linux-kernel - Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR

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Date:	Wed, 10 Feb 2016 19:38:19 -0800
From:	Guenter Roeck <linux@...ck-us.net>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Baruch Siach <baruch@...s.co.il>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org, Jiri Slaby <jslaby@...e.com>,
	kernel-testers@...r.kernel.org, Andrzej Hajda <a.hajda@...sung.com>
Subject: Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR_VALUE

On 02/10/2016 07:21 AM, Arnd Bergmann wrote:
> On Tuesday 09 February 2016 18:37:46 Guenter Roeck wrote:
>> On 02/09/2016 07:26 AM, Arnd Bergmann wrote:
>>> On Tuesday 09 February 2016 07:08:59 Guenter Roeck wrote:
>>>> IS_ERR_VALUE() assumes that its parameter is an unsigned long.
>>>> It can not be used to check if an unsigned int reflects an error.
>>>> Doing so can result in the following build warning.
>>>>
>>>> drivers/tty/serial/digicolor-usart.c: In function ‘digicolor_uart_probe’:
>>>> include/linux/err.h:21:38: warning:
>>>>           comparison is always false due to limited range of data type
>>>> drivers/tty/serial/digicolor-usart.c:485:6: note:
>>>>           in expansion of macro ‘IS_ERR_VALUE’
>>>>
>>>> If that warning is seen, an error return from platform_get_irq() is missed.
>>>>
>>>>
>>>
>>> The patch looks correct to me, but what compiler version and which kernel
>>> tree is it that triggered the warning?
>>>
>>> Andrzej Hajda just modified the definition of IS_ERR_VALUE(), and the
>>> changes are still under discussion, but I don't see that warning with
>>> any of the versions.
>>>
>> I see it with gcc 5.1 and 5.2 (and W=1). I did not see / notice Andrzej's patch.
>>
>> I agree that fixing the problem in IS_ERR_VALUE() is preferrable.
>>
>>
>
> Ah, W=1 explains it. We are still debating about the proper solution. Al Viro
> pointed out that most users of IS_ERR_VALUE() shouldn't be using it at all,
> so your patch is probably best here after all.
>

Yes, after looking into it some more I agree. Coccinelle should be able to handle
most of the conversions automatically. I actually tried to write a script, just
for the fun of it, but it misses some of the problem cases in patch mode.
Maybe I get it working tonight.

Guenter