Le 06/05/2015 14:23, Thomas Graf a écrit :

On 05/06/15 at 11:58am, Nicolas Dichtel wrote:

quoted

+/* Should be called with nsid_lock held. If a new id is assigned, the bool alloc
+ * is set to true, thus the caller knows that the new id must be notified via
+ * rtnl.
+ */
  static int __peernet2id(struct net *net, struct net *peer, bool *alloc)
  {
  	int id = idr_for_each(&net->netns_ids, net_eq_idr, peer);
  	bool alloc_it = *alloc;

-	ASSERT_RTNL();
-
  	*alloc = false;

  	/* Magic value for id 0. */

If split into __peernet2id() and __peernet2id_alloc() then this could
live with RCU protection I guess so we only take the lock when we
actually allocate.

The description of idr_for_each says:
"The caller must serialize idr_for_each() vs idr_get_new() and idr_remove()."

So, if I understand well, the lock is always needed.