netpoll rtnl_dereference() usage

From: Bjorn Helgaas
Date: Fri Mar 25 2016 - 13:30:44 EST

Hi Neil,

Since we're looking at netpoll, here's another question (or two).
0790bbb68f9d ("netpoll: cleanup sparse warnings") adds this:

@@ -1236,7 +1236,11 @@ void __netpoll_cleanup(struct netpoll *np)
struct netpoll_info *npinfo;
unsigned long flags;

- npinfo = np->dev->npinfo;
+ /* rtnl_dereference would be preferable here but
+ * rcu_cleanup_netpoll path can put us in here safely without
+ * holding the rtnl, so plain rcu_dereference it is
+ */
+ npinfo = rtnl_dereference(np->dev->npinfo);
if (!npinfo)

The comment seems to contradict the code: the comment says "we would
like to use rtnl_dereference(), but we have to use rcu_dereference()."
But the code in fact *does* use rtnl_dereference().

Also, "rcu_cleanup_netpoll" doesn't exist; maybe it's a typo for
rcu_cleanup_netpoll_info()? I don't see the path that leads from
rcu_cleanup_netpoll_info() to __netpoll_cleanup(), but I don't claim
to understand the netpoll async subtleties.