From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1763136AbYEFTDT (ORCPT ); Tue, 6 May 2008 15:03:19 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755771AbYEFTDF (ORCPT ); Tue, 6 May 2008 15:03:05 -0400 Received: from mail.parknet.ad.jp ([210.171.162.6]:40795 "EHLO mail.officemail.jp" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752532AbYEFTDB (ORCPT ); Tue, 6 May 2008 15:03:01 -0400 From: OGAWA Hirofumi To: Linus Torvalds Cc: Yinghai Lu , Greg KH , Ingo Molnar , Len Brown , "linux-kernel\@vger.kernel.org" , linux-acpi Subject: Re: acpi_cpu_freq_init warning... References: <86802c440805051951u153ebc21p15f0d73904496217@mail.gmail.com> <87k5i8hrmk.fsf@duaron.myhome.or.jp> Date: Wed, 07 May 2008 04:02:53 +0900 In-Reply-To: (Linus Torvalds's message of "Tue, 6 May 2008 07:47:18 -0700 (PDT)") Message-ID: <87skwvcl2a.fsf@duaron.myhome.or.jp> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii X-Anti-Virus: Kaspersky Anti-Virus for MailServers 5.5.10/RELEASE, bases: 24052007 #308098, status: clean Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Linus Torvalds writes: > On Tue, 6 May 2008, OGAWA Hirofumi wrote: >> - if ((drv->entry.next != drv->entry.prev) || >> + if ((drv->entry.next != drv->entry.prev) && >> (drv->entry.next != NULL)) { > > Umm. That code still makes no sense. > > The "drv->entry.next == drv->entry.prev" condition will trigger under > *three* different circumstances: > > - next/prev == NULL (uninitialized). Checked for by the explicit check > against NULL. > > - list empty (both next/prev point back to itself), which I assume the > check was *meant* for. > > - list has only *one* entry, when next/prev both point to the list head. > > and I'm pretty damn sure that whoever wrote that code didn't mean that > last one, but who knows.. > > The fact is, looking at next/prev this way is a sure way to have bugs. > > What is that PoS *trying* to test for? I assume it is meant to test for > > /* Is the list initialized and non-empty? */ > if (drv->entry.next && !list_empty(&drv->entry)) { > ... > > and dammit, just doing it that way is shorter and simpler. Whoops, sorry. You are right. diff -puN drivers/base/sys.c~fix-sys-bogus-warning drivers/base/sys.c --- linux-2.6/drivers/base/sys.c~fix-sys-bogus-warning 2008-05-07 03:51:00.000000000 +0900 +++ linux-2.6-hirofumi/drivers/base/sys.c 2008-05-07 04:01:14.000000000 +0900 @@ -175,8 +175,7 @@ int sysdev_driver_register(struct sysdev } /* Check whether this driver has already been added to a class. */ - if ((drv->entry.next != drv->entry.prev) || - (drv->entry.next != NULL)) { + if (drv->entry.next && !list_empty(&drv->entry)) { printk(KERN_WARNING "sysdev: class %s: driver (%p) has already" " been registered to a class, something is wrong, but " "will forge on!\n", cls->name, drv); _ -- OGAWA Hirofumi