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

Steven Rostedt
2014-04-22T18:16:55Z

On Tue, 22 Apr 2014 13:48:02 -0400
Steven Rostedt <rostedt@goodmis.org> wrote:

> I need to take a deeper look into the actual code. But as trylocks on
> UP are nops (always succeed), and if it expects to be able to do
> something in a critical section that is protected by spinlocks (again
> nops on UP), this would be broken for UP.

Reading the code, I see it's broken. We should add something like this:

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
diff --git a/kernel/timer.c b/kernel/timer.c
index cc34e42..a03164a 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1447,6 +1447,12 @@ static void run_timer_softirq(struct softirq_action *h)
__run_timers(base);
}

+#ifdef CONFIG_SMP
+#define timer_should_raise_softirq(lock) !spin_do_trylock(lock)
+#else
+#define timer_should_raise_softirq(lock) 1
+#endif
+
/*
* Called by the local, per-CPU timer interrupt on SMP.
*/
@@ -1467,7 +1473,7 @@ void run_local_timers(void)
return;
}

- if (!spin_do_trylock(&base->lock)) {
+ if (timer_should_raise_softirq(&base->lock)) {
raise_softirq(TIMER_SOFTIRQ);
return;
}