linux-kernel - Re: [PATCH v6] coccinelle: semantic code search for missing put

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Date:   Sun, 17 Feb 2019 12:37:18 +0100 (CET)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Markus Elfring <Markus.Elfring@....de>
cc:     Wen Yang <yellowriver2010@...mail.com>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Wen Yang <wen.yang99@....com.cn>,
        Cheng Shengyu <cheng.shengyu@....com.cn>,
        kernel-janitors@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>,
        Coccinelle <cocci@...teme.lip6.fr>
Subject: Re: [PATCH v6] coccinelle: semantic code search for missing
 put_device()



On Sun, 17 Feb 2019, Markus Elfring wrote:

> > +@...rch exists@
> > +local idexpression id;
> > +expression x,e,e1;
> > +position p1,p2;
> > +type T,T1,T2;
> > +@@
> > +
> > +id = of_find_device_by_node@p1(x)
> > +... when != e = id
>
> I suggest to increase your software development attention also for
> another implementation detail.
> Source code analysis triggers challenges for safe data flow handling.
> the semantic patch language supports search specifications for
> the exclusion of specific assignments.
>
> Does this SmPL code contain a questionable order for the source
> and target metavariables?
> Can the following variant be more appropriate?
>
> + ... when != id = e

This is possible, but I think unlikely.

>
>
> > +if (id == NULL || ...) { ... return ...; }
> > +... when != put_device(&id->dev)
> > +    when != platform_device_put(id)
> > +    when != of_dev_put(id)
> > +    when != if (id) { ... put_device(&id->dev) ... }
> > +    when != e1 = (T)id
>
> Would you like to avoid that the return value from the shown function call
> gets overwritten in the variable before it was used once at least
> (when a bit of extra C code is tolerated before a null pointer check)?

Indeed there should be a put then too, but again, it seems unlikely.

julia


>
> Regards,
> Markus
>