From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eric Dumazet <eric.dumazet@gmail.com>
Subject: Re: [PATCH net-next 1/2] macvtap: Let TUNSETOFFLOAD actually
 controll offload features.
Date: Wed, 19 Jun 2013 09:34:50 -0700
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On Wed, 2013-06-19 at 12:20 -0400, Vlad Yasevich wrote:

> That's the issue.  RTNL is not owned in the ioctl case.

So it was clearly wrong. The fix was simply to get RTNL in ioctl.

Unfortunately this was not spotted earlier, this is not a reason to add
more kludge.

RTNL is the only mutex needed for the write path.

A management path using RCU_BH and RTNL and a spinlock is wrong.