fix a lock order reversal in md_alloc

Hi Song,

the first patch in this series fixed the reported lock order reversal
in md_alloc.  The rest sort out the error handling in that function,
starting with the patch from Luis to handle add_disk errors, which
would otherwise conflict with the first patch.

Note that I have had a hard time verifying this all works fine as the
testsuite in mdadm already keeps failing a lot for me with the baseline
kernel. Some of thos reproducibly and others randomly.  Is there a
good document somehow describing what to expect from the mdadm test
suite?

Diffstat:
 drivers/md/md.c |   56 +++++++++++++++++++++++++++++---------------------------
 1 file changed, 29 insertions(+), 27 deletions(-)