From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1754520AbdBFQUd (ORCPT <rfc822;w@1wt.eu>);
        Mon, 6 Feb 2017 11:20:33 -0500
Received: from mail-yb0-f196.google.com ([209.85.213.196]:33800 "EHLO
        mail-yb0-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1754392AbdBFQU3 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Mon, 6 Feb 2017 11:20:29 -0500
Date: Mon, 6 Feb 2017 11:20:27 -0500
From: Tejun Heo <tj@kernel.org>
To: Martin Steigerwald <martin.steigerwald@teamix.de>
Cc: Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        Andrew Morton <akpm@osdl.org>, Ingo Molnar <mingo@elte.hu>,
        LKML <linux-kernel@vger.kernel.org>,
        Nicolas Dichtel <nicolas.dichtel@6wind.com>,
        Jay Lan <jlan@engr.sgi.com>, Martin Steigerwald <martin@lichtvoll.de>,
        Gerlof Langeveld <gerlof.langeveld@atoptool.nl>,
        Marc Haber <mh+debian-packages@zugschlus.de>,
        Ben Hutchings <ben@decadent.org.uk>,
        Balbir Singh <bsingharora@gmail.com>
Subject: Re: [REGRESSION] Two issues that prevent process accounting
 (taskstats) from working correctly
Message-ID: <20170206162027.GA31078@htj.duckdns.org>
References: <5967400.cFS0L5jxeH@merkaba>
 <20161219172549.GK3107@twins.programming.kicks-ass.net>
 <5854646.yRl4qIL1ZN@merkaba>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <5854646.yRl4qIL1ZN@merkaba>
User-Agent: Mutt/1.7.1 (2016-10-04)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

Hello,

On Mon, Feb 06, 2017 at 11:39:04AM +0100, Martin Steigerwald wrote:
> > Ben Hutchings reports:
> > 
> > "It looks like the taskstats bug was introduced by 513e3d2d11c9 as that
> > means cpumask_parse() may not initialise as many bits as
> > cpumask_subset() compares"

I see, so that patch switched parsing and printing to always use
nr_cpu_ids but left the comparison functions to keep using
nr_cpumask_bits which may be NR_CPUS instead of nr_cpu_ids.

> Okay, any conclusion out of this? Any feedback from the maintainers of this 
> code?

We can switch back the parse functions to nr_cpumask_bits, or just get
rid of nr_cpumask_bits and use nr_cpu_ids everywhere.  The only reason
we use nr_cpumask_bits is because on small configurations the constant
NR_CPUS can be more efficient than having to read out nr_cpu_ids
variable each time.

Hmm... I'll restore the parse functions to use nr_cpumask_bits instead
for now.  The confusing part was the output results.  Input should be
okay even if we flip between nr_cpu_ids and NR_CPUS.

Thanks.

-- 
tejun