Re: [PATCH 1/2] kthread: add barriers to set_kthread_struct() and to_kthread()

[Peter Zijlstra]

On Thu, Mar 16, 2017 at 11:38:43AM -0400, Tejun Heo wrote:
> On Thu, Mar 16, 2017 at 11:33:01AM -0400, Tejun Heo wrote:
> > > And perhaps we should add another helper, say,
> > > 
> > > 	#define lockless_assign_pointer(ptr, val)	\
> > > 		smp_store_release(&ptr, val)
> > > 
> > > for set_kthread_struct() ? it can have more users.
> > > 
> > > Not that I think you should change your patch, I am just asking.
> > 
> > Ah yeah, that would look better.  I vaguely remembered the new macro
> > but couldn't quite remember it fully. :)  Will update the patch.
> 
> Oops, as for adding lockless_assign_pointer(), wouldn't smp_wmb() be a
> better match for smp_read_barrier_depends()?  ISTR acquire/release
> pairs being more expensive on some archs.

88c1863066cc ("rcu: Define rcu_assign_pointer() in terms of smp_store_release()")