Re: [PATCH] padata: Replace delayed timer with immediate workqueue in padata_reorder

[Daniel Jordan]

On Thu, Jul 18, 2019 at 10:49:50PM +0800, Herbert Xu wrote:
> On Thu, Jul 18, 2019 at 10:25:15AM -0400, Daniel Jordan wrote:
> >
> > Which memory barrier do you mean?  I think you're referring to the one that
> > atomic_inc might provide?  If so, the memory model maintainers can correct me
> > here, but my understanding is that RMW atomic ops that don't return values are
> > unordered, so switching the lines has no effect.
> > 
> > Besides, the smp_mb__after_atomic is what orders the list insertion with the
> > trylock of pd->lock.
> 
> The primitive smp_mb__after_atomic only provides a barrier when
> used in conjunction with atomic_inc (and similar atomic ops).
> 
> The actual barrier may either be in smp_mb__after_atomic or the
> atomic op itself (which is the case on x86).  Since we need the
> barrier to occur after the list insertion we must move both of
> these after the list_add_tail.

Yes, my mistake!  Thanks for clarifying that.