LKML Archive on lore.kernel.org
help / color / mirror / Atom feed
From: Lyude Paul <lyude@redhat.com>
To: Daniel Vetter <daniel@ffwll.ch>, Zwane Mwaikambo <zwanem@gmail.com>
Cc: 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: Wed, 12 Aug 2020 11:44:56 -0400	[thread overview]
Message-ID: <a1141faf8c6a0a924d87132fb4a297cd6d47e09d.camel@redhat.com> (raw)
In-Reply-To: <CAKMK7uHxikojLQNbsnnfDfGZ3tFP9CRUTzvr+DsZghzQupaBGg@mail.gmail.com>

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?

> > 
> > > > To me it still makes sense to just check aux_dev because the chardev
> > > > has
> > > > no way to check before calling.
> > > > 
> > > > (gdb) list *drm_dp_aux_dev_get_by_minor+0x29
> > > > 0x17b39 is in drm_dp_aux_dev_get_by_minor
> > > > (drivers/gpu/drm/drm_dp_aux_dev.c:65).
> > > > 60      static struct drm_dp_aux_dev
> > > > *drm_dp_aux_dev_get_by_minor(unsigned index)
> > > > 61      {
> > > > 62              struct drm_dp_aux_dev *aux_dev = NULL;
> > > > 63
> > > > 64              mutex_lock(&aux_idr_mutex);
> > > > 65              aux_dev = idr_find(&aux_idr, index);
> > > > 66              if (!kref_get_unless_zero(&aux_dev->refcount))
> > > > 67                      aux_dev = NULL;
> > > > 68              mutex_unlock(&aux_idr_mutex);
> > > > 69
> > > > (gdb) p/x &((struct drm_dp_aux_dev *)(0x0))->refcount
> > > > $8 = 0x18
> > > > 
> > > > static int auxdev_open(struct inode *inode, struct file *file)
> > > > {
> > > >     unsigned int minor = iminor(inode);
> > > >     struct drm_dp_aux_dev *aux_dev;
> > > > 
> > > >     aux_dev = drm_dp_aux_dev_get_by_minor(minor);
> > > >     if (!aux_dev)
> > > >         return -ENODEV;
> > > > 
> > > >     file->private_data = aux_dev;
> > > >     return 0;
> > > > }
> > > > 
> > > > 
> > > > _______________________________________________
> > > > dri-devel mailing list
> > > > dri-devel@lists.freedesktop.org
> > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel
> 
> 
-- 
Cheers,
	Lyude Paul (she/her)
	Software Engineer at Red Hat


  reply	other threads:[~2020-08-12 15:45 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 [this message]
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
  -- 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

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=a1141faf8c6a0a924d87132fb4a297cd6d47e09d.camel@redhat.com \
    --to=lyude@redhat.com \
    --cc=daniel@ffwll.ch \
    --cc=dkwon@redhat.com \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=tcamuso@redhat.com \
    --cc=zwanem@gmail.com \
    --subject='Re: [PATCH] drm: assure aux_dev is nonzero before using it' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).