On 17-01-17 08:57 AM, David Miller wrote:

From: John Fastabend <john.fastabend@gmail.com>
Date: Sun, 15 Jan 2017 15:59:47 -0800

quoted

@@ -2358,7 +2371,10 @@ static void remove_vq_common(struct virtnet_info *vi)
 	/* Free unused buffers in both send and recv, if any. */
 	free_unused_bufs(vi);
 
-	free_receive_bufs(vi);
+	if (rtnl_is_locked())
+		_free_receive_bufs(vi);
+	else
+		free_receive_bufs(vi);
 
 	free_receive_page_frags(vi);
 

This doesn't work.  rtnl_is_locked() doesn't tell if _you_ own the mutex, it
just says that someone does.

So if we now execute this code without taking the RTNL lock just because some
other thread of control holds it, we introduce a race.

yeah this bit is junk. dang. Trying to get this locking right without duplicate
code or pushing around lock_me variables is getting tricky.

.John