blk-mq: don't handle failure in .get_budget

It is enough to just check if we can get the budget via .get_budget().
And we don't need to deal with device state change in .get_budget().

For SCSI, one issue to be fixed is that we have to call
scsi_mq_uninit_cmd() to free allocated ressources if SCSI device fails
to handle the request. And it isn't enough to simply call
blk_mq_end_request() to do that if this request is marked as
RQF_DONTPREP.

Fixes: 0df21c86bdbf(scsi: implement .get_budget and .put_budget for blk-mq)
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/blk-mq-sched.c

@@ -94,23 +94,18 @@ static void blk_mq_do_dispatch_sched(struct blk_mq_hw_ctx *hctx)
 
 	do {
 		struct request *rq;
-		blk_status_t ret;
 
 		if (e->type->ops.mq.has_work &&
 				!e->type->ops.mq.has_work(hctx))
 			break;
 
-		ret = blk_mq_get_dispatch_budget(hctx);
-		if (ret == BLK_STS_RESOURCE)
+		if (!blk_mq_get_dispatch_budget(hctx))
 			break;
 
 		rq = e->type->ops.mq.dispatch_request(hctx);
 		if (!rq) {
 			blk_mq_put_dispatch_budget(hctx);
 			break;
-		} else if (ret != BLK_STS_OK) {
-			blk_mq_end_request(rq, ret);
-			continue;
 		}
 
 		/*
@@ -146,22 +141,17 @@ static void blk_mq_do_dispatch_ctx(struct blk_mq_hw_ctx *hctx)
 
 	do {
 		struct request *rq;
-		blk_status_t ret;
 
 		if (!sbitmap_any_bit_set(&hctx->ctx_map))
 			break;
 
-		ret = blk_mq_get_dispatch_budget(hctx);
-		if (ret == BLK_STS_RESOURCE)
+		if (!blk_mq_get_dispatch_budget(hctx))
 			break;
 
 		rq = blk_mq_dequeue_from_ctx(hctx, ctx);
 		if (!rq) {
 			blk_mq_put_dispatch_budget(hctx);
 			break;
-		} else if (ret != BLK_STS_OK) {
-			blk_mq_end_request(rq, ret);
-			continue;
 		}
 
 		/*

block/blk-mq.c

@@ -1137,13 +1137,8 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 			}
 		}
 
-		if (!got_budget) {
-			ret = blk_mq_get_dispatch_budget(hctx);
-			if (ret == BLK_STS_RESOURCE)
-				break;
-			if (ret != BLK_STS_OK)
-				goto fail_rq;
-		}
+		if (!got_budget && !blk_mq_get_dispatch_budget(hctx))
+			break;
 
 		list_del_init(&rq->queuelist);
 
@@ -1170,7 +1165,6 @@ bool blk_mq_dispatch_rq_list(struct request_queue *q, struct list_head *list,
 			break;
 		}
 
- fail_rq:
 		if (unlikely(ret != BLK_STS_OK)) {
 			errors++;
 			blk_mq_end_request(rq, BLK_STS_IOERR);
@@ -1642,12 +1636,10 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 	if (!blk_mq_get_driver_tag(rq, NULL, false))
 		goto insert;
 
-	ret = blk_mq_get_dispatch_budget(hctx);
-	if (ret == BLK_STS_RESOURCE) {
+	if (!blk_mq_get_dispatch_budget(hctx)) {
 		blk_mq_put_driver_tag(rq);
 		goto insert;
-	} else if (ret != BLK_STS_OK)
-		goto fail_rq;
+	}
 
 	new_cookie = request_to_qc_t(hctx, rq);
 
@@ -1665,7 +1657,6 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
 		__blk_mq_requeue_request(rq);
 		goto insert;
 	default:
- fail_rq:
 		*cookie = BLK_QC_T_NONE;
 		blk_mq_end_request(rq, ret);
 		return;

block/blk-mq.h

@@ -147,14 +147,13 @@ static inline void blk_mq_put_dispatch_budget(struct blk_mq_hw_ctx *hctx)
 		q->mq_ops->put_budget(hctx);
 }
 
-static inline blk_status_t blk_mq_get_dispatch_budget(
-		struct blk_mq_hw_ctx *hctx)
+static inline bool blk_mq_get_dispatch_budget(struct blk_mq_hw_ctx *hctx)
 {
 	struct request_queue *q = hctx->queue;
 
 	if (q->mq_ops->get_budget)
 		return q->mq_ops->get_budget(hctx);
-	return BLK_STS_OK;
+	return true;
 }
 
 #endif

drivers/scsi/scsi_lib.c

@@ -1955,27 +1955,22 @@ static void scsi_mq_put_budget(struct blk_mq_hw_ctx *hctx)
 	put_device(&sdev->sdev_gendev);
 }
 
-static blk_status_t scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
+static bool scsi_mq_get_budget(struct blk_mq_hw_ctx *hctx)
 {
 	struct request_queue *q = hctx->queue;
 	struct scsi_device *sdev = q->queuedata;
-	blk_status_t ret;
-
-	ret = prep_to_mq(scsi_prep_state_check(sdev, NULL));
-	if (ret == BLK_STS_RESOURCE || ret != BLK_STS_OK)
-		return ret;
 
 	if (!get_device(&sdev->sdev_gendev))
 		goto out;
 	if (!scsi_dev_queue_ready(q, sdev))
 		goto out_put_device;
 
-	return BLK_STS_OK;
+	return true;
 
 out_put_device:
 	put_device(&sdev->sdev_gendev);
 out:
-	return BLK_STS_RESOURCE;
+	return false;
 }
 
 static blk_status_t scsi_queue_rq(struct blk_mq_hw_ctx *hctx,

include/linux/blk-mq.h

@@ -92,7 +92,7 @@ struct blk_mq_queue_data {
 
 typedef blk_status_t (queue_rq_fn)(struct blk_mq_hw_ctx *,
 		const struct blk_mq_queue_data *);
-typedef blk_status_t (get_budget_fn)(struct blk_mq_hw_ctx *);
+typedef bool (get_budget_fn)(struct blk_mq_hw_ctx *);
 typedef void (put_budget_fn)(struct blk_mq_hw_ctx *);
 typedef enum blk_eh_timer_return (timeout_fn)(struct request *, bool);
 typedef int (init_hctx_fn)(struct blk_mq_hw_ctx *, void *, unsigned int);