[PATCH net-next 1/1] netvsc: fix rtnl deadlock on unregister of vf

[Stephen Hemminger]

With new transparent VF support, it is possible to get a deadlock
when some of the deferred work is running and the unregister_vf
is trying to cancel the work element. The solution is to use
trylock and reschedule (similar to bonding and team device).

Reported-by: Vitaly Kuznetsov <vkuzn...@redhat.com>
Fixes: 0c195567a8f6 ("netvsc: transparent VF management")
Signed-off-by: Stephen Hemminger <sthem...@microsoft.com>
---
 drivers/net/hyperv/netvsc_drv.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/drivers/net/hyperv/netvsc_drv.c b/drivers/net/hyperv/netvsc_drv.c
index c71728d82049..e75c0f852a63 100644
--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -1601,7 +1601,11 @@ static void netvsc_vf_setup(struct work_struct *w)
        struct net_device *ndev = hv_get_drvdata(ndev_ctx->device_ctx);
        struct net_device *vf_netdev;
 
-       rtnl_lock();
+       if (!rtnl_trylock()) {
+               schedule_work(w);
+               return;
+       }
+
        vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
        if (vf_netdev)
                __netvsc_vf_setup(ndev, vf_netdev);
@@ -1655,7 +1659,11 @@ static void netvsc_vf_update(struct work_struct *w)
        struct net_device *vf_netdev;
        bool vf_is_up;
 
-       rtnl_lock();
+       if (!rtnl_trylock()) {
+               schedule_work(w);
+               return;
+       }
+
        vf_netdev = rtnl_dereference(ndev_ctx->vf_netdev);
        if (!vf_netdev)
                goto unlock;
-- 
2.11.0