mmc: block: Fix unsupported parallel dispatch of requests

The mmc block driver does not support parallel dispatch of requests. In
normal circumstances, all requests are anyway funneled through a single
work item, so parallel dispatch never happens. However it can happen if
there is no elevator.

Fix that by detecting if a dispatch is in progress and returning busy
(BLK_STS_RESOURCE) in that case

Fixes: 81196976ed94 ("mmc: block: Add blk-mq support")
Cc: stable@vger.kernel.org # v4.16+
Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/core/queue.c

@@ -238,10 +238,6 @@ static void mmc_mq_exit_request(struct blk_mq_tag_set *set, struct request *req,
 	mmc_exit_request(mq->queue, req);
 }
 
-/*
- * We use BLK_MQ_F_BLOCKING and have only 1 hardware queue, which means requests
- * will not be dispatched in parallel.
- */
 static blk_status_t mmc_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 				    const struct blk_mq_queue_data *bd)
 {
@@ -264,7 +260,7 @@ static blk_status_t mmc_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 
 	spin_lock_irq(q->queue_lock);
 
-	if (mq->recovery_needed) {
+	if (mq->recovery_needed || mq->busy) {
 		spin_unlock_irq(q->queue_lock);
 		return BLK_STS_RESOURCE;
 	}
@@ -291,6 +287,9 @@ static blk_status_t mmc_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 		break;
 	}
 
+	/* Parallel dispatch of requests is not supported at the moment */
+	mq->busy = true;
+
 	mq->in_flight[issue_type] += 1;
 	get_card = (mmc_tot_in_flight(mq) == 1);
 	cqe_retune_ok = (mmc_cqe_qcnt(mq) == 1);
@@ -333,9 +332,12 @@ static blk_status_t mmc_mq_queue_rq(struct blk_mq_hw_ctx *hctx,
 		mq->in_flight[issue_type] -= 1;
 		if (mmc_tot_in_flight(mq) == 0)
 			put_card = true;
+		mq->busy = false;
 		spin_unlock_irq(q->queue_lock);
 		if (put_card)
 			mmc_put_card(card, &mq->ctx);
+	} else {
+		WRITE_ONCE(mq->busy, false);
 	}
 
 	return ret;

drivers/mmc/core/queue.h

@@ -81,6 +81,7 @@ struct mmc_queue {
 	unsigned int		cqe_busy;
 #define MMC_CQE_DCMD_BUSY	BIT(0)
 #define MMC_CQE_QUEUE_FULL	BIT(1)
+	bool			busy;
 	bool			use_cqe;
 	bool			recovery_needed;
 	bool			in_recovery;