[PATCH RT 1/3] timer: do not spin_trylock() on UP

From: Steven Rostedt
Date: Wed Jul 02 2014 - 15:53:09 EST


3.10.44-rt46-rc1 stable review patch.
If anyone has any objections, please let me know.

------------------

From: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>

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

Cc: stable-rt@xxxxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Signed-off-by: Steven Rostedt <rostedt@xxxxxxxxxxx>
---
kernel/timer.c | 13 +++++++++++++
1 file changed, 13 insertions(+)

diff --git a/kernel/timer.c b/kernel/timer.c
index 26cca8b924e7..40cfa14131ca 100644
--- a/kernel/timer.c
+++ b/kernel/timer.c
@@ -1461,6 +1461,19 @@ void run_local_timers(void)
* 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);
--
2.0.0


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