[PATCHv2 3/3] nvme-pci: fix queue_rqs list splitting

[Keith Busch]

On Wed, Dec 29, 2021 at 06:46:02PM +0100, Christoph Hellwig wrote:
> I wonder if a restart label here would be a little cleaner, something
> like:

On second thought, this requires another check that the *rqlist is not
NULL before 'goto restart' since the safe iterator dereferences it. I'm
not sure this is cleaner than the original anymore.
 
> diff --git a/drivers/nvme/host/pci.c b/drivers/nvme/host/pci.c
> index 992ee314e91ba..29b433fd12bdd 100644
> --- a/drivers/nvme/host/pci.c
> +++ b/drivers/nvme/host/pci.c
> @@ -999,9 +999,11 @@ static bool nvme_prep_rq_batch(struct nvme_queue *nvmeq, struct request *req)
>  
>  static void nvme_queue_rqs(struct request **rqlist)
>  {
> -	struct request *req, *next, *prev = NULL;
> +	struct request *req, *next, *prev;
>  	struct request *requeue_list = NULL;
>  
> +restart:
> +	prev = NULL;
>  	rq_list_for_each_safe(rqlist, req, next) {
>  		struct nvme_queue *nvmeq = req->mq_hctx->driver_data;
>  
> @@ -1009,9 +1011,9 @@ static void nvme_queue_rqs(struct request **rqlist)
>  			/* detach 'req' and add to remainder list */
>  			rq_list_move(rqlist, &requeue_list, req, prev, next);
>  
> +			if (!prev)
> +				break;
>  			req = prev;
> -			if (!req)
> -				continue;
>  		}
>  
>  		if (!next || req->mq_hctx != next->mq_hctx) {
> @@ -1019,9 +1021,9 @@ static void nvme_queue_rqs(struct request **rqlist)
>  			req->rq_next = NULL;
>  			nvme_submit_cmds(nvmeq, rqlist);
>  			*rqlist = next;
> -			prev = NULL;
> -		} else
> -			prev = req;
> +			goto restart;
> +		}
> +		prev = req;
>  	}
>  
>  	*rqlist = requeue_list;