Subject: Re: [RFC PATCH] ixgbe: acquire RCU read lock when calling netdev_for_each_all_upper_dev_rcu()

From: John Fastabend <[email-masked]>
Date: Wed, 18 Dec 2013 22:38:13 -0800

On 12/18/2013 10:00 PM, Jiang Liu wrote:
> According to documentation for netdev_for_each_all_upper_dev_rcu(),
> caller should take RCU read lock, otherwise it will trigger following
> warnings. The simplest fix is to protect with rcu_read_lock()/
> rcu_read_unlock(). And this solutions passes basic tests.
>
> Otherwise we may need to introduce  netdev_for_each_all_upper_dev()
> as netdev_lower_get_next_private(), which assumes the caller has
> gained the lock to protect the list.
>
> Signed-off-by: Jiang Liu <[email-masked]>
> ---

Jiang,

The following patch addresses the same issue,

http://patchwork.ozlabs.org/patch/302711/
  [net,1/5] net: allow netdev_all_upper_get_next_dev_rcu with rtnl lock held

It is under review and solves the problem by having the call check for
the rtnl lock as well. Take a look. I think it is a slightly better fix
in that it doesn't clutter the driver with unnecessary rcu_read_lock()
and rcu_read_unlock() calls.

Thanks,
John