[PATCH] md 17 of 22 - Strengthen the locking of mddev.
Strengthen the locking of mddev. mddev is only ever locked in md.c, so we move {,un}lock_mddev out of the header and into md.c, and rename to mddev_{,un}lock for consistancy with mddev_{get,put,find}. When building arrays (typically at boot time) we now lock, and unlock as it is the "right" thing to do. The lock should never fail. When generating /proc/mdstat, we lock each array before inspecting it. In md_ioctl, we lock the mddev early and unlock at the end, rather than locking in two different places. In md_open we make sure we can get a lock before completing the open. This ensures that we sync with do_md_stop properly. In md_do_recovery, we lock each mddev before checking it's status. md_do_recovery must unlock while recovery happens, and a do_md_stop at this point will deadlock when md_do_recovery tries to regain the lock. This will be fixed in a later patch.
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