tasklet: busy loop workaround

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

include/linux/interrupt.h

@@ -474,10 +474,8 @@ static inline void tasklet_unlock(struct tasklet_struct *t)
 	clear_bit(TASKLET_STATE_RUN, &(t)->state);
 }
 
-static inline void tasklet_unlock_wait(struct tasklet_struct *t)
-{
-	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) { barrier(); }
-}
+extern void tasklet_unlock_wait(struct tasklet_struct *t);
+
 #else
 #define tasklet_trylock(t) 1
 #define tasklet_tryunlock(t)	1

kernel/softirq.c

@@ -23,6 +23,7 @@
 #include <linux/mm.h>
 #include <linux/notifier.h>
 #include <linux/percpu.h>
+#include <linux/delay.h>
 #include <linux/cpu.h>
 #include <linux/freezer.h>
 #include <linux/kthread.h>
@@ -816,6 +817,25 @@ void __init softirq_init(void)
 	open_softirq(HI_SOFTIRQ, tasklet_hi_action);
 }
 
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT_RT)
+
+void tasklet_unlock_wait(struct tasklet_struct *t)
+{
+	while (test_bit(TASKLET_STATE_RUN, &(t)->state)) {
+		/*
+		 * Hack for now to avoid this busy-loop:
+		 */
+#ifdef CONFIG_PREEMPT_RT
+		msleep(1);
+#else
+		barrier();
+#endif
+	}
+}
+EXPORT_SYMBOL(tasklet_unlock_wait);
+
+#endif
+
 static int ksoftirqd(void * __data)
 {
 	/* Priority needs to be below hardirqs */