From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758158Ab2ENWlg (ORCPT ); Mon, 14 May 2012 18:41:36 -0400 Received: from e35.co.us.ibm.com ([32.97.110.153]:51194 "EHLO e35.co.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756759Ab2ENWlf (ORCPT ); Mon, 14 May 2012 18:41:35 -0400 Date: Mon, 14 May 2012 15:41:23 -0700 From: "Paul E. McKenney" To: Tejun Heo Cc: linux-kernel@vger.kernel.org Subject: Re: [PATCH] workqueue: skip nr_running sanity check in worker_enter_idle() if trustee is active Message-ID: <20120514224123.GO2441@linux.vnet.ibm.com> Reply-To: paulmck@linux.vnet.ibm.com References: <20120506153814.GA25681@linux.vnet.ibm.com> <20120507194042.GG19417@google.com> <20120507205516.GD21152@linux.vnet.ibm.com> <20120507213449.GM19417@google.com> <20120514221250.GA8414@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120514221250.GA8414@google.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Content-Scanned: Fidelis XPS MAILER x-cbid: 12051422-6148-0000-0000-000005D5A42E Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 14, 2012 at 03:12:50PM -0700, Tejun Heo wrote: > >From 544ecf310f0e7f51fa057ac2a295fc1b3b35a9d3 Mon Sep 17 00:00:00 2001 > From: Tejun Heo > Date: Mon, 14 May 2012 15:04:50 -0700 > > worker_enter_idle() has WARN_ON_ONCE() which triggers if nr_running > isn't zero when every worker is idle. This can trigger spuriously > while a cpu is going down due to the way trustee sets %WORKER_ROGUE > and zaps nr_running. > > It first sets %WORKER_ROGUE on all workers without updating > nr_running, releases gcwq->lock, schedules, regrabs gcwq->lock and > then zaps nr_running. If the last running worker enters idle > inbetween, it would see stale nr_running which hasn't been zapped yet > and trigger the WARN_ON_ONCE(). > > Fix it by performing the sanity check iff the trustee is idle. > > Signed-off-by: Tejun Heo > Reported-by: "Paul E. McKenney" > Cc: stable@vger.kernel.org > --- > Sorry about the delay. After scratching my head quite a bit, I found > where during cpu-offlining such discrepancy may happen. I'm fairly > sure this is it but I might be wrong, so please include this patch in > your test setup and let me know how it goes. Thank you -- I have applied it, and will let you know how it goes. Thanx, Paul > Thank you. > > kernel/workqueue.c | 9 +++++++-- > 1 files changed, 7 insertions(+), 2 deletions(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 211eadb..c36c86c 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1213,8 +1213,13 @@ static void worker_enter_idle(struct worker *worker) > } else > wake_up_all(&gcwq->trustee_wait); > > - /* sanity check nr_running */ > - WARN_ON_ONCE(gcwq->nr_workers == gcwq->nr_idle && > + /* > + * Sanity check nr_running. Because trustee releases gcwq->lock > + * between setting %WORKER_ROGUE and zapping nr_running, the > + * warning may trigger spuriously. Check iff trustee is idle. > + */ > + WARN_ON_ONCE(gcwq->trustee_state == TRUSTEE_DONE && > + gcwq->nr_workers == gcwq->nr_idle && > atomic_read(get_gcwq_nr_running(gcwq->cpu))); > } > > -- > 1.7.7.3 >