On Wed, Mar 27, 2019 at 10:45:33AM +0800, jianchao.wang wrote: > 1. a hctx->fq.flush_rq of dead request_queue that shares the same tagset > The whole request_queue is cleaned up and freed, so the hctx->fq.flush is freed back to a slab > > 2. a removed io scheduler's sched request > The io scheduled is detached and all of the structures are freed, including the pages where sched > requests locates. > > So the pointers in tags->rqs[] may point to memory that is not used as a blk layer request. Oh, free as in kfree'd, not blk_mq_free_request. So it's a read-after- free that you're concerned about, not that anyone explicitly changed a request->state. We at least can't free the flush_queue until the queue is frozen. If the queue is frozen, we've completed the special fq->flush_rq where its end_io replaces tags->rqs[tag] back to the fq->orig_rq from the static_rqs, so nvme's iterator couldn't see the fq->flush_rq address if it's invalid. The sched_tags concern, though, appears theoretically possible.
