1 files changed, 15 insertions, 9 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index f12225f26b70..6fedf3a98581 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5738,15 +5738,10 @@ int sched_cpu_activate(unsigned int cpu)
 
 #ifdef CONFIG_SCHED_SMT
         /*
-         * The sched_smt_present static key needs to be evaluated on every
-         * hotplug event because at boot time SMT might be disabled when
-         * the number of booted CPUs is limited.
-         *
-         * If then later a sibling gets hotplugged, then the key would stay
-         * off and SMT scheduling would never be functional.
+         * When going up, increment the number of cores with SMT present.
          */
-        if (cpumask_weight(cpu_smt_mask(cpu)) > 1)
-                static_branch_enable_cpuslocked(&sched_smt_present);
+        if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+                static_branch_inc_cpuslocked(&sched_smt_present);
 #endif
         set_cpu_active(cpu, true);
 
@@ -5790,6 +5785,14 @@ int sched_cpu_deactivate(unsigned int cpu)
          */
         synchronize_rcu_mult(call_rcu, call_rcu_sched);
 
+#ifdef CONFIG_SCHED_SMT
+        /*
+         * When going down, decrement the number of cores with SMT present.
+         */
+        if (cpumask_weight(cpu_smt_mask(cpu)) == 2)
+                static_branch_dec_cpuslocked(&sched_smt_present);
+#endif
+
         if (!sched_smp_initialized)
                 return 0;
 
@@ -5851,11 +5854,14 @@ void __init sched_init_smp(void)
         /*
          * There's no userspace yet to cause hotplug operations; hence all the
          * CPU masks are stable and all blatant races in the below code cannot
-         * happen.
+         * happen. The hotplug lock is nevertheless taken to satisfy lockdep,
+         * but there won't be any contention on it.
          */
+        cpus_read_lock();
         mutex_lock(&sched_domains_mutex);
         sched_init_domains(cpu_active_mask);
         mutex_unlock(&sched_domains_mutex);
+        cpus_read_unlock();
 
         /* Move init over to a non-isolated CPU */
         if (set_cpus_allowed_ptr(current, housekeeping_cpumask(HK_FLAG_DOMAIN)) < 0)