linux-kernel - Re:Re: [PATCH] firmware: Hold a reference for of_find_compatible

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Message-ID: <578840ee.438c.181a5a58c00.Coremail.windhl@126.com>
Date:   Mon, 27 Jun 2022 22:51:38 +0800 (CST)
From:   "Liang He" <windhl@....com>
To:     "Greg KH" <gregkh@...uxfoundation.org>
Cc:     broonie@...nel.org, ckeepax@...nsource.cirrus.com,
        michal.simek@...inx.com, abhyuday.godhasara@...inx.com,
        simont@...nsource.cirrus.com, ronak.jain@...inx.com,
        peng.fan@....com, linux-kernel@...r.kernel.org
Subject: Re:Re: [PATCH] firmware: Hold a reference for
 of_find_compatible_node()



At 2022-06-27 22:09:43, "Greg KH" <gregkh@...uxfoundation.org> wrote:
>On Tue, Jun 21, 2022 at 11:26:25AM +0800, Liang He wrote:
>> In of_register_trusted_foundations(), we need to hold the reference
>> returned by of_find_compatible_node() and then use it to call
>> of_node_put() for refcount balance.
>> 
>> Signed-off-by: Liang He <windhl@....com>
>> ---
>>  include/linux/firmware/trusted_foundations.h | 8 ++++++--
>>  1 file changed, 6 insertions(+), 2 deletions(-)
>> 
>> diff --git a/include/linux/firmware/trusted_foundations.h b/include/linux/firmware/trusted_foundations.h
>> index be5984bda592..399471c2f1c7 100644
>> --- a/include/linux/firmware/trusted_foundations.h
>> +++ b/include/linux/firmware/trusted_foundations.h
>> @@ -71,12 +71,16 @@ static inline void register_trusted_foundations(
>>  
>>  static inline void of_register_trusted_foundations(void)
>>  {
>> +	struct device_node *np = of_find_compatible_node(NULL, NULL, "tlm,trusted-foundations");
>> +
>> +	of_node_put(np);
>> +	if (!np)
>
>While this is technically correct, you are now checking to see if this
>points to a memory location that you no longer know what it really
>belongs to.  C will let you do this, but it might be nicer to fix it up
>properly so it doesn't look like this.
>
>thanks,
>
>greg k-h

Hi，Greg KH，

Thanks very much for your effort to review my patch.

In fact, I have reported a commit for this kind of 'check-after-put' coding style:
https://lore.kernel.org/all/20220617112636.4041671-1-windhl@126.com/

But I have been told to keep such style and I think the explanation is also reasonable.
So when I make this patch, I am indeed confused what I should write.

Finally, I think it is better to be consistent with current coding style so
I chose this 'check-after-put' style.

But if you think it is better to use a normal order, i.e., check-then-put,
I am, of cause, very happy to send a new patch for this bug and I will
also keep to use this coding style in future.

Thanks again.

Liang