linux-kernel - Re: [patch] staging: speakup: safely close tty

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Date:   Tue, 11 Jul 2017 11:39:13 +0100
From:   Okash Khawaja <okash.khawaja@...il.com>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        linux-kernel@...r.kernel.org, William Hubbs <w.d.hubbs@...il.com>,
        Chris Brannon <chris@...-brannons.com>,
        Kirk Reiser <kirk@...sers.ca>, speakup@...ux-speakup.org,
        devel@...verdev.osuosl.org
Subject: Re: [patch] staging: speakup: safely close tty

Hi,

On Mon, Jul 10, 2017 at 12:55:44PM +0100, Alan Cox wrote:
> On Fri, 7 Jul 2017 20:13:01 +0100
> Okash Khawaja <okash.khawaja@...il.com> wrote:
> 
> > Speakup opens tty using tty_open_by_driver. When closing, it calls
> > tty_ldisc_release but doesn't close and remove the tty itself. As a
> > result, that tty cannot then be opened from user space. This patch calls
> > tty_release_struct which ensures that tty is safely removed and freed
> > up. It also calls tty_ldisc_release, so speakup doesn't need to call it.
> > 
> > This patch also unregisters N_SPEAKUP. It is registered when a speakup
> > module is loaded.
> 
> What happens if after you register it someone assigns that ldisc to
> another tty as well ?
> 
> You should register the ldisc when the relevant module is initialized and
> release it only when the module is unloaded. That way the module ref
> counts will handle cases where someone uses the ldisc with something else.
Sorry if I misunderstood it. That's what we do here.
spk_ttyio_initialise_ldisc is called separately for each module (e.g.
speakup_apollo, speakup_ltlk etc) when it is loaded. spk_ttyio_release
is also called separately for each module when it is unloaded. The ldisc
stays around until the last of the modules is unloaded.

> 
> I'd also btw strongly recommend putting the ldisc and the speakup tty
> driver as different modules.
Sure, that makes sense. I will do that following these patches.

Thanks,
Okash