From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754280AbcAVRMQ (ORCPT ); Fri, 22 Jan 2016 12:12:16 -0500 Received: from mail-wm0-f47.google.com ([74.125.82.47]:36847 "EHLO mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753265AbcAVRML (ORCPT ); Fri, 22 Jan 2016 12:12:11 -0500 Date: Fri, 22 Jan 2016 18:12:09 +0100 From: Michal Hocko To: Christoph Lameter Cc: Sasha Levin , LKML , "linux-mm@kvack.org" , Andrew Morton Subject: Re: mm, vmstat: kernel BUG at mm/vmstat.c:1408! Message-ID: <20160122171208.GD19465@dhcp22.suse.cz> References: <20160120212806.GA26965@dhcp22.suse.cz> <20160121082402.GA29520@dhcp22.suse.cz> <20160121165148.GF29520@dhcp22.suse.cz> <20160122140418.GB19465@dhcp22.suse.cz> <20160122161201.GC19465@dhcp22.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri 22-01-16 10:46:14, Christoph Lameter wrote: > On Fri, 22 Jan 2016, Michal Hocko wrote: > > > Could you repost the patch with the updated description? > > Subject: vmstat: Remove BUG_ON from vmstat_update > > If we detect that there is nothing to do just set the flag and do not check > if it was already set before. Races really do not matter. If the flag is > set by any code then the shepherd will start dealing with the situation > and reenable the vmstat workers when necessary again. > > Since 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and > shut down on idle") quiet_vmstat might update cpu_stat_off and mark a > particular cpu to be handled by vmstat_shepherd. This might trigger > a VM_BUG_ON in vmstat_update because the work item might have been > sleeping during the idle period and see the cpu_stat_off updated after > the wake up. The VM_BUG_ON is therefore misleading and no more > appropriate. Moreover it doesn't really suite any protection from real > bugs because vmstat_shepherd will simply reschedule the vmstat_work > anytime it sees a particular cpu set or vmstat_update would do the same > from the worker context directly. Even when the two would race the > result wouldn't be incorrect as the counters update is fully idempotent. > Fixes: 0eb77e988032 ("vmstat: make vmstat_updater deferrable again and shut down on idle" Reported-by: Sasha Levin Would be appropriate IMO > Signed-off-by: Christoph Lameter Acked-by: Michal Hocko Thanks! > > Index: linux/mm/vmstat.c > =================================================================== > --- linux.orig/mm/vmstat.c > +++ linux/mm/vmstat.c > @@ -1408,17 +1408,7 @@ static void vmstat_update(struct work_st > * Defer the checking for differentials to the > * shepherd thread on a different processor. > */ > - int r; > - /* > - * Shepherd work thread does not race since it never > - * changes the bit if its zero but the cpu > - * online / off line code may race if > - * worker threads are still allowed during > - * shutdown / startup. > - */ > - r = cpumask_test_and_set_cpu(smp_processor_id(), > - cpu_stat_off); > - VM_BUG_ON(r); > + cpumask_set_cpu(smp_processor_id(), cpu_stat_off); > } > } -- Michal Hocko SUSE Labs