Re: BUG: spinlock trylock failure on UP, i.MX28 3.12.15-rt25

Sebastian Andrzej Siewior
2014-05-02T19:37:16Z

* Thomas Gleixner | 2014-05-02 21:01:50 [+0200]:

>It's different as it CANNOT fail on UP. That's called from the idle
>code and there is no way that anything holds that lock on UP when idle
>runs.

Okay, so I will add the patch here. The same thing (mostly) but it will
also skip the irq_work_needs_cpu() check since we will run the timer
softirq anyway.

From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Date: Fri, 2 May 2014 21:31:50 +0200
Subject: [PATCH] timer: do not spin_trylock() on UP

This will void a warning comming from the spin-lock debugging code. The
lock avoiding idea is from Steven Rostedt.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
---
kernel/timer.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/kernel/timer.c b/kernel/timer.c
index 54596b5..8750875 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1455,18 +1455,31 @@ void run_local_timers(void)
struct tvec_base *base = __this_cpu_read(tvec_bases);

hrtimer_run_queues();
/*
* We can access this lockless as we are in the timer
* interrupt. If there are no timers queued, nothing to do in
* the timer softirq.
*/
#ifdef CONFIG_PREEMPT_RT_FULL
+
+#ifndef CONFIG_SMP
+ /*
+ * The spin_do_trylock() later may fail as the lock may be hold before
+ * the interrupt arrived. The spin-lock debugging code will raise a
+ * warning if the try_lock fails on UP. Since this is only an
+ * optimization for the FULL_NO_HZ case (not to run the timer softirq on
+ * an nohz_full CPU) we don't really care and shedule the softirq.
+ */
+ raise_softirq(TIMER_SOFTIRQ);
+ return;
+#endif
+
/* On RT, irq work runs from softirq */
if (irq_work_needs_cpu()) {
raise_softirq(TIMER_SOFTIRQ);
return;
}

if (!spin_do_trylock(&base->lock)) {
raise_softirq(TIMER_SOFTIRQ);
return;
--
2.0.0.rc0

>Thanks,
>
> tglx

Sebastian