tasklet-busy-loop-workaround.patch

From 9f2e31ae6e796e5262f03975a3782e50f64321de Mon Sep 17 00:00:00 2001
From: Ingo Molnar <mingo@elte.hu>
Date: Fri, 3 Jul 2009 08:29:56 -0500
Subject: [PATCH] tasklet: busy loop workaround

commit 4bd0125629790076941e1b663234cdbb22524421 in tip.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/include/linux/interrupt.h b/include/linux/interrupt.h
index 86cf03e..0fd5b27 100644
--- a/include/linux/interrupt.h
+++ b/include/linux/interrupt.h
@@ -476,10 +476,8 @@ 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
diff --git a/kernel/softirq.c b/kernel/softirq.c
index 1be5ff4..31db011 100644
--- a/kernel/softirq.c
+++ b/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>
@@ -811,6 +812,23 @@ 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 run_ksoftirqd(void * __data)
 {
 	/* Priority needs to be below hardirqs */
-- 
1.7.1.1