On 10/06/2016 01:47 AM, Davidlohr Bueso wrote:
On Wed, 05 Oct 2016, Waiman Long wrote:diff --git a/kernel/locking/osq_lock.c b/kernel/locking/osq_lock.c index 05a3785..1e6823a 100644 --- a/kernel/locking/osq_lock.c +++ b/kernel/locking/osq_lock.c @@ -12,6 +12,23 @@ */static DEFINE_PER_CPU_SHARED_ALIGNED(struct optimistic_spin_node, osq_node);+enum mbtype { + acquire, + release, + relaxed, +};No, please.+ +static __always_inline int+_atomic_cmpxchg_(const enum mbtype barrier, atomic_t *v, int old, int new)+{ + if (barrier == acquire) + return atomic_cmpxchg_acquire(v, old, new); + else if (barrier == release) + return atomic_cmpxchg_release(v, old, new); + else + return atomic_cmpxchg_relaxed(v, old, new); +}Things like the above are icky. How about something like below? I'm not crazy about it, but there are other similar macros, ie lockref. We still provide the osq_lock/unlock to imply acquire/release and the new _relaxed flavor, as I agree that should be the correct naming While I have not touched osq_wait_next(), the following are impacted:- node->locked is now completely without ordering for _relaxed() (currentlyits under smp_load_acquire, which does not match and the race is harmlessto begin with as we just iterate again. For the acquire flavor, it is alwaysformed with ctr dep + smp_rmb(). - If osq_lock() fails we never guarantee any ordering. What do you think? Thanks, Davidlohr
Yes, I am OK with your change. However, I need some additional changes in osq_wait_next() as well. Either it is changed to use the release variants of atomic_cmpxchg and xchg or using macro like what you did with osq_lock and osq_unlock. The release variant is needed in the osq_lock(). As osq_wait_next() is only invoked in the failure path of osq_lock(), the barrier type doesn't really matter.
Cheers, Longman -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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