On Mon, 2018-07-09 at 15:08 -0700, Paul E. McKenney wrote: > index f9c0ca2ccf0c..3350ece366ab 100644 > --- a/kernel/rcu/tree.c > +++ b/kernel/rcu/tree.c > @@ -2839,6 +2839,15 @@ void rcu_check_callbacks(int user) >                 rcu_bh_qs(); >         } >         rcu_preempt_check_callbacks(); > +       /* The load-acquire pairs with the store-release setting to true. */ > +       if (smp_load_acquire(this_cpu_ptr(&rcu_dynticks.rcu_urgent_qs))) { > +               /* Idle and userspace execution already are quiescent states. */ > +               if (rcu_is_cpu_rrupt_from_idle() && !user) { if (idle && !user) seems tautological and... illogical. If I make it 'if (!rcu_is_cpu_rrput_from_idle() && !user)' it seems to work better. Ripping out my debugging printks now to check that's still true... (Also, isn't userspace execution only a quiescent state if NO_HZ_FULL?) > +                       set_tsk_need_resched(current); > +                       set_preempt_need_resched(); > +               } > +               __this_cpu_write(rcu_dynticks.rcu_urgent_qs, false); > +       }