From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756575AbZAVJbV (ORCPT ); Thu, 22 Jan 2009 04:31:21 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757172AbZAVJax (ORCPT ); Thu, 22 Jan 2009 04:30:53 -0500 Received: from mail-ew0-f20.google.com ([209.85.219.20]:46902 "EHLO mail-ew0-f20.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757078AbZAVJav (ORCPT ); Thu, 22 Jan 2009 04:30:51 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=date:from:to:cc:subject:message-id:references:mime-version :content-type:content-disposition:in-reply-to:user-agent; b=puRmGw93+9+F9sk/y7lEa00TjqvYLyWFNyHWtLg4o/tIeb+U/EHwDDCWC2O/nY9Iah 8wpwbwld+OpWByL2An0PrPseh0rPiz+DxL1loJJNtN9SWs/xqGWmKbNgxj5GWX5xVvWZ OUUj10RPbLo5eX+GVQFOjS5IfNITdnA7bCYhs= Date: Thu, 22 Jan 2009 10:30:47 +0100 From: Frederic Weisbecker To: Lai Jiangshan Cc: Oleg Nesterov , Ingo Molnar , Andrew Morton , Peter Zijlstra , Eric Dumazet , Linux Kernel Mailing List Subject: Re: [PATCH 2/3] workqueue: not allow recursion run_workqueue Message-ID: <20090122093046.GC5891@nowhere> References: <497838F0.7020408@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <497838F0.7020408@cn.fujitsu.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 Thu, Jan 22, 2009 at 05:14:24PM +0800, Lai Jiangshan wrote: > 1) lockdep will complain when recursion run_workqueue > 2) works is not run orderly when recursion run_workqueue > > 3) BUG! > We use recursion run_workqueue to hidden deadlock when > keventd trying to flush its own queue. > > It's bug. When flush_workqueue()(nested in a work callback)returns, > the workqueue is not really flushed, the sequence statement of > this work callback will do some thing bad. > > So we should not allow workqueue trying to flush its own queue. > > Signed-off-by: Lai Jiangshan > --- > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 2f44583..1129cde 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -48,8 +48,6 @@ struct cpu_workqueue_struct { > > struct workqueue_struct *wq; > struct task_struct *thread; > - > - int run_depth; /* Detect run_workqueue() recursion depth */ > } ____cacheline_aligned; > > /* > @@ -262,13 +260,6 @@ EXPORT_SYMBOL_GPL(queue_delayed_work_on); > static void run_workqueue(struct cpu_workqueue_struct *cwq) > { > spin_lock_irq(&cwq->lock); > - cwq->run_depth++; > - if (cwq->run_depth > 3) { > - /* morton gets to eat his hat */ > - printk("%s: recursion depth exceeded: %d\n", > - __func__, cwq->run_depth); > - dump_stack(); > - } > while (!list_empty(&cwq->worklist)) { > struct work_struct *work = list_entry(cwq->worklist.next, > struct work_struct, entry); > @@ -311,7 +302,6 @@ static void run_workqueue(struct cpu_workqueue_struct *cwq) > spin_lock_irq(&cwq->lock); > cwq->current_work = NULL; > } > - cwq->run_depth--; > spin_unlock_irq(&cwq->lock); > } > > @@ -368,29 +358,20 @@ static void insert_wq_barrier(struct cpu_workqueue_struct *cwq, > > static int flush_cpu_workqueue(struct cpu_workqueue_struct *cwq) > { > - int active; > + int active = 0; > + struct wq_barrier barr; > > - if (cwq->thread == current) { > - /* > - * Probably keventd trying to flush its own queue. So simply run > - * it by hand rather than deadlocking. > - */ > - run_workqueue(cwq); > - active = 1; > - } else { > - struct wq_barrier barr; > + BUG_ON(cwq->thread == current); Hi Lai, BUG_ON seems perhaps a bit too much for such case. The system will run in an endless loop because of a mistake that will not have necessarily a fatal end. WARN_ON should be enough (plus the warn that lockdep will raise too in this case). Thanks. Frederic. > - active = 0; > - spin_lock_irq(&cwq->lock); > - if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) { > - insert_wq_barrier(cwq, &barr, &cwq->worklist); > - active = 1; > - } > - spin_unlock_irq(&cwq->lock); > - > - if (active) > - wait_for_completion(&barr.done); > + spin_lock_irq(&cwq->lock); > + if (!list_empty(&cwq->worklist) || cwq->current_work != NULL) { > + insert_wq_barrier(cwq, &barr, &cwq->worklist); > + active = 1; > } > + spin_unlock_irq(&cwq->lock); > + > + if (active) > + wait_for_completion(&barr.done); > > return active; > } >