Hi Prasad, On Tue, Oct 09, 2018 at 01:56:14PM -0700, Sodagudi Prasad wrote: > This is regarding - thread "try to fix contention between expire_timers and > try_to_del_timer_sync". > https://lkml.org/lkml/2017/7/28/172 > > I think this live lockup issue was discussed earlier but the final set of > changes were not concluded.
Well we basically need a way to pick a value for CPU_RELAX_WFE_THRESHOLD. Do you have any ideas? It could be determined at runtime if necessary. > 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); > } > cpu_relax(); > + udelay(1); > } > } > > @@ -1067,6 +1069,7 @@ int hrtimer_cancel(struct hrtimer *timer) > if (ret >= 0) > return ret; > cpu_relax(); > + udelay(1); > } > } > EXPORT_SYMBOL_GPL(hrtimer_cancel); This is just another bodge and likely to hurt in places where 1us is excessive because there isn't contention. Will
