netdev - Re: [Patch net-next] net_sched: hold tcf

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Date:	Thu, 17 Jul 2014 16:01:54 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	xiyou.wangcong@...il.com
Cc:	netdev@...r.kernel.org, jhs@...atatu.com, cwang@...pensource.com
Subject: Re: [Patch net-next] net_sched: hold tcf_lock in netdevice notifier

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Wed, 16 Jul 2014 14:25:31 -0700

> From: Cong Wang <cwang@...pensource.com>
> 
> We modify mirred action (m->tcfm_dev) in netdev event, we need to
> prevent on-going mirred actions from reading freed m->tcfm_dev.
> So we need to acquire this spin lock.
> 
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Cc: "David S. Miller" <davem@...emloft.net>
> Signed-off-by: Cong Wang <cwang@...pensource.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

FWIW, from looking at the code, this lock is definitely necessary.

The fact that device destruction is deferred to rtnl_unlock() only
means the problem is harder to hit, rather than impossible.
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