linux-kernel - Re: [PATCH] tty: Fix logic change introduced by wait_event_interruptible

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Date:	Fri, 21 Dec 2007 22:45:47 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	"Cory T. Tusar" <ctusar@...eon-central.com>
Cc:	linux-kernel@...r.kernel.org, jirislaby@...il.com,
	alan@...rguk.ukuu.org.uk, torvalds@...ux-foundation.org
Subject: Re: [PATCH] tty: Fix logic change introduced by
 wait_event_interruptible_timeout()

On Thu, 20 Dec 2007 16:39:21 -0500 "Cory T. Tusar" <ctusar@...eon-central.com> wrote:

> tty: Fix logic change introduced by wait_event_interruptible_timeout()
> 
> Commit 5a52bd4a2dcb570333ce6fe2e16cd311650dbdc8 introduced a subtle logic
> change in tty_wait_until_sent().  The original version would only error
> out of the 'do { ... } while (timeout)' loop if signal_pending() evaluated
> to true; a timeout or break due to an empty buffer would fall out of the
> loop and into the tty->driver->wait_until_sent handling.  The current
> implementation will error out on either a pending signal or an empty
> buffer, falling through to the tty->driver->wait_until_sent handling
> only on a timeout.
> 
> This change reverts the logic flow in tty_wait_until_sent() to match that
> prior to the aforementioned commit.
> 
> Signed-off-by: Cory T. Tusar <ctusar@...eon-central.com>
> 
> ---
> Please CC me on any replies; I'm not subscribed to lkml.  Thanks.
> 
>  drivers/char/tty_ioctl.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/char/tty_ioctl.c b/drivers/char/tty_ioctl.c
> index 1bdd2bf..e02d592 100644
> --- a/drivers/char/tty_ioctl.c
> +++ b/drivers/char/tty_ioctl.c
> @@ -62,7 +62,7 @@ void tty_wait_until_sent(struct tty_struct * tty, long timeout)
>  	if (!timeout)
>  		timeout = MAX_SCHEDULE_TIMEOUT;
>  	if (wait_event_interruptible_timeout(tty->write_wait,
> -			!tty->driver->chars_in_buffer(tty), timeout))
> +			!tty->driver->chars_in_buffer(tty), timeout) < 0)
>  		return;
>  	if (tty->driver->wait_until_sent)
>  		tty->driver->wait_until_sent(tty, timeout);
> 
> 

OK...  So what are the user-visible effects of this regression?  The caller
will run ->wait_until_sent() even after being signalled?  So the signal is
not promptly responded to?

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