netdev - Re: [PATCH net] net: sched: fix call_rcu() race on classifier module unloads

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Date:	Wed, 20 May 2015 11:32:56 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Daniel Borkmann <daniel@...earbox.net>,
	Cong Wang <cwang@...pensource.com>
CC:	David Miller <davem@...emloft.net>, subramanian.vijay@...il.com,
	netdev <netdev@...r.kernel.org>,
	John Fastabend <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Thomas Graf <tgraf@...g.ch>,
	Jamal Hadi Salim <jhs@...atatu.com>
Subject: Re: [PATCH net] net: sched: fix call_rcu() race on classifier module
 unloads

On 5/20/15 11:12 AM, Daniel Borkmann wrote:
>
> Effectively, every in-tree classifier (rsvp is the only exception)
> is making use of call_rcu(). Moreover, moving this into every
> ->destroy() handler would also be unnecessary overhead, imho, as
> this is only relevant when we actually _unload_ a module.

+1
indeed unregister_tcf_proto_ops() is only called at module unload time.
So there is no overhead from this rcu_barrier(). It's actually
mandatory. All modules with rcu callbacks should do that.

Acked-by: Alexei Starovoitov <ast@...mgrid.com>

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