linux-kernel - Re: Coccinelle: Checking of_node

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Date:   Thu, 11 Jul 2019 11:04:13 +0200
From:   Markus Elfring <Markus.Elfring@....de>
To:     Wen Yang <wen.yang99@....com.cn>, linux-pm@...r.kernel.org,
        kernel-janitors@...r.kernel.org
Cc:     Julia Lawall <julia.lawall@...6.fr>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Cheng Shengyu <cheng.shengyu@....com.cn>,
        Kumar Gala <galak@...nel.crashing.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Scott Wood <oss@...error.net>,
        Xue Zhihong <xue.zhihong@....com.cn>,
        Yi Wang <wang.yi59@....com.cn>, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: Coccinelle: Checking of_node_put() calls with SmPL

> 180                         break;                         --->  Jump out of the loop without releasing it

The device node reference is released behind this for loop.

> 183                 if (!of_device_is_available(state_node)) {
> 184                         of_node_put(state_node);

This function call was added by the commit “cpuidle: dt: Add missing 'of_node_put()'”
on 2017-06-12.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/cpuidle/dt_idle_states.c?id=b2cdd8e1b54849477a32d820acc2e87828a38f3d

> 185                         continue;                    --->  Release the object references within a loop

I became curious on the applicability of an other coding style
(for a software refactoring) at this place.
How do you think about to achieve the same effect by using a goto statement
instead of two statements in such an if branch?

> 208                 of_node_put(state_node);  -->  Release the object references within a loop
> 209         }
> 210
> 211         of_node_put(state_node);       -->    There may be double free here.

This information points a recurring challenge out for safe source code analysis.
How would you like to exclude the detection of false positives finally?

> This code pattern is very interesting

Thanks that you think also in this direction.

> and the coccinelle software should also recognize this pattern.

There are some open issues to consider for available analysis tools.
How will corresponding details be clarified then?

Regards,
Markus