cpuset: Fix incorrect memory_pressure control file mapping

cpuset: Fix incorrect memory_pressure control file mapping

commit 1c08c22c874ac88799cab1f78c40f46110274915 upstream.

The memory_pressure control file was incorrectly set up without
a private value (0, by default). As a result, this control
file was treated like memory_migrate on read. By adding back the
FILE_MEMORY_PRESSURE private value, the correct memory pressure value
will be returned.

Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 7dbdb199d3bf ("cgroup: replace cftype->mode with CFTYPE_WORLD_WRITABLE")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>