NVMe: Return correct value from interrupt handler

The interrupt handler currently reports whether it found any new
completion queue entries.  If the completion queue is primarily being
processed by a method other than the interrupt handler, it may return
IRQ_NONE so often that Linux thinks that the interrupt is being falsely
triggered.

To solve this problem, report whether any completion queue entries have
been seen since the last interrupt was received for this queue.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>

drivers/block/nvme-core.c

@@ -79,7 +79,8 @@ struct nvme_queue {
 	u16 sq_head;
 	u16 sq_tail;
 	u16 cq_head;
-	u16 cq_phase;
+	u8 cq_phase;
+	u8 cqe_seen;
 	unsigned long cmdid_data[];
 };
 
@@ -756,7 +757,7 @@ static void nvme_make_request(struct request_queue *q, struct bio *bio)
 	put_nvmeq(nvmeq);
 }
 
-static irqreturn_t nvme_process_cq(struct nvme_queue *nvmeq)
+static int nvme_process_cq(struct nvme_queue *nvmeq)
 {
 	u16 head, phase;
 
@@ -786,13 +787,14 @@ static irqreturn_t nvme_process_cq(struct nvme_queue *nvmeq)
 	 * a big problem.
 	 */
 	if (head == nvmeq->cq_head && phase == nvmeq->cq_phase)
-		return IRQ_NONE;
+		return 0;
 
 	writel(head, nvmeq->q_db + (1 << nvmeq->dev->db_stride));
 	nvmeq->cq_head = head;
 	nvmeq->cq_phase = phase;
 
-	return IRQ_HANDLED;
+	nvmeq->cqe_seen = 1;
+	return 1;
 }
 
 static irqreturn_t nvme_irq(int irq, void *data)
@@ -800,7 +802,9 @@ static irqreturn_t nvme_irq(int irq, void *data)
 	irqreturn_t result;
 	struct nvme_queue *nvmeq = data;
 	spin_lock(&nvmeq->q_lock);
-	result = nvme_process_cq(nvmeq);
+	nvme_process_cq(nvmeq);
+	result = nvmeq->cqe_seen ? IRQ_HANDLED : IRQ_NONE;
+	nvmeq->cqe_seen = 0;
 	spin_unlock(&nvmeq->q_lock);
 	return result;
 }