Re: [PATCH v3 5/5] psi: introduce psi monitor

On Tue, Jan 29, 2019 at 01:38:43PM +0100, Peter Zijlstra wrote:

On Thu, Jan 24, 2019 at 01:15:18PM -0800, Suren Baghdasaryan wrote:

quoted

+			atomic_set(&group->polling, polling);
+			/*
+			 * Memory barrier is needed to order group->polling
+			 * write before times[] read in collect_percpu_times()
+			 */
+			smp_mb__after_atomic();

That's broken, smp_mb__{before,after}_atomic() can only be used on
atomic RmW operations, something atomic_set() is _not_.

Also; the comment should explain _why_ not only what.