commit 89f82cbb upstream.

Use instead __copy_from_user_inatomic() and fallback to slow-path where
we drop and re-aquire the lock in case of fault.
Reported-by: Vaishali Thakkar <vaishali.thakkar@oracle.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>