[PATCH v10 1/8] cgroup/cpuset: Add top_cpuset check in update_tasks_cpumask()

Waiman Long
2022-05-03T16:21:42Z

Right now, update_tasks_cpumask() is not supposed to be called with top
cpuset. With cpuset partition that takes CPUs away from the top cpuset,
we may want to consider adjusting the cpu_allows mask of the tasks in
the top cpuset as well. However, we need more investigation to figure
out a way to do that without breaking non-cgroup aware applications in
the top cpuset. So move the top_cpuset check into update_tasks_cpumask()
and add a comment about possible future work.

Signed-off-by: Waiman Long <longman-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
---
kernel/cgroup/cpuset.c | 15 +++++++++------
1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 9390bfd9f1cd..d90f33b068a3 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1128,6 +1128,14 @@ static void update_tasks_cpumask(struct cpuset *cs)
struct css_task_iter it;
struct task_struct *task;

+ /*
+ * TODO: With cpuset partition that takes CPUs away from the top
+ * cpuset, we may want to properly adjust the cpus_allowed mask of
+ * tasks in the top cpuset as well.
+ */
+ if (cs == &top_cpuset)
+ return;
+
css_task_iter_start(&cs->css, 0, &it);
while ((task = css_task_iter_next(&it)))
set_cpus_allowed_ptr(task, cs->effective_cpus);
@@ -2092,12 +2100,7 @@ static int update_prstate(struct cpuset *cs, int new_prs)
update_flag(CS_CPU_EXCLUSIVE, cs, 0);
}

- /*
- * Update cpumask of parent's tasks except when it is the top
- * cpuset as some system daemons cannot be mapped to other CPUs.
- */
- if (parent != &top_cpuset)
- update_tasks_cpumask(parent);
+ update_tasks_cpumask(parent);

if (parent->child_ecpus_count)
update_sibling_cpumasks(parent, cs, &tmpmask);
--
2.27.0