From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754432AbXD1Xsf (ORCPT ); Sat, 28 Apr 2007 19:48:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754433AbXD1Xsf (ORCPT ); Sat, 28 Apr 2007 19:48:35 -0400 Received: from hellhawk.shadowen.org ([80.68.90.175]:4171 "EHLO hellhawk.shadowen.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754432AbXD1Xse (ORCPT ); Sat, 28 Apr 2007 19:48:34 -0400 Message-ID: <4633DD55.1020006@shadowen.org> Date: Sun, 29 Apr 2007 00:48:37 +0100 From: Andy Whitcroft User-Agent: Icedove 1.5.0.9 (X11/20061220) MIME-Version: 1.0 To: Andrew Morton CC: bbpetkov@yahoo.de, linux-kernel@vger.kernel.org, Jeremy Fitzhardinge Subject: Re: [PATCH] mm/memory.c: remove warning from an uninitialized spinlock. was: Re: 2.6.21-rc7-mm2 References: <20070425225716.8e9b28ca.akpm@linux-foundation.org> <20070426182519.GA4532@gollum.tnic> <20070427172230.94b82829.akpm@linux-foundation.org> In-Reply-To: <20070427172230.94b82829.akpm@linux-foundation.org> X-Enigmail-Version: 0.94.2.0 OpenPGP: url=http://www.shadowen.org/~apw/public-key Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Andrew Morton wrote: > On Thu, 26 Apr 2007 20:25:19 +0200 > Borislav Petkov wrote: > >> Remove build warning mm/memory.c:1491: warning: 'ptl' may be used uninitialized in this function. >> The spinlock pointer is assigned to null since it gets overwritten right away in >> pte_alloc_map_lock(). >> >> Signed-off-by: Borislav Petkov >> --- >> >> Index: linux-mm/mm/memory.c >> =================================================================== >> --- linux-mm.orig/mm/memory.c 2007-04-26 19:57:14.000000000 +0200 >> +++ linux-mm/mm/memory.c 2007-04-26 20:00:30.000000000 +0200 >> @@ -1488,7 +1488,7 @@ >> pte_t *pte; >> int err; >> struct page *pmd_page; >> - spinlock_t *ptl; >> + spinlock_t *ptl = NULL; >> >> pte = (mm == &init_mm) ? >> pte_alloc_kernel(pmd, addr) : >> > > yes, I've been staring unhappily at this for some time. > > Your change adds seven bytes of text to this function for no runtime > benefit, just to fix a build-time warning. It's a general problem. > > > Often we just leave the warning in place and curse gcc each time it flies > past. Sometimes the code can be restructured in a sensible fashion to > avoid the warning; often it cannot. > > But I don't think I want to put up with a warning coming out of core MM all > the time so let's go with the following silliness which adds no additional > runtime cost. > > --- a/mm/memory.c~add-apply_to_page_range-which-applies-a-function-to-a-pte-range-fix > +++ a/mm/memory.c > @@ -1455,7 +1455,7 @@ static int apply_to_pte_range(struct mm_ > pte_t *pte; > int err; > struct page *pmd_page; > - spinlock_t *ptl; > + spinlock_t *ptl = ptl; /* Suppress gcc warning */ > > pte = (mm == &init_mm) ? > pte_alloc_kernel(pmd, addr) : > _ > Perhaps we should have some kind definition helper. #define suppress_unused(x) x = x spinlock_t *suppress_unused(ptl); Perhaps? -apw