Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753359AbcLHLpD (ORCPT ); Thu, 8 Dec 2016 06:45:03 -0500 Received: from mail-wj0-f196.google.com ([209.85.210.196]:36521 "EHLO mail-wj0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751741AbcLHLpA (ORCPT ); Thu, 8 Dec 2016 06:45:00 -0500 Date: Thu, 8 Dec 2016 14:44:57 +0300 From: "Kirill A. Shutemov" To: =?iso-8859-1?B?Suly6W15?= Lefaure Cc: x86@kernel.org, Borislav Petkov , linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/vm86: fix compilation warning on a unused variable Message-ID: <20161208114457.GA26794@node.shutemov.name> References: <20161208043833.15088-1-jeremy.lefaure@lse.epita.fr> <20161208105011.2jmuvlgdnirnv33b@black.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20161208105011.2jmuvlgdnirnv33b@black.fi.intel.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1630 Lines: 38 On Thu, Dec 08, 2016 at 01:50:11PM +0300, Kirill A. Shutemov wrote: > On Wed, Dec 07, 2016 at 11:38:33PM -0500, Jérémy Lefaure wrote: > > When CONFIG_TRANSPARENT_HUGEPAGE is disabled, split_huge_pmd is a no-op > > stub. In such case, vma is unused and a compiler raises a warning: > > > > arch/x86/kernel/vm86_32.c: In function ‘mark_screen_rdonly’: > > arch/x86/kernel/vm86_32.c:180:26: warning: unused variable ‘vma’ > > [-Wunused-variable] > > struct vm_area_struct *vma = find_vma(mm, 0xA0000); > > ^~~ > > Adding __maybe_unused in the vma declaration fixes this warning. > > Hm. pmd_trans_huge() is zero if CONFIG_TRANSPARENT_HUGEPAGE is not set. > Compiler should get rid of whole block of code under the 'if'. > > Could you share your kernel config which triggers the warning? > And what compiler do you use? Okay, I see the problem. It still doesn't make sense. Why would compiler check for unused warnings before dropping unused code. What about something like this, instead: diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index 6f14de45b5ce..b538452a127e 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -180,7 +180,7 @@ static inline int split_huge_page(struct page *page) } static inline void deferred_split_huge_page(struct page *page) {} #define split_huge_pmd(__vma, __pmd, __address) \ - do { } while (0) + do { (void)__vma; } while (0) static inline void split_huge_pmd_address(struct vm_area_struct *vma, unsigned long address, bool freeze, struct page *page) {} -- Kirill A. Shutemov