netdev - Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl

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Message-ID: <20080822100708.GA14345@gondor.apana.org.au>
Date:	Fri, 22 Aug 2008 20:07:08 +1000
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	David Miller <davem@...emloft.net>
Cc:	jarkao2@...il.com, netdev@...r.kernel.org, denys@...p.net.lb
Subject: Re: [PATCH] pkt_sched: Destroy gen estimators under rtnl_lock().

On Fri, Aug 22, 2008 at 01:55:13AM -0700, David Miller wrote:
>
> > > We've got at least the RX and TX queues.  That makes two locks and
> > > two lists.
> > 
> > RX currently doesn't add anything to the list.
> 
> That's correct, currently ingress qdiscs only support a hierarchy of
> single root and that's it.

We seem to be talking about different things.

Yes the ingress hierachy has a single root, i.e., it's a tree.  But
that has nothing to do with what I was talking about.  I'm talking
about the list at dev->rx_queue.qdisc_sleeping->list which is
certainly not guaranteed to be empty.

If you look at qdisc_create you'll find that every time we create
a non-root ingress qdisc we add it to that list (we have to,
otherwise qdisc_lookup doesn't work at all for ingress qdiscs).
So when somebody on the TX side does a qdisc_lookup they may be
walking the RX list without any protection.  Similarly, if somebody
on the ingress side does qdisc_lookup they may walk the TX lists
without protection.

Cheers,
-- 
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Email: Herbert Xu ~{PmV>HI~} <herbert@...dor.apana.org.au>
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