[PATCH V2] virtio-blk: Ensure no requests in virtqueues before deleting vqs.

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Ensure no remaining requests in virtqueues before resetting vdev and
deleting virtqueues. Otherwise these requests will never be completed.
It may cause the system to become unresponsive.

Function blk_mq_quiesce_queue() can ensure that requests have become
in_flight status, but it cannot guarantee that requests have been
processed by the device. Virtqueues should never be deleted before
all requests become complete status.

Function blk_mq_freeze_queue() ensure that all requests in virtqueues
become complete status. And no requests can enter in virtqueues.

Signed-off-by: Yi Sun <yi.sun@xxxxxxxxxx>
 drivers/block/virtio_blk.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 3b6b9abb8ce1..14ecc14ce8db 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -1595,14 +1595,15 @@ static int virtblk_freeze(struct virtio_device *vdev)
 	struct virtio_blk *vblk = vdev->priv;
+	/* Ensure no requests in virtqueues before deleting vqs. */
+	blk_mq_freeze_queue(vblk->disk->queue);
 	/* Ensure we don't receive any more interrupts */
 	/* Make sure no work handler is accessing the device. */
-	blk_mq_quiesce_queue(vblk->disk->queue);
@@ -1620,7 +1621,7 @@ static int virtblk_restore(struct virtio_device *vdev)
-	blk_mq_unquiesce_queue(vblk->disk->queue);
+	blk_mq_unfreeze_queue(vblk->disk->queue);
 	return 0;

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