[ Upstream commit 49b6c01f ]

One more place where we must not be able
to be preempted or to be interrupted in RT.

Always actually disable interrupts during
synchronization cycle.
Signed-off-by: Kirill Tkhai <tkhai@yandex.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>