fault_in_user_writeable — Fault in user address and verify RW access
|u32 __user * uaddr|
Slow path to fixup the fault we just took in the atomic write
We have no generic implementation of a non-destructive write to the
user address. We know that we faulted in the atomic pagefault
disabled section so we can as well avoid the #PF overhead by
get_user_pages right away.