On Wed, Jan 17 2018 at 11:06pm -0500,
Ming Lei <ming....@redhat.com> wrote:
> If we run into blk_mq_request_direct_issue(), when queue is busy, we
> don't want to dispatch this request into hctx->dispatch_list, and
> what we need to do is to return the queue busy info to caller, so
> that caller can deal with it well.
>
> Fixes: 396eaf21ee ("blk-mq: improve DM's blk-mq IO merging via
> blk_insert_cloned_request feedback")
> Reported-by: Laurence Oberman <lober...@redhat.com>
> Reviewed-by: Mike Snitzer <snit...@redhat.com>
> Signed-off-by: Ming Lei <ming....@redhat.com>
> ---
> block/blk-mq.c | 22 ++++++++++------------
> 1 file changed, 10 insertions(+), 12 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 4d4af8d712da..1af7fa70993b 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -1856,15 +1856,6 @@ static blk_status_t __blk_mq_issue_directly(struct
> blk_mq_hw_ctx *hctx,
> return ret;
> }
>
> -static void __blk_mq_fallback_to_insert(struct request *rq,
> - bool run_queue, bool bypass_insert)
> -{
> - if (!bypass_insert)
> - blk_mq_sched_insert_request(rq, false, run_queue, false);
> - else
> - blk_mq_request_bypass_insert(rq, run_queue);
> -}
> -
> static blk_status_t __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
> struct request *rq,
> blk_qc_t *cookie,
> @@ -1873,9 +1864,16 @@ static blk_status_t __blk_mq_try_issue_directly(struct
> blk_mq_hw_ctx *hctx,
> struct request_queue *q = rq->q;
> bool run_queue = true;
>
> - /* RCU or SRCU read lock is needed before checking quiesced flag */
> + /*
> + * RCU or SRCU read lock is needed before checking quiesced flag.
> + *
> + * When queue is stopped or quiesced, ignore 'bypass_insert' from
> + * blk_mq_request_direct_issue(), and return BLK_STS_OK to caller,
> + * and avoid driver to try to dispatch again.
> + */
> if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
> run_queue = false;
> + bypass_insert = false;
> goto insert;
> }
>
> @@ -1892,10 +1890,10 @@ static blk_status_t
> __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
>
> return __blk_mq_issue_directly(hctx, rq, cookie);
> insert:
> - __blk_mq_fallback_to_insert(rq, run_queue, bypass_insert);
> if (bypass_insert)
> return BLK_STS_RESOURCE;
>
> + blk_mq_sched_insert_request(rq, false, run_queue, false);
> return BLK_STS_OK;
> }
OK so you're just leveraging blk_mq_sched_insert_request()'s
ability to resort to__blk_mq_insert_request() if !q->elevator.
