From mboxrd@z Thu Jan 1 00:00:00 1970 From: Guenter Roeck Subject: Re: [PATCH] tty/serial: digicolor: Fix bad usage of IS_ERR_VALUE Date: Thu, 11 Feb 2016 07:13:22 -0800 Message-ID: <20160211151322.GA30389@roeck-us.net> References: <1455030539-10798-1-git-send-email-linux@roeck-us.net> <4571887.rTPndCnv20@wuerfel> <56BAA27A.9050605@roeck-us.net> <20160211104650.GU10826@n2100.arm.linux.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: <20160211104650.GU10826@n2100.arm.linux.org.uk> Sender: linux-kernel-owner@vger.kernel.org To: Russell King - ARM Linux Cc: Arnd Bergmann , linux-arm-kernel@lists.infradead.org, Baruch Siach , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, Andrzej Hajda , linux-serial@vger.kernel.org, Jiri Slaby , kernel-testers@vger.kernel.org List-Id: linux-serial@vger.kernel.org On Thu, Feb 11, 2016 at 10:46:50AM +0000, Russell King - ARM Linux wrot= e: > On Tue, Feb 09, 2016 at 06:37:46PM -0800, 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 =E2=80=98digico= lor_uart_probe=E2=80=99: > > >>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 =E2=80=98IS_ERR_VALUE=E2=80=99 > > >> > > >>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 w= ith > > >any of the versions. > > > > > I see it with gcc 5.1 and 5.2 (and W=3D1). I did not see / notice A= ndrzej's patch. > >=20 > > I agree that fixing the problem in IS_ERR_VALUE() is preferrable. >=20 > I disagree. What happens if (eg) you decide to do this: >=20 > u8 irq; >=20 > irq =3D platform_get_irq(...); > if (IS_ERR_VALUE(irq)) > ... >=20 > is that the fault of IS_ERR_VALUE() that it will never be true? No, = it's > a programming error in the caller, because the caller is using the wr= ong > type here - in fact, you can't do anything in IS_ERR_VALUE() to corre= ct > that. >=20 Yes, I think we all reached that conclusion by now. Thanks, Guenter