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From:   Alexandru Ardelean <ardeleanalex@gmail.com>
Date:   Fri, 20 Nov 2020 13:54:20 +0200
Message-ID: <CA+U=Dsp8Aws7_GARfgNE4w_1pK-hDVW9WVsWHF1TfZUEUo0Hbw@mail.gmail.com>
Subject: Re: [Cocci] Proposal for a new checkpatch check; matching
 _set_drvdata() & _get_drvdata()
To:     Julia Lawall <julia.lawall@inria.fr>
Cc:     Joe Perches <joe@perches.com>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        Robo Bot <apw@canonical.com>,
        Alexandru Ardelean <alexandru.ardelean@analog.com>,
        LKML <linux-kernel@vger.kernel.org>,
        cocci <cocci@systeme.lip6.fr>
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On Fri, Nov 20, 2020 at 12:47 PM Julia Lawall <julia.lawall@inria.fr> wrote:
>
>
>
> On Thu, 19 Nov 2020, Joe Perches wrote:
>
> > On Thu, 2020-11-19 at 17:16 +0200, Andy Shevchenko wrote:
> > > On Thu, Nov 19, 2020 at 4:09 PM Alexandru Ardelean
> > > <ardeleanalex@gmail.com> wrote:
> > > >
> > > > Hey,
> > > >
> > > > So, I stumbled on a new check that could be added to checkpatch.
> > > > Since it's in Perl, I'm reluctant to try it.
> > > >
> > > > Seems many drivers got to a point where they now call (let's say)
> > > > spi_set_drvdata(), but never access that information via
> > > > spi_get_drvdata().
> > > > Reasons for this seem to be:
> > > > 1. They got converted to device-managed functions and there is no
> > > > longer a remove hook to require the _get_drvdata() access
> > > > 2. They look like they were copied from a driver that had a
> > > > _set_drvdata() and when the code got finalized, the _set_drvdata() was
> > > > omitted
> > > >
> > > > There are a few false positives that I can notice at a quick look,
> > > > like the data being set via some xxx_set_drvdata() and retrieved via a
> > > > dev_get_drvdata().
> > >
> > > I can say quite a few. And this makes a difference.
> > > So, basically all drivers that are using PM callbacks would rather use
> > > dev_get_drvdata() rather than bus specific.
> > >
> > > > I think checkpatch reporting these as well would be acceptable simply
> > > > from a reviewability perspective.
> > > >
> > > > I did a shell script to quickly check these. See below.
> > > > It's pretty badly written but it is enough for me to gather a list.
> > > > And I wrote it in 5 minutes :P
> > > > I initially noticed this in some IIO drivers, and then I suspected
> > > > that this may be more widespread.
> > >
> > > It seems more suitable for coccinelle.
> >
> > To me as well.
>
> To me as well, since it seems to involve nonlocal information.
>
> I'm not sure to understand the original shell script. Is there
> something interesting about pci_set_drvdata?

Ah, it's a stupid script I wrote in 5 minutes, so I did not bother to
make things smart.
In the text-matching I did in shell, there are some entries that come
from comments and docs.
It's only about 3-4 entries, so I just did a visual/manual ignore.

In essence:
The script searches for all strings that contain _set_drvdata.
The separators are whitespace.
It creates a list of all  xxxx_set_drvdata functions.
For each xxxx_set_drvdata function:
    It checks all files that have a xxxx_set_drvdata entry, but no
xxxx_get_drvdata

I piped this output into a file and started manually checking the drivers.
There is one [I forget which function] that is xxxx_set_drvdata() but
equivalent is xxxx_drvdata()

As Andy said, some precautions must be taken in places where
xxxx_set_drvdata() is called but dev_get_drvdata() is used.
Cases like PM suspend/resume calls.
And there may be some cases outside this context.


>
> julia