Messages in this thread | | | Date | Mon, 19 Feb 2018 21:28:44 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH] tools/memory-model: remove rb-dep, smp_read_barrier_depends, and lockless_dereference |
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On Mon, Feb 19, 2018 at 11:41:23AM -0800, Paul E. McKenney wrote: > On Mon, Feb 19, 2018 at 12:14:45PM -0500, Alan Stern wrote: > > This leaves us with a question: Do we want to change the kernel by > > adding memory barriers after unsuccessful RMW operations on Alpha, or > > do we want to change the model by excluding such operations from > > address dependencies? > > I vote for adding the barrier on Alpha. However, I don't know of any > code in the Linux kernel that relies on read-to-read address dependency > ordering headed by a failing RMW operation, so I don't feel all that > strongly about this.
Right, but not knowing doesn't mean doesn't exist, and most certainly doesn't mean will never exist.
> > Note that operations like atomic_add_unless() already include memory > > barriers. > > And I don't see an atomic_add_unless_relaxed(), so we are good on this > one. So far, anyway! ;-)
Not the point, add_unless() is a conditional operation, and therefore doesn't need to imply anything when failing.
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