linux-kernel - Re: [Bug #14388] keyboard under X with 2.6.31

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Date:	Fri, 16 Oct 2009 02:38:38 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Paul Fulghum <paulkf@...rogate.com>,
	Boyan <btanastasov@...oo.co.uk>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Kernel Testers List <kernel-testers@...r.kernel.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Ed Tomlinson <edt@....ca>
Subject: Re: [Bug #14388] keyboard under X with 2.6.31

Hi,

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
> index 0296612..66fa4e1 100644
> --- a/drivers/char/tty_buffer.c
> +++ b/drivers/char/tty_buffer.c
> @@ -468,7 +468,7 @@ static void flush_to_ldisc(struct work_struct *work)
>   */
>  void tty_flush_to_ldisc(struct tty_struct *tty)
>  {
> -	flush_to_ldisc(&tty->buf.work.work);
> +	flush_delayed_work(&tty->buf.work);
>  }

This might wait unnecessary scheduled-work on input_available_p(). This
is nitpick though, we can call tty_flush_to_ldisc() only when data is
unavailable.

I.e. the following or something,

static inline int input_available_p(struct tty_struct *tty, int amt)
{
	int try = 0;

retry:
	if (tty->icanon) {
		if (tty->canon_data)
			return 1;
	} else if (tty->read_cnt >= (amt ? amt : 1))
		return 1;

	if (!checked) {
		tty_flush_to_ldisc(tty);
		try = 1;
		goto retry;
	}

	return 0;
}

> +void flush_delayed_work(struct delayed_work *dwork)
> +{
> +	if (del_timer(&dwork->timer)) {
> +		struct cpu_workqueue_struct *cwq;
> +		cwq = wq_per_cpu(keventd_wq, get_cpu());
> +		__queue_work(cwq, &dwork->work);
> +		put_cpu();
> +	}
> +	flush_work(&dwork->work);
> +}
> +EXPORT_SYMBOL(flush_delayed_work);
> +
> +/**

Sorry if I'm missing the point. Doesn't this have (possible) race with
schedule_delayed_work() (i.e. by tty writer)?

             cpu0                                      cpu1

    if (del_timer(&dwork->timer)) {
                                            // cpu0 doesn't set _PENDING
                                            schedule_delayed_work()
        cwq = wq_per_cpu();
        __queue_work(cwq, &dwork->work);
        put_cpu();
    }
                                            // run timer
                                            delayed_work_timer_fn()
                                                __queue_work()
                                                    list_add_tail()
                                                // re-add without list_del(),
                                                // so this will break the list?
    flush_work(&dwork->work);

Thanks.
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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