On Fri, 2017-09-01 at 01:27 +0800, Ming Lei wrote: > @@ -1413,9 +1414,17 @@ static struct request *blk_old_get_request(struct request_queue *q, > /* create ioc upfront */ > create_io_context(gfp_mask, q->node); > > - ret = blk_queue_enter(q, !(gfp_mask & __GFP_DIRECT_RECLAIM)); > + /* > + * When queue is frozen, we still need to allocate req for > + * REQF_PREEMPT. > + */ > + if ((flags & BLK_MQ_REQ_PREEMPT) && blk_queue_is_frozen(q)) > + blk_queue_enter_live(q); > + else > + ret = blk_queue_enter(q, !(gfp_mask & __GFP_DIRECT_RECLAIM)); Hello Ming, Sorry but I doubt that calling blk_queue_enter_live() from inside blk_old_get_request() is safe. Calling blk_queue_enter_live() is only safe before a request queue has been marked dead. What prevents a kernel thread that holds a reference on a request queue and that is running concurrently with blk_cleanup_queue() to call blk_old_get_request() after a queue has been marked dead? Thanks, Bart.
