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

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Date:   Sat, 29 Jun 2019 09:40:36 +0200
From:   Markus Elfring <Markus.Elfring@....de>
To:     Wen Yang <wen.yang99@....com.cn>, linux-kernel@...r.kernel.org,
        cocci@...teme.lip6.fr
Cc:     Yi Wang <wang.yi59@....com.cn>,
        Julia Lawall <Julia.Lawall@...6.fr>,
        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

>> +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.

* 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.

Regards,
Markus