On Wed, Aug 12, 2020 at 12:16 AM Zwane Mwaikambo <zwanem@xxxxxxxxx> 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 > > > > > > > > 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@xxxxxxxxxxxxxxxxxxxxx > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel