btrfs: replace seed device followed by unmount causes kernel WARNING

reproducer:
mount /dev/sdb /btrfs
btrfs dev add /dev/sdc /btrfs
btrfs rep start -B /dev/sdb /dev/sdd /btrfs
umount /btrfs

WARNING: CPU: 0 PID: 12661 at fs/btrfs/volumes.c:891 __btrfs_close_devices+0x1b0/0x200 [btrfs]()
::

__btrfs_close_devices()
::
        WARN_ON(fs_devices->open_devices);

After the seed device has been replaced the new target device
is no more a seed device. So we need to update the device
numbers in the fs_devices as pointed by the fs_info.

Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Chris Mason <clm@fb.com>

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 096b4a3..361a66e 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -1819,7 +1819,13 @@ void btrfs_rm_dev_replace_srcdev(struct btrfs_fs_info *fs_info,
 
        WARN_ON(!mutex_is_locked(&fs_info->fs_devices->device_list_mutex));
 
-       fs_devices = fs_info->fs_devices;
+       /*
+        * in case of fs with no seed, srcdev->fs_devices will point
+        * to fs_devices of fs_info. However when the dev being replaced is
+        * a seed dev it will point to the seed's local fs_devices. In short
+        * srcdev will have its correct fs_devices in both the cases.
+        */
+       fs_devices = srcdev->fs_devices;
 
        list_del_rcu(&srcdev->dev_list);
        list_del_rcu(&srcdev->dev_alloc_list);