a few weeks, see:
>
> commit f7da9c081517daba70f9f9342e09d7a6322ba323
> Author: Jinjie Ruan <ruanjinjie@...wei.com>
> Date:   Fri Sep 1 15:30:56 2023 +0800
>
>     iommu/tegra-smmu: Drop unnecessary error check for for debugfs_create_dir()
>
>     The debugfs_create_dir() function returns error pointers.
>     It never returns NULL.
>
>     As Baolu suggested, this patch removes the error checking for
>     debugfs_create_dir in tegra-smmu.c. This is because the DebugFS kernel API
>     is developed in a way that the caller can safely ignore the errors that
>     occur during the creation of DebugFS nodes. The debugfs APIs have
>     a IS_ERR() judge in start_creating() which can handle it gracefully. So
>     these checks are unnecessary.
>
>     Fixes: d1313e7896e9 ("iommu/tegra-smmu: Add debugfs support")
>     Signed-off-by: Jinjie Ruan <ruanjinjie@...wei.com>
>     Suggested-by: Baolu Lu <baolu.lu@...ux.intel.com>
>     Acked-by: Thierry Reding <treding@...dia.com>
>     Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
>     Link: https://lore.kernel.org/r/20230901073056.1364755-1-ruanjinjie@huawei.com
>     Signed-off-by: Joerg Roedel <jroedel@...e.de>
>

Thanks for the explanation,
regards
Dario

> Thierry



-- 

Dario Binacchi

Senior Embedded Linux Developer

dario.binacchi@...rulasolutions.com

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