Re: [PATCH RFC tip/core/rcu 14/14] rcu/nohz: Make multi_cpu_stop() enable tick on all online CPUs

[Peter Zijlstra]

On Fri, Aug 02, 2019 at 08:15:01AM -0700, Paul E. McKenney wrote:
> The multi_cpu_stop() function relies on the scheduler to gain control from
> whatever is running on the various online CPUs, including any nohz_full
> CPUs running long loops in kernel-mode code.  Lack of the scheduler-clock
> interrupt on such CPUs can delay multi_cpu_stop() for several minutes
> and can also result in RCU CPU stall warnings.  This commit therefore
> causes multi_cpu_stop() to enable the scheduler-clock interrupt on all
> online CPUs.

This sounds wrong; should we be fixing sched_can_stop_tick() instead to
return false when the stop task is runnable?