linux-kernel - Re: [PATCH] kdesu broken

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Message-ID: <20090729121753.41d2dd4b@lxorguk.ukuu.org.uk>
Date:	Wed, 29 Jul 2009 12:17:53 +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

> IOW, the whole argument really hinges on the fact that calling 
> flush_to_ldisc() manually (without any locking) is really not 
> fundamentally any different from the delayed work doing it from a timer. 

Which means the hangup path should be doing a cancel_delayed_work() in
the case where its not resetting the termios as well and since it isn't
you can't actually (fingers crossed) make the problem worse, its merely as
broken as before.

Ok

> And when we _do_ disable the timer, we also make that flush_to_ldisc() 
> function be a no-op, so the "tty_ldisc_halt()" effectively stops both the 
> timer and (conceptually) the manual call case too. 
> 
> So now we have one remaining case, namely the case of the ldisc then being 
> re-initialized and TTY_LDISC is set again. But at that point, calling 
> flush_to_ldisc() had better be ok again, wouldn't you agree?

The ldisc re-init via SETD should be fine as it locks versus hangup
anyway and always has to.

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