On Tue, Aug 14, 2018 at 04:16:41PM -0700, Linus Torvalds wrote: > On Tue, Aug 14, 2018 at 3:56 PM Keith Busch <keith.bu...@linux.intel.com> > wrote: > > > > You just want to ensure the '*dbbuf_db = value' isn't reordered, right? > > The order dependency might be more obvious if done as: > > > > WRITE_ONCE(*dbbuf_db, value); > > > > if (!nvme_dbbuf_need_event(READ_ONCE(*dbbuf_ei), value, old_value)) > > return false; > > > > And 'volatile' is again redundant. > > Yes, using READ_ONCE/WRITE_ONCE obviates the need for volatile, but it > does *not* impose a memory ordering. > > It imposes an ordering on the compiler, but not on the CPU, so you > still want the "mb()" there
I mistakenly recalled memory-barriers.txt mentioned order was enforced on the CPU, but that's true only for overlapping memory, which this is not. Thanks for the correction.
