softirq-fix-nohz-pending-issue-for-real.patch

Subject: softirq: Fix nohz pending issue for real
From: Thomas Gleixner <tglx@linutronix.de>
Date: Mon, 12 Nov 2012 22:07:34 +0100

We really need to iterate through all softirqs to find a potentially
blocked runner.

T1 runs softirq X (that cleared pending bit for X)

Interrupt raises softirq Y

T1 gets blocked on a lock and lock owner is not runnable

T1 schedules out

CPU goes idle and complains about pending softirq Y.

Now iterating over all softirqs lets us find the runner for X and
eliminate Y from the to warn about list as well.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
 kernel/softirq.c |   13 ++++---------
 1 file changed, 4 insertions(+), 9 deletions(-)

Index: linux-stable/kernel/softirq.c
===================================================================
--- linux-stable.orig/kernel/softirq.c
+++ linux-stable/kernel/softirq.c
@@ -100,20 +100,15 @@ void softirq_check_pending_idle(void)
 {
 	static int rate_limit;
 	struct softirq_runner *sr = &__get_cpu_var(softirq_runners);
-	u32 warnpending, pending = local_softirq_pending();
+	u32 warnpending = local_softirq_pending();
+	int i;
 
 	if (rate_limit >= 10)
 		return;
 
-	warnpending = pending;
-
-	while (pending) {
-		struct task_struct *tsk;
-		int i = __ffs(pending);
-
-		pending &= ~(1 << i);
+	for (i = 0; i < NR_SOFTIRQS; i++) {
+		struct task_struct *tsk = sr->runner[i];
 
-		tsk = sr->runner[i];
 		/*
 		 * The wakeup code in rtmutex.c wakes up the task
 		 * _before_ it sets pi_blocked_on to NULL under