[5.6,021/194] virtio-blk: handle block_device_operations callbacks after hot unplug

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0736248999b0d..d52f33881ab6e 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -32,6 +32,15 @@  struct virtio_blk_vq {
 } ____cacheline_aligned_in_smp;
 
 struct virtio_blk {
+	/*
+	 * This mutex must be held by anything that may run after
+	 * virtblk_remove() sets vblk->vdev to NULL.
+	 *
+	 * blk-mq, virtqueue processing, and sysfs attribute code paths are
+	 * shut down before vblk->vdev is set to NULL and therefore do not need
+	 * to hold this mutex.
+	 */
+	struct mutex vdev_mutex;
 	struct virtio_device *vdev;
 
 	/* The disk structure for the kernel. */
@@ -43,6 +52,13 @@  struct virtio_blk {
 	/* Process context for config space updates */
 	struct work_struct config_work;
 
+	/*
+	 * Tracks references from block_device_operations open/release and
+	 * virtio_driver probe/remove so this object can be freed once no
+	 * longer in use.
+	 */
+	refcount_t refs;
+
 	/* What host tells us, plus 2 for header & tailer. */
 	unsigned int sg_elems;
 
@@ -294,10 +310,55 @@  static int virtblk_get_id(struct gendisk *disk, char *id_str)
 	return err;
 }
 
+static void virtblk_get(struct virtio_blk *vblk)
+{
+	refcount_inc(&vblk->refs);
+}
+
+static void virtblk_put(struct virtio_blk *vblk)
+{
+	if (refcount_dec_and_test(&vblk->refs)) {
+		ida_simple_remove(&vd_index_ida, vblk->index);
+		mutex_destroy(&vblk->vdev_mutex);
+		kfree(vblk);
+	}
+}
+
+static int virtblk_open(struct block_device *bd, fmode_t mode)
+{
+	struct virtio_blk *vblk = bd->bd_disk->private_data;
+	int ret = 0;
+
+	mutex_lock(&vblk->vdev_mutex);
+
+	if (vblk->vdev)
+		virtblk_get(vblk);
+	else
+		ret = -ENXIO;
+
+	mutex_unlock(&vblk->vdev_mutex);
+	return ret;
+}
+
+static void virtblk_release(struct gendisk *disk, fmode_t mode)
+{
+	struct virtio_blk *vblk = disk->private_data;
+
+	virtblk_put(vblk);
+}
+
 /* We provide getgeo only to please some old bootloader/partitioning tools */
 static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
 {
 	struct virtio_blk *vblk = bd->bd_disk->private_data;
+	int ret = 0;
+
+	mutex_lock(&vblk->vdev_mutex);
+
+	if (!vblk->vdev) {
+		ret = -ENXIO;
+		goto out;
+	}
 
 	/* see if the host passed in geometry config */
 	if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) {
@@ -313,11 +374,15 @@  static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
 		geo->sectors = 1 << 5;
 		geo->cylinders = get_capacity(bd->bd_disk) >> 11;
 	}
-	return 0;
+out:
+	mutex_unlock(&vblk->vdev_mutex);
+	return ret;
 }
 
 static const struct block_device_operations virtblk_fops = {
 	.owner  = THIS_MODULE,
+	.open = virtblk_open,
+	.release = virtblk_release,
 	.getgeo = virtblk_getgeo,
 };
 
@@ -657,6 +722,10 @@  static int virtblk_probe(struct virtio_device *vdev)
 		goto out_free_index;
 	}
 
+	/* This reference is dropped in virtblk_remove(). */
+	refcount_set(&vblk->refs, 1);
+	mutex_init(&vblk->vdev_mutex);
+
 	vblk->vdev = vdev;
 	vblk->sg_elems = sg_elems;
 
@@ -822,8 +891,6 @@  static int virtblk_probe(struct virtio_device *vdev)
 static void virtblk_remove(struct virtio_device *vdev)
 {
 	struct virtio_blk *vblk = vdev->priv;
-	int index = vblk->index;
-	int refc;
 
 	/* Make sure no work handler is accessing the device. */
 	flush_work(&vblk->config_work);
@@ -833,18 +900,21 @@  static void virtblk_remove(struct virtio_device *vdev)
 
 	blk_mq_free_tag_set(&vblk->tag_set);
 
+	mutex_lock(&vblk->vdev_mutex);
+
 	/* Stop all the virtqueues. */
 	vdev->config->reset(vdev);
 
-	refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref);
+	/* Virtqueues are stopped, nothing can use vblk->vdev anymore. */
+	vblk->vdev = NULL;
+
 	put_disk(vblk->disk);
 	vdev->config->del_vqs(vdev);
 	kfree(vblk->vqs);
-	kfree(vblk);
 
-	/* Only free device id if we don't have any users */
-	if (refc == 1)
-		ida_simple_remove(&vd_index_ida, index);
+	mutex_unlock(&vblk->vdev_mutex);
+
+	virtblk_put(vblk);
 }
 
 #ifdef CONFIG_PM_SLEEP