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

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Date:	Wed, 10 Feb 2016 16:21:19 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Guenter Roeck <linux@...ck-us.net>
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 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.

	Arnd