Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751839AbdHaIJa (ORCPT ); Thu, 31 Aug 2017 04:09:30 -0400 Received: from merlin.infradead.org ([205.233.59.134]:36138 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750772AbdHaIJ1 (ORCPT ); Thu, 31 Aug 2017 04:09:27 -0400 Date: Thu, 31 Aug 2017 10:09:22 +0200 From: Peter Zijlstra To: Thomas Gleixner Cc: Borislav Petkov , Sebastian Andrzej Siewior , lkml Subject: Re: WARNING: possible circular locking dependency detected Message-ID: <20170831080922.daaypuxatenmpkfo@hirez.programming.kicks-ass.net> References: <20170825100304.5cwrlrfwi7f3zcld@pd.tnic> <20170828145808.btuqpe2bvxymljyg@hirez.programming.kicks-ass.net> <20170829194948.GD32112@worktop.programming.kicks-ass.net> <20170830054730.GF32112@worktop.programming.kicks-ass.net> <20170831073739.ytexc7omldyb5lgy@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 652 Lines: 16 On Thu, Aug 31, 2017 at 09:55:57AM +0200, Thomas Gleixner wrote: > > Arghh!!! > > > > And allowing us to create events for offline CPUs (possible I think, but > > maybe slightly tricky) won't solve that, because we're already holding > > the hotplug_lock during PREPARE. > > There are two ways to cure that: > > 1) Have a pre cpus_write_lock() stage which is serialized via > cpus_add_remove_lock, which is the outer lock for hotplug. > > There we can sanely create stuff and fail with all consequences. True, if you're willing to add more state to that hotplug thing I'll try and make that perf patch that allows attaching to offline CPUs.