From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1031112AbXD1F7J (ORCPT ); Sat, 28 Apr 2007 01:59:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1031111AbXD1F7J (ORCPT ); Sat, 28 Apr 2007 01:59:09 -0400 Received: from smtp111.plus.mail.re2.yahoo.com ([206.190.53.36]:37800 "HELO smtp111.plus.mail.re2.yahoo.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1031107AbXD1F7G (ORCPT ); Sat, 28 Apr 2007 01:59:06 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=s1024; d=yahoo.de; h=Received:X-YMail-OSG:Received:Date:From:To:Cc:Subject:Message-ID:Reply-To:References:MIME-Version:Content-Type:Content-Disposition:Content-Transfer-Encoding:In-Reply-To:User-Agent; b=jb4opM7mNy2bpwP8Hd6/ElbIKsQxM51/Cp3Srh+st6tJRAVVF31ANKVq/g4o1Sk3OP42vHcQF4hArrpOxfPyTtJ3FzPINQYQGGpvr5Jh9zoVa5KvikgL7TIdwQ9aXrNRtRhctE0mYTpeQ6xun2QnuHzW7QOkqZ7aRhI/QnrQwOQ= ; X-YMail-OSG: dBvz4vsVM1k2TnTFjFzlt_vOkKpxdJimQ8Vp1OmQCxrg4DvMOJK8BXdz0_qs7WM.PuClFwFVDA-- Date: Sat, 28 Apr 2007 07:57:40 +0200 From: Borislav Petkov To: Andrew Morton 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: <20070428055740.GA4957@gollum.tnic> Reply-To: bbpetkov@yahoo.de References: <20070425225716.8e9b28ca.akpm@linux-foundation.org> <20070426182519.GA4532@gollum.tnic> <20070427172230.94b82829.akpm@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20070427172230.94b82829.akpm@linux-foundation.org> User-Agent: Mutt/1.5.13 (2006-08-11) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 27, 2007 at 05:22:30PM -0700, 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) : > _ Yeah, I saw in other places that usually a NULL/0 is assigned to such a type of pointer. However, writing code which looks pretty silly just to shut up gcc is pretty senseless, IMHO. Isn't there such a tweak in gcc to say that this pointer is going to be assigned to later on, so don't issue a warning. Something like __attribute__ __address_will_be_overwritten_so_don't_bother_warning_me__? /me going to read gcc docs... -- Regards/Gruß, Boris.