From: Li Zefan <lizefan@huawei.com>
Date: Thu, 13 Jun 2013 07:11:44 +0000 (+0800)
Subject: cpuset: fix to migrate mm correctly in a corner case
X-Git-Tag: omap-for-v3.11/fixes-for-merge-window~43^2~1
X-Git-Url: http://git.openpandora.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=f047cecf2cfc9595b1f39c9aab383bb0682f5a53;p=pandora-kernel.git

cpuset: fix to migrate mm correctly in a corner case

Before moving tasks out of empty cpusets, update_tasks_nodemask()
is called, which calls do_migrate_pages(xx, from, to). Then those
tasks are moved to an ancestor, and do_migrate_pages() is called
again.

The first time: from = node_to_be_offlined, to = empty.
The second time: from = empty, to = ancestor's nodemask.

so looks like no pages will be migrated.

Fix this by:

- Don't call update_tasks_nodemask() on empty cpusets.
- Pass cs->old_mems_allowed to do_migrate_pages().

v4: added comment in cpuset_hotplug_update_tasks() and rephased comment
    in cpuset_attach().

Signed-off-by: Li Zefan <lizefan@huawei.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
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