Re: [PATCH] drm: Fix possible race conditions while unplugging DRM device

[Oleksandr Andrushchenko]

On 05/29/2018 10:02 AM, Daniel Vetter wrote:
> On Tue, May 22, 2018 at 05:13:04PM +0300, Oleksandr Andrushchenko wrote:
> > From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >
> > When unplugging a hotpluggable DRM device we first unregister it
> > with drm_dev_unregister and then set drm_device.unplugged flag which
> > is used to mark device critical sections with drm_dev_enter()/
> > drm_dev_exit() preventing access to device resources that are not
> > available after the device is gone.
> > But drm_dev_unregister may lead to hotplug uevent(s) fired to
> > user-space on card and/or connector removal, thus making it possible
> > for user-space to try accessing a disconnected device.
> >
> > Fix this by first making sure device is properly marked as
> > disconnected and only then unregister it.
> >
> > Fixes: bee330f3d672 ("drm: Use srcu to protect drm_device.unplugged")
> >
> > Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> > Reported-by: Andrii Chepurnyi <andrii_chepurnyi@xxxxxxxx>
> > Cc: "Noralf TrÃnnes" <noralf@xxxxxxxxxxx>
> Nice catch.
>
> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
> I think you need to push this to drm-misc-next-fixes to make sure it's on
> the 4.17 train.
Sure, after I have r-b from Noralf
> -Daniel
>
> > ---
> >   drivers/gpu/drm/drm_drv.c | 14 +++++++-------
> >   1 file changed, 7 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> > index b553a6f2ff0e..7af748ed1c58 100644
> > --- a/drivers/gpu/drm/drm_drv.c
> > +++ b/drivers/gpu/drm/drm_drv.c
> > @@ -369,13 +369,6 @@ EXPORT_SYMBOL(drm_dev_exit);
> >    */
> >   void drm_dev_unplug(struct drm_device *dev)
> >   {
> > -	drm_dev_unregister(dev);
> > -
> > -	mutex_lock(&drm_global_mutex);
> > -	if (dev->open_count == 0)
> > -		drm_dev_put(dev);
> > -	mutex_unlock(&drm_global_mutex);
> > -
> >   	/*
> >   	 * After synchronizing any critical read section is guaranteed to see
> >   	 * the new value of ->unplugged, and any critical section which might
> > @@ -384,6 +377,13 @@ void drm_dev_unplug(struct drm_device *dev)
> >   	 */
> >   	dev->unplugged = true;
> >   	synchronize_srcu(&drm_unplug_srcu);
> > +
> > +	drm_dev_unregister(dev);
> > +
> > +	mutex_lock(&drm_global_mutex);
> > +	if (dev->open_count == 0)
> > +		drm_dev_put(dev);
> > +	mutex_unlock(&drm_global_mutex);
> >   }
> >   EXPORT_SYMBOL(drm_dev_unplug);
> >   
> > --
> > 2.17.0
> >
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@xxxxxxxxxxxxxxxxxxxxx
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel