lkml.org 
[lkml]   [2019]   [Apr]   [15]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] drm/i915: Use drm_dev_unplug()
On Fri, Apr 05, 2019 at 08:41:16AM +0100, Chris Wilson wrote:
> Quoting Janusz Krzysztofik (2019-04-05 08:26:57)
> > From: Janusz Krzysztofik <janusz.krzysztofik@intel.com>
> >
> > The driver does not currently support unbinding from a device which is
> > in use. Since open file descriptors may still be pointing into kernel
> > memory where the device structures used to be, entirely correct kernel
> > panics protect the driver from being unbound as we should not be
> > unbinding it before those dangling pointers have been made safe.
> >
> > According to the documentation found inside drivers/gpu/drm/drm_drv.c,
> > drm_dev_unplug() should be used instead of drm_dev_unregister() in
> > order to make a device inaccessible to users as soon as it is unpluged.
> > Follow that advice to make those possibly dangling pointers safe,
> > protected by DRM layer from a user who is otherwise left pointing into
> > possibly reused kernel memory after the driver has been unbound from
> > the device.
> >
> > Signed-off-by: Janusz Krzysztofik <janusz.krzysztofik@intel.com>
> > ---
> > drivers/gpu/drm/i915/i915_drv.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
> > index 9df65d386d11..66163378c481 100644
> > --- a/drivers/gpu/drm/i915/i915_drv.c
> > +++ b/drivers/gpu/drm/i915/i915_drv.c
> > @@ -1596,7 +1596,7 @@ static void i915_driver_unregister(struct drm_i915_private *dev_priv)
> > i915_pmu_unregister(dev_priv);
> >
> > i915_teardown_sysfs(dev_priv);
> > - drm_dev_unregister(&dev_priv->drm);
> > + drm_dev_unplug(&dev_priv->drm);
>
> I think we may have our onion inverted here. We want to stop the users
> as the first step, then start removing the entries. (That will also
> nicely invert the order from register, which is what we typically
> expect).
>
> After calling i915_driver_unregister(); call i915_gem_set_wedged() to
> immediately (give or take external fences) cancel inflight operations.

I think we still need the above patch, since drm_dev_unplug ==
drm_dev_unregister + "make sure userspace can't get at us anymore". We
could/should probably drop drm_dev_unplug and move that additional code to
drm_dev_unregister, but there's some minutea in how we refcount the
drm_device between the two. So not quite as clean a job.

There's also drm_put_dev (not to be mistaken with drm_dev_put), for added
confusion. I think ideally we'd unify all three of drm_dev_unregister,
drm_dev_unplug and drm_put_dev to one, deprecating all the others. But
that's work :-)
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

\
 
 \ /
  Last update: 2019-04-15 11:30    [W:0.046 / U:6.196 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site