[QUESTION] How to fix the race of "mdadm --add" and "mdadm mdadm --incremental --export"

[Li Xiao Keng <lixiaokeng@xxxxxxxxxx>]

Hi,
   Here we meet a question. When we add a new disk to a raid, it may return
-EBUSY.
   The main process of --add（for example md0, sdf):
       1.dev_open(sdf)
       2.add_to_super
       3.write_init_super
       4.fsync(fd)
       5.close(fd)
       6.ioctl(ADD_NEW_DISK).
   However, there will be some udev(change of sdf) event after step5. Then
"/usr/sbin/mdadm --incremental --export $devnode --offroot $env{DEVLINKS}"
will be run, and the sdf will be added to md0. After that, step6 will return
-EBUSY.
   It is a problem to user. First time adding disk does not return success
but disk is actually added. And I have no good idea to deal with it. Please
give some great advice.

Regards,
Li Xiao Keng