ck_stack: Add fences for ABA-friendly push_mpmc.

include/ck_stack.h

@@ -197,10 +197,12 @@ ck_stack_pop_mpmc(struct ck_stack *target)
 	struct ck_stack original, update;
 
 	original.generation = ck_pr_load_ptr(&target->generation);
+	ck_pr_fence_load();
 	original.head = ck_pr_load_ptr(&target->head);
 	if (original.head == NULL)
 		return NULL;
 
+	/* Order with respect to next pointer. */
 	ck_pr_fence_load();
 
 	update.generation = original.generation + 1;
@@ -212,6 +214,7 @@ ck_stack_pop_mpmc(struct ck_stack *target)
 
 		update.generation = original.generation + 1;
 
+		/* Order with respect to next pointer. */
 		ck_pr_fence_load();
 		update.head = original.head->next;
 	}
@@ -228,6 +231,7 @@ ck_stack_trypop_mpmc(struct ck_stack *target, struct ck_stack_entry **r)
 	struct ck_stack original, update;
 
 	original.generation = ck_pr_load_ptr(&target->generation);
+	ck_pr_fence_load();
 	original.head = ck_pr_load_ptr(&target->head);
 	if (original.head == NULL)
 		return false;
@@ -271,7 +275,7 @@ ck_stack_push_mpnc(struct ck_stack *target, struct ck_stack_entry *entry)
 	struct ck_stack_entry *stack;
 
 	entry->next = NULL;
-	ck_pr_fence_store();
+	ck_pr_fence_store_atomic();
 	stack = ck_pr_fas_ptr(&target->head, entry);
 	ck_pr_store_ptr(&entry->next, stack);
 	ck_pr_fence_store();
@@ -289,7 +293,6 @@ ck_stack_push_spnc(struct ck_stack *target, struct ck_stack_entry *entry)
 
 	entry->next = target->head;
 	target->head = entry;
-
 	return;
 }