netdev - Re: [PATCH net-next V3] net: dynamic ingress

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Message-ID: <1286196720.18293.196.camel@edumazet-laptop>
Date:	Mon, 04 Oct 2010 14:52:00 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Jarek Poplawski <jarkao2@...il.com>
Cc:	hadi@...erus.ca, David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next V3] net: dynamic ingress_queue allocation

Le lundi 04 octobre 2010 à 14:06 +0200, Jarek Poplawski a écrit :

> Right, but then at least in qdisc_lookup():
> 
> if (dev_ingress_queue(dev))
> 	q = qdisc_match_from_root(dev_ingress_queue(dev), handle);
> 
> you should use a variable instead of the second dereference (rtnl isn't
> mandatory here).

I am lost.

If rntl is not mandatory, what is the lock that protects us ?

qdisc_lookup() _is_ called under the protection of a lock.
Or as soon as we return from it, result could change under us.

Please name it, and I'll use it :

rcu_dereference_protected(dev->ingress_queue, lockdep_is_held(THISLOCK))



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