Hi,

In the block layer, we abuse sysfs to export some per-device debugging
information. I was looking into moving this to debugfs, but I realized
that debugfs doesn't have a mechanism to ensure that a file associated
with a device is safe to use when the device is removed. 

At a quick glance, HID has some per-device information in debugfs.
However, I don't see any sort of protection against a device being
removed. I was easily able to trigger an oops by reading from
/sys/kernel/debug/hid/*/rdesc in a loop and removing the USB device
(trace attached).

How can I safely export per-device debugging information to debugfs?

Thanks,
Omar