On Wed, Oct 11, 2017 at 08:59:48AM -0700, Paul E. McKenney wrote: > On Wed, Oct 11, 2017 at 04:17:25PM +0100, David Howells wrote: > > I will, however, quibble with the appropriateness of the name READ_ONCE()... > > I still think it's not sufficiently obvious that this is a barrier and the > > barrier is after. Maybe READ_AND_BARRIER()? > > Linus was unhappy with READ_ONCE_CTRL() to tag control dependencies, but > indicated that he might consider it if it helped code-analysis tools. > Adding Dmitry Vyukov for his thoughts on whether tagging READ_ONCE() > for dependencies would help. Me, I would suggest READ_ONCE_DEP(), but > let's figure out if the bikeshed needs to be painted before arguing over > the color. ;-) Count me one vote for the READ_ONCE() name. This is about dependent reads, which are nothing special on anything except Alpha. We want to remove the exception/specialness from the memory model; and therefore have to fix up all primitives that could possibly be used for these reads to unconditionally issue the barrier (on Alpha). The alternative is: rm -rf arch/alpha. Adding something like READ_ONCE_DEP() does not rid us of the idea that dependent reads are special and thus defeats the purpose, we might as well retain lockless_dereference(). Now; any user of dependent reads must use READ_ONCE() in any case, to avoid load tearing and reloads. So using READ_ONCE() for the dependent reads is not extra or additional (note we'll also have to add the barrier to all our relaxed and release atomics and anything else that implies READ_ONCE and doesn't already imply smp_mb() after).
