Fix a problem where ds_request() returned an error without releasing the
ds lock.
Reported-by: NStephane Eranian <eranian@gmail.com>
Signed-off-by: NMarkus Metzger <markus.t.metzger@gmail.com>
Cc: <stable@kernel.org>
Signed-off-by: NIngo Molnar <mingo@elte.hu>