From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757956AbXD1AWf (ORCPT ); Fri, 27 Apr 2007 20:22:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757957AbXD1AWf (ORCPT ); Fri, 27 Apr 2007 20:22:35 -0400 Received: from smtp1.linux-foundation.org ([65.172.181.25]:33464 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757956AbXD1AWd (ORCPT ); Fri, 27 Apr 2007 20:22:33 -0400 Date: Fri, 27 Apr 2007 17:22:30 -0700 From: Andrew Morton To: bbpetkov@yahoo.de Cc: 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 Message-Id: <20070427172230.94b82829.akpm@linux-foundation.org> In-Reply-To: <20070426182519.GA4532@gollum.tnic> References: <20070425225716.8e9b28ca.akpm@linux-foundation.org> <20070426182519.GA4532@gollum.tnic> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 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 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) : _