On Mon, Jul 3, 2017 at 9:18 AM, Paul E. McKenney
<paul...@linux.vnet.ibm.com> wrote:
>
> Agreed, and my next step is to look at spin_lock() followed by
> spin_is_locked(), not necessarily the same lock.
Hmm. Most (all?) "spin_is_locked()" really should be about the same
thread that took the lock (ie it's about asserts and lock debugging).
The optimistic ABBA avoidance pattern for spinlocks *should* be
spin_lock(inner)
...
if (!try_lock(outer)) {
spin_unlock(inner);
.. do them in the right order ..
so I don't think spin_is_locked() should have any memory barriers.
In fact, the core function for spin_is_locked() is arguably
arch_spin_value_unlocked() which doesn't even do the access itself.
Linus
