linux-kernel - Re: [Regression] kdesu broken

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Date:	Sat, 25 Jul 2009 16:32:51 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>, Ray Lee <ray-lk@...rabbit.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [Regression] kdesu broken

On Sat, 25 Jul 2009 23:55:39 +0900
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp> wrote:

> Alan Cox <alan@...rguk.ukuu.org.uk> writes:
> 
> > Actually try this:
> 
> Thanks. This patch improved situation. However, if slave writes big data
> to buffer, it seems we still have the problem.
> 
> > +	tty_flip_buffer_push(tty->link);
> 
> This is handling the pending buffer, but in flush_to_ldisc(), if
> !tty->receive_room, it seems still delay the ->receive_buf().

Agreed - we could

	wait_event_interruptible(tty->write_wait,
			tty->link->receive_room);

or similar.

Good to know the initial fix works. To actually do it cleanly probably
wants a way to pass a logical channel close through the tty layer which
isn't I think too hard

	set a new TTY_OTHER_CLOSING in the pty code
	set TTY_OTHER_CLOSED in the flip_buffer_push code if we empty the
	buffer queue and TTY_OTHER_CLOSING is set.

That would also avoid using tty->low_latency=1 in the pty layer which I
worry may harm PPP gateway performance and the like.
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