Use a subsystem lock, not a per-object lock. Really we want to lock
at mutex granularity where possible, but (1) that has non-trivial
memory overhead vs. e.g. directly spinning on the mutex state and (2)
the locking in a few places was originally designed to protect access
to the mutex *owner* priority, which is not 1:1 with a single mutex.
Basically the priority-inheriting mutex code will need some rework
before it works as a fine-grained locking abstraction in SMP.
Note that this fixes an invisible bug: with the older code,
k_mutex_unlock() would actually call irq_unlock() twice along the path
where there was a new owner, which is benign on existing architectures
(so long as the key argument is unchanged) but was never guaranteed to
work. With a spinlock, unlocking an unlocked/unowned lock is a
detectable assertion condition.
Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
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