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SubjectRe: [PATCH] drm: assure aux_dev is nonzero before using it
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On Tue, 2020-08-18 at 10:58 -0700, Zwane Mwaikambo wrote:
> On Wed, 12 Aug 2020, Lyude Paul wrote:
>
> > On Wed, 2020-08-12 at 16:10 +0200, Daniel Vetter wrote:
> > > On Wed, Aug 12, 2020 at 12:16 AM Zwane Mwaikambo <zwanem@gmail.com>
> > > wrote:
> > > > On Tue, 11 Aug 2020, Daniel Vetter wrote:
> > > >
> > > > > On Mon, Aug 10, 2020 at 10:11:50AM -0700, Zwane Mwaikambo wrote:
> > > > > > Hi Folks,
> > > > > > I know this thread eventually dropped off due to not
> > > > > > identifying
> > > > > > the underlying issue. It's still occuring on 5.8 and in my case it
> > > > > > happened because the udev device nodes for the DP aux devices were
> > > > > > not
> > > > > > cleaned up whereas the kernel had no association with them. I can
> > > > > > reproduce the bug just by creating a device node for a non-
> > > > > > existent
> > > > > > minor
> > > > > > device and calling open().
> > > > >
> > > > > Hm I don't have that thread anymore, but generally these bugs are
> > > > > solved
> > > > > by not registering the device before it's ready for use. We do have
> > > > > drm_connector->late_register for that stuff. Just a guess since I'm
> > > > > not
> > > > > seeing full details here.
> > > >
> > > > In this particular case, the physical device disappeared before the
> > > > nodes
> > > > were cleaned up. It involves putting a computer to sleep with a
> > > > monitor
> > > > plugged in and then waking it up with the monitor unplugged.
> > >
> > > We also have early_unregister for the reverse, but yes this sounds
> > > more tricky ... Adding Lyude who's been working on way too much
> > > lifetime fun around dp recently.
> > > -Daniel
> > >
> > Hi-I think just checking whether the auxdev is NULL or not is a reasonable
> > fix, although I am curious as to how exactly the aux dev's parent is
> > getting
> > destroyed before it's child, which I would have thought would be the only
> > way
> > you could hit this?
>
> Hi, If this is acceptable, would you consider an updated patch against
> 5.8?

Sure-although the process to getting this into stable is to get the patch into
drm-next first, then it can get cherry-picked into the stable kernel branches.
See https://www.kernel.org/doc/html/latest/process/stable-kernel-rules.html

>
> Thanks,
> Zwane
>
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat

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