linux-kernel - Re: Coccinelle: Checking of_node

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Date:   Thu, 11 Jul 2019 07:41:01 -0700
From:   Tyrel Datwyler <tyreld@...ux.vnet.ibm.com>
To:     wen.yang99@....com.cn, Markus.Elfring@....de, julia.lawall@...6.fr
Cc:     wang.yi59@....com.cn, linux-pm@...r.kernel.org, rjw@...ysocki.net,
        daniel.lezcano@...aro.org, kernel-janitors@...r.kernel.org,
        linux-kernel@...r.kernel.org, oss@...error.net, paulus@...ba.org,
        xue.zhihong@....com.cn, linuxppc-dev@...ts.ozlabs.org,
        cheng.shengyu@....com.cn
Subject: Re: Coccinelle: Checking of_node_put() calls with SmPL

On 07/10/2019 11:35 PM, wen.yang99@....com.cn wrote:
>>> we developed a coccinelle script to detect such problems.
>>
>> Would you find the implementation of the function “dt_init_idle_driver”
>> suspicious according to discussed source code search patterns?
>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/cpuidle/dt_idle_states.c?id=e9a83bd2322035ed9d7dcf35753d3f984d76c6a5#n208
>> https://elixir.bootlin.com/linux/v5.2/source/drivers/cpuidle/dt_idle_states.c#L208
>>
>>
>>> This script is still being improved.
>>
>> Will corresponding software development challenges become more interesting?
> 
> Hello Markus,
> This is the simplified code pattern for it:
> 
> 172         for (i = 0; ; i++) {

This loop can only be exited on a break.

> 173                 state_node = of_parse_phandle(...);     ---> Obtain here
> ...
> 177                 match_id = of_match_node(matches, state_node);
> 178                 if (!match_id) {
> 179                         err = -ENODEV;                              
> 180                         break;                         --->  Jump out of the loop without releasing it
> 181                 }
> 182 
> 183                 if (!of_device_is_available(state_node)) {
> 184                         of_node_put(state_node);
> 185                         continue;                    --->  Release the object references within a loop
> 186                 }
> ...
> 208                 of_node_put(state_node);  -->  Release the object references within a loop

This is required at the end of every loop or continue to free the reference.
Only a break will exit the loop where we hit the below of_node_put().

> 209         }
> 210 
> 211         of_node_put(state_node);       -->    There may be double free here.

None of the break conditions call of_node_put(), so it needs to be called here.

-Tyrel

> 
> This code pattern is very interesting and the coccinelle software should also recognize this pattern.
> 
> Regards,
> Wen
>