> 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.
