[PATCH net v2] netvsc: add rcu_read locking to netvsc callback

[PATCH net v2] netvsc: add rcu_read locking to netvsc callback

[Stephen Hemminger]

The receive callback (in tasklet context) is using RCU to get reference
to associated VF network device but this is not safe. RCU read lock
needs to be held. Found by running with full lockdep debugging
enabled.

Fixes: f207c10d9823 ("hv_netvsc: use RCU to protect vf_netdev")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
---
v2 - fix commit message

 drivers/net/hyperv/netvsc_drv.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index c9414c054852..fcab8019dda0 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -659,6 +659,7 @@ int netvsc_recv_callback(struct hv_device *device_obj,
 	 * policy filters on the host). Deliver these via the VF
 	 * interface in the guest.
 	 */
+	rcu_read_lock();
 	vf_netdev = rcu_dereference(net_device_ctx->vf_netdev);
 	if (vf_netdev && (vf_netdev->flags & IFF_UP))
 		net = vf_netdev;
@@ -667,6 +668,7 @@ int netvsc_recv_callback(struct hv_device *device_obj,
 	skb = netvsc_alloc_recv_skb(net, packet, csum_info, *data, vlan_tci);
 	if (unlikely(!skb)) {
 		++net->stats.rx_dropped;
+		rcu_read_unlock();
 		return NVSP_STAT_FAIL;
 	}
 
@@ -696,6 +698,7 @@ int netvsc_recv_callback(struct hv_device *device_obj,
 	 * TODO - use NAPI?
 	 */
 	netif_rx(skb);
+	rcu_read_unlock();
 
 	return 0;
 }
-- 
2.11.0

Re: [PATCH net v2] netvsc: add rcu_read locking to netvsc callback

[David Miller]

From: Stephen Hemminger <stephen@networkplumber.org>
Date: Wed, 11 Jan 2017 09:16:32 -0800

> The receive callback (in tasklet context) is using RCU to get reference
> to associated VF network device but this is not safe. RCU read lock
> needs to be held. Found by running with full lockdep debugging
> enabled.
> 
> Fixes: f207c10d9823 ("hv_netvsc: use RCU to protect vf_netdev")
> Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
> ---
> v2 - fix commit message

Applied and queued up for -stable.