linux-kernel - Re: [PATCH] kdesu broken

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Date:	Wed, 29 Jul 2009 17:39:55 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
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

>  		tty_ldisc_deref(ld);
> +		tty_ldisc_halt(tty);
> +		tty_ldisc_wait_idle(tty);

Needs to be
	mutex_lock(&tty->ldisc_mutex);
	if (tty->ldisc)
		....
	}
	mutex_unlock(&tty->ldisc_mutex)

We can't wait for the reference to go away if we hold one, and if we
don't hold one the ldisc reference might go away during the hangup if we
close()

Odds of hitting it minimal however. Or maybe we need a smarter
tty_ldisc_wait_self_idle(ld) ?

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