On Mon, Jun 08, 2020 at 05:58:33PM +0200, Peter Zijlstra wrote: > > A request can only be completed once. > > Sure, but that doesn't help. > > CPU0 CPU1 > > raise_blk_irq() BLOCK_SOFTIRQ > IPI -> CPU1 > > // picks up thing from CPU0 > req->complete(req); > > > <big hole where CSD is active and request completed> > > <IPI> > trigger_softirq() > > > What happens to a struct request after completion, is it free()d > or reused? If reused, how do we guarantee CSD completion before > free()ing? The request is freed in the block layer sense by __blk_mq_free_request (which doesn't actually free the memory, so it eventually gets reused). __blk_mq_free_request is called from blk_mq_end_request which is called from the drivers ->complete_rq method, which is called from the block softirq. What is the method to guaranteed CSD completion?
