usb: cdc-wdm: close race between read and workqueue

usb: cdc-wdm: close race between read and workqueue

wdm_read() cannot race with itself. However, in
service_outstanding_interrupt() it can race with the
workqueue, which can be triggered by error handling.

Hence we need to make sure that the WDM_RESPONDING
flag is not just only set but tested.

Fixes: afba937e540c9 ("USB: CDC WDM driver")
Cc: stable <[email protected]>
Signed-off-by: Oliver Neukum <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Greg Kroah-Hartman <[email protected]>