Re: [Xen-devel] [PATCH v7 6/9] spinlock: Introduce spin_lock_cb()

[Julien Grall <julien.grall@xxxxxxx>]

On 14/08/17 15:39, Boris Ostrovsky wrote:
> > > +#define spin_lock_kick(l)                       \
> > > +({                                              \to understand why
> > > you need a stronger one here
> > > +    smp_mb();                                   \
> > arch_lock_signal() has already a barrier for ARM. So we have a double
> > barrier now.
> >
> > However, the barrier is slightly weaker (smp_wmb()). I am not sure why
> > you need to use a stronger barrier here. What you care is the write to
> > be done before signaling, read does not much matter. Did I miss anything?
> Yes, smp_wmb() should be sufficient.
>
> Should I then add arch_lock_signal_wmb() --- defined as
> arch_lock_signal() for ARM and smp_wmb() for x86?
I am not an x86 expert. Do you know why the barrier is not in 
arch_lock_signal() today?
> -boris
>
> > Cheers,
> >
> > > +    arch_lock_signal();                         \
> > > +})
> > > +
> > >  /* Ensure a lock is quiescent between two critical operations. */
> > >  #define spin_barrier(l)               _spin_barrier(l)
--
Julien Grall

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