linux-kernel - Re: [PATCH] atkbd: cancel delayed work before freeing its structure

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Message-ID: <20081107154325.GD9368@redhat.com>
Date:	Fri, 7 Nov 2008 16:43:25 +0100
From:	Oleg Nesterov <oleg@...hat.com>
To:	dmitry.torokhov@...il.com, Jiri Pirko <jpirko@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH] atkbd: cancel delayed work before freeing its structure

On 11/05, Jiri Pirko wrote:
>
> diff --git a/drivers/input/keyboard/atkbd.c b/drivers/input/keyboard/atkbd.c
> index 22016ca..f3bbf49 100644
> --- a/drivers/input/keyboard/atkbd.c
> +++ b/drivers/input/keyboard/atkbd.c
> @@ -824,7 +824,7 @@ static void atkbd_disconnect(struct serio *serio)
>  	atkbd_disable(atkbd);
>
>  	/* make sure we don't have a command in flight */
> -	flush_scheduled_work();
> +	cancel_delayed_work_sync(&atkbd->event_work);

Ping. Dmitry, could you take a look?

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(). If schedule_delayed_work()
fails we can race with the soon-to-be-executed atkbd_event_work(), in that
case that test_and_set_bit() + test_and_clear_bit(->event_mask) save us,
but wmb() can't help again.

Another question is why do we need ->event_mutex? OK, it can serialize
multiple instances of atkbd_event_work() running on the different CPUs,
but in that case atkbd_reconnect() needs this lock too? It also calls
atkbd_set_repeat_rate/atkbd_set_leds.

I don't understand this code, don't take my words too seriously, just
curious.

Oleg.

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