Merge branch 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip

Pull scheduler fixes from Ingo Molnar:
 "Two smaller fixes - plus a context tracking tracing fix that is a bit
  bigger"

* 'sched-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip:
  tracing/context-tracking: Add preempt_schedule_context() for tracing
  sched: Fix clear NOHZ_BALANCE_KICK
  sched/x86: Construct all sibling maps if smt

2 files changed, 57 insertions, 4 deletions

diff --git a/kernel/context_tracking.c b/kernel/context_tracking.c
index 85bdde1137eb..383f8231e436 100644
--- a/kernel/context_tracking.c
+++ b/kernel/context_tracking.c
@@ -70,6 +70,46 @@ void user_enter(void)
         local_irq_restore(flags);
 }
 
+#ifdef CONFIG_PREEMPT
+/**
+ * preempt_schedule_context - preempt_schedule called by tracing
+ *
+ * The tracing infrastructure uses preempt_enable_notrace to prevent
+ * recursion and tracing preempt enabling caused by the tracing
+ * infrastructure itself. But as tracing can happen in areas coming
+ * from userspace or just about to enter userspace, a preempt enable
+ * can occur before user_exit() is called. This will cause the scheduler
+ * to be called when the system is still in usermode.
+ *
+ * To prevent this, the preempt_enable_notrace will use this function
+ * instead of preempt_schedule() to exit user context if needed before
+ * calling the scheduler.
+ */
+void __sched notrace preempt_schedule_context(void)
+{
+        struct thread_info *ti = current_thread_info();
+        enum ctx_state prev_ctx;
+
+        if (likely(ti->preempt_count || irqs_disabled()))
+                return;
+
+        /*
+         * Need to disable preemption in case user_exit() is traced
+         * and the tracer calls preempt_enable_notrace() causing
+         * an infinite recursion.
+         */
+        preempt_disable_notrace();
+        prev_ctx = exception_enter();
+        preempt_enable_no_resched_notrace();
+
+        preempt_schedule();
+
+        preempt_disable_notrace();
+        exception_exit(prev_ctx);
+        preempt_enable_notrace();
+}
+EXPORT_SYMBOL_GPL(preempt_schedule_context);
+#endif /* CONFIG_PREEMPT */
 
 /**
  * user_exit - Inform the context tracking that the CPU is
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index e1a27f918723..e8b335016c52 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -633,7 +633,19 @@ void wake_up_nohz_cpu(int cpu)
 static inline bool got_nohz_idle_kick(void)
 {
         int cpu = smp_processor_id();
-        return idle_cpu(cpu) && test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu));
+
+        if (!test_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu)))
+                return false;
+
+        if (idle_cpu(cpu) && !need_resched())
+                return true;
+
+        /*
+         * We can't run Idle Load Balance on this CPU for this time so we
+         * cancel it and clear NOHZ_BALANCE_KICK
+         */
+        clear_bit(NOHZ_BALANCE_KICK, nohz_flags(cpu));
+        return false;
 }
 
 #else /* CONFIG_NO_HZ_COMMON */
@@ -1393,8 +1405,9 @@ static void sched_ttwu_pending(void)
 
 void scheduler_ipi(void)
 {
-        if (llist_empty(&this_rq()->wake_list) && !got_nohz_idle_kick()
-            && !tick_nohz_full_cpu(smp_processor_id()))
+        if (llist_empty(&this_rq()->wake_list)
+                        && !tick_nohz_full_cpu(smp_processor_id())
+                        && !got_nohz_idle_kick())
                 return;
 
         /*
@@ -1417,7 +1430,7 @@ void scheduler_ipi(void)
         /*
          * Check if someone kicked us for doing the nohz idle load balance.
          */
-        if (unlikely(got_nohz_idle_kick() && !need_resched())) {
+        if (unlikely(got_nohz_idle_kick())) {
                 this_rq()->idle_balance = 1;
                 raise_softirq_irqoff(SCHED_SOFTIRQ);
         }