ring: guarantee dequeue ordering before tail update

Consumer queue dequeuing must be guaranteed to be done fully before
the tail is updated. This is not guaranteed with a read barrier,
changed to a write barrier just before tail update which in practice
guarantees correct order of reads and writes.

Signed-off-by: Juhamatti Kuusisaari <juhamatti.kuusisaari@coriant.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>

lib/librte_ring/rte_ring.h

@@ -756,7 +756,7 @@ __rte_ring_sc_do_dequeue(struct rte_ring *r, void **obj_table,
 
 	/* copy in table */
 	DEQUEUE_PTRS();
-	rte_smp_rmb();
+	rte_smp_wmb();
 
 	__RING_STAT_ADD(r, deq_success, n);
 	r->cons.tail = cons_next;