On Thu, May 27, 2021 at 04:31:51PM +0200, Peter Zijlstra wrote: > On Thu, May 27, 2021 at 04:10:16PM +0200, Peter Zijlstra wrote: > > On Tue, May 25, 2021 at 04:14:26PM +0100, Will Deacon wrote: > > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > > > index 42e2aecf087c..6cb9677d635a 100644 > > > --- a/kernel/sched/core.c > > > +++ b/kernel/sched/core.c > > > @@ -3529,6 +3529,19 @@ try_to_wake_up(struct task_struct *p, unsigned int state, int wake_flags) > > > if (!(p->state & state)) > > > goto unlock; > > > > > > +#ifdef CONFIG_FREEZER > > > + /* > > > + * If we're going to wake up a thread which may be frozen, then > > > + * we can only do so if we have an active CPU which is capable of > > > + * running it. This may not be the case when resuming from suspend, > > > + * as the secondary CPUs may not yet be back online. See __thaw_task() > > > + * for the actual wakeup. > > > + */ > > > + if (unlikely(frozen_or_skipped(p)) && > > > + !cpumask_intersects(cpu_active_mask, task_cpu_possible_mask(p))) > > > + goto unlock; > > > +#endif > > > + > > > trace_sched_waking(p); > > > > > > /* We're going to change ->state: */ > > > > OK, I really hate this. This is slowing down the very hot wakeup path > > for the silly freezer that *never* happens. Let me try and figure out if > > there's another option. > > > How's something *completely* untested like this? I'm not seeing how this handles tasks which weren't put in the freezer because they have PF_FREEZER_SKIP set. For these tasks, we need to make sure that they don't become runnable before we have onlined a core which is capable of running them, and this could occur because of any old wakeup (i.e. whatever it was that they blocked on). Will
