ftrace: fix wakeups

Signed-off-by: NIngo Molnar <mingo@elte.hu>
Signed-off-by: NThomas Gleixner <tglx@linutronix.de>

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);

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
  */

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