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

diff --git a/include/linux/kthread.h b/include/linux/kthread.h
index 8d27403888ce93fd655e631f6d5ebbdf6e520e2b..c92c1149ee6e103e90fea2c1c093070078bdf3da 100644 (file)
--- a/include/linux/kthread.h
+++ b/include/linux/kthread.h
@@ -100,6 +100,7 @@ void kthread_unpark(struct task_struct *k);
 void kthread_parkme(void);
 void kthread_exit(long result) __noreturn;
 void kthread_complete_and_exit(struct completion *, long) __noreturn;
+int kthreads_update_housekeeping(void);
 
 int kthreadd(void *unused);
 extern struct task_struct *kthreadd_task;

diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 801694de82a3c57696401c53fd9650500b2ae2a1..9a8292b7c7f10f13749759f845116fa851170362 100644 (file)
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -1208,11 +1208,10 @@ void cpuset_update_tasks_cpumask(struct cpuset *cs, struct cpumask *new_cpus)
 
                if (top_cs) {
                        /*
+                        * PF_KTHREAD tasks are handled by housekeeping.
                         * PF_NO_SETAFFINITY tasks are ignored.
-                        * All per cpu kthreads should have PF_NO_SETAFFINITY
-                        * flag set, see kthread_set_per_cpu().
                         */
-                       if (task->flags & PF_NO_SETAFFINITY)
+                       if (task->flags & (PF_KTHREAD | PF_NO_SETAFFINITY))
                                continue;
                        cpumask_andnot(new_cpus, possible_mask, subpartitions_cpus);
                } else {

diff --git a/kernel/kthread.c b/kernel/kthread.c
index 968fa5868d2162b757ad60efa1029993745197a2..03008154249c7e9cc3ce503da002133ba39a166a 100644 (file)
--- 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",

diff --git a/kernel/sched/isolation.c b/kernel/sched/isolation.c
index a30d19b641f7c2e188d040bd8ff765e5a315cd85..3b725d39c06e94bd2fb28916e191e52119d85c89 100644 (file)
--- a/kernel/sched/isolation.c
+++ b/kernel/sched/isolation.c
@@ -156,6 +156,9 @@ int housekeeping_update(struct cpumask *isol_mask)
        err = tmigr_isolated_exclude_cpumask(isol_mask);
        WARN_ON_ONCE(err < 0);
 
+       err = kthreads_update_housekeeping();
+       WARN_ON_ONCE(err < 0);
+
        kfree(old);
 
        return 0;