From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932685AbdKBNmV (ORCPT ); Thu, 2 Nov 2017 09:42:21 -0400 Received: from Galois.linutronix.de ([146.0.238.70]:54357 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754716AbdKBNmU (ORCPT ); Thu, 2 Nov 2017 09:42:20 -0400 Date: Thu, 2 Nov 2017 14:42:14 +0100 (CET) From: Thomas Gleixner To: Michal Hocko cc: linux-mm@kvack.org, Peter Zijlstra , Johannes Weiner , Mel Gorman , Tejun Heo , LKML Subject: Re: [PATCH 2/2] mm: drop hotplug lock from lru_add_drain_all In-Reply-To: <20171102131647.wihtjsuaisfqefg5@dhcp22.suse.cz> Message-ID: References: <20171102093613.3616-1-mhocko@kernel.org> <20171102093613.3616-3-mhocko@kernel.org> <20171102123749.zwnlsvpoictnmp53@dhcp22.suse.cz> <20171102131647.wihtjsuaisfqefg5@dhcp22.suse.cz> User-Agent: Alpine 2.20 (DEB 67 2015-01-07) 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 Thu, 2 Nov 2017, Michal Hocko wrote: > On Thu 02-11-17 14:02:53, Thomas Gleixner wrote: > > On Thu, 2 Nov 2017, Michal Hocko wrote: > > > On Thu 02-11-17 10:36:13, Michal Hocko wrote: > > > [...] > > > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > > > > index 67330a438525..8c6e9c6d194c 100644 > > > > --- a/mm/page_alloc.c > > > > +++ b/mm/page_alloc.c > > > > @@ -6830,8 +6830,12 @@ void __init free_area_init(unsigned long *zones_size) > > > > > > > > static int page_alloc_cpu_dead(unsigned int cpu) > > > > { > > > > + unsigned long flags; > > > > > > > > + local_irq_save(flags); > > > > lru_add_drain_cpu(cpu); > > > > + local_irq_restore(flags); > > > > + > > > > drain_pages(cpu); > > > > > > I was staring into the hotplug code and tried to understand the context > > > this callback runs in and AFAIU IRQ disabling is not needed at all > > > because cpuhp_thread_fun runs with IRQ disabled when offlining an online > > > cpu. I have a bit hard time to follow the code due to all the > > > indirection so please correct me if I am wrong. > > > > No. That function does neither run from the cpu hotplug thread of the > > outgoing CPU nor its called with interrupts disabled. > > > > The callback is in the DEAD section, i.e. its called on the controlling CPU > > _after_ the hotplugged CPU vanished completely. > > OK, so IIUC there is no race possible because kworkders simply do not > run on that cpu anymore. The CPU is gone and the kworker should have been drained and stopped. Tejun? Thanks, tglx