Re: [PATCH] scripts: coccinelle: allow list_entry_is_head() to use pos

[Julia Lawall]

On Fri, 30 Jul 2021, Daniel Thompson wrote:

> Currently use_after_iter.cocci generates false positives for code of the
> following form:
> ~~~
> 	list_for_each_entry(d, &ddata->irq_list, node) {
> 		if (irq == d->irq)
> 			break;
> 	}
>
> 	if (list_entry_is_head(d, &ddata->irq_list, node))
> 		return IRQ_NONE;
> ~~~
> [This specific example comes from drivers/power/supply/cpcap-battery.c]
>
> Most list macros use list_entry_is_head() as loop exit condition meaning it
> is not unsafe to reuse pos (a.k.a. d) in the code above.
>
> Let's avoid reporting these cases.

Applied.

The function is really nice.  The use_after_iter.cocci rule gives a lot of
false positives where people have used random variables as flags to
indicate how the loop was executed...

thanks,
julia

>
> Signed-off-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> ---
>
> Notes:
>     I'm pretty much a complete beginner w.r.t. SmPL. This is written
>     entirely by finding previous fixes and emulating them!
>
>     However I did test it by running the checker across the current kernel
>     tree. The changes reduced the error count by four... which was small
>     enough for me to eyeball each one and check they match the pattern I
>     was targetting.
>
>  scripts/coccinelle/iterators/use_after_iter.cocci | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/scripts/coccinelle/iterators/use_after_iter.cocci b/scripts/coccinelle/iterators/use_after_iter.cocci
> index 9be48b520879..676edd562eef 100644
> --- a/scripts/coccinelle/iterators/use_after_iter.cocci
> +++ b/scripts/coccinelle/iterators/use_after_iter.cocci
> @@ -123,6 +123,8 @@ hlist_for_each_entry_safe(c,...) S
>  |
>  list_remove_head(x,c,...)
>  |
> +list_entry_is_head(c,...)
> +|
>  sizeof(<+...c...+>)
>  |
>   &c->member
>
> base-commit: 2734d6c1b1a089fb593ef6a23d4b70903526fe0c
> --
> 2.30.2
>
>