3 files changed, 31 insertions, 4 deletions

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 652d380ae563..a3970b563757 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -246,6 +246,8 @@ extern asmlinkage void schedule_tail(struct task_struct *prev);
 extern void init_idle(struct task_struct *idle, int cpu);
 extern void init_idle_bootup_task(struct task_struct *idle);
 
+extern int runqueue_is_locked(void);
+
 extern cpumask_t nohz_cpu_mask;
 #if defined(CONFIG_SMP) && defined(CONFIG_NO_HZ)
 extern int select_nohz_load_balancer(int cpu);
diff --git a/kernel/sched.c b/kernel/sched.c
index 673b588b713b..9ca4a2e6a236 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -642,6 +642,24 @@ static inline void update_rq_clock(struct rq *rq)
 # define const_debug static const
 #endif
 
+/**
+ * runqueue_is_locked
+ *
+ * Returns true if the current cpu runqueue is locked.
+ * This interface allows printk to be called with the runqueue lock
+ * held and know whether or not it is OK to wake up the klogd.
+ */
+int runqueue_is_locked(void)
+{
+        int cpu = get_cpu();
+        struct rq *rq = cpu_rq(cpu);
+        int ret;
+
+        ret = spin_is_locked(&rq->lock);
+        put_cpu();
+        return ret;
+}
+
 /*
  * Debugging: various feature bits
  */
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 65173b14b914..2ca9d66aa74e 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -70,12 +70,13 @@ static DECLARE_WAIT_QUEUE_HEAD(trace_wait);
 
 unsigned long trace_flags = TRACE_ITER_PRINT_PARENT;
 
-/*
- * FIXME: where should this be called?
- */
 void trace_wake_up(void)
 {
-        if (!(trace_flags & TRACE_ITER_BLOCK))
+        /*
+         * The runqueue_is_locked() can fail, but this is the best we
+         * have for now:
+         */
+        if (!(trace_flags & TRACE_ITER_BLOCK) && !runqueue_is_locked())
                 wake_up(&trace_wait);
 }
 
@@ -657,6 +658,8 @@ trace_function(struct trace_array *tr, struct trace_array_cpu *data,
         entry->fn.ip            = ip;
         entry->fn.parent_ip     = parent_ip;
         spin_unlock_irqrestore(&data->lock, irq_flags);
+
+        trace_wake_up();
 }
 
 void
@@ -686,6 +689,8 @@ __trace_special(void *__tr, void *__data,
         entry->special.arg2     = arg2;
         entry->special.arg3     = arg3;
         spin_unlock_irqrestore(&data->lock, irq_flags);
+
+        trace_wake_up();
 }
 
 #endif
@@ -759,6 +764,8 @@ tracing_sched_wakeup_trace(struct trace_array *tr,
         entry->ctx.next_prio    = wakee->prio;
         __trace_stack(tr, data, flags, 5);
         spin_unlock_irqrestore(&data->lock, irq_flags);
+
+        trace_wake_up();
 }
 
 #ifdef CONFIG_FTRACE