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Date:	Thu, 03 Apr 2014 08:10:52 +0200
From:	Takashi Iwai <tiwai@...e.de>
To:	Jiri Slaby <jslaby@...e.cz>
Cc:	Samo Pogacnik <samo_pogacnik@....net>,
	Jean Delvare <jdelvare@...e.de>, Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Struan Bartlett <struan.bartlett@...il.com>,
	Andreas Schwab <schwab@...ux-m68k.org>,
	gnomes@...rguk.ukuu.org.uk, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] ttyprintk: Fix wrong tty_unregister_driver() call in the error path

At Wed, 02 Apr 2014 14:24:33 +0200,
Jean Delvare wrote:
> 
> Le Wednesday 02 April 2014 à 12:29 +0200, Takashi Iwai a écrit :
> > ttyprintk driver calls tty_unregister_driver() wrongly in the error
> > path of tty_register_driver().  Also, setting ttyprintk_driver to NULL
> > is utterly superfluous, so let's get rid of it, too.
> > 
> > Reported-by: Jean Delvare <jdelvare@...e.de>
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> > ---
> >  drivers/char/ttyprintk.c | 2 --
> >  1 file changed, 2 deletions(-)
> > 
> > diff --git a/drivers/char/ttyprintk.c b/drivers/char/ttyprintk.c
> > index daea84c41743..2a39c5790364 100644
> > --- a/drivers/char/ttyprintk.c
> > +++ b/drivers/char/ttyprintk.c
> > @@ -210,10 +210,8 @@ static int __init ttyprintk_init(void)
> >  	return 0;
> >  
> >  error:
> > -	tty_unregister_driver(ttyprintk_driver);
> >  	put_tty_driver(ttyprintk_driver);
> >  	tty_port_destroy(&tpk_port.port);
> > -	ttyprintk_driver = NULL;
> >  	return ret;
> >  }
> >  device_initcall(ttyprintk_init);
> 
> Reviewed-by: Jean Delvare <jdelvare@...e.de>

Meanwhile, I found that tty_unregister_driver() was added
intentionally in the commit f06fb543c1d0,
    TTY: ttyprintk, unregister tty driver on failure
    
    When the tty_printk driver fails to create a node in sysfs, the
    system
    crashes. It is because the driver registers a tty driver and frees
    it
    without deregistering it first. The fix is easy: add a call to
    tty_unregister_driver to the fail path.

But, I failed to see why this is needed in the current code.

Jiri, is your fix still valid at all?


thanks,

Takashi
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