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Fri, 20 Nov 2020 05:27:12 -0800 (PST) MIME-Version: 1.0 References: <4af50412-a22f-4ca1-adb0-d732438c6669@metafoo.de> In-Reply-To: <4af50412-a22f-4ca1-adb0-d732438c6669@metafoo.de> From: Alexandru Ardelean Date: Fri, 20 Nov 2020 15:27:01 +0200 Message-ID: To: Lars-Peter Clausen X-Greylist: Sender IP whitelisted, Sender e-mail whitelisted, not delayed by milter-greylist-4.4.3 (isis.lip6.fr [132.227.60.2]); Fri, 20 Nov 2020 14:27:16 +0100 (CET) X-Greylist: Sender DNS name whitelisted, not delayed by milter-greylist-4.4.3 (isis.lip6.fr [IPv6:2001:660:3302:283c:0:0:0:2]); Fri, 20 Nov 2020 14:27:13 +0100 (CET) X-Scanned-By: MIMEDefang 2.78 on 132.227.60.2 X-Scanned-By: MIMEDefang 2.78 Cc: LKML , Robo Bot , Andy Shevchenko , Joe Perches , Alexandru Ardelean , cocci Subject: Re: [Cocci] Proposal for a new checkpatch check; matching _set_drvdata() & _get_drvdata() X-BeenThere: cocci@systeme.lip6.fr X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: cocci-bounces@systeme.lip6.fr Errors-To: cocci-bounces@systeme.lip6.fr On Fri, Nov 20, 2020 at 3:16 PM Lars-Peter Clausen wrote: > > On 11/20/20 12:54 PM, Alexandru Ardelean wrote: > > On Fri, Nov 20, 2020 at 12:47 PM Julia Lawall 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 > >>>> 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: Yeah, it would probably be a good idea to start with a few simple checks, then scale it. If we go for the existing _set_drvdata() / _get_drvdata() pair checks, there is a risk of breaking things. > > * 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 > _______________________________________________ Cocci mailing list Cocci@systeme.lip6.fr https://systeme.lip6.fr/mailman/listinfo/cocci