linux-kernel - Re: [PATCHv4 05/17] pps: access pps device by direct pointer

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Message-ID: <20101121141226.1576758b@lxorguk.ukuu.org.uk>
Date:	Sun, 21 Nov 2010 14:12:26 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Rodolfo Giometti <giometti@...eenne.com>
Cc:	Alexander Gordeev <lasaine@....cs.msu.su>,
	linux-kernel@...r.kernel.org,
	"Nikita V. Youshchenko" <yoush@...msu.su>,
	linuxpps@...enneenne.com, Greg Kroah-Hartman <gregkh@...e.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>
Subject: Re: [PATCHv4 05/17] pps: access pps device by direct pointer


> Maybe this lock is useless... however, are we sure that before setting
> tty->disc_data to pps its value is null? Otherwise the dcd_change may
> be called with an oops! We cannot control serial port IRQ
> generation... :-/

tty->disc_data is LDISC private. It may be any arbitary value on entry to
the ldisc open method.


> > +	spin_lock_irq(&pps_ldisc_lock);
> > +	tty->disc_data = NULL;
> > +	spin_unlock_irq(&pps_ldisc_lock);

And you don't need to set it to NULL after - some ldiscs do this mostly
as a debug aid.

Alan
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