On Thu, Mar 07, 2019 at 11:47:53AM +1100, Michael Ellerman wrote: > The mutex unlock fast path is just: > > if (atomic_long_cmpxchg_release(&lock->owner, curr, 0UL) == curr) > return true; > > And because it's the "release" variant we just use lwsync, which doesn't > order MMIO. If it was just atomic_long_cmpxchg() that would work because > we use sync for those. > > __up_write() uses atomic_long_sub_return_release(), so same story. As does spin_unlock() of course, which is a great segway into... my RCsc desires :-) If all your unlocks were to have SYNC, your locks would, aside from ordering MMIO, also be RCsc, Win-Win :-) There is, of course, that pesky little performance detail that keeps getting in the way.
