linux-kernel - Re: [RFC PATCH] ixgbe: acquire RCU read lock when calling netdev_for_each_all_upper_dev

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Message-ID: <52B29455.6010109@intel.com>
Date:	Wed, 18 Dec 2013 22:38:13 -0800
From:	John Fastabend <john.r.fastabend@...el.com>
To:	Jiang Liu <jiang.liu@...ux.intel.com>
CC:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Bruce Allan <bruce.w.allan@...el.com>,
	Carolyn Wyborny <carolyn.wyborny@...el.com>,
	Don Skidmore <donald.c.skidmore@...el.com>,
	Greg Rose <gregory.v.rose@...el.com>,
	Alex Duyck <alexander.h.duyck@...el.com>,
	John Ronciak <john.ronciak@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jacob Keller <jacob.e.keller@...el.com>,
	e1000-devel@...ts.sourceforge.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ixgbe: acquire RCU read lock when calling netdev_for_each_all_upper_dev_rcu()

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 <jiang.liu@...ux.intel.com>
> ---

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
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