From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752197AbeBZHtn (ORCPT ); Mon, 26 Feb 2018 02:49:43 -0500 Received: from mail-ua0-f193.google.com ([209.85.217.193]:45076 "EHLO mail-ua0-f193.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752002AbeBZHtl (ORCPT ); Mon, 26 Feb 2018 02:49:41 -0500 X-Google-Smtp-Source: AG47ELvbm4/IzLcd718We5PqFgxeLjS8PmzeZZfk1KI8E8YmDFoP7yN2yYC2B2LwNK3gj9xDvS4mGMAHHO1++dsSTYM= MIME-Version: 1.0 In-Reply-To: <55d52f37-c24d-c2da-43c6-73a55403d3b6@c-s.fr> References: <20180225172236.29650-1-malat@debian.org> <20180225172236.29650-6-malat@debian.org> <55d52f37-c24d-c2da-43c6-73a55403d3b6@c-s.fr> From: Mathieu Malaterre Date: Mon, 26 Feb 2018 08:49:20 +0100 X-Google-Sender-Auth: np-Qa_as9v6m6xUmNe1MiuRMqbI Message-ID: Subject: Re: [PATCH 05/21] powerpc: Avoid comparison of unsigned long >= 0 in pfn_valid To: Christophe LEROY Cc: Michael Ellerman , LKML , Paul Mackerras , Jiri Slaby , linuxppc-dev Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id w1Q7nlSN011420 On Mon, Feb 26, 2018 at 7:32 AM, Christophe LEROY wrote: > > > Le 25/02/2018 à 18:22, Mathieu Malaterre a écrit : >> >> Rewrite comparison since all values compared are of type `unsigned long`. >> >> Fix a warning (treated as error in W=1): >> >> CC arch/powerpc/kernel/irq.o >> In file included from ./include/linux/bug.h:5:0, >> from ./include/linux/cpumask.h:13, >> from ./include/linux/smp.h:13, >> from ./include/linux/kernel_stat.h:5, >> from arch/powerpc/kernel/irq.c:35: >> ./include/linux/dma-mapping.h: In function ‘dma_map_resource’: >> ./arch/powerpc/include/asm/page.h:129:32: error: comparison of unsigned >> expression >= 0 is always true [-Werror=type-limits] >> #define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < max_mapnr) >> ^ >> Suggested-by: Segher Boessenkool >> Signed-off-by: Mathieu Malaterre >> --- >> arch/powerpc/include/asm/page.h | 3 ++- >> 1 file changed, 2 insertions(+), 1 deletion(-) >> >> diff --git a/arch/powerpc/include/asm/page.h >> b/arch/powerpc/include/asm/page.h >> index 8da5d4c1cab2..19dea64e7ed2 100644 >> --- a/arch/powerpc/include/asm/page.h >> +++ b/arch/powerpc/include/asm/page.h >> @@ -126,7 +126,8 @@ extern long long virt_phys_offset; >> #ifdef CONFIG_FLATMEM >> #define ARCH_PFN_OFFSET ((unsigned long)(MEMORY_START >> >> PAGE_SHIFT)) >> -#define pfn_valid(pfn) ((pfn) >= ARCH_PFN_OFFSET && (pfn) < >> max_mapnr) >> +#define pfn_valid(pfn) \ >> + (((pfn) - ARCH_PFN_OFFSET) < (max_mapnr - >> ARCH_PFN_OFFSET)) > > > What will happen when ARCH_PFN_OFFSET is not nul and pfn is lower than > ARCH_PFN_OFFSET ? I assumed that normal unsigned integers modulo would make the test fail. But for some particular value of max_mapnr the two are indeed not equivalent. > Christophe > > >> #endif >> #define virt_to_pfn(kaddr) (__pa(kaddr) >> PAGE_SHIFT) >> >