From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Torokhov Subject: Re: [PATCH] atkbd: cancel delayed work before freeing its structure Date: Tue, 11 Nov 2008 11:30:38 -0500 Message-ID: <20081111112741.ZZRA012@mailhub.coreip.homeip.net> References: <20081105153140.25132ca1@psychotron.englab.brq.redhat.com> <20081107154325.GD9368@redhat.com> <20081111145155.GA24881@anvil.corenet.prv> <20081111172050.GC18214@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from rn-out-0910.google.com ([64.233.170.187]:42362 "EHLO rn-out-0910.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751144AbYKKQal (ORCPT ); Tue, 11 Nov 2008 11:30:41 -0500 Received: by rn-out-0910.google.com with SMTP id k40so1910973rnd.17 for ; Tue, 11 Nov 2008 08:30:40 -0800 (PST) Content-Disposition: inline In-Reply-To: <20081111172050.GC18214@redhat.com> Sender: linux-input-owner@vger.kernel.org List-Id: linux-input@vger.kernel.org To: Oleg Nesterov Cc: Jiri Pirko , linux-kernel@vger.kernel.org, linux-input@vger.kernel.org On Tue, Nov 11, 2008 at 06:20:50PM +0100, Oleg Nesterov wrote: > On 11/11, Dmitry Torokhov wrote: > > > > On Fri, Nov 07, 2008 at 04:43:25PM +0100, Oleg Nesterov wrote: > > > > > > While we are here, what is the reason for atkbd_schedule_event_work()->wmb() ? > > > It looks absolutely bogus. Is it for atkbd_event_work() ? In that case it > > > is not needed, it must see all previous STOREs because both queue_work() and > > > run_workqueue() take cwq->lock. And in any case, > > > test_and_set_bit(WORK_STRUCT_PENDING) implies mb(). > > > > I wanted to be sure that event_mask is set before we schedule event_work > > and I don't want to rely on details of queue_delayed_work > > implementation. If the fact that queue_delayed_work acts as a barrier > > would be listed part of its published spec I would gladly remove wmb() > > from atkbd. > > Yes, queue_delayed_work() acts as a barrier for the work->func(), otherwise > almost any code which uses wqs is broken. > > But let me repeat, if queue_delayed_work() fails becuase this work is > already queued we (in this particular case) need mb(), not wmb(). Or > atkbd_schedule_event_work() can miss a bit in ->event_mask. So I think > this wmb() is misleading. Could you please explain why wmb() is not enough and full mb() is needed in this case? I thought that if write happens before we decide whether to schedule event_work or not it would be enough. > And unneeded because queue_work() implies mb(), > but this is not really documented. > It would be great if we can get it documented and then i'd drop *mb() from atkbd. Thanks. -- Dmitry