Re: [patch 1/3] tty: resolve tty contention between kernel and user space

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Okash Khawaja <okash.khawaja@gmail.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jslaby@suse.com>,
	Samuel Thibault <samuel.thibault@ens-lyon.org>,
	Alan Cox <gnomes@lxorguk.ukuu.org.uk>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	William Hubbs <w.d.hubbs@gmail.com>,
	Chris Brannon <chris@the-brannons.com>,
	Kirk Reiser <kirk@reisers.ca>,
	speakup@linux-speakup.org, devel@driverdev.osuosl.org
Subject: Re: [patch 1/3] tty: resolve tty contention between kernel and user space
Date: Mon, 10 Jul 2017 18:21:37 +0300	[thread overview]
Message-ID: <CAHp75VeEjExnouxPqxPg8uVBJXRiWOpLSSypeDMNTheD3aJLNg@mail.gmail.com> (raw)
In-Reply-To: <20170710083105.GA719@sanghar>

On Mon, Jul 10, 2017 at 11:31 AM, Okash Khawaja <okash.khawaja@gmail.com> wrote:
> On Sun, Jul 09, 2017 at 06:04:17PM +0300, Andy Shevchenko wrote:
>> On Sun, Jul 9, 2017 at 2:41 PM, Okash Khawaja <okash.khawaja@gmail.com> wrote:
>>
>> > +struct tty_struct *tty_kopen(dev_t device)
>> > +{
>> > +       struct tty_struct *tty;
>> > +       struct tty_driver *driver = NULL;
>> > +       int index = -1;
>> > +
>> > +       mutex_lock(&tty_mutex);
>> > +       driver = tty_lookup_driver(device, NULL, &index);
>> > +       if (IS_ERR(driver)) {
>>
>> > +               mutex_unlock(&tty_mutex);
>> > +               return ERR_CAST(driver);
>>
>> Hmm... perhaps
>>
>> tty = ERR_CAST(driver);
>> goto out_unlock;
>>
>> See below for further details.
>>
> Sorry missed this one out. Since tty_lookup_driver has failed, we don't
> need to down the refcount on driver. So we can return here, without
> going to out_unlock.

Yeah, and my point is to use goto with the symmetric giveups of lock
and reference.

-- 
With Best Regards,
Andy Shevchenko