tree 8b2d2e4d73f6063f76842d6814caf6649942862f
parent 70f7ca9a0262784d0b80727860a63d64ab228e7b
author Alan Stern <stern@rowland.harvard.edu> 1465584175 -0400
committer Greg Kroah-Hartman <gregkh@linuxfoundation.org> 1470752058 +0200

USB: remove race condition in usbfs/libusb when using reap-after-disconnect

Hans de Goede has reported a difficulty in the Linux port of libusb.
When a device is removed, the poll() system call in usbfs starts
returning POLLERR as soon as udev->state is set to
USB_STATE_NOTATTACHED, but the outstanding URBs are not available for
reaping until some time later (after usbdev_remove() has been called).
This is awkward for libusb or other usbfs clients, although not an
insuperable problem.

At any rate, it's easy to change usbfs so that it returns POLLHUP as
soon as the state becomes USB_STATE_NOTATTACHED but it doesn't return
POLLERR until after the outstanding URBs have completed.  That's what
this patch does; it uses the fact that ps->list is always on the
dev->filelist list until usbdev_remove() takes it off, which happens
after all the outstanding URBs have been cancelled.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Reported-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>