From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753923Ab1LACK5 (ORCPT ); Wed, 30 Nov 2011 21:10:57 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:57576 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753289Ab1LACK4 (ORCPT ); Wed, 30 Nov 2011 21:10:56 -0500 Date: Wed, 30 Nov 2011 18:12:05 -0800 From: Andrew Morton To: Dimitri Sivanich Cc: linux-kernel@vger.kernel.org, Thomas Gleixner Subject: Re: [PATCH] specific do_timer_cpu value for nohz off mode Message-Id: <20111130181205.2eccd879.akpm@linux-foundation.org> In-Reply-To: <20111201020631.GA30097@sgi.com> References: <20111108191149.GA7236@sgi.com> <20111122160802.e99d6218.akpm@linux-foundation.org> <20111130152959.GA19205@sgi.com> <20111130161131.31cdccff.akpm@linux-foundation.org> <20111201020631.GA30097@sgi.com> X-Mailer: Sylpheed 2.7.1 (GTK+ 2.18.9; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 30 Nov 2011 20:06:31 -0600 Dimitri Sivanich wrote: > On Wed, Nov 30, 2011 at 04:11:31PM -0800, Andrew Morton wrote: > > On Wed, 30 Nov 2011 09:29:59 -0600 > > Dimitri Sivanich wrote: > > > > > +static ssize_t sysfs_store_do_timer_cpu(struct sys_device *dev, > > > + struct sysdev_attribute *attr, > > > + const char *buf, size_t size) > > > +{ > > > + struct sysdev_ext_attribute *ea = SYSDEV_TO_EXT_ATTR(attr); > > > + unsigned int new; > > > + int rv; > > > + > > > +#ifdef CONFIG_NO_HZ > > > + /* nohz mode not supported */ > > > + if (tick_nohz_enabled) > > > + return -EINVAL; > > > +#endif > > > + > > > + rv = kstrtouint(buf, 0, &new); > > > + if (rv) > > > + return rv; > > > + > > > + if (new >= NR_CPUS || !cpu_online(new)) > > > + return -ERANGE; > > > + > > > + *(unsigned int *)(ea->var) = new; > > > + return size; > > > +} > > > > checkpatch tells us: > > > > WARNING: usage of NR_CPUS is often wrong - consider using cpu_possible(), num_possible_cpus(), for_each_possible_cpu(), etc > > I think a check against num_possible_cpus() should be OK. You want cpu_possible(). Or maybe cpu_present(). > > > > I think the check can just be removed? Surely cpu_online(1000000000) > > will return false? > > A value > NR_CPUS and < MAX_INT caused a panic in sysfs_store_do_timer_cpu, > presumably from the cpu_online() check. The check against NR_CPUS avoided > the panic. OK. Well, it's not a panic: static inline unsigned int cpumask_check(unsigned int cpu) { #ifdef CONFIG_DEBUG_PER_CPU_MAPS WARN_ON_ONCE(cpu >= nr_cpumask_bits); #endif /* CONFIG_DEBUG_PER_CPU_MAPS */ return cpu; } so we can't do cpu_online(insane number)