linux-kernel - [PATCH] scripts: coccinelle: allow list_entry_is

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Message-Id: <20210730095856.2038286-1-daniel.thompson@linaro.org>
Date:   Fri, 30 Jul 2021 10:58:56 +0100
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Julia Lawall <Julia.Lawall@...ia.fr>,
        Gilles Muller <Gilles.Muller@...ia.fr>,
        Nicolas Palix <nicolas.palix@...g.fr>,
        Michal Marek <michal.lkml@...kovi.net>
Cc:     Daniel Thompson <daniel.thompson@...aro.org>,
        cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org
Subject: [PATCH] scripts: coccinelle: allow list_entry_is_head() to use pos

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.

Signed-off-by: Daniel Thompson <daniel.thompson@...aro.org>
---

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