From: Eric Dumazet <eric.dumazet@gmail.com>
To: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: David Miller <davem@davemloft.net>, netdev@vger.kernel.org
Subject: Re: [RFC] NETDEV_UNREGISTER_BATCH seems unused nowaday ?
Date: Fri, 10 Aug 2012 17:01:19 +0200 [thread overview]
Message-ID: <1344610879.31104.2715.camel@edumazet-glaptop> (raw)
In-Reply-To: <87vcgq955v.fsf@xmission.com>
On Fri, 2012-08-10 at 07:45 -0700, Eric W. Biederman wrote:
> Can someone help bring me up to speed. What has changed in the
> dst ref counting that has invalidated our previous solutions?
>
In fact your patch (850a545bd8a416484 net: Move rcu_barrier from
rollback_registered_many to netdev_run_todo.) reinstated the problem
again. You didnt notice, but other people can see the problem.
> As for the idea of putting an rcu_barrier inside of the rtnl_lock. I
> really don't like it. You are trading off a 1000ms singled threaded wait
> without locks for extending the hold times of rtnl lock by 12ms or so.
>
We probably can keep the rcu_barrier() in netdev_run_todo() and kick the
UNREGISTER_FINAL in netdev_run_todo() too.
I'll try that.
> We already have an rcu_barrier on that path in netdev_run_todo,
> so we can reorganize things to use that barrier I would be much
> happer. Furthermore I talked to Paul McKenney a while ago
> about creating an rcu_barrier expedited and he really did not
> like the idea.
>
> Reading through the code we really should get dst_rcu_free
> out of the header and make it non-line. dst_rcu_free can't
> possibly be called from a location where it can be inlined.
>
> Trying to understand your analysis I have stared at the code for
> a while and I am definitely not seeing any rcu callbacks that
> result in calling rt_free. So one of us is missing something.
Recent commits add the rt_free() calls.
Of course, if you unregister a dummy device you wont see the problem.
If you unregister a real device, you definitely hit the problem.
next prev parent reply other threads:[~2012-08-10 15:01 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-10 9:27 [RFC] NETDEV_UNREGISTER_BATCH seems unused nowaday ? Eric Dumazet
2012-08-10 10:42 ` David Miller
2012-08-10 11:06 ` Eric Dumazet
2012-08-10 14:45 ` Eric W. Biederman
2012-08-10 15:01 ` Eric Dumazet [this message]
2012-08-10 17:55 ` Paul E. McKenney
2012-08-10 14:46 ` [PATCH] net: remove delay at device dismantle Eric Dumazet
2012-08-10 15:42 ` [PATCH net-next v2] " Eric Dumazet
2012-08-11 5:54 ` Eric Dumazet
2012-08-11 5:57 ` David Miller
2012-08-23 2:18 ` David Miller
2012-08-23 2:25 ` Gao feng
2012-08-23 2:51 ` David Miller
2012-08-23 2:58 ` Eric Dumazet
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