On Mon, 2015-07-13 at 17:54 +0200, Peter Zijlstra wrote: > That said, I don't think this could even happen on PPC because we have > load_acquire and store_release, this means that: > > *A = a > lwsync > store_release M > load_acquire N > lwsync > *B = b > > And since the store to M is wrapped inside two lwsync there must be > strong store order, and because the load from N is equally wrapped in > two lwsyncs there must also be strong load order. > > In fact, no store/load can cross from before the first lwsync to after > the latter and the other way around. > > So in that respect it does provide full load-store ordering. What it > does not provide is order for M and N, nor does it provide transitivity, > but looking at our documentation I'm not at all sure we guarantee that > in any case. The problem is if you have a load after the second lwsync, that load can go up pass the store release. This has caused issues when N or M is what you are trying to order against. That's why we had to add a sync to spin_is_locked or similar. Ben. > > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-arch" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
