From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751982AbdBMNJE (ORCPT ); Mon, 13 Feb 2017 08:09:04 -0500 Received: from szxga03-in.huawei.com ([119.145.14.66]:55546 "EHLO szxga03-in.huawei.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751867AbdBMNJC (ORCPT ); Mon, 13 Feb 2017 08:09:02 -0500 Subject: Re: [PATCH] sched/isolcpus: Show isolated cpu map To: Peter Zijlstra References: <1486979039-17874-1-git-send-email-wangkefeng.wang@huawei.com> <20170213120650.GN6515@twins.programming.kicks-ass.net> CC: Ingo Molnar , , , Prarit Bhargava , Tejun Heo From: Kefeng Wang Message-ID: <46f994b0-ca60-65d7-3675-c01aeda5e439@huawei.com> Date: Mon, 13 Feb 2017 21:07:02 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20170213120650.GN6515@twins.programming.kicks-ass.net> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.177.19.180] X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Peter +Tejun On 2017/2/13 20:06, Peter Zijlstra wrote: > On Mon, Feb 13, 2017 at 05:43:59PM +0800, Kefeng Wang wrote: >> The commit a6e4491c682a ("sched/isolcpus: Output warning when the >> 'isolcpus=' kernel parameter is invalid") adds an error message >> when specified cpu bigger than nr_cpu_ids, but nr_cpumask_bits in >> cpulist_parse() could be nr_cpu_ids or NR_CPUS. >> >> eg, NR_CPUS=64, nr_cpu_ids=8 in ARM64, cpulist_parse() won't return >> -ERANGE if isolcpus=1-10; >> > > But why does cpulist_parse() use nr_cpumask_bits, that seems to be the > problem, so why not look there? > > Paste the Tejun's patch, commit 4d59b6ccf000862beed6fc0765d3209f98a8d8a2 Author: Tejun Heo Date: Wed Feb 8 14:30:56 2017 -0800 cpumask: use nr_cpumask_bits for parsing functions Commit 513e3d2d11c9 ("cpumask: always use nr_cpu_ids in formatting and parsing functions") converted both cpumask printing and parsing functions to use nr_cpu_ids instead of nr_cpumask_bits. While this was okay for the printing functions as it just picked one of the two output formats that we were alternating between depending on a kernel config, doing the same for parsing wasn't okay. nr_cpumask_bits can be either nr_cpu_ids or NR_CPUS. We can always use nr_cpu_ids but that is a variable while NR_CPUS is a constant, so it can be more efficient to use NR_CPUS when we can get away with it. Converting the printing functions to nr_cpu_ids makes sense because it affects how the masks get presented to userspace and doesn't break anything; however, using nr_cpu_ids for parsing functions can incorrectly leave the higher bits uninitialized while reading in these masks from userland. As all testing and comparison functions use nr_cpumask_bits which can be larger than nr_cpu_ids, the parsed cpumasks can erroneously yield false negative results. This made the taskstats interface incorrectly return -EINVAL even when the inputs were correct. Fix it by restoring the parse functions to use nr_cpumask_bits instead of nr_cpu_ids. Link: http://lkml.kernel.org/r/20170206182442.GB31078@htj.duckdns.org Fixes: 513e3d2d11c9 ("cpumask: always use nr_cpu_ids in formatting and parsing functions") Signed-off-by: Tejun Heo Reported-by: Martin Steigerwald Debugged-by: Ben Hutchings Cc: [4.0+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds