Re: Time to make dynamically allocated devt the default for scsi disks?

[James Bottomley <James.Bottomley@HansenPartnership.com>]

On Fri, 2016-08-12 at 14:29 -0700, Dan Williams wrote:
> Before spending effort trying to flush the destruction of old bdi
> instances before new ones are registered, is it rather time to
> complete the conversion of sd to only use dynamically allocated devt?

Do we have to go that far?  Surely your fix is extensible: the only
reason it doesn't work for us is that the gendisk holds the parent
without a reference, so we can free the SCSI device before its child
gendisk (good job no-one actually uses gendisk->parent after we've
released it ...).  If we fix that it would mean SCSI can't release the
sdev until after the queue is dead and the bdi namespace released, so
isn't something like this the easy fix?

James

---

diff --git a/block/genhd.c b/block/genhd.c
index fcd6d4f..54ae4ae 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -514,7 +514,7 @@ static void register_disk(struct device *parent, struct gendisk *disk)
 	struct hd_struct *part;
 	int err;
 
-	ddev->parent = parent;
+	ddev->parent = get_device(parent);
 
 	dev_set_name(ddev, "%s", disk->disk_name);
 
@@ -1144,6 +1144,7 @@ static void disk_release(struct device *dev)
 	hd_free_part(&disk->part0);
 	if (disk->queue)
 		blk_put_queue(disk->queue);
+	put_device(dev->parent);
 	kfree(disk);
 }
 struct class block_class = {