Re: [PATCH 1/5] vt: Fix replacement console check when unbinding

From: Daniel Vetter <daniel@ffwll.ch>
To: David Herrmann <dh.herrmann@gmail.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>,
	Intel Graphics Development <intel-gfx@lists.freedesktop.org>,
	Jiri Slaby <jslaby@suse.cz>, LKML <linux-kernel@vger.kernel.org>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH 1/5] vt: Fix replacement console check when unbinding
Date: Fri, 6 Jun 2014 09:49:53 +0200	[thread overview]
Message-ID: <20140606074953.GB7416@phenom.ffwll.local> (raw)
In-Reply-To: <CANq1E4RE+B+AhCfybzbJE--iQ_T7Z4TOsSSp7KEHNjpBM=4eqQ@mail.gmail.com>

On Fri, Jun 06, 2014 at 09:16:13AM +0200, David Herrmann wrote:
> Hi
> 
> On Thu, Jun 5, 2014 at 4:58 PM, Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
> > I don't fully understand the magic of the vt register/unregister
> > logic, but apparently everything but the inital console (as set
> > in the conswitchp pointer) is marked with FLAG_MODULE. Which means
> > if something unregistered the boot vt driver (e.g. i915.ko kicking
> > out vga_con) there's nothing left when trying to unbind e.g. fbcon
> > through sysfs.
> >
> > But we always have the dummy console hanging around, so this test
> > is fairly dubious. What we actually want is simply a different console
> > than the one we want to unbind.
> 
> For unknown reasons, you can disable the dummy console via Kconfig, so
> it's not guaranteed to be around. But your comment is still valid.

Right, I'll reword this a bit to clarify.
> 
> >
> > Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> > Cc: Jiri Slaby <jslaby@suse.cz>
> > Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> > ---
> >  drivers/tty/vt/vt.c | 3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> >
> > diff --git a/drivers/tty/vt/vt.c b/drivers/tty/vt/vt.c
> > index 3ad0b61e35b4..ea600f482eeb 100644
> > --- a/drivers/tty/vt/vt.c
> > +++ b/drivers/tty/vt/vt.c
> > @@ -3155,8 +3155,7 @@ int do_unbind_con_driver(const struct consw *csw, int first, int last, int deflt
> >         for (i = 0; i < MAX_NR_CON_DRIVER; i++) {
> >                 con_back = &registered_con_driver[i];
> >
> > -               if (con_back->con &&
> > -                   !(con_back->flag & CON_DRIVER_FLAG_MODULE)) {
> > +               if (con_back->con && con_back->con != csw) {
> 
> Funny thing is, if you run do_bind_con_driver() on the range first,
> you kick out the existing driver and can then unload it regardless
> whether the fallback was FLAG_MODULE or not. Therefore, I think that
> change is safe. This is:
> 
> Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
> 
> Thanks
> David
> 
> >                         defcsw = con_back->con;
> >                         retval = 0;
> >                         break;
> > --
> > 1.8.1.4
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@lists.freedesktop.org
> > http://lists.freedesktop.org/mailman/listinfo/dri-devel

-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch