linux-kernel - Re: [PATCH 1/2] tty: serial: samsung_tty: Fix a memory leak in s3c24xx_serial

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Date:   Sat, 10 Jun 2023 19:32:57 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Andi Shyti <andi.shyti@...nel.org>
Cc:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        Alim Akhtar <alim.akhtar@...sung.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jirislaby@...nel.org>,
        Thomas Abraham <thomas.abraham@...aro.org>,
        Kukjin Kim <kgene.kim@...sung.com>,
        linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-serial@...r.kernel.org
Subject: Re: [PATCH 1/2] tty: serial: samsung_tty: Fix a memory leak in
 s3c24xx_serial_getclk() in case of error

On 10/06/2023 19:10, Andi Shyti wrote:
> On Sat, Jun 10, 2023 at 06:23:58PM +0200, Krzysztof Kozlowski wrote:
>> On 10/06/2023 16:54, Andi Shyti wrote:
>>> On Sat, Jun 10, 2023 at 04:07:51PM +0200, Christophe JAILLET wrote:
>>>> Le 10/06/2023 à 12:26, Andi Shyti a écrit :
>>>>>> @@ -1459,8 +1459,10 @@ static unsigned int s3c24xx_serial_getclk(struct s3c24xx_uart_port *ourport,
>>>>>>   			continue;
>>>>>>   		rate = clk_get_rate(clk);
>>>>>> -		if (!rate)
>>>>>> +		if (!rate) {
>>>>>> +			clk_put(clk);
>>>>>>   			continue;
>>>>>
>>>>> could you also print an error here?
>>>>>
>>>>
>>>> Is:
>>>> 	dev_err(ourport->port.dev,
>>>> 		"Failed to get clock rate for %s.\n", clkname);
>>
>> Why do we need it? Most of other users of clk_get_rate() don't print.
> 
> that's not a reason not to print it.

This is the reason, because it was the conscious choice - not to print,
otherwise drivers are unreadable.

> 
>> Probably because such condition is highly unlikely if not impossible.
> 
> still... that's not a reason not to print it.

It is a reason not to print it in the driver. Code readability is more
important than adding error messages for every possible case in the driver.

> 
> All errors are unlikely and if it's unlikely, why there is no
> unlikely(!rate)? Which doesn't improve the reason not to print
> it.
> 
> The more unlikely, the lauder you need to be:
> 
> WARN_ON(!rate)... maybe too much!
> BUG_ON(!rate)... way too much!
> 
> But these are inversely proportional to the likeliness of the
> error.
> 
>> This makes simple function unnecessarily bigger...
> 
> and... that's not a reason not to print it :)

This is the reason not to print it in the driver, because it makes the
code less maintainable. Such unlikely errors should be handled by core,
not by every driver. If this error message here is reasonable, I would
argue that it is reasonable to add it to other places... try doing it.
You will see to what silly code it leads.

It's like adding dev_err to regmap_mmio read/write failures - code will
be difficult to read.

Best regards,
Krzysztof