netdev - Re: [PATCH v2 net-next 5/5] net_sched: act

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Date:	Wed, 26 Aug 2015 10:17:01 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>
CC:	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 5/5] net_sched: act_bpf: remove spinlock in
 fast path

On 08/26/2015 05:06 AM, Alexei Starovoitov wrote:
> Similar to act_gact/act_mirred, act_bpf can be lockless in packet processing
> with extra care taken to free bpf programs after rcu grace period.
> Replacement of existing act_bpf (very rare) is done with synchronize_rcu()
> and final destruction is done from tc_action_ops->cleanup() callback that is
> called from tcf_exts_destroy()->tcf_action_destroy()->__tcf_hash_release() when
> bind and refcnt reach zero which is only possible when classifier is destroyed.
> Previous two patches fixed the last two classifiers (tcindex and rsvp) to
> call tcf_exts_destroy() from rcu callback.
>
> Similar to gact/mirred there is a race between prog->filter and
> prog->tcf_action. Meaning that the program being replaced may use
> previous default action if it happened to return TC_ACT_UNSPEC.
> act_mirred race betwen tcf_action and tcfm_dev is similar.
> In all cases the race is harmless.
> Long term we may want to improve the situation by replacing the whole
> tc_action->priv as single pointer instead of updating inner fields one by one.
>
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>

Looks good to me, thanks!

Acked-by: Daniel Borkmann <daniel@...earbox.net>
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