On Thu, 5 Oct 2017 22:19:15 +0000 (UTC) Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx> 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. Not only is preemption disabled (which is true for all spinlocks, at least with non PREEMPT_RT), but the rq->lock must also only be taken with interrupts disabled (for PREEMPT_RT as well). Because it can also be taken in interrupt context. -- Steve
