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

OGAWA Hirofumi
2009-10-15T17:38:38Z

Hi,

Linus Torvalds <torvalds@linux-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@mail.parknet.co.jp>