Re: Linux 3.19-rc3

Kent Overstreet
2015-01-06T11:58:51Z

On Tue, Jan 06, 2015 at 12:48:42PM +0100, Peter Zijlstra wrote:
>
>
> Looking at that closure stuff, why is there an smp_mb() in
> closure_wake_up() ? Typically wakeup only needs to imply a wmb.
>
> Also note that __closure_wake_up() starts with a fully serializing
> instruction (xchg) and thereby already implies the full barrier.

Probably no good reason, that code is pretty old :)

If I was to hazard a guess, I had my own lockless linked lists before llist.h
existed and perhaps I did it with atomic_xchg() - which was at least documented
to not imply a barrier. I suppose it should just be dropped.