linux-kernel - Re: [v2] coccinelle: semantic code search for missing of_node

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Date:   Sat, 29 Jun 2019 09:49:04 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...6.fr>
To:     Markus Elfring <Markus.Elfring@....de>
cc:     Wen Yang <wen.yang99@....com.cn>, linux-kernel@...r.kernel.org,
        cocci@...teme.lip6.fr, Yi Wang <wang.yi59@....com.cn>,
        Gilles Muller <Gilles.Muller@...6.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [v2] coccinelle: semantic code search for missing of_node_put



On Sat, 29 Jun 2019, Markus Elfring wrote:

> >> +if (x == NULL || ...) S
> >> +... when != e = (T)x
> >> +    when != true x == NULL
> >
> > I wonder if this code exclusion specification is really required
> > after a null pointer was checked before.
>
> I would like to add another view for this implementation detail.
>
> The when constraint can express a software desire which can be reasonable
> to some degree. You would like to be sure that a null pointer will not occur
> after a corresponding check succeeded.

He wants to be sure that the true branch through a NULL pointer check is
not taken.

> * But I feel unsure about the circumstances under which the Coccinelle software
>   can determine this aspect actually.
>
> * I find that it can eventually make sense only after the content of
>   the local variable (which is identified by “x”) was modified.
>   Thus I would find the exclusion of assignments more useful at this place.

I assume that it was added because it was found to be useful.  Please
actually try things out before declaring them to be useless.

julia