virtio-blk: don't keep queue frozen during system suspend

Commit 4ce6e2d ("virtio-blk: Ensure no requests in virtqueues before
deleting vqs.") replaces queue quiesce with queue freeze in virtio-blk's
PM callbacks. And the motivation is to drain inflight IOs before suspending.

block layer's queue freeze looks very handy, but it is also easy to cause
deadlock, such as, any attempt to call into bio_queue_enter() may run into
deadlock if the queue is frozen in current context. There are all kinds
of ->suspend() called in suspend context, so keeping queue frozen in the
whole suspend context isn't one good idea. And Marek reported lockdep
warning[1] caused by virtio-blk's freeze queue in virtblk_freeze().

[1] https://lore.kernel.org/linux-block/[email protected]/

Given the motivation is to drain in-flight IOs, it can be done by calling
freeze & unfreeze, meantime restore to previous behavior by keeping queue
quiesced during suspend.

Cc: Yi Sun <[email protected]>
Cc: Michael S. Tsirkin <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Stefan Hajnoczi <[email protected]>
Cc: [email protected]
Reported-by: Marek Szyprowski <[email protected]>
Signed-off-by: Ming Lei <[email protected]>
Acked-by: Stefan Hajnoczi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>

Author: Ming Lei

drivers/block/virtio_blk.c

@@ -1586,9 +1586,12 @@ static void virtblk_remove(struct virtio_device *vdev)
 static int virtblk_freeze(struct virtio_device *vdev)
 {
 	struct virtio_blk *vblk = vdev->priv;
+	struct request_queue *q = vblk->disk->queue;
 
 	/* Ensure no requests in virtqueues before deleting vqs. */
-	blk_mq_freeze_queue(vblk->disk->queue);
+	blk_mq_freeze_queue(q);
+	blk_mq_quiesce_queue_nowait(q);
+	blk_mq_unfreeze_queue(q);
 
 	/* Ensure we don't receive any more interrupts */
 	virtio_reset_device(vdev);
@@ -1612,8 +1615,8 @@ static int virtblk_restore(struct virtio_device *vdev)
 		return ret;
 
 	virtio_device_ready(vdev);
+	blk_mq_unquiesce_queue(vblk->disk->queue);
 
-	blk_mq_unfreeze_queue(vblk->disk->queue);
 	return 0;
 }
 #endif