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cgroup: suppress spurious de-populated events

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During task migration, tasks may transfer between two css_sets which
are associated with the same cgroup.  If those tasks are the only
tasks in the cgroup, this currently triggers a spurious de-populated
event on the cgroup.

Fix it by bumping up populated count before bumping it down during
migration to ensure that it doesn't reach zero spuriously.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Zefan Li <lizefan@huawei.com>
This commit is contained in:
Tejun Heo 2016-03-03 09:57:57 -05:00
parent 2378d8b8ba
commit 20b454a61f
1 changed files with 3 additions and 2 deletions
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5
kernel/cgroup.c
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@ -678,6 +678,9 @@ static void css_set_move_task(struct task_struct *task,
{
lockdep_assert_held(&css_set_lock);
if (to_cset && !css_set_populated(to_cset))
css_set_update_populated(to_cset, true);
if (from_cset) {
struct css_task_iter *it, *pos;
@ -711,8 +714,6 @@ static void css_set_move_task(struct task_struct *task,
*/
WARN_ON_ONCE(task->flags & PF_EXITING);
if (!css_set_populated(to_cset))
css_set_update_populated(to_cset, true);
rcu_assign_pointer(task->cgroups, to_cset);
list_add_tail(&task->cg_list, use_mg_tasks ? &to_cset->mg_tasks :
&to_cset->tasks);