linux-kernel - [PATCH v12 01/10] cgroup/cpuset: Enable update_tasks_cpumask() on top

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Date:   Thu,  1 Sep 2022 16:57:36 -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 v12 01/10] cgroup/cpuset: Enable update_tasks_cpumask() on top_cpuset

Previously, update_tasks_cpumask() is not supposed to be called with
top cpuset. With cpuset partition that takes CPUs away from the top
cpuset, adjusting the cpus_mask of the tasks in the top cpuset is
necessary. Percpu kthreads, however, are ignored.

Fixes: ee8dde0cd2ce ("cpuset: Add new v2 cpuset.sched.partition flag")
Signed-off-by: Waiman Long <longman@...hat.com>
---
 kernel/cgroup/cpuset.c | 18 +++++++++++-------
 1 file changed, 11 insertions(+), 7 deletions(-)

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 1f3a55297f39..50bf837571ac 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -33,6 +33,7 @@
 #include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/kmod.h>
+#include <linux/kthread.h>
 #include <linux/list.h>
 #include <linux/mempolicy.h>
 #include <linux/mm.h>
@@ -1127,10 +1128,18 @@ static void update_tasks_cpumask(struct cpuset *cs)
 {
 	struct css_task_iter it;
 	struct task_struct *task;
+	bool top_cs = cs == &top_cpuset;
 
 	css_task_iter_start(&cs->css, 0, &it);
-	while ((task = css_task_iter_next(&it)))
+	while ((task = css_task_iter_next(&it))) {
+		/*
+		 * Percpu kthreads in top_cpuset are ignored
+		 */
+		if (top_cs && (task->flags & PF_KTHREAD) &&
+		    kthread_is_per_cpu(task))
+			continue;
 		set_cpus_allowed_ptr(task, cs->effective_cpus);
+	}
 	css_task_iter_end(&it);
 }
 
@@ -2092,12 +2101,7 @@ 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);
-- 
2.31.1