[dm-devel] [PATCH 7/7] block: store the holder kobject in bd_holder_disk

[Christoph Hellwig]

We hold a reference to the holder kobject for each bd_holder_disk,
so to make the code a bit more robust, use a reference to it instead
of the block_device.  As long as no one clears ->bd_holder_dir in
before freeing the disk, this isn't strictly required, but it does
make the code more clear and more robust.

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/holder.c | 23 ++++++++++-------------
 1 file changed, 10 insertions(+), 13 deletions(-)

diff --git a/block/holder.c b/block/holder.c
index dd9327b43ce05..a8c355b9d0806 100644
--- a/block/holder.c
+++ b/block/holder.c
@@ -4,7 +4,7 @@
 
 struct bd_holder_disk {
 	struct list_head	list;
-	struct block_device	*bdev;
+	struct kobject		*holder_dir;
 	int			refcnt;
 };
 
@@ -14,7 +14,7 @@ static struct bd_holder_disk *bd_find_holder_disk(struct block_device *bdev,
 	struct bd_holder_disk *holder;
 
 	list_for_each_entry(holder, &disk->slave_bdevs, list)
-		if (holder->bdev == bdev)
+		if (holder->holder_dir == bdev->bd_holder_dir)
 			return holder;
 	return NULL;
 }
@@ -82,27 +82,24 @@ int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	}
 
 	INIT_LIST_HEAD(&holder->list);
-	holder->bdev = bdev;
 	holder->refcnt = 1;
+	holder->holder_dir = kobject_get(bdev->bd_holder_dir);
+
 	ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
 	if (ret)
-		goto out_free_holder;
-	ret = add_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
+		goto out_put_holder_dir;
+	ret = add_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
 	if (ret)
 		goto out_del_symlink;
 	list_add(&holder->list, &disk->slave_bdevs);
 
-	/*
-	 * del_gendisk drops the initial reference to bd_holder_dir, so we need
-	 * to keep our own here to allow for cleanup past that point.
-	 */
-	kobject_get(bdev->bd_holder_dir);
 	mutex_unlock(&disk->open_mutex);
 	return 0;
 
 out_del_symlink:
 	del_symlink(disk->slave_dir, bdev_kobj(bdev));
-out_free_holder:
+out_put_holder_dir:
+	kobject_put(holder->holder_dir);
 	kfree(holder);
 out_unlock:
 	mutex_unlock(&disk->open_mutex);
@@ -131,8 +128,8 @@ void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk)
 	holder = bd_find_holder_disk(bdev, disk);
 	if (!WARN_ON_ONCE(holder == NULL) && !--holder->refcnt) {
 		del_symlink(disk->slave_dir, bdev_kobj(bdev));
-		del_symlink(bdev->bd_holder_dir, &disk_to_dev(disk)->kobj);
-		kobject_put(bdev->bd_holder_dir);
+		del_symlink(holder->holder_dir, &disk_to_dev(disk)->kobj);
+		kobject_put(holder->holder_dir);
 		list_del_init(&holder->list);
 		kfree(holder);
 	}
-- 
2.30.2