Hello! One of the callback-invocation forward-progress issues turns out to be nohz_full CPUs not turning their scheduling-clock interrupt back on when running in kernel mode. Given that callback floods can cause RCU's callback-invocation loop to run for some time, it would be good for this loop to re-enable this interrupt. Of course, this problem applies to pretty much any kernel code that might loop for an extended time period, not just RCU. I took a quick look at kernel/time/tick-sched.c and the closest thing I found was tick_nohz_full_kick_cpu(), except that (1) it isn't clear that this does much when invoked on the current CPU and (2) it doesn't help in rcutorture TREE04. In contrast, disabling NO_HZ_FULL and using RCU_NOCB_CPU instead works quite well. So what should I be calling instead of tick_nohz_full_kick_cpu() to re-enable the current CPU's scheduling-clock interrupt? Thanx, Paul
