block: store the holder kobject in bd_holder_disk

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.

Orignally-From: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20221115141054.1051801-10-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/block/holder.c b/block/holder.c
index c8e4620..3332142 100644 (file)
--- 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;
 }
@@ -94,8 +94,9 @@ 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 = bdev->bd_holder_dir;
+
        ret = add_symlink(disk->slave_dir, bdev_kobj(bdev));
        if (ret)
                goto out_free_holder;
@@ -140,8 +141,8 @@ 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);
        }