always fails

This patch, recently added to md-next causes the test to always fail:

7e6ba434cc60 ("md: don't unregister sync_thread with reconfig_mutex held")

The errors are:

    mdadm: No active reshape to revert on /dev/loop0
    ERROR: active raid5 not found

Before the patch, the error seen is below.

--

fails rarely

Fails about 1 in every 30 runs with errors:

    mdadm: Merging with already-assembled /dev/md/0
    mdadm: backup file /tmp/md-backup inaccessible: No such file or directory
    mdadm: failed to add /dev/loop1 to /dev/md/0: Invalid argument
    mdadm: failed to add /dev/loop2 to /dev/md/0: Invalid argument
    mdadm: failed to add /dev/loop3 to /dev/md/0: Invalid argument
    mdadm: failed to add /dev/loop0 to /dev/md/0: Invalid argument
    mdadm: /dev/md/0 assembled from 1 drive - need all 5 to start it
            (use --run to insist).

    grep: /sys/block/md*/md/sync_action: No such file or directory

    ERROR: active raid5 not found