On Tue, Nov 17, 2020 at 03:37:24PM +0000, Valentin Schneider wrote: > >> + /* > >> + * This field must not be in the scheduler word above due to wakelist > >> + * queueing no longer being serialized by p->on_cpu. However: > >> + * > >> + * p->XXX = X; ttwu() > >> + * schedule() if (p->on_rq && ..) // false > >> + * smp_mb__after_spinlock(); if (smp_load_acquire(&p->on_cpu) && > >> //true > >> + * deactivate_task() ttwu_queue_wakelist()) > >> + * p->on_rq = 0; p->sched_remote_wakeup = Y; > >> + * > >> + * guarantees all stores of 'current' are visible before > >> + * ->sched_remote_wakeup gets used, so it can be in this word. > >> + */ > > > > Isn't the control dep between that ttwu() p->on_rq read and > > p->sched_remote_wakeup write "sufficient"? > > smp_acquire__after_ctrl_dep() that is, since we need > ->on_rq load => 'current' bits load + store
I don't think we need that extra barrier; after all, there will be a complete schedule() between waking the task and it actually becoming current.
