From: stephen hemminger <stephen@networkplumber.org>
Date: Fri, 4 Aug 2017 12:14:00 -0700
Patch-mainline: v4.14-rc1
Subject: netvsc: fix rtnl deadlock on unregister of vf
Git-commit: fb84af8a4397ee664a51c2da1dd64fb3d582ee24
References: fate#323887, bsc#1052442

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 <vkuznets@redhat.com>
Fixes: 0c195567a8f6 ("netvsc: transparent VF management")
Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Olaf Hering <ohering@suse.de>
---
 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
--- 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;