Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR_VALUE

[Guenter Roeck]

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 âdigicolor_uart_probeâ:
> > > > 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 âIS_ERR_VALUEâ
> > > >
> > > > 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