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From: Thomas Gleixner <tglx@linutronix.de>
Date: Fri, 3 Jul 2009 13:16:38 -0500
Subject: softirq: Sanitize softirq pending for NOHZ/RT
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
include/linux/interrupt.h | 2 +
kernel/softirq.c | 61 ++++++++++++++++++++++++++++++++++++++++++++++
kernel/time/tick-sched.c | 8 ------
3 files changed, 64 insertions(+), 7 deletions(-)
Index: linux-stable/include/linux/interrupt.h
===================================================================
--- linux-stable.orig/include/linux/interrupt.h
+++ linux-stable/include/linux/interrupt.h
@@ -458,6 +458,8 @@ extern void __raise_softirq_irqoff(unsig
extern void raise_softirq_irqoff(unsigned int nr);
extern void raise_softirq(unsigned int nr);
+extern void softirq_check_pending_idle(void);
+
/* This is the worklist that queues up per-cpu softirq work.
*
* send_remote_sendirq() adds work to these lists, and
Index: linux-stable/kernel/softirq.c
===================================================================
--- linux-stable.orig/kernel/softirq.c
+++ linux-stable/kernel/softirq.c
@@ -61,6 +61,67 @@ char *softirq_to_name[NR_SOFTIRQS] = {
"TASKLET", "SCHED", "HRTIMER", "RCU"
};
+#ifdef CONFIG_NO_HZ
+# ifdef CONFIG_PREEMPT_RT_FULL
+/*
+ * On preempt-rt a softirq might be blocked on a lock. There might be
+ * no other runnable task on this CPU because the lock owner runs on
+ * some other CPU. So we have to go into idle with the pending bit
+ * set. Therefor we need to check this otherwise we warn about false
+ * positives which confuses users and defeats the whole purpose of
+ * this test.
+ *
+ * This code is called with interrupts disabled.
+ */
+void softirq_check_pending_idle(void)
+{
+ static int rate_limit;
+ u32 warnpending = 0, pending = local_softirq_pending();
+
+ if (rate_limit >= 10)
+ return;
+
+ if (pending) {
+ struct task_struct *tsk;
+
+ tsk = __get_cpu_var(ksoftirqd);
+ /*
+ * The wakeup code in rtmutex.c wakes up the task
+ * _before_ it sets pi_blocked_on to NULL under
+ * tsk->pi_lock. So we need to check for both: state
+ * and pi_blocked_on.
+ */
+ raw_spin_lock(&tsk->pi_lock);
+
+ if (!tsk->pi_blocked_on && !(tsk->state == TASK_RUNNING))
+ warnpending = 1;
+
+ raw_spin_unlock(&tsk->pi_lock);
+ }
+
+ if (warnpending) {
+ printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
+ pending);
+ rate_limit++;
+ }
+}
+# else
+/*
+ * On !PREEMPT_RT we just printk rate limited:
+ */
+void softirq_check_pending_idle(void)
+{
+ static int rate_limit;
+
+ if (rate_limit < 10) {
+ printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
+ local_softirq_pending());
+ rate_limit++;
+ }
+}
+# endif
+#endif
+
/*
* we cannot loop indefinitely here to avoid userspace starvation,
* but we also don't want to introduce a worst case 1/HZ latency
Index: linux-stable/kernel/time/tick-sched.c
===================================================================
--- linux-stable.orig/kernel/time/tick-sched.c
+++ linux-stable/kernel/time/tick-sched.c
@@ -438,13 +438,7 @@ static bool can_stop_idle_tick(int cpu,
return false;
if (unlikely(local_softirq_pending() && cpu_online(cpu))) {
- static int ratelimit;
-
- if (ratelimit < 10) {
- printk(KERN_ERR "NOHZ: local_softirq_pending %02x\n",
- (unsigned int) local_softirq_pending());
- ratelimit++;
- }
+ softirq_check_pending_idle();
return false;
}
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