debugfs vs. device removal

From	Omar Sandoval <osandov@osandov.com>
Newsgroups	linux.kernel
Subject	debugfs vs. device removal
Date	2017-01-19 16:50 +0100
Message-ID	<t1n8n-3mv-37@gated-at.bofh.it> (permalink)
Organization	linux.* mail to news gateway

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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

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debugfs vs. device removal Omar Sandoval <osandov@osandov.com> - 2017-01-19 16:50 +0100
  Re: debugfs vs. device removal Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-19 17:00 +0100
    Re: debugfs vs. device removal Jiri Kosina <jikos@kernel.org> - 2017-01-19 17:10 +0100
      Re: debugfs vs. device removal Omar Sandoval <osandov@osandov.com> - 2017-01-19 18:40 +0100
        Re: debugfs vs. device removal Greg Kroah-Hartman <gregkh@linuxfoundation.org> - 2017-01-19 19:30 +0100
          Re: debugfs vs. device removal Omar Sandoval <osandov@osandov.com> - 2017-01-19 20:50 +0100

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