On Thu, Apr 05, 2018 at 07:28:08PM +0200, Peter Zijlstra wrote: > On Thu, Apr 05, 2018 at 05:59:07PM +0100, Will Deacon wrote: > > @@ -340,12 +341,17 @@ void queued_spin_lock_slowpath(struct qspinlock > > *lock, u32 val) > > goto release; > > > > /* > > + * Ensure that the initialisation of @node is complete before we > > + * publish the updated tail and potentially link @node into the > > + * waitqueue. > > + */ > > + smp_wmb(); > > Maybe an explicit note to where the matching barrier lives..
Oh man, that's not a simple thing to write: there isn't a matching barrier! Instead, we rely on dependency ordering for two cases: * We access a node by decoding the tail we get back from the xchg - or - * We access a node by following our own ->next pointer I could say something like: "Pairs with dependency ordering from both xchg_tail and explicit dereferences of node->next" but it's a bit cryptic :( Will
