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From: Oleg Nesterov <oleg@redhat.com>
To: Dmitry Torokhov <dmitry.torokhov@gmail.com>
Cc: Jiri Pirko <jpirko@redhat.com>,
	linux-kernel@vger.kernel.org, linux-input@vger.kernel.org
Subject: Re: [PATCH] atkbd: cancel delayed work before freeing its structure
Date: Tue, 11 Nov 2008 18:20:50 +0100	[thread overview]
Message-ID: <20081111172050.GC18214@redhat.com> (raw)
In-Reply-To: <20081111145155.GA24881@anvil.corenet.prv>

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. And unneeded because queue_work() implies mb(),
but this is not really documented.

Oleg.

  reply	other threads:[~2008-11-11 17:20 UTC|newest]

Thread overview: 6+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2008-11-05 14:31 [PATCH] atkbd: cancel delayed work before freeing its structure Jiri Pirko
2008-11-07 15:43 ` Oleg Nesterov
2008-11-11 14:51   ` Dmitry Torokhov
2008-11-11 17:20     ` Oleg Nesterov [this message]
2008-11-11 16:30       ` Dmitry Torokhov
2008-11-11 18:24         ` Oleg Nesterov

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