livelock with hrtimer cpu_base->lock

From: Sodagudi Prasad
Date: Tue Oct 09 2018 - 16:56:17 EST

Hi Will,

This is regarding - thread "try to fix contention between expire_timers and try_to_del_timer_sync".

I think this live lockup issue was discussed earlier but the final set of changes were not concluded.
I would like to check whether you have new updates on this issue or not. This problem is observed with 4.14 .64 stable kernel too.
We see this problem 2 times in overnight testing.

I have to add the following code to avoid live lock. I am thinking that fixing this at the cpu_relax() level.

+++ b/kernel/time/hrtimer.c
@@ -52,6 +52,7 @@
#include <linux/timer.h>
#include <linux/freezer.h>
#include <linux/compat.h>
+#include <linux/delay.h>

#include <linux/uaccess.h>

@@ -152,6 +153,7 @@ struct hrtimer_clock_base *lock_hrtimer_base(const struct hrtimer *timer,
raw_spin_unlock_irqrestore(&base->cpu_base->lock, *flags);
+ udelay(1);

@@ -1067,6 +1069,7 @@ int hrtimer_cancel(struct hrtimer *timer)
if (ret >= 0)
return ret;
+ udelay(1);

Note:- Timer event streaming is enabled and still live lock observed.

-Thanks, Prasad

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