linux-kernel - [PATCH v11 1/8] cgroup/cpuset: Add top_cpuset check in update_tasks

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Date:   Tue, 10 May 2022 11:34:06 -0400
From:   Waiman Long <longman@...hat.com>
To:     Tejun Heo <tj@...nel.org>, Zefan Li <lizefan.x@...edance.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Jonathan Corbet <corbet@....net>, Shuah Khan <shuah@...nel.org>
Cc:     cgroups@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Roman Gushchin <guro@...com>, Phil Auld <pauld@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Frederic Weisbecker <frederic@...nel.org>,
        Marcelo Tosatti <mtosatti@...hat.com>,
        Michal Koutný <mkoutny@...e.com>,
        Waiman Long <longman@...hat.com>
Subject: [PATCH v11 1/8] cgroup/cpuset: Add top_cpuset check in update_tasks_cpumask()

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@...hat.com>
---
 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