Userspace listens to the KOBJ_ADD uevent generated in add_disk. At that
point we haven't created the serial attribute file, therefore depending
on how fast udev reacts, the /dev/disk/by-id/ entry doesn't always get
created.

This race condition can be easily reproduced by hot plugging a number of
virtio-blk disks.

Also in systemd, there used to be a related workaround in udev rules
called 'WAIT_FOR="serial"', but it is removed in later versions.

Now let's generate a KOBJ_CHANGE event after the attributes are ready.

Signed-off-by: Fam Zheng <redacted>
---
 drivers/block/virtio_blk.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index f3a59f9..cd9a036 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c

@@ -733,7 +733,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 
 	virtio_device_ready(vdev);
 
-	add_disk(vblk->disk, true);
+	add_disk(vblk->disk, false);
 	err = device_create_file(disk_to_dev(vblk->disk), &dev_attr_serial);
 	if (err)
 		goto out_del_disk;

@@ -746,6 +746,7 @@ static int virtblk_probe(struct virtio_device *vdev)
 					 &dev_attr_cache_type_ro);
 	if (err)
 		goto out_del_disk;
+	disk_gen_uevents(vblk->disk);
 	return 0;
 
 out_del_disk:

-- 
2.9.0