Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754019AbaLHTa1 (ORCPT ); Mon, 8 Dec 2014 14:30:27 -0500 Received: from e06smtp10.uk.ibm.com ([195.75.94.106]:56586 "EHLO e06smtp10.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751119AbaLHTa0 (ORCPT ); Mon, 8 Dec 2014 14:30:26 -0500 Date: Mon, 8 Dec 2014 20:30:18 +0100 From: David Hildenbrand To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, rafael.j.wysocki@intel.com, peterz@infradead.org, srivatsa.bhat@linux.vnet.ibm.com, oleg@redhat.com, bp@suse.de, jkosina@suse.cz Subject: Re: [PATCH v1] CPU hotplug: active_reader not woken up in some cases - deadlock Message-ID: <20141208203018.24f23bdb@thinkpad-w530> In-Reply-To: <20141208190803.GR25340@linux.vnet.ibm.com> References: <1418062383-39657-1-git-send-email-dahi@linux.vnet.ibm.com> <20141208183134.GQ25340@linux.vnet.ibm.com> <20141208195814.663007dd@thinkpad-w530> <20141208190803.GR25340@linux.vnet.ibm.com> Organization: IBM Deutschland GmbH X-Mailer: Claws Mail 3.11.1 (GTK+ 2.24.24; x86_64-redhat-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-TM-AS-MML: disable X-Content-Scanned: Fidelis XPS MAILER x-cbid: 14120819-0041-0000-0000-000002674CF7 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > > active_writer is cleared while holding cpuhp_lock, so this should be safe, > > right? > > You lost me on that one. Don't we get to that piece of code precisely > because we don't hold any of the CPU-hotplug locks? If so, the > writer might well hold all the locks it needs, and might well change > cpu_hotplug.active_writer out from under us. > > What am I missing here? > > Thanx, Paul I was missing that cpuhp_lock_* are simply lockdep anotations ... it's getting late :) So you're right, we need to verify that we don't get a 0 on the second access. Will send an updated version soon. Thanks! -- 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/