Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932671AbaLJRvq (ORCPT ); Wed, 10 Dec 2014 12:51:46 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51406 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932268AbaLJRvp (ORCPT ); Wed, 10 Dec 2014 12:51:45 -0500 Date: Wed, 10 Dec 2014 18:50:55 +0100 From: Oleg Nesterov To: David Hildenbrand 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: <20141210175055.GA11802@redhat.com> References: <1418217721-42919-1-git-send-email-dahi@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1418217721-42919-1-git-send-email-dahi@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/10, David Hildenbrand wrote: > > @@ -127,20 +119,16 @@ void put_online_cpus(void) > { > if (cpu_hotplug.active_writer == current) > return; > - if (!mutex_trylock(&cpu_hotplug.lock)) { > - atomic_inc(&cpu_hotplug.puts_pending); > - cpuhp_lock_release(); > - return; > - } > - > - if (WARN_ON(!cpu_hotplug.refcount)) > - cpu_hotplug.refcount++; /* try to fix things up */ > > - if (!--cpu_hotplug.refcount && unlikely(cpu_hotplug.active_writer)) > - wake_up_process(cpu_hotplug.active_writer); > - mutex_unlock(&cpu_hotplug.lock); > - cpuhp_lock_release(); > + if (atomic_dec_and_test(&cpu_hotplug.refcount) && > + waitqueue_active(&cpu_hotplug.wq)) > + wake_up(&cpu_hotplug.wq); OK, waitqueue_active() looks safe... prepare_to_wait() has a barrier. > void cpu_hotplug_begin(void) > { > + DEFINE_WAIT(wait); > + > cpu_hotplug.active_writer = current; > > - cpuhp_lock_acquire(); > for (;;) { > + cpuhp_lock_acquire(); not sure I understand why did you move cpuhp_lock_acquire() into the loop, but this is minor. > mutex_lock(&cpu_hotplug.lock); > - apply_puts_pending(1); > - if (likely(!cpu_hotplug.refcount)) > + prepare_to_wait(&cpu_hotplug.wq, &wait, TASK_UNINTERRUPTIBLE); > + if (likely(!atomic_read(&cpu_hotplug.refcount))) > break; > - __set_current_state(TASK_UNINTERRUPTIBLE); > mutex_unlock(&cpu_hotplug.lock); > + cpuhp_lock_release(); > schedule(); > } > + > + finish_wait(&cpu_hotplug.wq, &wait); > } 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. -- 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/