On Sun, Aug 04, 2019 at 04:43:17PM +0200, Peter Zijlstra wrote: > 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? And even without that; I don't understand how we're not instantly preempted the moment we enqueue the stop task. Any enqueue, should go through check_preempt_curr() which will be an instant resched_curr() when we just woke the stop class.
