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.
-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;
> }
>
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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