From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tejun Heo Subject: Re: [PATCH v2 5/7] x86, acpi, cpu-hotplug: Introduce apicid_to_cpuid[] array to store persistent cpuid <-> apicid mapping. Date: Sat, 26 Sep 2015 13:56:22 -0400 Message-ID: <20150926175622.GC3572@htj.duckdns.org> References: <1441859269-25831-1-git-send-email-tangchen@cn.fujitsu.com> <1441859269-25831-6-git-send-email-tangchen@cn.fujitsu.com> <20150910195532.GK8114@mtj.duckdns.org> <56066AC9.6020703@cn.fujitsu.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from mail-yk0-f182.google.com ([209.85.160.182]:36582 "EHLO mail-yk0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753217AbbIZR41 (ORCPT ); Sat, 26 Sep 2015 13:56:27 -0400 Content-Disposition: inline In-Reply-To: <56066AC9.6020703@cn.fujitsu.com> Sender: linux-acpi-owner@vger.kernel.org List-Id: linux-acpi@vger.kernel.org To: Tang Chen Cc: jiang.liu@linux.intel.com, mika.j.penttila@gmail.com, mingo@redhat.com, akpm@linux-foundation.org, rjw@rjwysocki.net, hpa@zytor.com, yasu.isimatu@gmail.com, isimatu.yasuaki@jp.fujitsu.com, kamezawa.hiroyu@jp.fujitsu.com, izumi.taku@jp.fujitsu.com, gongzhaogang@inspur.com, qiaonuohan@cn.fujitsu.com, x86@kernel.org, linux-acpi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org On Sat, Sep 26, 2015 at 05:52:09PM +0800, Tang Chen wrote: > >>+static int allocate_logical_cpuid(int apicid) > >>+{ > >>+ int i; > >>+ > >>+ /* > >>+ * cpuid <-> apicid mapping is persistent, so when a cpu is up, > >>+ * check if the kernel has allocated a cpuid for it. > >>+ */ > >>+ for (i = 0; i < max_logical_cpuid; i++) { > >>+ if (cpuid_to_apicid[i] == apicid) > >>+ return i; > >>+ } > >>+ > >>+ /* Allocate a new cpuid. */ > >>+ if (max_logical_cpuid >= nr_cpu_ids) { > >>+ WARN_ONCE(1, "Only %d processors supported." > >>+ "Processor %d/0x%x and the rest are ignored.\n", > >>+ nr_cpu_ids - 1, max_logical_cpuid, apicid); > >>+ return -1; > >>+ } > >So, the original code didn't have this failure mode, why is this > >different for the new code? > > It is not different. Since max_logical_cpuid is new, this is ensure it won't > go beyond NR_CPUS. If the above condition can happen, the original code should have had a similar check as above, right? Sure, max_logical_cpuid is a new thing but that doesn't seem to change whether the above condition can happen or not, no? Thanks. -- tejun