Re: spin_lock implicit/explicit memory barrier

[Davidlohr Bueso]

On Thu, 11 Aug 2016, Peter Zijlstra wrote:

> On Wed, Aug 10, 2016 at 04:29:22PM -0700, Davidlohr Bueso wrote:
>
> > (1) As Manfred suggested, have a patch 1 that fixes the race against mainline
> > with the redundant smp_rmb, then apply a second patch that gets rid of it
> > for mainline, but only backport the original patch 1 down to 3.12.
>
> I have not followed the thread closely, but this seems like the best
> option. Esp. since 726328d92a42 ("locking/spinlock, arch: Update and fix
> spin_unlock_wait() implementations") is incomplete, it relies on at
> least 6262db7c088b ("powerpc/spinlock: Fix spin_unlock_wait()") to sort
> PPC.

Yeah, and we'd also need the arm bits; which reminds me, aren't alpha
ldl_l/stl_c sequences also exposed to this delaying of the publishing
when a non-owner peeks at the lock? Right now sysv sem's would be busted
when doing either is_locked or unlock_wait, shouldn't these be pimped up
to full smp_mb()s?

Thanks,
Davidlohr