linux-kernel - Re: [PATCH v7] Input: Add userio module

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Message-ID: <20151024222626.GA18702@dtor-pixel>
Date:	Sat, 24 Oct 2015 15:26:26 -0700
From:	Dmitry Torokhov <dmitry.torokhov@...il.com>
To:	David Herrmann <dh.herrmann@...il.com>
Cc:	Stephen Chandler Paul <cpaul@...hat.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Linux API <linux-api@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mauro Carvalho Chehab <mchehab@....samsung.com>,
	Greg KH <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>, Joe Perches <joe@...ches.com>,
	Jiri Slaby <jslaby@...e.com>,
	Vishnu Patekar <vishnupatekar0510@...il.com>,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>,
	Benjamin Tissoires <benjamin.tissoires@...hat.com>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH v7] Input: Add userio module

On Thu, Oct 08, 2015 at 07:20:59PM +0200, David Herrmann wrote:
> On Mon, Oct 5, 2015 at 5:55 PM,  <cpaul@...hat.com> wrote:
> > +static int userio_char_release(struct inode *inode, struct file *file)
> > +{
> > +       struct userio_device *userio = file->private_data;
> > +
> > +       /* Don't free the serio port here, serio_unregister_port() does
> > +        * this for us */
> > +       if (userio->running)
> > +               serio_unregister_port(userio->serio);
> > +       else
> > +               kfree(userio->serio);
> > +
> > +       kfree(userio);
> 
> I'm not very familiar with the serio-subsystem, but is there a
> guarantee that .write() will not be called once unregistered? I can
> see that it's not scheduled by userio anymore, but maybe there's an
> async path that can trigger .write() callbacks. Dunno.. I'll leave
> that to Dmitry.

I think this is OK. When port is unregistered we the driver will be
disconnected from it, and is not supposed to call serio_write() anymore.
In fact, it should not access port after calling serio_close(). If it
keeps the pointer and uses it is a bug in the other driver; we can't
really do much about it.

Thanks.

-- 
Dmitry
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