[dm-devel] holders not working properly, regression [was: Re: use regular gendisk registration in device mapper v2]

[Christoph Hellwig]

Manually reverting "block: remove the extra kobject reference in
bd_link_disk_holder" as show below fixed the issue for me.  I'll spend
some more time tomorrow trying to fully understan the life time rules
tomorrow before sending a patch, though.

---
>From 6b94f5435900d23769db8d07ff47415aab4ac63e Mon Sep 17 00:00:00 2001
From: Christoph Hellwig <hch at lst.de>
Date: Thu, 19 Aug 2021 20:01:43 +0200
Subject: Revert "block: remove the extra kobject reference in
 bd_link_disk_holder"

This reverts commit fbd9a39542ecdd2ade55869c13856b2590db3df8.
---
 block/holder.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/block/holder.c b/block/holder.c
index 4568cc4f6827..ecbc6941e7d8 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -106,6 +106,12 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	}
 
 	list_add(&holder->list, &disk->slave_bdevs);
+	/*
+	 * bdev could be deleted beneath us which would implicitly destroy
+	 * the holder directory.  Hold on to it.
+	 */
+	kobject_get(bdev->bd_holder_dir);
+
 out_unlock:
 	mutex_unlock(&disk->open_mutex);
 	return ret;
@@ -138,6 +144,7 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
 		if (disk->slave_dir)
 			__unlink_disk_holder(bdev, disk);
+		kobject_put(bdev->bd_holder_dir);
 		list_del_init(&holder->list);
 		kfree(holder);
 	}
-- 
2.30.2