On Tue, 22 Apr 2014 13:48:02 -0400
Steven Rostedt [off-list ref] wrote:

quoted

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;
	}