linux-kernel - Re: [PATCHv5 05/17] tty: don't allow ldisc dcd

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Message-ID: <20101125163035.3105747b@desktopvm.lvknet>
Date:	Thu, 25 Nov 2010 16:30:35 +0300
From:	Alexander Gordeev <lasaine@....cs.msu.su>
To:	Alan Cox <alan@...ux.intel.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-kernel@...r.kernel.org,
	"Nikita V\. Youshchenko" <yoush@...msu.su>,
	linuxpps@...enneenne.com, Rodolfo Giometti <giometti@...eenne.com>,
	Greg Kroah-Hartman <gregkh@...e.de>,
	Arnd Bergmann <arnd@...db.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Nick Piggin <npiggin@...nel.dk>,
	Jason Wessel <jason.wessel@...driver.com>,
	Philippe Langlais <philippe.langlais@...ricsson.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCHv5 05/17] tty: don't allow ldisc dcd_change() after ldisc
 halt

В Wed, 24 Nov 2010 22:36:00 +0000
Alan Cox <alan@...ux.intel.com> пишет:

> > Yes, indeed, it's a bug. Please consider the following example:
> > 
> >      CPU1                                      CPU2
> > =========================================================
> > uart_handle_dcd_change() {		tty_set_ldisc() {
> >   ld = tty_ldisc_ref(...)			  ...
> 
> [We have a reference]
> >   ...					  tty_ldisc_halt(...)
> 					  [Should block]
> 
> > I think tty code is exactly the right place to fix this bug; this is
> > what my patch is for.
> 
> More special case magic on top of the current crap isn't the right fix
> here, tty_ldisc_halt needs to wait for the references to hit zero.

Didn't know that current design is crap. :)
Ok, I think I'll add a new waitqueue and a new bit (TTY_LDISC_NOREF)
that halt will wait for. Is it good?

-- 
  Alexander

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