On Fri, Oct 06, 2017 at 10:32:19AM +0200, Peter Zijlstra wrote: > > AFAIU the scheduler rq->lock is held while preemption is disabled. > > synchronize_sched() is used here to ensure that all pre-existing > > preempt-off critical sections have completed. > > > > So saying that we use synchronize_sched() to synchronize with rq->lock > > would be stretching the truth a bit. It's actually only true because the > > scheduler holding the rq->lock is surrounded by a preempt-off > > critical section. > > No, rq->lock is sufficient, note that rq->lock is a raw_spinlock_t which > implies !preempt. Yes, we also surround the rq->lock usage with a > slightly larger preempt_disable() section but that's not in fact > required for this.
That's what it is, according to the current sources: we seemed to agree that a preempt-off critical section is what we rely on here and that the start of this critical section is not marked by that raw_spin_lock. Andrea
