md: flush ->event_work before stopping array.
NeilBrown authored
commit ee5d004f

 upstream.

The 'event_work' worker used by dm-raid may still be running
when the array is stopped.  This can result in an oops.

So flush the workqueue on which it is run after detaching
and before destroying the device.
Reported-by: default avatarHeinz Mauelshagen <heinzm@redhat.com>
Signed-off-by: default avatarNeilBrown <neilb@suse.com>
Fixes: 9d09e663

 ("dm: raid456 basic support")
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
f2051e82