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 S932367AbdELTuK (ORCPT <rfc822;w@1wt.eu>);
        Fri, 12 May 2017 15:50:10 -0400
Received: from merlin.infradead.org ([205.233.59.134]:52222 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1757427AbdELTuI (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 12 May 2017 15:50:08 -0400
Date: Fri, 12 May 2017 21:49:56 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: linux-kernel@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Masami Hiramatsu <mhiramat@kernel.org>
Subject: Re: [RFC][PATCH 0/5] perf/tracing/cpuhotplug: Fix locking order
Message-ID: <20170512194956.GH4626@worktop.programming.kicks-ass.net>
References: <20170512171544.100715273@goodmis.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170512171544.100715273@goodmis.org>
User-Agent: Mutt/1.5.22.1 (2013-10-16)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, May 12, 2017 at 01:15:44PM -0400, Steven Rostedt wrote:
>  2) Allow for get_online_cpus() to nest

So Thomas and me have been avoiding doing this.

In general we avoid nested locking in the kernel. Nested locking makes
an absolute mockery of locking rules and what all gets protected.

Yes, its much easier.. But we managed to kill the BKL, so surely we can
fix the hotplug lock too, right ;-)