linux-kernel - Re: [v4l-dvb-maintainer] [2.6 patch] dvb_frontend

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Date:	Sat, 11 Aug 2007 13:13:59 +0200
From:	"Markus Rechberger" <mrechberger@...il.com>
To:	"Trent Piepho" <xyzzy@...akeasy.org>
Cc:	"Manu Abraham" <abraham.manu@...il.com>,
	v4l-dvb-maintainer@...uxtv.org, linux-kernel@...r.kernel.org,
	"Adrian Bunk" <bunk@...sta.de>
Subject: Re: [v4l-dvb-maintainer] [2.6 patch] dvb_frontend_ioctl(): fix check-after-use

On 8/11/07, Trent Piepho <xyzzy@...akeasy.org> wrote:
> On Fri, 10 Aug 2007, Markus Rechberger wrote:
> > On 8/1/07, Manu Abraham <abraham.manu@...il.com> wrote:
> > > On 7/31/07, Adrian Bunk <bunk@...sta.de> wrote:
> > > > The Coverity checker spotted that we have already oops'ed if "fe" was
> > > NULL.
> > > >
> > > > --- linux-2.6.23-rc1-mm1/drivers/media/dvb/dvb-core/dvb_frontend.c.old
> > > > +++ linux-2.6.23-rc1-mm1/drivers/media/dvb/dvb-core/dvb_frontend.c
> > > > @@ -706,11 +706,11 @@ static int dvb_frontend_ioctl(struct ino
> > > > -       if (!fe || fepriv->exit)
> > > > +       if (fepriv->exit)
> > > >                 return -ENODEV;
> >
> > This issue has been known for a while including some other problems at
> > that part.
> >
> >
> http://article.gmane.org/gmane.linux.drivers.dvb/35351/match=patch+dvb_net+hotplugging+support
> >
> > this includes a link where this and more got discussed in May.
>
> For dvb_net_close, I like the patch I already posted better.  To fix the
> check-after-use, it's not "use" part that's the problem, it's the "check"
> part
> that isn't necessary.
>
> I traced the dvb-net code,
> http://article.gmane.org/gmane.linux.kernel/543689,
> and I'm sure that dvbdev can't be NULL.
>
> My patch also deletes a few pieces of duplicated code by calling
> dvb_generic_release().
>
> The only problem is that practically no one uses dvb-net, so it's very hard
> to
> test these patches.
>

I didn't see this patch, it would be fine if it would get applied.

> In all the dvb code, were is the locking for device open and release?  I
> don't
> see it.  What is preventing two threads from trying to open and/or close the
> same dvb device at the same time?
>

Haven't looked at that yet, since I moreover work to get the em28xx
driver included now.

Markus
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