Commit f047cecf authored by Li Zefan's avatar Li Zefan Committed by Tejun Heo
Browse files

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: default avatarLi Zefan <lizefan@huawei.com>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 88fa523b

kernel/cpuset.c

+19 −6
Original line number Diff line number Diff line
@@ -1563,9 +1563,18 @@ static void cpuset_attach(struct cgroup *cgrp, struct cgroup_taskset *tset) 
		struct cpuset *mems_oldcs = effective_nodemask_cpuset(oldcs);



		mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);

		if (is_memory_migrate(cs))

			cpuset_migrate_mm(mm, &mems_oldcs->mems_allowed,



		/*

		 * old_mems_allowed is the same with mems_allowed here, except

		 * if this task is being moved automatically due to hotplug.

		 * In that case @mems_allowed has been updated and is empty,

		 * so @old_mems_allowed is the right nodesets that we migrate

		 * mm from.

		 */

		if (is_memory_migrate(cs)) {

			cpuset_migrate_mm(mm, &mems_oldcs->old_mems_allowed,

					  &cpuset_attach_nodemask_to);

		}

		mmput(mm);

	}
@@ -2152,10 +2161,12 @@ retry: 


	/*

	 * If sane_behavior flag is set, we need to update tasks' cpumask

	 * for empty cpuset to take on ancestor's cpumask.

	 * for empty cpuset to take on ancestor's cpumask. Otherwise, don't

	 * call update_tasks_cpumask() if the cpuset becomes empty, as

	 * the tasks in it will be migrated to an ancestor.

	 */

	if ((sane && cpumask_empty(cs->cpus_allowed)) ||

	    !cpumask_empty(&off_cpus))

	    (!cpumask_empty(&off_cpus) && !cpumask_empty(cs->cpus_allowed)))

		update_tasks_cpumask(cs, NULL);



	mutex_lock(&callback_mutex);
@@ -2164,10 +2175,12 @@ retry: 


	/*

	 * If sane_behavior flag is set, we need to update tasks' nodemask

	 * for empty cpuset to take on ancestor's nodemask.

	 * for empty cpuset to take on ancestor's nodemask. Otherwise, don't

	 * call update_tasks_nodemask() if the cpuset becomes empty, as

	 * the tasks in it will be migratd to an ancestor.

	 */

	if ((sane && nodes_empty(cs->mems_allowed)) ||

	    !nodes_empty(off_mems))

	    (!nodes_empty(off_mems) && !nodes_empty(cs->mems_allowed)))

		update_tasks_nodemask(cs, NULL);



	is_empty = cpumask_empty(cs->cpus_allowed) ||

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