On Wed, Aug 11, 2021 at 10:38:38PM +0800, Ming Lei wrote:
> Inside blk_mq_queue_tag_busy_iter() we already grabbed request's
> refcount before calling ->fn(), so needn't to grab it one more time
> in blk_mq_check_expired().
>
> Signed-off-by: Ming Lei <ming.lei@xxxxxxxxxx>
> ---
> block/blk-mq.c | 25 +++++++------------------
> 1 file changed, 7 insertions(+), 18 deletions(-)
>
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index d2725f94491d..4d3457d2957f 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -917,6 +917,10 @@ void blk_mq_put_rq_ref(struct request *rq)
> __blk_mq_free_request(rq);
> }
>
> +/*
> + * This request won't be re-allocated because its refcount is held when
> + * calling this callback.
> + */
> static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
> struct request *rq, void *priv, bool reserved)
> {
> @@ -930,27 +934,12 @@ static bool blk_mq_check_expired(struct blk_mq_hw_ctx *hctx,
> return true;
>
> /*
> - * We have reason to believe the request may be expired. Take a
> - * reference on the request to lock this request lifetime into its
> - * currently allocated context to prevent it from being reallocated in
> - * the event the completion by-passes this timeout handler.
> - *
> - * If the reference was already released, then the driver beat the
> - * timeout handler to posting a natural completion.
> - */
> - if (!refcount_inc_not_zero(&rq->ref))
> - return true;
> -
> - /*
> - * The request is now locked and cannot be reallocated underneath the
> - * timeout handler's processing. Re-verify this exact request is truly
> - * expired; if it is not expired, then the request was completed and
> - * reallocated as a new request.
> + * Re-verify this exact request is truly expired; if it is not expired,
> + * then the request was completed and reallocated as a new request
> + * after returning from blk_mq_check_expired().
> */
> if (blk_mq_req_expired(rq, next))
> blk_mq_rq_timed_out(rq, reserved);
There's no need to check expired twice if the iterator is already taking a
reference. I had this double check because I didn't want to penalize normal IO
by preventing it from completing while the timeout handler is running, but it
looks like the current timeout iterator is going to do that anyway.
> -
> - blk_mq_put_rq_ref(rq);
> return true;
> }
