* Oleg Nesterov <[email protected]> wrote:
> static inline void ccids_read_lock(void)
> {
> atomic_inc(&ccids_lockct);
> spin_unlock_wait(&ccids_lock);
> }
>
> This looks racy, in theory atomic_inc() and spin_unlock_wait() could
> be re-ordered. However, in this particular case we have an "optimized"
> smp_mb_after_atomic_inc(), perhaps it is good that the caller can
> choose the "right" barrier by hand.
_all_ default locking and atomic APIs should be barrier-safe i believe.
(and that includes atomic_inc() too) Most people dont have barriers on
their mind when their code. _If_ someone is barrier-conscious then we
should have barrier-less APIs too for that purpose of squeezing the last
half cycle out of the code, but it should be a non-default choice. The
reason: nobody notices an unnecessary barrier, but a missing barrier can
be nasty.
Ingo
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