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

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Message-ID: <20170710161231.GA417@sanghar>
Date:   Mon, 10 Jul 2017 17:12:31 +0100
From:   Okash Khawaja <okash.khawaja@...il.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Samuel Thibault <samuel.thibault@...-lyon.org>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        "linux-kernel@...r.kernel.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 1/3] tty: resolve tty contention between kernel and user
 space

On Mon, Jul 10, 2017 at 06:21:37PM +0300, Andy Shevchenko wrote:
> On Mon, Jul 10, 2017 at 11:31 AM, Okash Khawaja <okash.khawaja@...il.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@...il.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.
Ah okay I see your point. Sure, I don't mind either way. However, this
code closely follows tty_open_by_driver, so I have tried to keep the
same pattern for sake of consistency :)

Thanks,
Okash