On Fri, Jun 03, 2016 at 01:47:34PM +0100, Will Deacon wrote: > > Now, the normal atomic_foo_acquire() stuff uses smp_mb() as per > > smp_mb__after_atomic(), its just ARM64 and PPC that go all 'funny' and > > need this extra barrier. Blergh. So lets shelf this issue for a bit. > > Hmm... I certainly plan to get qspinlock up and running for arm64 in the > near future, so I'm not keen on shelving it for very long. Sure; so short term we could always have arm64/ppc specific versions of these functions where the difference matters. Alternatively we need to introduce yet another barrier like: smp_mb__after_acquire() Or something like that, which is a no-op by default except for arm64 and ppc. But I'm thinking nobody really wants more barrier primitives :/ (says he who just added one). > > This unordered store however, can be delayed (store buffer) such that > > the loads from spin_unlock_wait/spin_is_locked can pass up before it > > (even on TSO arches). > > Right, and this is surprisingly similar to the LL/SC problem imo. Yes and no. Yes because its an unordered store, no because a competing ll/sc cannot make it fail the store and retry as done per your and boqun's fancy solution. -- To unsubscribe from this list: send the line "unsubscribe netfilter-devel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
