[Bug 219220] syscalls (ioctls) on USB devices are very slow

[bugzilla-noreply at freebsd.org]

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=219220

--- Comment #35 from Hans Petter Selasky <hselasky at FreeBSD.org> ---
Hi,

Each USB device instance has a global SX lock. This lock is held during detach.
usbconfig also acquire this lock. If the USB detach cannot complete, because
character devices towards user-space cannot be destroyed, because user-space
apps via libusb keep file /dev/ugenX.Y handles open, then enumeration will
appear frozen until this situation is resolved?

Is that more clear?

--HPS

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