s390/dcssblk: fix kernel crash with list_add corruption

Commit fb08a19 ("dax: simplify the dax_device <-> gendisk
association") introduced new logic for gendisk association, requiring
drivers to explicitly call dax_add_host() and dax_remove_host().

For dcssblk driver, some dax_remove_host() calls were missing, e.g. in
device remove path. The commit also broke error handling for out_dax case
in device add path, resulting in an extra put_device() w/o the previous
get_device() in that case.

This lead to stale xarray entries after device add / remove cycles. In the
case when a previously used struct gendisk pointer (xarray index) would be
used again, because blk_alloc_disk() happened to return such a pointer, the
xa_insert() in dax_add_host() would fail and go to out_dax, doing the extra
put_device() in the error path. In combination with an already flawed error
handling in dcssblk (device_register() cleanup), which needs to be
addressed in a separate patch, this resulted in a missing device_del() /
klist_del(), and eventually in the kernel crash with list_add corruption on
a subsequent device_add() / klist_add().

Fix this by adding the missing dax_remove_host() calls, and also move the
put_device() in the error path to restore the previous logic.

Fixes: fb08a19 ("dax: simplify the dax_device <-> gendisk association")
Cc: <stable@vger.kernel.org> # 5.17+
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: gerald-schaefer

drivers/s390/block/dcssblk.c

@@ -412,6 +412,7 @@ dcssblk_shared_store(struct device *dev, struct device_attribute *attr, const ch
 	}
 	list_del(&dev_info->lh);
 
+	dax_remove_host(dev_info->gd);
 	kill_dax(dev_info->dax_dev);
 	put_dax(dev_info->dax_dev);
 	del_gendisk(dev_info->gd);
@@ -707,9 +708,9 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 	goto out;
 
 out_dax_host:
+	put_device(&dev_info->dev);
 	dax_remove_host(dev_info->gd);
 out_dax:
-	put_device(&dev_info->dev);
 	kill_dax(dev_info->dax_dev);
 	put_dax(dev_info->dax_dev);
 put_dev:
@@ -789,6 +790,7 @@ dcssblk_remove_store(struct device *dev, struct device_attribute *attr, const ch
 	}
 
 	list_del(&dev_info->lh);
+	dax_remove_host(dev_info->gd);
 	kill_dax(dev_info->dax_dev);
 	put_dax(dev_info->dax_dev);
 	del_gendisk(dev_info->gd);