[PATCH net 3/3] netvsc: fix RCU warning from set_multicast

[Stephen Hemminger]

do_set_multicast runs in a work queue and therefore is not holding
RCU read lock. This causes:

WARNING: suspicious RCU usage
4.12.0-rc2-net-00284-ge23454766d55-dirty #2 Not tainted
-----------------------------
drivers/net/hyperv/netvsc_drv.c:65 suspicious rcu_dereference_check() usage!

Fix by acquiring rtnl_lock which is ok in the work queue context.

Better fix is to move do_set_mulitcast into rndis_filter.c but
that has more complex impacts, so hold off until net-next.

Signed-off-by: Stephen Hemminger <sthem...@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 34 ++++++++++++++++++----------------
 1 file changed, 18 insertions(+), 16 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index 252e5d52d17e..ba5c4d037b76 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -62,24 +62,26 @@ static void do_set_multicast(struct work_struct *w)
                container_of(w, struct net_device_context, work);
        struct hv_device *device_obj = ndevctx->device_ctx;
        struct net_device *ndev = hv_get_drvdata(device_obj);
-       struct netvsc_device *nvdev = rcu_dereference(ndevctx->nvdev);
+       struct netvsc_device *nvdev;
        struct rndis_device *rdev;
 
-       if (!nvdev)
-               return;
-
-       rdev = nvdev->extension;
-       if (rdev == NULL)
-               return;
-
-       if (ndev->flags & IFF_PROMISC)
-               rndis_filter_set_packet_filter(rdev,
-                       NDIS_PACKET_TYPE_PROMISCUOUS);
-       else
-               rndis_filter_set_packet_filter(rdev,
-                       NDIS_PACKET_TYPE_BROADCAST |
-                       NDIS_PACKET_TYPE_ALL_MULTICAST |
-                       NDIS_PACKET_TYPE_DIRECTED);
+       rtnl_lock();
+       nvdev = rtnl_dereference(ndevctx->nvdev);
+       if (nvdev)
+               rdev = nvdev->extension;
+
+               if (rdev) {
+                       if (ndev->flags & IFF_PROMISC)
+                               rndis_filter_set_packet_filter(rdev,
+                                                              
NDIS_PACKET_TYPE_PROMISCUOUS);
+                       else
+                               rndis_filter_set_packet_filter(rdev,
+                                                              
NDIS_PACKET_TYPE_BROADCAST |
+                                                              
NDIS_PACKET_TYPE_ALL_MULTICAST |
+                                                              
NDIS_PACKET_TYPE_DIRECTED);
+               }
+       }
+       rtnl_unlock();
 }
 
 static void netvsc_set_multicast_list(struct net_device *net)
-- 
2.11.0