[PATCH rcu 4/6] rcu: Avoid running boost kthreads on isolated CPUs

[Paul E. McKenney]

From: Zqiang <qiang.zhang1211@xxxxxxxxx>

When the boost kthreads are created on systems with nohz_full CPUs,
the cpus_allowed_ptr is set to housekeeping_cpumask(HK_FLAG_KTHREAD).
However, when the rcu_boost_kthread_setaffinity() is called, the original
affinity will be changed and these kthreads can subsequently run on
nohz_full CPUs.  This commit makes rcu_boost_kthread_setaffinity()
restrict these boost kthreads to housekeeping CPUs.

Signed-off-by: Zqiang <qiang.zhang1211@xxxxxxxxx>
Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
---
 kernel/rcu/tree_plugin.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/rcu/tree_plugin.h b/kernel/rcu/tree_plugin.h
index f44580276fbdc..87fc4609b7563 100644
--- a/kernel/rcu/tree_plugin.h
+++ b/kernel/rcu/tree_plugin.h
@@ -1203,8 +1203,9 @@ static void rcu_boost_kthread_setaffinity(struct rcu_node *rnp, int outgoingcpu)
 		if ((mask & leaf_node_cpu_bit(rnp, cpu)) &&
 		    cpu != outgoingcpu)
 			cpumask_set_cpu(cpu, cm);
+	cpumask_and(cm, cm, housekeeping_cpumask(HK_FLAG_RCU));
 	if (cpumask_weight(cm) == 0)
-		cpumask_setall(cm);
+		cpumask_copy(cm, housekeeping_cpumask(HK_FLAG_RCU));
 	set_cpus_allowed_ptr(t, cm);
 	free_cpumask_var(cm);
 }
-- 
2.31.1.189.g2e36527f23