[PATCH 4.9 09/78] netvsc: fix deadlock betwen link status and removal

[Greg Kroah-Hartman]

4.9-stable review patch.  If anyone has any objections, please let me know.

------------------

From: stephen hemminger <stephen@xxxxxxxxxxxxxxxxxx>


[ Upstream commit 9b4e946ce14e20d7addbfb7d9139e604f9fda107 ]

There is a deadlock possible when canceling the link status
delayed work queue. The removal process is run with RTNL held,
and the link status callback is acquring RTNL.

Resolve the issue by using trylock and rescheduling.
If cancel is in process, that block it from happening.

Fixes: 122a5f6410f4 ("staging: hv: use delayed_work for netvsc_send_garp()")
Signed-off-by: Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 drivers/net/hyperv/netvsc_drv.c |    7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

--- a/drivers/net/hyperv/netvsc_drv.c
+++ b/drivers/net/hyperv/netvsc_drv.c
@@ -1084,7 +1084,12 @@ static void netvsc_link_change(struct wo
 	bool notify = false, reschedule = false;
 	unsigned long flags, next_reconfig, delay;
 
-	rtnl_lock();
+	/* if changes are happening, comeback later */
+	if (!rtnl_trylock()) {
+		schedule_delayed_work(&ndev_ctx->dwork, LINKCHANGE_INT);
+		return;
+	}
+
 	if (ndev_ctx->start_remove)
 		goto out_unlock;