Messages in this thread | | | Subject | Re: [Cocci] Proposal for a new checkpatch check; matching _set_drvdata() & _get_drvdata() | From | Lars-Peter Clausen <> | Date | Fri, 20 Nov 2020 14:16:00 +0100 |
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On 11/20/20 12:54 PM, Alexandru Ardelean wrote: > 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. > Doing something like this with coccinelle is fairly easy.
But I'd be very cautious about putting such a script into the kernel. It will result in too many false positive drive-by patches. Such a script will not detect cases such as:
* Driver is split over multiple files. One file does ..._set_drvdata(), another does ..._get_drvdata().
* Framework uses drvdata to exchange data with the driver. E.g driver is expected to call set_drvdata() and then the framework uses get_drvdata() to retrieve the data. This is not a very good pattern, but there are some palces int he kernel where this is used. I believe for example V4L2 uses this.
- Lars
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