Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965434AbaLLIqt (ORCPT ); Fri, 12 Dec 2014 03:46:49 -0500 Received: from e06smtp12.uk.ibm.com ([195.75.94.108]:39337 "EHLO e06smtp12.uk.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965351AbaLLIqr (ORCPT ); Fri, 12 Dec 2014 03:46:47 -0500 Date: Fri, 12 Dec 2014 09:46:36 +0100 From: David Hildenbrand To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, heiko.carstens@de.ibm.com, borntraeger@de.ibm.com, rafael.j.wysocki@intel.com, paulmck@linux.vnet.ibm.com, peterz@infradead.org, bp@suse.de, jkosina@suse.cz Subject: Re: [PATCH v4] CPU hotplug: active_writer not woken up in some cases - deadlock Message-ID: <20141212094636.754ab1f8@thinkpad-w530> In-Reply-To: <20141210175055.GA11802@redhat.com> References: <1418217721-42919-1-git-send-email-dahi@linux.vnet.ibm.com> <20141210175055.GA11802@redhat.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: 14121208-0009-0000-0000-0000025A682A Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > This is subjective, but how about > > static bool xxx(void) > { > mutex_lock(&cpu_hotplug.lock); > if (atomic_read(&cpu_hotplug.refcount) == 0) > return true; > mutex_unlock(&cpu_hotplug.lock); > return false; > } > > void cpu_hotplug_begin(void) > { > cpu_hotplug.active_writer = current; > > cpuhp_lock_acquire(); > wait_event(&cpu_hotplug.wq, xxx()); > } > > instead? > > Oleg. > [ 50.662459] do not call blocking ops when !TASK_RUNNING; state=2 set at [<000000000017340e>] prepare_to_wait_event+0x7a/0x124 [ 50.662472] ------------[ cut here ]------------ [ 50.662475] WARNING: at kernel/sched/core.c:7301 [ 50.662477] Modules linked in: [ 50.662482] CPU: 5 PID: 225 Comm: cpu_start_stop. Not tainted 3.18.0+ #59 [ 50.662485] task: 0000000001f94b20 ti: 0000000001ffc000 task.ti: 0000000001ffc000 ... Looks like your suggestion won't work. We can only set the task to TASK_UNINTERRUPTIBLE after taking the lock. David -- 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/