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From: Lyude Paul <lyude@redhat.com>
To: Zwane Mwaikambo <zwanem@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>,
	tcamuso@redhat.com, dkwon@redhat.com,
	Linux Kernel <linux-kernel@vger.kernel.org>,
	dri-devel <dri-devel@lists.freedesktop.org>
Subject: Re: [PATCH] drm: assure aux_dev is nonzero before using it
Date: Tue, 08 Sep 2020 14:41:42 -0400	[thread overview]
Message-ID: <5b63113be2e02d15268470d54b0cffeae06c5292.camel@redhat.com> (raw)
In-Reply-To: <alpine.DEB.2.21.2008181057090.8571@montezuma.home>

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


  reply	other threads:[~2020-09-08 18:45 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-10 17:11 Zwane Mwaikambo
2020-08-11  8:58 ` Daniel Vetter
2020-08-11 22:16   ` Zwane Mwaikambo
2020-08-12 14:10     ` Daniel Vetter
2020-08-12 15:44       ` Lyude Paul
2020-08-12 20:21         ` Zwane Mwaikambo
2020-09-04  7:21           ` [PATCH]] drm/dp check aux_dev before use in drm_dp_aux_dev_get_by_minor() Zwane Mwaikambo
2020-09-07 11:05             ` Ville Syrjälä
2020-09-08 16:18               ` Zwane Mwaikambo
2020-08-18 17:58         ` [PATCH] drm: assure aux_dev is nonzero before using it Zwane Mwaikambo
2020-09-08 18:41           ` Lyude Paul [this message]
  -- strict thread matches above, loose matches on Subject: below --
2019-05-23 11:09 tcamuso
2019-05-24  8:36 ` Jani Nikula
2019-05-24 10:48   ` tony camuso
2019-05-24 11:58     ` Ville Syrjälä
2019-07-10 13:47   ` Tony Camuso
2019-07-10 13:56     ` Ville Syrjälä
2019-07-12 16:07       ` Tony Camuso
2019-07-12 17:06         ` Ville Syrjälä
2019-07-12 17:35           ` Tony Camuso
2019-09-23 15:03           ` Tony Camuso
2019-09-23 15:22             ` Ville Syrjälä

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