[Bug 201421] locking issues prevent new process creation

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https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=201421

--- Comment #4 from Hans Petter Selasky <hselasky at FreeBSD.org> ---
(In reply to John Baldwin from comment #3)
Hi,

If you run "usbconfig" as root, and if it doesn't respond, looks like it is
hanging, it typically means USB is not able to detach one of the device
drivers. In recent past it is know that sudden detach of USB memory sticks can
cause this error, because of refcounts inside CAM / SCSI not going to zero.

Also you need to ensure that any USB MIDI devices gets closed by the
application when they receive a read error. Else the open file handle will
block further USB enumeration. And will also lock other applications which are
enumerating USB on that particular USB device.

When running KGDB, you could check the backtrace of the USB explore threads.

ps auxwH | grep -i usb

Did you try 10-stable or 9-stable and not the release branches. From time to
time bugfixes are merged to these branches.

--HPS

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