Patch "cgroup/cpuset: Inherit parent's load balance state in v2" has been added to the 6.4-stable tree

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This is a note to let you know that I've just added the patch titled

    cgroup/cpuset: Inherit parent's load balance state in v2

to the 6.4-stable tree which can be found at:
    http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
     cgroup-cpuset-inherit-parent-s-load-balance-state-in.patch
and it can be found in the queue-6.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.



commit ca242ff701ca149b4f318614d1a0105865c3c637
Author: Waiman Long <longman@xxxxxxxxxx>
Date:   Tue Jun 27 10:35:00 2023 -0400

    cgroup/cpuset: Inherit parent's load balance state in v2
    
    [ Upstream commit c8c926200c55454101f072a4b16c9ff5b8c9e56f ]
    
    Since commit f28e22441f35 ("cgroup/cpuset: Add a new isolated
    cpus.partition type"), the CS_SCHED_LOAD_BALANCE bit of a v2 cpuset
    can be on or off. The child cpusets of a partition root must have the
    same setting as its parent or it may screw up the rebuilding of sched
    domains. Fix this problem by making sure the a child v2 cpuset will
    follows its parent cpuset load balance state unless the child cpuset
    is a new partition root itself.
    
    Fixes: f28e22441f35 ("cgroup/cpuset: Add a new isolated cpus.partition type")
    Signed-off-by: Waiman Long <longman@xxxxxxxxxx>
    Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
    Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 2c76fcd9f0bcb..7c5153273c1a8 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1611,11 +1611,16 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 		}
 
 		/*
-		 * Skip the whole subtree if the cpumask remains the same
-		 * and has no partition root state and force flag not set.
+		 * Skip the whole subtree if
+		 * 1) the cpumask remains the same,
+		 * 2) has no partition root state,
+		 * 3) force flag not set, and
+		 * 4) for v2 load balance state same as its parent.
 		 */
 		if (!cp->partition_root_state && !force &&
-		    cpumask_equal(tmp->new_cpus, cp->effective_cpus)) {
+		    cpumask_equal(tmp->new_cpus, cp->effective_cpus) &&
+		    (!cgroup_subsys_on_dfl(cpuset_cgrp_subsys) ||
+		    (is_sched_load_balance(parent) == is_sched_load_balance(cp)))) {
 			pos_css = css_rightmost_descendant(pos_css);
 			continue;
 		}
@@ -1698,6 +1703,20 @@ static void update_cpumasks_hier(struct cpuset *cs, struct tmpmasks *tmp,
 
 		update_tasks_cpumask(cp, tmp->new_cpus);
 
+		/*
+		 * On default hierarchy, inherit the CS_SCHED_LOAD_BALANCE
+		 * from parent if current cpuset isn't a valid partition root
+		 * and their load balance states differ.
+		 */
+		if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+		    !is_partition_valid(cp) &&
+		    (is_sched_load_balance(parent) != is_sched_load_balance(cp))) {
+			if (is_sched_load_balance(parent))
+				set_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
+			else
+				clear_bit(CS_SCHED_LOAD_BALANCE, &cp->flags);
+		}
+
 		/*
 		 * On legacy hierarchy, if the effective cpumask of any non-
 		 * empty cpuset is changed, we need to rebuild sched domains.
@@ -3245,6 +3264,14 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
 		cs->use_parent_ecpus = true;
 		parent->child_ecpus_count++;
 	}
+
+	/*
+	 * For v2, clear CS_SCHED_LOAD_BALANCE if parent is isolated
+	 */
+	if (cgroup_subsys_on_dfl(cpuset_cgrp_subsys) &&
+	    !is_sched_load_balance(parent))
+		clear_bit(CS_SCHED_LOAD_BALANCE, &cs->flags);
+
 	spin_unlock_irq(&callback_lock);
 
 	if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags))



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