[PATCH 1/2] blk-mq: introduce blk_mq_tagset_wait_request_completed()

[Yi Sun]

In some cases, it is necessary to wait for all requests to become complete
status before performing other operations. Otherwise, these requests will never
be processed successfully.

For example, when the virtio device is in hibernation, the virtqueues
will be deleted. It must be ensured that virtqueue is not in use before being deleted.
Otherwise the requests in the virtqueue will be lost. This function can ensure
that all requests have been taken out of the virtqueues.

Prepare for fixing this kind of issue by introducing
blk_mq_tagset_wait_request_completed().

Signed-off-by: Yi Sun <yi.sun@xxxxxxxxxx>
---
 block/blk-mq-tag.c     | 29 +++++++++++++++++++++++++++++
 include/linux/blk-mq.h |  1 +
 2 files changed, 30 insertions(+)

diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index cc57e2dd9a0b..cb0ef5f66c61 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -479,6 +479,35 @@ void blk_mq_tagset_wait_completed_request(struct blk_mq_tag_set *tagset)
 }
 EXPORT_SYMBOL(blk_mq_tagset_wait_completed_request);
 
+static bool blk_mq_tagset_count_inflight_rqs(struct request *rq, void *data)
+{
+	unsigned int *count = data;
+
+	if (blk_mq_request_started(rq) && !blk_mq_request_completed(rq))
+		(*count)++;
+	return true;
+}
+
+/**
+ * blk_mq_tagset_wait_request_completed - Wait for all inflight requests
+ * to become completed.
+ *
+ * Note: This function has to be run after all IO queues are shutdown.
+ */
+void blk_mq_tagset_wait_request_completed(struct blk_mq_tag_set *tagset)
+{
+	while (true) {
+		unsigned int count = 0;
+
+		blk_mq_tagset_busy_iter(tagset,
+				blk_mq_tagset_count_inflight_rqs, &count);
+		if (!count)
+			break;
+		msleep(20);
+	}
+}
+EXPORT_SYMBOL(blk_mq_tagset_wait_request_completed);
+
 /**
  * blk_mq_queue_tag_busy_iter - iterate over all requests with a driver tag
  * @q:		Request queue to examine.
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index a676e116085f..17768e154193 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -891,6 +891,7 @@ void blk_mq_run_hw_queues(struct request_queue *q, bool async);
 void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs);
 void blk_mq_tagset_busy_iter(struct blk_mq_tag_set *tagset,
 		busy_tag_iter_fn *fn, void *priv);
+void blk_mq_tagset_wait_request_completed(struct blk_mq_tag_set *tagset);
 void blk_mq_tagset_wait_completed_request(struct blk_mq_tag_set *tagset);
 void blk_mq_freeze_queue(struct request_queue *q);
 void blk_mq_unfreeze_queue(struct request_queue *q);
-- 
2.25.1