Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755250AbaJUPVZ (ORCPT ); Tue, 21 Oct 2014 11:21:25 -0400 Received: from cantor2.suse.de ([195.135.220.15]:52085 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751561AbaJUPVX (ORCPT ); Tue, 21 Oct 2014 11:21:23 -0400 Date: Tue, 21 Oct 2014 17:21:21 +0200 (CEST) From: Jiri Kosina To: Dave Jones cc: Peter Zijlstra , Ingo Molnar , "Rafael J. Wysocki" , Pavel Machek , linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org, "Paul E. McKenney" Subject: Re: lockdep splat in CPU hotplug In-Reply-To: <20141021151043.GA11800@redhat.com> Message-ID: References: <20141021151043.GA11800@redhat.com> User-Agent: Alpine 2.00 (LNX 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 21 Oct 2014, Dave Jones wrote: > > I am seeing the lockdep report below when resuming from suspend-to-disk > > with current Linus' tree (c2661b80609). > > > > The reason for CCing Ingo and Peter is that I can't make any sense of one > > of the stacktraces lockdep is providing. > > > > Please have a look at the very first stacktrace in the dump, where lockdep > > is trying to explain where cpu_hotplug.lock#2 has been acquired. It seems > > to imply that cpuidle_pause() is taking cpu_hotplug.lock, but that's not > > the case at all. > > Could inlining be confusing the trace here ? > > You can get from cpuidle_pause to cpuidle_uninstall_idle_handler -> synchronize_rcu > -> synchronize_sched -> synchronize_sched_expedited which > does a try_get_online_cpus which will take the cpu_hotplug.lock Looks like this indeed is something that lockdep *should* report (*), although I would be suprised that stack unwinder would be so confused by this -- there is no way for synchronize_sched_expedited() to be inlined all the way to cpuidle_pause(). (*) there are multiple places where cpu_hotplug.lock -> cpuidle_lock lock dependency is assumed. The patch that Dave pointed out adds cpuidle_lock -> cpu_hotplug.lock dependency. Still not clear whether this is what's happening here ... anyway, adding Paul to CC. -- Jiri Kosina SUSE Labs -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/