On Mon, Jun 08, 2020 at 09:33:42AM -0700, Christoph Hellwig wrote: > 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?
There isn't one, it was meant to be used with static allocations. Frederic proposed changing all these to irq_work, and I think I'll go do that. First dinner though.
