Re: root MD array is still in use upon shutdown possible fix

[Neil Brown <neilb@suse.de>]

On Friday October 6, czigola@elte.hu wrote:
> Hi!
> 
> When my root filesystem is on an MD (RAID5) array, I can't cleanly shut 
> down (trying to change the array ro, even when nothing else than the 
> kernel threads and init and one bash are running, and the root fs is ro 
> remounted), because I've got "md: md0 still in use" kernel messages. 
> Usually it doesn't cause any problems, but it possibly could leave the 
> array in an inconsistent state (resync required after reboot).

When your machine shuts down, all md arrays are automatically switched to
read-only *after* the root filesystem has been unmounted.  You should
get a message 
    md: stopping all md devices.

if you get e.g.
    md: md0 still in use.
*after* that message then there might be a problem.  Otherwise
everything should be fine.

That being said, it is possible that your patch is OK.  I've been
meaning to review the rules for switching an array to read-only for
ages, but it never got to the top of the todo list.  e.g. do you want
to be able to switch an array to read-only when a filesystem is
mounted read-write off it.  If you don't, how do you check?  If you
do, what about in-flight write requests?  Do you need to wait for them
to complete? How? It isn't as straight forward as one might like.

NeilBrown
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