kthread: Honour kthreads preferred affinity after cpuset changes

When cpuset isolated partitions get updated, unbound kthreads get
indifferently affine to all non isolated CPUs, regardless of their
individual affinity preferences.

For example kswapd is a per-node kthread that prefers to be affine to
the node it refers to. Whenever an isolated partition is created,
updated or deleted, kswapd's node affinity is going to be broken if any
CPU in the related node is not isolated because kswapd will be affine
globally.

Fix this with letting the consolidated kthread managed affinity code do
the affinity update on behalf of cpuset.

Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Waiman Long <longman@redhat.com>
Cc: Michal Koutný <mkoutny@suse.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Marco Crivellari <marco.crivellari@suse.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Waiman Long <longman@redhat.com>
Cc: cgroups@vger.kernel.org

1 files changed, 31 insertions, 10 deletions

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 968fa5868d21..03008154249c 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -891,14 +891,7 @@ out:
 }
 EXPORT_SYMBOL_GPL(kthread_affine_preferred);
 
-/*
- * Re-affine kthreads according to their preferences
- * and the newly online CPU. The CPU down part is handled
- * by select_fallback_rq() which default re-affines to
- * housekeepers from other nodes in case the preferred
- * affinity doesn't apply anymore.
- */
-static int kthreads_online_cpu(unsigned int cpu)
+static int kthreads_update_affinity(bool force)
 {
 	cpumask_var_t affinity;
 	struct kthread *k;
@@ -924,7 +917,8 @@ static int kthreads_online_cpu(unsigned int cpu)
 		/*
 		 * Unbound kthreads without preferred affinity are already affine
 		 * to housekeeping, whether those CPUs are online or not. So no need
-		 * to handle newly online CPUs for them.
+		 * to handle newly online CPUs for them. However housekeeping changes
+		 * have to be applied.
 		 *
 		 * But kthreads with a preferred affinity or node are different:
 		 * if none of their preferred CPUs are online and part of
@@ -932,7 +926,7 @@ static int kthreads_online_cpu(unsigned int cpu)
 		 * But as soon as one of their preferred CPU becomes online, they must
 		 * be affine to them.
 		 */
-		if (k->preferred_affinity || k->node != NUMA_NO_NODE) {
+		if (force || k->preferred_affinity || k->node != NUMA_NO_NODE) {
 			kthread_fetch_affinity(k, affinity);
 			set_cpus_allowed_ptr(k->task, affinity);
 		}
@@ -943,6 +937,33 @@ static int kthreads_online_cpu(unsigned int cpu)
 	return ret;
 }
 
+/**
+ * kthreads_update_housekeeping - Update kthreads affinity on cpuset change
+ *
+ * When cpuset changes a partition type to/from "isolated" or updates related
+ * cpumasks, propagate the housekeeping cpumask change to preferred kthreads
+ * affinity.
+ *
+ * Returns 0 if successful, -ENOMEM if temporary mask couldn't
+ * be allocated or -EINVAL in case of internal error.
+ */
+int kthreads_update_housekeeping(void)
+{
+	return kthreads_update_affinity(true);
+}
+
+/*
+ * Re-affine kthreads according to their preferences
+ * and the newly online CPU. The CPU down part is handled
+ * by select_fallback_rq() which default re-affines to
+ * housekeepers from other nodes in case the preferred
+ * affinity doesn't apply anymore.
+ */
+static int kthreads_online_cpu(unsigned int cpu)
+{
+	return kthreads_update_affinity(false);
+}
+
 static int kthreads_init(void)
 {
 	return cpuhp_setup_state(CPUHP_AP_KTHREADS_ONLINE, "kthreads:online",