linux-kernel - Re: [PATCH] kdesu broken

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Date:	Wed, 29 Jul 2009 09:05:46 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
cc:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	"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: [PATCH] kdesu broken



On Wed, 29 Jul 2009, Alan Cox wrote:

> > The tty_ldisc_hangup() already does tty_ldisc_wait_idle() after disabling 
> > the timer (and clearing the TTY_LDISC bit), so that all seems fine 
> > already. No?
> 
> We only do tty_ldisc_wait_idle if tty->driver->flags & TTY_RESET_TERMIOS
> is set that I can see ?

I agree, but that's also the only time we do that 'tty_ldisc_halt()' that 
cancels the timer. So if there is something that depends on the 
flush_to_ldisc() not happening, the bug was pre-existing since it never 
got rid of the flush to begin with, so the flush_to_ldisc() would happen 
at some random later time as a result of the delayed-work timer.

That said, I suspect that from a sanity standpoint, I suspect something 
like the appended migth be a good idea. But I think it's an independent 
issue (and unless somebody can actually point to an actual problem, I'd 
only apply something like this during the merge window, not after -rc4).

		Linus
---
 drivers/char/tty_ldisc.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/char/tty_ldisc.c b/drivers/char/tty_ldisc.c
index acd76b7..640b100 100644
--- a/drivers/char/tty_ldisc.c
+++ b/drivers/char/tty_ldisc.c
@@ -778,6 +778,8 @@ void tty_ldisc_hangup(struct tty_struct *tty)
 		if (ld->ops->hangup)
 			ld->ops->hangup(tty);
 		tty_ldisc_deref(ld);
+		tty_ldisc_halt(tty);
+		tty_ldisc_wait_idle(tty);
 	}
 	/*
 	 * FIXME: Once we trust the LDISC code better we can wait here for
@@ -794,8 +796,6 @@ void tty_ldisc_hangup(struct tty_struct *tty)
 		mutex_lock(&tty->ldisc_mutex);
 		if (tty->ldisc) {	/* Not yet closed */
 			/* Switch back to N_TTY */
-			tty_ldisc_halt(tty);
-			tty_ldisc_wait_idle(tty);
 			tty_ldisc_reinit(tty);
 			/* At this point we have a closed ldisc and we want to
 			   reopen it. We could defer this to the next open but
--
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